MonographCirripedia.txt

THE

RAY SOCIETY.

INSTITUTED MDCCCXLIV.

[Illustration]

LONDON.

MDCCCLI.




A MONOGRAPH

ON THE SUB-CLASS

CIRRIPEDIA,

WITH

FIGURES OF ALL THE SPECIES.



BY

CHARLES DARWIN, F.R.S., F.G.S.



THE LEPADIDÆ;

OR,

PEDUNCULATED CIRRIPEDES.



LONDON:

PRINTED FOR THE RAY SOCIETY.

MDCCCLI.



C. AND J. ADLARD, PRINTERS, BARTHOLOMEW




PREFACE.


My duty, in acknowledging the great obligations under which I lie to
many naturalists, affords me most sincere pleasure. I had originally
intended to have described only a single abnormal Cirripede, from the
shores of South America, and was led, for the sake of comparison, to
examine the internal parts of as many genera as I could procure. Under
these circumstances, Mr. J. E. Gray, in the most disinterested manner,
suggested to me making a Monograph on the entire class, although he
himself had already collected materials for this same object.
Furthermore, Mr. Gray most kindly gave me his strong support, when I
applied to the Trustees of the British Museum for the use of the public
collection; and I here most respectfully beg to offer my grateful
acknowledgments to the Trustees, for their most liberal and unfettered
permission of examining, and when necessary, disarticulating the
specimens in the magnificent collection of Cirripedes, commenced by Dr.
Leach, and steadily added to, during many years, by Mr. Gray.
Considering the difficulty in determining the species in this class, had
it not been for this most liberal permission by the Trustees, the public
collection would have been of no use to me, or to any other naturalist,
in systematically classifying the Cirripedes.

Previously to Mr. Gray suggesting to me the present Monograph, Mr.
Stutchbury, of Bristol, had offered to intrust to me his truly beautiful
collection, the fruit of many years' labour. At that time I refused this
most generous offer, intending to confine myself to anatomical
observations; but I have since accepted it, and still have the entire
splendid collection for my free use. Mr. Stutchbury, with unwearied
kindness, further supplied me with fresh specimens for dissection, and
with much valuable information. At about the same period, Mr. Cuming
strongly urged me to take up the subject, and his advice had more weight
with me than that of almost any other person. He placed his whole
magnificent collection at my disposal, and urged me to treat it as if it
were my own: whenever I told him that I thought it necessary, he
permitted me to open unique specimens of great value, and dissect the
included animal. I shall always feel deeply honoured by the confidence
reposed in me by Mr. Cuming and Mr. Stutchbury.

I lie under obligations to so many naturalists, that I am, in truth, at
a loss how to express my gratitude. Mr. Peach, over and over again, sent
me fresh specimens of several species, and more especially of
_Scalpellum vulgare_, which were of invaluable assistance to me in
making out the singular sexual relations in that species. Mr. Peach,
furthermore, made for me observations on several living individuals. Mr.
W. Thompson, the distinguished Natural Historian of Ireland, has sent me
the finest collection of British species, and their varieties, which I
have seen, together with many very valuable MS. observations, and the
results of experiments. Prof. Owen procured for me the loan of some very
interesting specimens in the College of Surgeons, and has always given
me his invaluable advice and opinion, when consulted by me. Professor E.
Forbes has been, as usual, most kind in obtaining for me specimens and
information of all kinds. To the Rev. R. T. Lowe I am indebted for his
particularly interesting collection of Cirripedes from the Island of
Madeira--a collection offering a singular proof what treasures skill and
industry can discover in the most confined locality. The well-known
conchologist, Mr. J. G. Jeffreys, has sent for my examination a very
fine collection of British specimens, together with a copious MS. list
of synonyms, with the authorities quoted. To the kindness of Messrs. M^c
Andrew, Lovell Reeve, G. Busk, G. B. Sowerby, Sen., D. Sharpe,
Bowerbank, Hancock, Adam White, Dr. Baird, Sir John Richardson, and
several other gentlemen, I am greatly indebted for specimens and
information: to Mr. Hancock I am further indebted for several long and
interesting letters on the burrowing of Cirripedes.

Nor are my obligations confined to British naturalists. Dr. Aug. Gould,
of Boston, has most kindly transmitted to me some very interesting
specimens; as has Prof. Agassiz other specimens collected by himself in
the Southern States. To Mr. J. D. Dana, I am much indebted for several
long letters, containing original and valuable information on points
connected with the anatomy of the Cirripedia. To Mr. Conrad I am
likewise indebted for information and assistance. Both the celebrated
Professors, Milne Edwards and Müller, have lent me, from the great
public collections under their charge, specimens which I should not
otherwise have seen. To Professor W. Dunker, of Cassel, I am indebted
for the examination of his whole collection. I have, in a former
publication, expressed my thanks to Professor Steenstrup, but I must be
permitted here to repeat them, for a truly valuable present of a
specimen of the _Anelasma squalicola_ of this work. I will conclude my
thanks to all the above British and foreign naturalists, by stating my
firm conviction, that if a person wants to ascertain how much true
kindness exists amongst the disciples of Natural History, he should
undertake, as I have done, a Monograph on some tribe of animals, and let
his wish for assistance be generally known.

Had it not been for the Ray Society, I know not how the present volume
could have been published; and therefore I beg to return my most sincere
thanks to the Council of this distinguished Institution. To Mr. G. B.
Sowerby, Junr., I am under obligations for the great care he has taken
in making preparatory drawings, and in subsequently engraving them. I
believe naturalists will find that the ten plates here given are
faithful delineations of nature.

In Monographs, it is the usual and excellent custom to give a history of
the subject, but this has been so fully done by Burmeister, in his
'Beiträge zur Naturgeschichte der Rankenfüsser,' and by M. G. Martin St.
Ange, in his 'Mémoire sur l'Organisation des Cirripèdes,' that it would
be superfluous here to repeat the same list of authors. I will only add,
that since the date, 1834, of the above works, the only important papers
with which I am acquainted, are, 1st. Dr. Coldstream 'On the Structure
of the Shell in Sessile Cirripedes,' in the 'Encyclopædia of Anatomy and
Physiology;' 2d. Dr. Lovén 'On the Alepas squalicola,' ('Ofversigt of
Kongl. Vetens.,' &c. Stockholm, 1844, p. 192,) giving a short but
excellent account of this abnormal Cirripede; 3d. Professor Leidy's very
interesting discovery, ('Proceedings of the Academy of Natural
Sciences,' Philadelphia, vol. iv, No. I, Jan. 1848,) of eyes in a mature
Balanus; 4th. Mr. A. Hancock's Memoir, ('Annals of Natural History, 2d
series, Nov. 1849,) on his Alcippe lampas, the type of a new order of
Cirripedes; 5th. Mr. Goodsir's Paper, ('Edinburgh New Philosoph.
Journal,' July 1843,) on the Larvæ in the First Stage of Development in
Balanus; 6th. Mr. C. Spence Bate's valuable Paper on the same subject,
lately published, (Oct. 1851,) in the 'Annals of Natural History;' and
lastly, M. Reinhardt has described, in the 'Copenhagen Journal of
Natural History, Jan. 1851,' the _Lithotrya Nicobarica_, and has
discussed its powers of burrowing into rocks.

I have given the specific or diagnostic characters, deduced from the
external parts alone, in both Latin and English. As I found, during the
progress of this work, that a similarly abbreviated character of the
softer internal parts, was very useful in discriminating the species, I
have inserted it after the ordinary specific character.

In those cases in which a genus includes only a single species, I have
followed the practice of some botanists, and given only the generic
character, believing it to be impossible, before a second species is
discovered, to know which characters will prove of specific, in
contradistinction to generic, value.

In accordance with the Rules of the British Association, I have
faithfully endeavoured to give to each species the first name attached
to it, subsequently to the introduction of the binomial system, in 1758,
in the tenth edition[1] of the 'Systema Naturæ.' In accordance with the
Rules, I have rejected all names before this date, and all MS. names. In
one single instance, for reasons fully assigned in the proper place, I
have broken through the great law of priority. I have given much fewer
synonyms than is usual in conchological works; this partly arises from
my conviction that giving references to works, in which there is not any
original matter, or in which the Plates are not of a high order of
excellence, is absolutely injurious to the progress of natural history,
and partly, from the impossibility of feeling certain to which species
the short descriptions given in most works are applicable;--thus, to
take the commonest species, the _Lepas anatifera_, I have not found a
single description (with the exception of the anatomical description by
M. Martin St. Ange) by which this species can be certainly discriminated
from the almost equally common _Lepas Hillii_. I have, however, been
fortunate in having been permitted to examine a considerable number of
authentically named specimens, (to which I have attached the sign (!)
used by botanists,) so that several of my synonyms are certainly
correct.

   [1] In the Rules published by the British Association, the 12th
   edition, (1766,) is specified, but I am informed by Mr.
   Strickland that this is an error, and that the binomial method
   was followed in the 10th edition.

The Lepadidæ, or pedunculated Cirripedes, have been neglected under a
systematic point of view, to a degree which I cannot quite understand:
no doubt they are subject to considerable variation, and as long as the
internal surfaces of the valves and all the organs of the animal's body,
are passed over as unimportant, there will occasionally be some
difficulty in the identification of the several forms, and still more in
settling the limits of the variability of the species. But I suspect the
pedunculated Cirripedes have, in fact, been neglected owing to their
close affinity, and the consequent necessity of their being included in
the same Work with the Sessile Cirripedes; for these latter will ever
present, I am fully convinced, insuperable difficulties in their
identification by external characters alone.

I will here only further remark, that in the Introduction I have given
my reasons for assigning distinct names to the several Valves, and to
some parts of the included animal's body; and that in the Introductory
Remarks, under the general description of the Lepadidæ, I have given an
abstract of my Anatomical Observations.




CORRIGENDA AND ADDENDA.


Page

12, twenty lines from bottom, _for_ "hinder pair of true thoracic
          limbs," _read_ "pair of true thoracic limbs."

42, 43. I should have added, that the number of the segments in the
          cirri increases with the age of the specimen; but that the
          relative numbers in the different cirri keep, as far as I have
          seen, nearly constant; hence the numbers are often given in
          the descriptions.

99 et passim, _for_ Pæcilasma, _read_ Poecilasma.

156. In a foot-note, I have alluded to a new genus of sessile
          Cirripedes, under the name of Siphonicella, I now find that
          this species has been called, by Professor Steenstrup,
          _Xenobalanus globicipitis_.




MONOGRAPH

ON

THE CIRRIPEDIA.




INTRODUCTION.


I should have been enabled to have made this Volume more complete, had I
deferred its publication until I had finished my examination of all the
other known Cirripedes; but my work would thus have been rendered
inconveniently large. Until this examination is completed, it will be
more prudent not to discuss, in detail, the position of the Lepadidæ
amongst the Cirripedia, or of these latter in the great class of
Crustacea, to which they now, by almost universal consent, have been
assigned. I may, however, remark that I believe the Cirripedia do not
approach, by a single character, any animal beyond the confines of the
Crustacea: where such an approach has been imagined, it has been founded
on erroneous observations; for instance, the closed tube within the
stomach, described by M. Martin St. Ange (to whose excellent paper I am
greatly indebted), as indicating an affinity to the Annelides, is, I am
convinced, nothing but a strong epithelial lining, which I have often
seen ejected with the excrement. Again, a most distinguished author has
stated that the Cirripedia differ from the Crustacea:--1st. In having "a
calcareous shell and true mantle;" but there is no essential difference,
as shown by Burmeister, in the shells in these two classes; and
Cirripedes certainly have no more claim to a mantle than have the
bivalve entomostraca. 2d. "In the sexes joined in one individual;" but
this, as we shall see, is not constant, nor of very much weight, even if
constant. 3d. "In the body not being ringed;" but if the outer
integument of the thorax of any Cirripede be well cleaned, it will be
seen, (as was long ago shown by Martin St. Ange), to be most distinctly
articulated. 4th. "In having salivary glands;" but these glands are, in
truth, the ovaria. 5th. "In the liver being formed on the molluscous
type;" I do not think this is the case, but I do not quite understand
the point in question. 6th. "In not having a head or organs of sense;"
this is singularly erroneous: Professor Leidy has shown the existence of
eyes in the mature Cirripede; the antennæ, though preserved, certainly
become functionless soon after the last metamorphosis; but there exist
other organs of sense, which I believe serve for smelling and hearing:
and lastly, so far from there being no head, the whole of the Cirripede
externally visible, consists exclusively of the three anterior segments
of the head.

The sub-class, Cirripedia, can be divided into three Orders; the first
of which, mainly characterised by having six pair of thoracic cirri,
includes all common Cirripedes: these latter may be divided into three
families,--the Lepadidæ, or pedunculated Cirripedes, the subject of the
present memoir; the Verrucidæ containing the single genus Verruca or
Clisia; and, lastly, the Balanidæ, which consist of two very distinct
sub-families, the Balaninæ and Chthamalinæ. Of the other two Orders
above alluded to, one will, I believe, contain the remarkable burrowing
genus Alcippe, lately described by Mr. Hancock, and a second burrowing
genus, or rather family, obtained by me on the coast of South America.
The third Order is highly singular, and differs as much from all other
Cirripedes as does a Lernæa from other crustaceans; it has a suctorial
mouth, but is destitute of an anus; it has not any limbs, and is as
plainly articulated as the larva of a fly; it is entirely naked, without
valves, carapace, or capitulum, and is attached to the Cirripede, in the
sack of which it is parasitic, by _two_ distinct threads, terminating in
the usual larval, prehensile antennæ. I intend to call this Cirripede,
Proteolepas. I mention it here for the sake of calling attention to any
parasite at all answering to this description.


NOMENCLATURE OF THE VALVES.

[Illustration: Figure I.

CAPITULUM.]

[Illustration: Figure II.

SCUTUM of LEPAS.]

[Illustration: Figure III.

TERGUM of LEPAS.]

Although the present volume is strictly systematic, I will, under the
general description of the Lepadidæ, give a very brief abstract of some
of the most interesting points in their internal anatomy, and in the
metamorphoses of the whole class, which I hope hereafter to treat, with
the necessary illustrations, in detail. I enter on the subject of the
metamorphoses the more readily, as by this means alone can the
homologies of the different parts be clearly understood.


_On the Names given to the different parts of Cirripedes._

I have unwillingly found it indispensable to give names to several
valves, and to some few of the softer parts of Cirripedes. The
accompanying figure of an imaginary Scalpellum includes every valve; the
two most important valves of Lepas are also given, in which the
direction of the lines of growth and general shape differ from those of
Scalpellum as much as they do in any genus. The names which I have
imposed will, I hope, be thus acquired without much difficulty.

Whoever will refer to the published descriptions of recent and fossil
Cirripedia, will find the utmost confusion in the existing nomenclature:
thus, the valve named in the woodcut the _Scutum_, has been designated
by various well-known naturalists as the "ventral," the "anterior," the
"inferior," the "ante-lateral," and the "latero-inferior" valve; the
first two of these titles have, moreover, been applied to the rostrum or
rostral valve of sessile Cirripedes. The _Tergum_ has been called the
"dorsal," the "posterior," the "superior," the "central," the
"terminal," the "postero-lateral," and the "latero-superior" valve. The
_Carina_ has received the first two of these identical epithets, viz.
the "dorsal" and the "posterior;" and likewise has been called the
"keel-valve." The confusion, however, becomes far worse, when any
individual valve is described, for the very same margin which is
anterior or inferior in the eyes of one author, is the posterior or
superior in those of another; it has often happened to me that I have
been quite unable even to conjecture to which margin or part of a valve
an author was referring. Moreover, the length of these double titles is
inconvenient. Hence, as I have to describe all the recent and fossil
species, I trust I may be thought justified in giving short names to
each of the more important valves, these being common to the
pedunculated and sessile Cirripedes.

The part supported by the peduncle, and which is generally, though not
always, protected by valves, I have designated the _Capitulum_.

The title of _Peduncle_, which is either naked or squamiferous, requires
no explanation; the scales on it, and the lower valves of the capitulum,
are arranged in whorls, which, in the Latin specific descriptions, I
have called by the botanical term of verticillus.

I have applied the term _Scutum_ to the most important and persistent of
the valves, and which can generally be recognised by the hollow giving
attachment to the adductor scutorum muscle, from the resemblance which
the two valves taken together bear to a shield, and from their office of
protecting the front side of the body. From the protection afforded by
the two _Terga_ to the dorso-lateral surface of the animal, these valves
have been thus called. The term _Carina_[2] is a mere translation of
the name already used by some authors, of Keel-Valve.

   [2] In the Carina of Fossil Species of Scalpellum, I have found
   it necessary to distinguish different parts, viz., A, the tectum,
   of which half is seen; B, the parietes; and C, the
   intra-parietes.

The _Rostrum_ has been so called from its relative position to the
carina or keel. There is often a _Sub-carina_ and a _Sub-rostrum_.

The remaining valves, when present, have been called _Latera_; there is
always one large upper one inserted between the lower halves of the
scuta and terga, and this I have named the Upper Latus or Latera; the
other latera in Pollicipes are numerous, and require no special names;
in Scalpellum, where there are at most only three pair beneath the Upper
Latera, it is convenient to speak of them (_vide_ Woodcut, I,) as the
_Carinal_, _Infra-median_, and _Rostral Latera_.

As each valve often requires (especially amongst the fossil species) a
distinct description, I have found it indispensable to give names to
each margin. These have mostly been taken from the name of the adjoining
valve, (see fig. I.) In Lepas, Pollicipes, &c., the margin of the scutum
adjoining the tergum and upper latus, is not divided (fig. II) into two
distinct lines, as it is in Scalpellum, and is therefore called the
Tergo-lateral margin. In Scalpellum (fig. I) these two margins are
separately named Tergal and Lateral. The angle formed by the meeting of
the basal and lateral or tergo-lateral margins, I call the Baso-lateral
angle; that formed by the basal and occludent margins, I call, from its
closeness to the Rostrum, the Rostral angle. In Pollicipes the carinal
margin of the tergum can be divided into an upper and lower carinal
margin; of this there is only a trace (fig. I) in Scalpellum.

That margin in the scuta and terga which opens and _shuts_ for the
exsertion and retraction of the cirri, I have called the Occludent
margin. In the terga of Lepas (fig. III) and some other genera, the
occludent margin is highly protuberant and arched, or even formed of two
distinct sides.

Occasionally, I have referred to what I have called the _primordial
valves_: these are not calcified; they are formed at the first
exuviation, when the larval integuments are shed: in mature Cirripedes
they are always seated, when not worn away, on the umbones of the
valves.

The membrane connecting the valves, and forming the peduncle, and
sometimes in a harder condition replacing the valves, I have often found
it convenient to designate by its proper chemical name of _Chitine_,
instead of by horny, or other such equivalents. When this membrane at
any articulation sends in rigid projections or crests, for the
attachment of muscles or any other purpose, I call them, after Audouin,
_apodemes_. For the underlying true skin, I use the term _corium_.

The animal's body is included within the capitulum, within what I call
the _sack_ (see Pl. IV, figs. 2 and 8´ _a_, and Pl. IX, fig. 4). The
body consists of the _thorax_ supporting the cirri, and of an especial
enlargement, or downward prolongation of the thorax, which includes the
stomach, and which I have called the _prosoma_. (Pl. IX, fig. 4 _n_).
The cirri are composed of two arms or _rami_, supported on a common
segment or support, which I call the _pedicel_. The _caudal appendages_
are two little projections, either uni-or multi-articulate (Pl. IV, fig.
8´ _a_), on each side of the anus, and just above the long
proboscis-like penis. On the thorax and prosoma, or on the pedicels of
the cirri, there are in several genera, long, thin, tapering filaments,
which have generally been supposed to serve as branchiæ; these I call
simply _filaments_, or _filamentary appendages_ (Pl. IX, fig. 4 _g-l_).
The mouth (fig. 4 _b_) is prominent, and consists of _palpi_ soldered to
the _labrum_; _mandibles_, _maxillæ_, and _outer maxillæ_, these latter
serve as an under lip; to these several organs I sometimes apply the
title used by Entomologists, of "trophi." Beneath the outer maxillæ,
there are either two simple orifices or tubular projections; these, I
believe, serve as organs of smell, and have hence called them the
_olfactory orifices_. Within the sack, there are often two sheets of ova
(Pl. IV, fig. 2 _b_), these I call (after Steenstrup, and other
authors) the _ovigerous Lamellæ_; they are united to two little folds of
skin (Pl. IV, fig. 2 _f_), which I call the _ovigerous Fræna_.

From the peculiar curved position which the animal's body occupies
within the capitulum, I have found it far more convenient (not to
mention the confusion of nomenclature already existing) to apply the
term Rostral instead of ventral, and Carinal instead of dorsal, to
almost all the external and internal parts of the animal. Cirripedes
have generally been figured with their surfaces of attachment downwards,
hence I speak of the lower or Basal margins and angles, and of those
pointing in an opposite direction as the Upper; strictly speaking, as we
shall presently see, the exact centre of the usually broad and flat
surface of attachment is the anterior end of the animal, and the upper
tips of the Terga, the posterior end of that part of the animal which is
externally visible; but in some cases, for instance in Coronula, where
the base is _deeply concave_, and where the width of the shell far
exceeds the depth, it seemed almost ridiculous to call this, the
anterior extremity; as likewise does it in Balanus to call the united
tips of the Terga, lying deeply within the shell, the most posterior
point of the animal, as seen externally.

I have followed the example of Botanists, and added the interjection [!]
to synonyms, when I have seen an authentic specimen bearing the name in
question.

Every locality, under each species, is given from specimens ticketed in
a manner and under circumstances appearing to me worthy of full
confidence,--the specific determination being in each case made by
myself.




CLASS--CRUSTACEA. SUB-CLASS--CIRRIPEDIA.

FAMILY--LEPADIDÆ.


_Cirripedia pedunculo flexili, musculis instructo: scutis[3] musculo
adductore solummodô instructis: valvis cæteris, siquæ adsunt, in annulum
immobilem haud conjunctis._

Cirripedia having a peduncle, flexible, and provided with muscles.
Scuta[3] furnished only with an adductor muscle: other valves, when
present, not united into an immovable ring.

    Metamorphoses; larva, first stage, pp. 9-12; larva, second
    stage, p. 13; larva, last stage, p. 14; its carapace, ib.;
    acoustic organs, p. 15; antennæ, ib.; eyes, p. 16; mouth, p. 17;
    thorax and limbs, p. 18; abdomen, p. 19; viscera, ib.; immature
    cirripede, p. 20; homologies of parts, p. 25.

    Description of mature Lepadidæ, p. 28; capitulum, ib.; peduncle,
    p. 31; attachment, p. 33; filamentary appendages, p. 38; shape
    of body, and muscular system, p. 39; mouth, ib.; cirri, p. 42;
    caudal appendages, p. 43; alimentary canal, 44; circulatory
    system, p. 46; nervous system, ib.; eyes, p. 49; olfactory
    organs, p. 52; acoustic(?) organs, p. 53; male sexual organs, p.
    55; female organs, p. 56; ovigerous lamellæ, p. 58; ovigerous
    fræna, ib.; exuviation, p. 61; rate of growth, ib.; size, ib.;
    affinities of family, p. 64; range and habitats, p. 65;
    geological history, p. 66.

   [3] The meaning of this and all other terms is given in the
   Introduction, at pp. 3-7.

_Metamorphoses._--I will here briefly describe the Metamorphoses, as far
as known, common to all Cirripedia, but more especially in relation to
the present family. I may premise, that since Vaughan Thompson's capital
discovery of the larvæ in the last stage of development in Balanus, much
has been done on this subject: this same author subsequently
published[4] in the 'Philosophical Transactions,' an account of the
larvæ of Lepas and Conchoderma (Cineras) in the first stage; and seeing
how totally distinct they were from the larva of the latter stage in
Balanus, he erroneously attributed the difference to the difference in
the two families, instead of to the stage of development. Burmeister[5]
first showed, and the discovery is an important one, that in Lepas the
larvæ pass through two totally different stages. This has subsequently
been proved by implication to be the case in Balanus, by Goodsir,[6] who
has given excellent drawings of the larva in the first stage; and quite
lately, Mr. C. Spence Bate, of Swansea, has made other detailed
observations and drawings of the larvæ of five species in this same
early stage, and has most kindly permitted me to quote from his
unpublished paper[7]. I am enabled to confirm and generalise these
observations, in all the Cirripedes in the Order containing the Balanidæ
and Lepadidæ.

   [4] Philosophical Transactions, 1835, p. 355, Pl. vi.

   [5] Beiträge zur Naturgeschichte der Rankenfüsser, 1834. Mr. J.
   E. Gray, however, briefly described, in 1833, (Proceedings,
   Zoological Society, October,) the larva in the first stage of
   Balanus; in this notice the anterior end of the larva is
   described as the posterior.

   [6] Edinburgh New Philosophical Journal, July 1843, Pls. iii and
   iv.

   [7] This will appear in the October number (1851) of the 'Annals
   of Natural History.'

The ova, and consequently the larvæ of the Lepadidæ, in the _First
Stage_, whilst within the sack of the parent, vary in length from .007
to .009 in Lepas, to .023 of an inch in Scalpellum: my chief examination
of these larvæ has been confined to those of _Scalpellum vulgare_; but I
saw them in all the other genera. The larva is somewhat depressed, but
nearly globular; the carapace anteriorly is truncated, with lateral
horns; the sternal surface is flat and broad, and formed of thinner
membrane than the dorsal. The horns just alluded to are long in Lepas
and short in Scalpellum; their ends are either rounded and excessively
transparent, or, as in Ibla, furnished with an abrupt, minute, sharp
point: within these horns, I distinctly saw a long filiformed organ,
bearing excessively fine hairs in lines, so exactly like the long
plumose spines on the prehensile antennæ of the larvæ in the last stage;
that I have not the least doubt, that these horns are the cases in which
antennæ are in process of formation. Posteriorly to them, on the
sternal surface, near each other, there are two other minute, doubly
curved, pointed horns, about .004 in length, directed posteriorly; and
within these I again saw a most delicate articulated filiformed organ on
a thicker pedicel: in an excellent drawing, by Mr. C. S. Bate, of the
larva of a Chthamalus (_Balanus punctatus_ of British authors), after
having kept alive and moulted once, these organs are distinctly shown as
articulated antennæ (without a case), directed forwards: hence, before
the first moult in Scalpellum, we have two pair of antennæ in process of
formation. Anteriorly to the bases of these smaller antennæ is seated
the heart-shaped eye, (as I believe it to be,) .001 in diameter, with
apparently a single lens, surrounded, except at the apex, by
dark-reddish pigment-cells. In some cases, as in some species of Lepas,
the larvæ, when first excluded from the egg, have not an eye, or a very
imperfect one.

There are three pairs of limbs, seated close together in a longitudinal
line, but some way apart in a transverse direction: the first pair
always consists of a single spinose ramus, it is not articulated in
Scalpellum, but is multi-articulate in some genera; it is directed
forwards. The other two pair have each two rami, supported on a common
haunch or pedicel: in both pair, the longer ramus is multi-articulate,
and the shorter ramus is without articulations, or with only traces of
them: the longer spines borne on these limbs (at least, in Scalpellum
and Chthamalus,) are finely plumose. The abdomen terminates, a little
beyond the posterior end of the carapace, in a slightly upturned horny
point; a short distance anteriorly to this point, a strong, spinose,
forked projection depends from the abdominal surface.

Messrs. V. Thompson, Goodsir, and Bate, have kept alive for several days
the larvæ of Lepas, Conchoderma, Balanus, Verruca, and Chthamalus, and
have described the changes which supervene between the first and third
exuviations. The most conspicuous new character is the great elongation
of the posterior point of the carapace into an almost filiform, spinose
point in Lepas, Conchoderma, Chthamalus, and Balanus, but not according
to Goodsir, in one of the species of the latter genus. The posterior
point, also, of the abdomen becomes developed in Balanus (Goodsir) into
two very long, spear-like processes, serrated on their outer sides; in
Lepas and Conchoderma, according to Thompson, into a single, tapering
spinose projection; and in Chthamalus, as figured by Mr. Bate, the
posterior bifid point, as well as the depending ventral fork, increase
much in size. Another important change, which has been particularly
attended to by Mr. Bate, is the appearance of spinose projections and
spines (some of which are thick, curved, and strongly plumose, or,
almost pectinated along their inner sides) on the pedicels and lower
segments of the shorter rami of the two posterior pairs of limbs.

The mouth in its earliest condition alone remains to be described; in
_S. vulgare_, it is seated on a very slight prominence, in a most
remarkable situation, namely, in a central point between the bases of
the three pairs of legs. I traced by dissection the oesophagus for some
little way, until lost in the cellular and oily matter filling the whole
animal, and it was directed anteriorly, which is the direction that
might have been expected, from the course followed by the oesophagus in
the larva in the last stage, and in mature Cirripedes. Mr. A. Hancock
has called my attention to a probosciformed projection on the under side
of the larva of _Lepas fascicularis_, when just escaped from the egg.
Mr. Bate has described this same proboscis in Balanus and Chthamalus,
and states the important fact, that it is capable of being moved by the
animal; and, lastly, I have seen it in an Australian Chthamalus, and in
Ibla, of remarkable size. This proboscis, which is always directed
posteriorly, (like the mouth in the mature animal,) certainly answers to
the mouth as made out by dissection in Scalpellum; and I believe I saw,
as has Mr. Bate, a terminal orifice: it certainly does not possess any
trophi. In Ibla (in which the larva is large enough for dissection), the
base of the proboscis arises posteriorly to the first pair of legs, and
the orifice at the other end reaches beyond or posteriorly to the point,
where the mouth in Scalpellum opens, namely between the middle pair of
legs. The mouth being either so largely probosciformed or seated only on
a slight eminence, in two genera so closely allied as Ibla and
Scalpellum, and (judging from Mr. Thompson's figures, and from what I
have seen myself,) in the species of the same genus Lepas, is a singular
difference: in the cases in which, at first, the proboscis is absent, it
would probably soon be developed. I cannot but suppose that the inwardly
directed spines on the bases of the two posterior legs, which are so
rapidly developed, serve some important end, namely, as organs of
prehension for the larvæ, like the mandibles and maxillæ of mature
Cirripedes, for seizing their prey, and conveying it to their moveable
mouths, conveniently seated for this purpose.

The first pair of legs answers, as I believe from reasons hereafter to
be assigned, to the outer pair of maxillipods in the higher crustacea;
and the other four legs to the first two pair of thoracic limbs in these
same crustacea; this being the case, the highly remarkable position of
the mouth in the larva, either between the bases of the two posterior
pair of legs, or at least posteriorly to the first pair, together with
the probable functions of the spiny points springing from the basal
segments of the two hinder pair of true thoracic limbs, forcibly bring
to mind the anomalous structure of the mouth being situated in the
middle of the under side of the thorax, in Limulus,--that most ancient
of crustaceans, and therefore one likely to exhibit a structure now
embryonic in other orders. I will only further remark, that I suspect
that the truncation of the anterior end of the carapace, has been
effected by the segments having been driven inwards, and consequently,
that the larger antennæ within the lateral horns, though standing more
in front than the little approximate pair, are normally the posterior
of the two pair. According to Milne Edwards, the posterior pair are
normally seated outside the anterior pair, and this is the case with
those within the lateral horns.

_Larva in the Second Stage._--Notwithstanding the considerable changes,
already briefly given, which the larva undergoes during the first two or
three exuviations after leaving the egg, all these forms may be
conveniently classed under the first stage. The larva in the Second
stage is known only from a single specimen described, figured, and found
by Burmeister,[8] adhering to sea-weed in the midst of other larvæ of
Lepas in the last stage. In its general shape and compressed form, it
seems to come nearer to the last than to the first stage. It has only
three pair of legs, situated much more posteriorly on the body than in
the first stage, and all directed posteriorly; they are much shorter
than heretofore, and resemble rather closely those of the last stage,
with the important exception that the first pair has only one ramus. It
is this circumstance which leaves no doubt on my mind, that we here have
the three pair of limbs, of the first stage, metamorphosed. The body is
prolonged some way behind these limbs, and ends in a blunt, rounded
point, in which, probably, are developed the three posterior pair of
legs and the abdomen of the larva in the last stage. The mouth is now
seated some way anteriorly to the limbs, is large and probosciformed,
and is, I presume, still destitute of trophi. There are now two closely
approximate eyes, but as yet both are _simple_. The smaller pair of
antennæ has disappeared. The whole animal was attached to the sea-weed
by a (I presume, pair of,) "fleischigen Fortsatz," which Burmeister
considers as the prehensile antennæ, to be presently described, in an
early state of development. I have little doubt that this is correct,
for in an abnormal Cirripede of another order, in which the larva
appears in the _first_ stage with prehensile antennæ, the eggs have two
great projecting horns including these organs, and attached by their
tips, through some unknown means, to the sack of the parent, apparently
in the same manner as Burmeister's larva was attached to the sea-weed. I
will only further remark on the larva of this Second stage, that its
chief development since the first stage, has been towards its anterior
end. The next great development, to be immediately described, is towards
the posterior end of the animal.

   [8] Beiträge zur Naturgeschichte der Rankenfüsser, s. 16, Tab. i,
   figs. 3, 4.

_Larva, Last Stage._--My chief examination has been directed, at this
stage of development, to the larvæ of _Lepas australis_, which are of
unusual size, namely, from .065 to even almost .1 of an inch in length;
I examined, however, the larvæ of several other species of Lepas, of
Ibla and of Balanus, with less care, but sufficiently to show that in
all essential points of organisation they were identical; this, indeed,
might have been inferred from the similarity of the larval prehensile
antennæ, preserved in the bases of all mature Cirripedes, and which I
have carefully inspected in almost every genus. The larvæ in this final
stage, in most of the genera, have increased many times in size since
their exclusion from the egg; for instance, in _Lepas australis_, from
.007 to .065, or even to .1 of an inch. They are now much compressed,
nearly of the shape of a cypris or mussel-shell, with the anterior end
the thickest, the sternal surface nearly or quite straight, and the
dorsal arched. Almost the whole of what is externally visible consists
of the carapace; for the thorax and limbs are hidden and enclosed by its
backward prolongation; and even at the anterior end of the animal, the
narrow sternal surface can be drawn up, so as to be likewise enclosed.
As in several Stomapod crustaceans, the part of the head bearing the
antennæ and organs of sense, in front of the mouth, equals, or even
exceeds in length, and more than exceeds in bulk, the posterior part of
the body, consisting of the enclosed thorax and abdomen. I will now
briefly describe, in the following order, the carapace, the organs of
sense, mouth, thorax and limbs, abdomen, and internal viscera.

The form of the _Carapace_ has been sufficiently described; it consists
of thick chitine membrane, marked with lines, and sometimes with stars
and other patterns; it is obscurely divided into two halves by a line or
suture along part of the dorsal margin; these halves or two valves are
drawn together by an adductor muscle, in the same relative position as
in the mature Cirripede. The part overhanging and enclosing the thorax
is lined by an excessively delicate membrane, obviously homologous with
the lining of the sack in the mature animal, and is nothing but a
duplicature of the carapace, rendered very thin from being on the under
or protected side: a layer of true skin or corium, probably double,
separates these two folds.

_Acoustic Organs._--On the borders of the carapace, at the anterior end,
on the sternal surface, there are two minute orifices, in _L. australis_
.002 in diameter, sometimes having a distinct border round them; the
membrane of the carapace on the inside is prolonged upwards and inwards
in two short funnel-shaped tubes, lodged in closed sacks of the corium:
within these sacks on each side a delicate bag is suspended, and hangs
in the mouth of the above funnel; at the upper end a large nerve could
be distinctly seen to enter the bag: I cannot doubt that this is a
sense-organ; from its position and from the animal not feeding (as we
shall presently see), I conclude that it is an acoustic organ.

_Antennæ._--These are large and conspicuous; they are attached very
obliquely on the sternal surface, a little way from the anterior end of
the carapace, beyond which, when exserted, they extend;[9] they can (at
least in Ibla) be retracted within the carapace. They consist of three
segments: the first or basal one is much larger than the others, and
apparently always has a single spine on the outer distal margin. The
second segment consists either of a large, thin, circular, sucking disc,
or is hoof-like (Tab. V, figs. 5, 10, 11, 12); in all cases it is
furnished with one or more spines, (seven very long ones in Lepas,) on
the exterior-hinder margin. The third and ultimate segment is small; it
is articulated on the upper surface of the disc, and is directed
rectangularly outwards; it is sometimes notched, and even shows traces
of being bifid; it bears about seven spines at the end; some of these
spines are hooked, others simple, and in _Lepas_ and _Conchoderma_, two
or three are very long, highly flexible, and plumose, a double row of
excessively fine hairs being articulated on them. I can hardly doubt
that these latter spines, (within which the purple corium could be seen
to enter a little way,) floating laterally outwards, serve as feelers.
The antennæ, at first, are well furnished with muscles. They serve, in
Lepas, according to Mr. King, and in Balanus, according to Mr. Bate, and
as I saw myself in another unnamed order, for the purpose of walking,
one limb being stretched out before the other; but their main function
is to attach the larva for its final metamorphosis into a Cirripede. The
disc can adhere even to so smooth a surface as a glass tumbler.[10] The
attachment is at first manifestly voluntary, but soon becomes
involuntary and permanent, being effected by special and most remarkable
means, which will be most conveniently described in a later part of this
Introduction. I will here only state that I traced with ease the two
cement-ducts running from two large glandular bodies, to within the
antennæ up to the discs.

   [9] Mr. J. D. Dana, who has examined these organs in the larvæ of
   Lepas, informs me in a letter, that in his opinion they
   "correspond with the inferior antennæ, the superior being
   wanting, as in most Daphnidæ." He continues--"I know of no case
   in which the inferior are obsolete when the superior are
   developed; but the reverse is often true." In position these
   antennæ certainly correspond to the inferior and central pair of
   the larva in the first stage, which belong, as it would appear,
   to the first segment of the body; but judging from the drawing by
   Burmeister of the larva in the second stage, I am, in some
   respects, more inclined to consider that they correspond to the
   larger pair seen within the lateral horns of the carapace in the
   first stage.

   [10] Rev. B. L. King. Annual Report of B. Institution of
   Cornwall, 1848, p. 55.

_Eyes._--Close behind the basal articulations of the antennæ, the
sternal surface consists of two approximate, elongated, narrow, flat
pieces, or segments. These Burmeister considers as the basal segments
of the antennæ: as they are not cylindrical, I do not see the grounds
for this conclusion: their posterior ends are rounded, and the membrane
forming them is reflected inwards, in the form of two, forked, horny
apodemes, together resembling two letters, =UU=, close together; these
project up, inside the animal, for at least one third of its thickness
from the sternal to the dorsal surface. The two great, almost spherical
eyes in _L. australis_, each 1/150th of an inch in diameter, are
attached to the outer arms, thus, =°UU°=, in the position of the two
full stops. Hence the eyes are included within the carapace. Each eye
consists of eight or ten lenses, varying in diameter in the same
individual from 1/2000 to 3/2000th of an inch, enclosed in a common
membranous bag or cornea, and thus attached to the outer apodemes. The
lenses are surrounded half way up by a layer of dark pigment-cells. The
nerve does not enter the bluntly-pointed basal end of the common eye,
but on one side of the apodeme. The structure here described is exactly
that found, according to Milne Edwards, in certain crustacea. In
specimens _just attached_, in which no absorption has taken place, two
long muscles with transverse striæ may be found attached to the knobbed
tips of the two middle arms of the two =°UU°=, and running up to the
antero-dorsal surface of the carapace, where they are attached; other
muscles (without transverse striæ) are attached round the bases, on both
sides of both forks. The action of these muscles would inevitably move
the eyes, but I suspect that their function may be to draw up the
narrow, deeply folded, sternal surface, and thus cause the retraction of
the great prehensile antennæ within the carapace.

_Mouth._--This is seated in exactly the same position as in the mature
Cirripede, on a slight prominence, fronting the thoracic limbs, and so
far within the carapace, that it was obviously quite unfitted for the
seizure of prey; and it was equally obvious, that the limbs were
natatory, and incapable of carrying food to the mouth. This enigma was
at once explained by an examination of the mouth, which was found to be
in a rudimentary condition and absolutely closed, so that there would be
no use in prey being seized. Underneath this slightly prominent and
closed mouth, I found all the masticatory organs of a Cirripede, in an
immature condition. The state of the mouth will be at once understood,
if we suppose very fluid matter to be poured over the protuberant mouth
of a Cirripede, so as to run a little way down, in the shape of internal
crests, between the different parts, and in the shape of a short,
shrivelled, certainly closed tube, a little way (.008 of an inch in _L.
australis_) down the oesophagus. Hence, the larva in this, its last
stage, cannot eat; it may be called a _locomotive Pupa_;[11] its whole
organisation is apparently adapted for the one great end of finding a
proper site for its attachment and final metamorphosis.

   [11] M. Dujardin has lately ('Comptes Rendus,' Feb. 5, 1850, as
   cited in 'Annals of Nat. History,' vol. v, p. 318,) discovered
   that the "Hypopi are Acari with eight feet, without either mouth
   or intestine, and which, being deprived of all means of
   alimentation, fix themselves at will, so as to undergo a final
   metamorphosis, and they become Gamasi or Uropodi." Here, then, we
   have an almost exactly analogous case. M. Dujardin asks--"Ought,
   therefore, the Hypopi to be called larvæ, when, under that
   denomination, have hitherto been comprised animals capable of
   nourishing themselves?"

_Thorax and Limbs._--The thorax is much compressed, and consists of six
segments, corresponding with the six pair of natatory legs; the anterior
segments are much plainer (even the first being distinctly separated by
a fold from the mouth), than the posterior segments, which is exactly
the reverse of what takes place in the mature Cirripede; in the latter,
the first segment is confounded with the part bearing the mouth. The
epimeral elements of the thorax are distinguishable; the sternal surface
is very narrow, and is covered with complicated folds and ridges. The
six pair of legs are all close, one behind the other, and all are alike
in having a haunch or pedicel of two segments, directed forwards,
bearing two arms or rami, each composed of two segments, the outer
ramus being a little longer than the inner one. On the lower segments
in both rami of all the limbs, there is a single spine. In all the
limbs, the obliquely truncated summit of the terminal segment of the
inner ramus bears three very long, beautifully plumose spines: in the
first pair, the summit of the outer ramus bears four, and in the five
succeeding pair, six similar spines. This difference, small as it is, is
interesting, as recalling the much greater difference between the first
and succeeding pairs, in the first and second stage of development. The
terminal segments of all the rami, bearing the long plumose spines, are
directed backwards. The limbs and thorax are well furnished with
striated muscles. The animal, according to Mr. King, swims with great
rapidity, back downwards. The limbs can be withdrawn within the
carapace.

_Abdomen and Caudal Appendages._--The abdomen is small, and its
structure might easily be overlooked without careful dissection of the
different parts: it consists of three segments; the first can be seen to
be distinct from the last thoracic segment, bearing the sixth pair of
limbs, only from the fold of the epimeral element, and from its
difference in shape; the second segment is very short, but quite
distinct; the third is four or five times as long as the second, and
bears at the end two little appendages, each consisting of two segments,
the lower one with a single spine, and the upper one with three, very
long, plumose spines, like those on the rami of the thoracic limbs. The
abdomen contains only the rectum and two delicate muscles running into
the two appendages, between the bases of which the anus is seated.

_Internal Viscera._--Within the body, in front of the mouth, it was easy
to find the stomach (with two pear-shaped cæca at the upper end),
running first anteriorly, and then curving back and reaching the anus by
a long rectum, difficult to be followed: it appeared, however, to me,
that this stomach had more relation to the young Cirripede, of which
every part could now generally be traced, than to the larva, with its
closed and rudimentary mouth: the fact, however, of its being prolonged
to the anus, which is in a different position in the larva and mature
state, shows that the stomach serves, at least, as an excretory channel.
Besides the stomach, the several muscles already alluded to, and much
pulpy and oily matter, the only other internal organs consist of two
long, rather thick, gut-formed masses, into the anterior ends of which
the cement-ducts running from the prehensile antennæ could be traced.
These masses are formed of irregular orange balls, about .001 of an inch
in diameter, made up of rather large cells, so to have a grape-like
appearance, held together by a transparent pale yellowish substance, but
apparently not enclosed in a membrane: these masses lie rather
obliquely, and approach each other at their anterior ends; they extend
from above the compound eyes, to the cæca of the stomach to which they
cohere, but in young specimens, they extend some way beyond the cæca,
between the folds of the carapace. The two cement-ducts, at the points
where they enter these bodies, expand and are lost; at this point, also,
the little orange-coloured masses of cells have the appearance of being
broken down into a finer substance. Within the cement-ducts I saw a
distinct chord of rather opaque cellular matter. We shall presently see,
that these gut-formed masses are the incipient ovaria.

_The Young Cirripede within the Larva._--Several times I succeeded in
dissecting off the integuments of the lately-attached larva, and in
displaying the young _Lepas australis_ entire. The following description
applies to the Cirripede in this state; but for convenience sake, I
shall occasionally refer to its condition when a little more advanced. I
may premise, and the fact in itself is curious, that the bivalve-like
shell of the larva, together with the compound eyes, is first moulted,
and some time afterwards, the inner lining of the sack, together with
the integuments of the thorax and of the natatory legs: hence, I often
found specimens, which externally seemed to have perfected their
metamorphoses, but which, within their sacks, retained all the
characters of the natatory larva. According to Mr. King, the larva of
Lepas throws off its external shell five days after becoming attached.
Whilst the young Lepas is closely packed within the larva, the
capitulum, as known by the five valves, about equals in length the
peduncle. The peduncle occupies the anterior half of the larva; when
fully stretched, it becomes narrower and slightly longer than the
capitulum; the separation between the capitulum and peduncle is almost
arbitrary in the mature animal, and corresponds with no particular line
in the larva. Even at this early period, the muscles of the peduncle are
quite distinct. No vestige is preserved in the outer integument, of the
sternal and dorsal sutures of the larval carapace; but in the corium of
the peduncle, three coloured marks which occur near the eyes, and two
little curled marks which occur near the acoustic orifices of the larva,
are all preserved for some time after maturity. The compound eyes, as we
have seen, are attached to apodemes, springing from the sternal surface
of the larval carapace, and are consequently cast off with it: whilst
the young Cirripede is packed within the larva, the outer integument of
its peduncle necessarily forms a deep transverse fold passing over the
eyes and apodemes, and this, as we shall presently see, plays an
important part in the future position of the animal. The antennæ are not
moulted with the carapace, but left cemented to the surface of
attachment; their muscles are converted into sinewy fibres, the corium
after a short period is absorbed, and they are then preserved in a
functionless condition. No trace of the two acoustic sacks can be
perceived in the corium of the young Cirripede, excepting the coloured
marks above alluded to.

In the young capitulum, the five valves stand some way apart from each
other; they are elegant objects under the microscope; they are not
calcified, but consist exclusively of chitine; they are rather thick,
composed of an outer membrane lined by hexagonal prisms, quite unlike
any other membrane in the animal. These valves, which I have called
_primordial_ valves, resemble pretty closely in shape the valves of the
mature animal; the fork of the carina, however, is indicated only by a
slight constriction above the lower end. After the exuviation of the
larval integuments, and when calcification commences, the first layer of
shell is deposited under, and then round these primordial valves. The
latter, in well preserved old specimens, may often be detected on the
umbones of the scuta, terga, and carina, but not on the umbones of any
other valves.

The _mouth_ seems one of the earliest parts developed: in the youngest
larva dissected, I could make out at least points corresponding with
each organ; and, at the period when the young Cirripede could be
dissected out of its larval envelopes, their general details were quite
plain. The labrum, however, had not become bullate. The mouth, as we
have seen, is formed under the rudimentary mouth of the larva, and at
the same relative spot occupied by the probosciformed mouth of the larva
in the second stage. Thus far, in the young Cirripede and larva, there
has been no great change in the relative positions of the parts: the
rudimentary eyes, however, of the former are developed posteriorly to
(or above, as applied to a Cirripede,) the cast-off compound eyes of the
larva; but the position of the mouth, of the antennæ, and of the several
coloured marks in the corium, prove to demonstration, the correspondence
in both of part to part. The case is rather different with what follows.

The _Cirri_ are developed at first of considerable length, so that the
young animal may soon provide itself with food; in _Lepas australis_
they are of great length, the sixth pair consisting of seventeen or
eighteen obscure segments. The extreme tips of the twenty-four rami of
the six pair of cirri, are formed within the twenty-four, corresponding,
little, bi-segmental rami of the six pair of natatory legs; but as the
cirri are many times longer than these legs, they occupy in a bundle
the whole thorax of the larva; no part whatever of the thorax of the
Cirripede is formed within the thorax of the larva, but (together with
the pedicels of the anterior cirri) within the cephalic cavity. As a
consequence of this, the longitudinal axis of the thorax of the young
Cirripede lies almost transversely to the longitudinal axis of the
larva; and the Cirripede, from this transverse position of its thorax,
comes to be, as it were, internally, almost cut in twain, and the sack
thus produced. As soon as the young Cirripede is free and can move
itself, the cirri are curled up, and the thorax is advanced towards the
orifice of the capitulum, its longitudinal axis resuming the position of
approximate parallelism to the longitudinal axis of the whole body,
which it had in the larval condition. The reader will, perhaps,
understand what I mean, if he will look at the mature Cirripede, figured
in Pl. IX, fig. 4. In this, he will see that the body or thorax is
united to the peduncle only by a small part below the mouth; on the
other hand, if he imagines the whole bottom of the body (as high up as
the letter _h_) united and blended into the peduncle, he will see the
state in which these parts exist in the larva. Now, let him greatly
shorten the cirri, so as to resemble the natatory legs of the larva, and
then imagine a young Cirripede, with cirri _of full length_, formed
within the old one, he will see that the new thorax supporting the cirri
will have to be developed in an almost transverse position,--the animal
consequently being internally almost separated into twain.

Of the internal organs, whilst the Cirripede is still within the larva,
I have already mentioned the stomach with its pair of cæca: from the
retracted position of the thorax and rudimentary abdomen, and
consequently of the anus, compared with these parts in the larva, the
alimentary canal is not above half its former length. There is, as yet,
no trace of the filaments supposed by some to act as branchiæ, at the
base of the first pair of cirri. Nor could I perceive a trace of the
testes or vesiculæ seminales: the penis is represented by a minute,
apparently imperforate projection. I have already briefly described the
pair of large, gut-formed bodies in the larva, into the anterior ends of
which the cement-ducts ran, and evidently derived their slightly opaque,
cellular contents. At a very early age, before the young Cirripede can
be distinctly made out, the posterior ends of these gut-formed bodies
are absorbed, so as not to pass beyond the cæca of the stomach. When the
young Cirripede is plainly developed within the larva, these bodies in a
relatively reduced condition are still distinct near the cæca, and at
the opposite or anterior end (_i. e._ lower, in the position in which
Cirripedes are usually figured), they have branched out into a sheet of
delicate inosculating tubes; these could be traced by every stage,
until, in the young perfected Cirripede, they filled the peduncle as
ordinary ovarian tubes. In the larva, the two gut-formed bodies or
incipient ovaria keep of equal thickness from one to the other end, but
in the mature Cirripede, the ovarian tubes in the peduncle and the
small, glandular, grape-like masses, near the stomach-cæca, are
connected only by a delicate tube; this I failed in tracing in specimens
in the very immature condition of those now under description.

The larva fixes itself with its sternal surface parallel and close to
the surface of attachment, and the antennæ become cemented to it: if the
Cirripede, after its metamorphosis had remained in this position, the
cirri could not have been exserted, or only against the surface of
attachment; but there is a special provision, that the young Cirripede
shall immediately assume its proper position at right angles to the
position which it held whilst within the larva, namely with its
posterior end upwards. This is effected in a singular manner by the
exuviation of the great compound eyes, which we have seen are fastened
to the outer arms of the double =°UU°=-like, sternal apodemes: these
together with the eyes stretch transversely across, and internally far
up into, the body of the larva; and, as the whole has to be rejected or
moulted, the membrane of the peduncle of the young Cirripede has
necessarily to be formed with a wide and deep inward fold, extending
transversely across it; this when stretched open, after the exuviation
of the larval carapace and apodemes, necessarily causes the sternal side
of the peduncle to be longer than the dorsal, and, as a consequence,
gives to the young Cirripede its normal position, at right angles to
that of the larva when first attached.

       *       *       *       *       *

I may here state, that I have examined the larvæ in this the final or
perfect stage in four species of Lepas, in _Conchodermavirgata_, _Ibla
quadrivalvis_, and, though rather less minutely, in _Balanus
balanoides_, and I find all essential points of organisation similar.
With the exception of diversities in the proportional sizes of the
different parts, and in the patterns on the carapace, the differences,
even in the arrangement of the spines on the limbs and antennæ, are less
than I should have anticipated.

I have in this abstract treated the metamorphoses at greater length than
I should otherwise have done, on account of the great importance of
arriving at a correct homological interpretation of the different parts
of the mature animal. In Crustacea, according to the ordinary view,
there are twenty-one segments; of these I can recognise in the
Cirripede, on evidence as good as can generally be obtained, all with
the exception of the four terminal abdominal segments; these do not
occur in any species known to me, in any stage of its development. If
that part of the larva in front of the mouth, bearing the eyes, the
prehensile antennæ, and in an earlier stage two pair of antennæ, be
formed, as is admitted in all other Crustacea, of three segments, then
beyond a doubt, from the absolute correspondence of every part, and even
every coloured mark, the peduncle of the Lepadidæ is likewise thus
formed. The peduncle being filled by the branching ovarian tubes is no
objection to this view, for I am informed on the high authority of Mr.
J. D. Dana,[12] that this is the case with the cephalo-thorax in some
true Crustaceans, for instance, in Sapphirina. To proceed, the mouth,
formed of mandibles, maxillæ, and outer maxillæ, correspond with the
fourth, fifth, and sixth segments of the archetype Crustacean.
Posteriorly to the mouth, we come, in the larva, to a rather wide
interspace without any apparent articulation or organ, and then to the
thorax, formed of six segments, bearing the six pair of limbs, of which
the first pair differs slightly from the others. The thorax is succeeded
by three small segments, differently shaped, with the posterior one
alone bearing appendages; these segments, I cannot doubt, from their
appearance alone, and from their apparent function of steering the body,
are abdominal segments. If this latter view be correct, the thoracic
segments are the six posterior ones of the normal seven segments, and
there must be two segments missing between the outer maxillæ and first
thoracic pair of legs, which latter on this view springs from the ninth
segment. Now, in a very singular Cirripede, already alluded to under the
name of Proteolepas, the two missing segments are present, the mouth
being actually succeeded by eight segments, and these by the three usual
abdominal segments,--every segment in the body being as distinct as in
an Annelid: hence in Proteolepas, adding the three segments for the
mouth and three for the carapace, we have altogether seventeen
segments, which, as I stated, is the full number ever observed in any
Cirripede, the four missing ones being abdominal, and, I presume, the
four terminal segments. That the cavity in which the thorax is lodged,
in the larva and therefore in the mature Cirripede, is simply formed by
the backward production of the carapace, does not require any
discussion. The valves have no homological signification.

   [12] This distinguished naturalist has given his opinion in the
   'American Journal of Science,' March, 1846, that "the pedicel of
   Anatifa corresponds to a pair of antennæ in the young;" although
   the peduncle or pedicel is undoubtedly thus terminated, even in
   mature individuals, I think it has been shown that it is the
   whole of the anterior part of the larva in front of the mouth,
   which is directly converted into the peduncle. Professor E.
   Forbes, in his Lectures, and Professor Steenstrup, in his
   'Untersuchungen über das vorkommen des Hermaphroditismus in der
   Natur,' ch. v, have considered the peduncle as a pair of fused
   legs. Lovén has taken, judging from a single sentence, the same
   view of the homologies of the external parts as I have done; in
   his description of _Alepas squalicola_, (Ofversigt of Kongl.
   Vetens., &c., Stockholm, 1844, pp. 192-4), he uses the following
   words: "Capitis reliquæ partes, ut in Lepadibus semper, in
   _pedunculum mutatæ et involucrum_," &c.; his involucrum is the
   same as the capitulum of this work.

As we have just seen that the first pair of natatory legs is borne on
the ninth segment of the body, so it must be with the first pair of
cirri, which consequently correspond to the outer maxillipods (the two
inner pair of maxillipods or pied-machoires being here aborted) of the
higher Crustacea, and hence their difference from the five posterior
pair, which correspond with the five, ordinary pair of ambulatory legs
in these same Crustacea. The part of the body, which I have called the
prosoma, that is the protuberant, non-articulated, lower part of the
thorax (Pl. IX, fig. 4 _n_), is a special development, either of the
ninth segment, bearing the first pair of cirri, or of the segments
corresponding with the organs of the mouth. The three abdominal segments
of the larva are represented in the mature Cirripede, in the Order
containing the Lepadidæ, only by a minute, triangular gusset, let in
between the V-shaped tergal arches of the last thoracic segment: in this
gusset, small as it is, is seated the anus, and on each side the caudal
appendages, often rudimentary and sometimes absent. In another order, I
may remark, (including, probably, the Alcippe of Mr. Hancock,) the
cirri, of which there are only three pair, are abdominal.

I feel much confidence, that the homologies here given are correct. The
cause of their having been generally overlooked arises, I believe, from
the peculiar manner, already described, in which the animal, during its
last metamorphosis, is internally almost intersected: even for some
little time after discovering that the larval antennæ were always
embedded in the centre of the surface of attachment, I did not perceive,
that this was the anterior end of the whole animal. The accompanying
woodcut gives at a glance, a view of the homologies of the external
parts: the upper figure (from Milne Edwards) is a Stomapod Crustacean,
Leucifer of Vaughan Thompson, and the abdomen, which we know becomes in
Cirripedes, after the metamorphosis, rudimentary, and therefore does not
fairly enter into the comparison, is given only in faint lines: the
lower figure is a mature Lepas, with the antennæ and eyes, which are
actually present in the larva, retained and supposed to have gone on
growing. All that we externally see of a Cirripede, whether pedunculated
or sessile, is the three anterior segments of the head of a Crustacean,
with its anterior end permanently cemented to a surface of attachment,
and with its posterior end projecting vertically from it.

[Illustration: [_m._--Mouth.]]


CAPITULUM.

I will now proceed to a general description of the different parts and
organs in the Lepadidæ. The Capitulum is usually much flattened, but
sometimes broadly oval in section. It is generally formed of five or
more valves, connected together by very narrow or broad strips of
membrane; sometimes the valves are rudimental or absent, when the whole
consists of membrane. When the valves are numerous, and they
occasionally exceed a hundred in number, they are arranged in whorls,
with each valve generally so placed as to cover the interval between the
two valves above. Of all the valves, the scuta are the most persistent;
then come the terga, and then the carina; the rostrum and latera occur
only in Scalpellum and Pollicipes, and in a rudimentary condition in
Lithotrya, and, perhaps, in the fossil genus Loricula. The valves are
formed sometimes of chitine (as in Ibla and Alepas), but usually of
shell, which varies from transparency to entire opacity. The shell is
generally white, occasionally reddish or purple; exteriorly, the valves
are covered by more or less persistent, generally yellow, strong
membrane. The scuta and terga are always considerably larger than the
other valves: in the different genera the valves differ so much in shape
that little can be predicated of them in common; even the direction of
their lines of growth differs,--thus, in Lepas and some allied genera,
the chief growth of the scuta and of the carina is upwards, whereas in
Pollicipes and Lithotrya, it is entirely downwards; in Oxynaspis, and
some species of Scalpellum, it is both upwards and downwards. Even in
the same species, there is often very considerable variation in the
exact shape of the valves, more especially of the terga. The adductor
muscle is always attached to a point not far from the middle of the
scuta, and it generally has a pit for its attachment. In several genera,
namely, Pæcilasma, Dichelaspis, Conchoderma, and Alepas, the scuta show
a tendency to be bilobed or trilobed. The valves are placed either at
some distance from each other, or close together; but their growing
margins very rarely overlap each other, though this is sometimes the
case with their upper, free, tile-like apices; in a few species the
scuta and terga are articulated together, or united by a fold. The
membrane connecting the valves, where they do not touch each other, is
like that forming the peduncle, and is sometimes brilliantly coloured
crimson-red; generally, it appears blueish-gray, from the corium being
seen through. Small pointed spines, connected with the underlying
corium by tubuli, are not unfrequently articulated on this membrane: the
tubuli, however, are often present where there are no spines. To allow
of the growth of the capitulum, the membrane between the valves splits
at each period of exuviation, when a new strip of membrane is formed
beneath, connected on each side with a fresh layer of shell,--the old
and outer slips of membrane disintegrating and disappearing: when there
are many valves, the line of splitting is singularly complicated. This
membrane consists of chitine,[13] and is composed of numerous fine
laminæ. After the valves have been placed in acid, a residue, very
different in bulk in different genera, is left, also composed of
successive laminæ of chitine. It appears to me that each single lamina
of calcified chitine, composing the shell, must once have been
continuous with a non-calcified lamina in the membrane connecting the
several valves: at the line where this change in calcification
supervenes, the chitine generally assumes some colour, and becomes much
harder and more persistent; and as the whole valve is formed of
component laminæ thus edged (the once continuous laminæ of non-calcified
chitine connecting the valves, having disintegrated and disappeared) the
surfaces of the valves are generally left covered by a persistent
membrane, constituted of these edgings: this membrane has been called
the epidermis. In some genera, as in Lepas, this so-called epidermis is
seldom preserved, excepting on the last zone of growth: in Scalpellum
and Pollicipes it usually covers the whole valves. It appears to me that
the laminæ of chitine, and of calcified chitine composing the valves,
are both formed not by secretion, but by the metamorphosis of an outer
layer of corium into these substances.

   [13] Chitine is confined to the Articulata. It was Dr. C. Schmidt
   (Contributions, &c., being a Physiologico-Chemical investigation:
   in Taylor's 'Scientific Memoirs,' vol. v), who discovered that
   the membrane connecting the valves and forming the peduncle, and
   the tissues of the internal animal, were composed of this
   substance. But Dr. Schmidt says that the valves in Lepas are
   composed of 3.09 of albuminates, and 96.81 of incombustible
   residue; I cannot but think that the existence of the albuminates
   is an error caused by Dr. Schmidt's belief that the Cirripedia
   were intermediate between Crustacea and Mollusca, in the shells
   of which latter, the animal basis consists of albuminates. For
   after placing the valves of Lepas and Pollicipes in cold acid, I
   found that the membrane left could _not be dissolved_ in boiling
   caustic potash, but could, though slowly, (and without change of
   colour,) in boiling muriatic acid; and these are the main
   diagnostic characters of Chitine, compared with albuminous
   substances. I may add, that Schmidt was also induced to consider
   the shells of Cirripedia as having the same nature with those of
   Mollusca, from finding that in the above 96.81 of incombustible
   matter, 99.3 consisted of carbonate and only 0.7 of phosphate of
   lime; but Dr. Schmidt's own analyses prove how extremely variable
   the proportions of these salts are in the Crustacea, as the
   following instance shows:--

                         _Lobster._ _Squilla._

     Phosphate of Lime     12.06      47.52
     Carbonate of Lime     87.94      52.48

   And, therefore, it is not very surprising that Cirripedia should
   have still less phosphate of lime in their shells, than has a
   lobster compared with a squilla.

Within the capitulum is the sack, which, together with the upper
internal part of the peduncle, encloses the animal's body. The sack is
lined by a most delicate membrane of chitine, under which there is a
double layer of corium; this double layer is united together by short,
strong, transverse bundles of fibres, branched at both ends:[14] in some
genera, the ovarian tubes extend between these two layers. We have seen,
under the head of the Metamorphoses, that the delicate tunic lining the
sack is simply a duplicature of the thick membrane and valves forming
the capitulum, the whole being the posterior portion of the carapace of
the larva slightly modified.

   [14] I am much indebted to Mr. Inman of Liverpool for having
   kindly sent me excellent specimens illustrating this structure.

_Peduncle._--Its length varies greatly in different species, and even in
the same species, according to the situation occupied by the individual;
its lower end is sometimes pointed, but generally only a little narrower
than the upper end. In outline, the peduncle is usually flattened, but
sometimes quite cylindrical. It is composed of very strong, generally
thick, transparent membrane, rarely coloured reddish, and often
penetrated by numerous tubuli. The underlying corium is sometimes
coloured in longitudinal bands. At each period of growth a new and
larger integument is formed under the old one, which gradually
disintegrates and disappears; the extreme lower point is often deserted
by the corium, and ceases to grow, whilst the whole upper part still
continues increasing in diameter: in length the chief addition is made
(as is clearly seen in those genera having calcified scales), round the
upper margin, at the base of the capitulum. The surface of the membrane
is either naked or superficially clothed with minute, pointed,
articulated spines, or it is penetrated by calcified scales or styles,
(in Ibla alone formed of chitine,) which pass through it to the corium,
and are added to at their bases, like the valves, at each period of
growth. In Lithotrya alone the scales of the peduncle are moulted
together with the connecting membrane. These scales on the peduncle are
generally placed symmetrically in whorls, with each scale corresponding
with the junctions of two scales, both above and below. Except in
_Scalpellum ornatum_ and the fossil _Loricula pulchella_, they are very
small compared with the valves of the capitulum. When the scales are
symmetrical, new ones are first formed only round the summit of the
peduncle, and only those in the few uppermost whorls continue to grow or
to be added to at their bases; afterwards membrane is deposited under
them. The shelly matter of the scales resembles that of the valves, and
the manner of growth is the same; tubuli generally run to and through
them from the corium. From the continued enlargement of the membrane of
the peduncle, the scales come to stand, in the lower portion, some way
apart. In Ibla, new horny styles are formed indifferently in all parts
of the peduncle. In some species of Pollicipes, the calcareous styles
are not symmetrical or symmetrically arranged; and besides those first
formed round the top of the peduncle, there are other and larger ones
formed near its base. Lastly, in Lithotrya we have a row of calcareous
discs or an irregular, basal cup, formed in the same manner as the
valves of the capitulum: in this genus alone (as already stated,) the
calcified scales are moulted, and here alone their edges are serrated.

The peduncle is lined within by three layers of muscles, longitudinal,
transverse, and oblique, all destitute of the transverse striæ,
characteristic of voluntary muscles; they run from the bottom of the
peduncle to the base of the capitulum, as in Lepas, or half way up it,
as in Conchoderma; in Alepas alone they surround the whole capitulum up
to its summit. In Lithotrya there are two little, fan-like, transverse
muscles (involuntary), extending from the basal points of the terga to a
central line on the under side of the carina. The gentle swaying
to and fro movements, and the great power of longitudinal
contraction,--movements apparently common, as I infer from facts
communicated to me by Mr. Peach, to all the Pedunculata,--are produced
by these muscles. The interior of the peduncle is filled up with a great
mass of branching ovarian tubes; but in Ibla and Lithotrya, the upper
part of the peduncle is occupied by the animal's body.

_Means of Attachment._--If the peduncle be very carefully removed (Tab.
IX, fig. 7 and Tab. I, fig. 6 _b_), from the surface of attachment,
quite close to the end, but not at the actual apex, the larval
prehensile antennæ can always be found: these have been sufficiently
described for our present purpose under the head of the Metamorphoses;
but I may add, that the diagnostic differences between them in the
several genera are briefly given, for a special purpose, in a discussion
on the sexes of Scalpellum at the end of that genus. We have seen in the
larva, that the cement-ducts, with their opaque cellular contents, can
be traced from within the discs of the antennæ to the anterior or lower
ends of the two gut-formed bodies, which it can be demonstrated are the
incipient ovaria.

In mature Cirripedes these ducts can be followed, in a slightly sinuous
course, along the muscles on each side within the peduncle, till they
expand into two small organs, which I have called cement-glands. These
glands are found with great difficulty, except in _Conchoderma aurita_,
where they are placed on each side under the inner layer of corium, at
the bottom of the sack, so as to be just above the top of the peduncle;
they resemble in shape a retort, (Pl. IX, fig. 3.). In _Pollicipes
mitella_ and _polymerus_ they lie half way down the peduncle, close
together, and apparently enclosed within a common membrane; in these two
species the broad end of the gland is bent towards the neck of the
retort. In Scalpellum the position is the same, but the shape is more
globular. In Ibla the structure is more simple, namely, a tube slightly
enlarged, running downwards, bent a little upwards, and then resuming
its former downward course, the lower portion forming the duct. The
gland contains a strongly coherent, pulpy, opaque, cellular mass, like
that in the cement-ducts; but in some instances, presently to be
mentioned, this cellular mass becomes converted within either the ducts
or gland, or within both, into transparent, yellow, tough cement.
Generally in Conchoderma, Pollicipes, and Scalpellum, two ovarian tubes,
but in one specimen of _Conchoderma aurita_, three tubes, and in Ibla
one tube could be seen running into or forming the gland; of the nature
of the tubes there could not be the least doubt, for at a little
distance from the glands they gave out branches (Pl. IX, fig. 3),
containing ova in every state of development. In some specimens as in
that figured of _Conchoderma aurita_, the ovarian tube on one side of
the gland is larger than on the other, and has rather the appearance of
being deeply embedded in the gland than of forming it; but, in other
specimens, the two ovarian tubes first formed a little pouch, into which
their cellular contents could be clearly seen to enter; and then this
pouch expanded into the gland; thus quite removing a doubt which I had
sometimes felt, whether the ovarian tube was not simply attached to or
embedded in the gland, without any further connection. By dissection
the multiple external coats of the gland and ovarian tubes could be seen
to be continuous. The cellular contents of the tubes passed into the
more opaque cellular contents of the gland, by a layer of transparent,
pulpy, pale, yellowish substance. There appeared in several instances to
be a relation, between the state of fulness and condition of the
contents of the gland, and of the immediately adjoining portions of the
ovarian tubes. In one specimen of _Pollicipes mitella_ it was clear that
the altered, tough, yellow, transparent, non-cellular contents of the
two glands and ducts, had actually invaded for some little distance, the
two ovarian tubes which ran into them, thus showing the continuity of
the whole. From these facts I conclude, without hesitation, that the
gland itself is a part of an ovarian tube specially modified; and
further, that the cellular matter, which in the ovarian tubes serves for
the development of the ova, is, by the special action of the walls of
the gland, changed into the opaquer cellular matter in the ducts, and
this again subsequently into that tissue or substance, which cements the
Cirripede to its surface of attachment.

As the individuals grow and increase in size, so do the glands and
cement-ducts; but it seems often to happen, that when a specimen is
immovably attached, the cementing apparatus ceases to act, and the
cellular contents of the duct become converted into a thread of
transparent tough cement; the investing membrane, also, of the ducts, in
Conchoderma sometimes becomes hard and mamillated. I have already
alluded to the case of a Pollicipes, in which both glands and ducts, and
even a small portion of the two adjoining ovarian tubes, had become thus
filled up. As in sessile Cirripedes, at every fresh period of growth a
new cement gland is formed, it has occurred to me, that possibly in
Pollicipes something similar may take place. In sessile Cirripedes, the
old cement-glands are all preserved in a functionless condition,
adhering to the membranous or calcareous basis, each new larger one
attached to that last formed, and each giving out cement-ducts, which,
bifurcating in the most complicated manner, pass outside the shell and
thus attach it to some foreign body.

The cement, removed from the outside of a Cirripede, consists of a thin
layer of very tough, bright-brown, transparent, laminated substance,
exhibiting no structure under the highest powers, or at most a very fine
dotted appearance, like a mezzotinto drawing. It is of the nature of
chitine; but boiling caustic potash has rather more effect on it than on
true chitine; and I think boiling nitric acid rather less effect. In one
single instance, namely, in Coronula, the cement comes out of the four
orifices of the two bifurcating ducts, in the shape of distinct cells,
which, between the whale's skin and the basal membrane, arrange
themselves so as to make a circular, continuous slip of cement; then the
cells blend together, and are converted into transparent, structureless
cement. Cementing tissue or membrane would, perhaps, have been a more
correct title than cement; but, in ordinary cases, its appearance is so
little like that of an organised tissue, that I have for this reason,
and for brevity-sake, preferred the simple term of Cement.

In the larva the cement always escapes through the prehensile antennæ;
and it thus continues to do throughout life in most or all of the
species of Lepas, Conchoderma, Dichelaspis and Ibla. In the first two of
these genera, the cement escapes from the borders of the lower side of
the disc or penultimate segment of the antennæ, and can be there seen
radiating out like spokes, which at their ends divide into finer and
finer branches, till a uniform sheet of cement is formed, fastening the
antennæ and the adjoining part of the peduncle down to the surface of
attachment. In _Dichelaspis Warwickii_ and _Scalpellum Peronii_, the
cement, or part at least, comes out of the ultimate segment of the
antennæ, in the shape of one tube, within another tube of considerable
diameter and length. In _Scalpellum vulgare_, and probably in some of
the other species, which live attached to corallines, the cement soon
ceases to debouch from the antennæ, but instead, bursts through a row of
orifices on the rostral margin of the peduncle (Pl. IX, fig. 7), by
which means this margin is symmetrically fastened down to the delicate,
horny branches of the zoophyte. In Pollicipes, the two cement-ducts,
either together or separately (Pl. IX, fig. 2, 2 _a´_), wind about the
bottom of the peduncle in the most tortuous course, at each bend pouring
out cement through a hole in the membrane of the peduncle. In Ibla the
lower part of the peduncle is internally filled by cement, and thus
rendered rigid. In _Lepas fascicularis_ a vesicular ball of cement
surrounding the peduncle is thus formed (Pl. I, fig. 6), and serves as a
float! All these curious, special adaptations are described under the
respective genera. How the cement forces its way through the antennæ,
and often through apertures in the thick membrane of the peduncle, I do
not understand. I do not believe, though some appearances favoured the
notion, that the duct itself debouches and divides, at least this is not
the case in Coronula, but only that the internal chord of cellular
matter thus acts and spreads itself out; nor do I understand how, when
the antennæ and immediately adjoining parts are once cemented down, any
more cement can escape; yet this must take place, as may be inferred
from the breadth of the cemented, terminal portion of the peduncle in
Lepas and Conchoderma; and from the often active condition in old
individuals of the cementing organs.

I have entered on this subject at some length, (and I wish I had space
for more illustrations,) from its offering, perhaps, the most curious
point in the natural history of the Cirripedia. It is the one chief
character of the Sub-class. I am well aware how extremely improbable it
must appear, that part of an ovarian tube should be converted into a
gland, in which cellular matter is modified, so that instead of aiding
in the development of new beings, it forms itself into a tissue or
substance, which leaves the body[15] in order to fasten it to a foreign
support. But on no other view can the structure, clearly seen by me both
in the mature Cirripede and in the larva, be explained, and I feel no
hesitation in advancing it. I may here venture to quote the substance of
a remark made by Professor Owen, when I communicated to him the
foregoing facts, namely, that there was a new problem to solve,--new
work to perform,--to attach permanently a crustacean to a foreign body;
and that hence no one could, _a priori_, tell by what singular and novel
means this would be effected.

   [15] The protrusion of the egg-bearing pouches in Cyclops and its
   kindred genera, outside the body, offers a feeble analogy with
   what takes place in Cirripedes. Professor Allman ('Annals of
   Natural History,' vol. xx, p. 7,) who has attended to the
   subject, says that the external egg-bearing pouches are "a
   portion of the membrane of the true ovaries:" if the membrane of
   these pouches had been specially made adhesive, the analogy would
   have been closer.

_Filamentary Appendages._--These have generally been considered to act
as branchiæ; they occur at the bases of the first pair of cirri in
Lepas, Alepas, Conchoderma, and in three species of Pollicipes: in
Conchoderma there are similar appendages attached to the pedicels of the
cirri (Pl. IX, fig. 4, _g-k_); and in the above three species of
Pollicipes there is a double row of them on the prosoma: their numbers
differ in different species (in some there being none) of the same
genus, and even in different individuals of the same species; they are
entirely absent in the majority of the genera. These facts would
indicate that they are not of high functional importance; and they seem
so generally occupied by testes (Pl. iv, fig. 5), that I suspect their
function is quite as much to give room for the development of these
glands, as to serve for respiratory purposes. With the exception of the
four above-named genera, the mere surface of the body and of the sack
must be sufficient for respiration: in _Conchoderma aurita_ the two
great expansions of surface, afforded by the folded, tubular, ear-like
projections, aid, as I believe, towards this end.

The shape of the body varies, owing to the greater or less development
of the lower part of the prosoma, the greater or less distance of the
first from the second pair of cirri, and of the mouth from the adductor
scutorum muscle, (Pl. IX, fig. 4, and Pl. IV, 8 _a´_). In all the
genera, the body is much flattened. I may here mention a few particulars
about the muscular system. One of the largest muscular masses is formed
by the adductor scutorum, and by the muscles which surround in a double
layer (the fasciæ being oblique to each other) the whole of the upper
part of the prosoma. From under the adductor, a pair of delicate muscles
runs to the basal edge of the labrum, so as to retract the whole mouth,
and two other pair to the integument between the mouth and the adductor,
so as to fold it: again, there are other delicate muscles in some (for
instance in _Lepas Hillii_) if not in all the Lepadidæ, crossing each
other in the most singular loops, and serving apparently to fold the
membrane between the occludent edges of the scuta. Within the prosoma
there is a strong adductor muscle, running straight from side to side,
for the purpose, as it appears, of flattening the body. The thorax, on
the dorsal and ventral surfaces, is well furnished with straight and
oblique muscles (without striæ), which straighten and curl up this part
of the body. The muscles running into the pedicels of the cirri, cross
each other on the ventral surface of the thorax; the muscles within the
rami are attached to the upper segments of the pedicels. Finally, I may
remark that the whole of the body and the cirri are capable of many
diversified movements.

_Mouth._--This is prominent, and almost probosciformed (Pl. IX, fig. 4
_b_), and in the abnormal Anelasma (Pl. IV, fig. 2 _d_), quite
probosciformed,--such, also, was its character in the larval condition.
In outline, it is either sub-triangular, or oval with the longer axis
transverse; the whole is capable, as well as the separate organs, of
considerable movement, as I have seen in living sessile Cirripedes. It
is composed (Tab. V, fig. 2) of a labrum, swollen or bullate, often to
such an extent as to equal in its longitudinal axis the rest of the
mouth; of palpi soldered to the labrum; of mandibles, maxillæ, and outer
maxillæ, the latter serving as a lower lip. These organs have only their
upper segments free, but there are traces, clearly seen in the mandibles
(Pl. X, fig. 1, _a_, _b_), of their being formed of three segments. The
two lower segments are laterally united, and open into each other, the
prominence of the mouth being thus caused: this condition appears to me
curious, and is, to a certain limited extent, intermediate between those
articulated animals which have their trophi soldered into a proboscis,
and those furnished with entirely free masticatory or prehensile organs.
The palpi adhere to the corners of the labrum; and I call them palpi
only from seeing that they spring laterally from above the upper
articulation of the mandibles. The prominence of the mouth, measured
from the basal fold by which the whole is separated from the body, is
much greater on the half formed by the labrum and mandibles, than on the
other half facing the cirri. The trophi surround a cavity--the
supra-oesophageal cavity--in the middle of which, between the mandibles
is seated the orifice of the oesophagus. The oesophagus is surrounded by
long, fine, muscular fasciæ, radiating in all directions, opposing the
constrictor muscles, and is capable of violent swallowing
movements,--constriction after constriction being seen to run down its
whole course: there are also some fine muscles attached to the membrane
forming the supra-oesophageal cavity. The trophi serve merely for the
prehension of prey, and not for mastication.

The _Labrum_, as stated, is always bullate or swollen; and sometimes the
upper exterior part forms, as in Ibla (Pl. IV, fig. 8 _a_, _c_), and
Dichelaspis, an overhanging blunt point. The object, I suspect, of this
bullate form is to give, in the upper part, attachment to longer muscles
running to the lateral surfaces of the mandibles, and lower down to the
oesophagus. The crest close over the supra-oesophageal cavity, is
generally furnished with small, often bead-like teeth. The _Palpi_ are
small, their apices never actually touching each other; they are more or
less blunt, not differing much in shape in the different genera (Pl. X,
figs. 6 to 8), and clothed with spines. They are not capable of
movement; their function seems to be to prevent prey, brought by the
cirri, escaping over the labrum; I infer this from finding in Anelasma
and in the male of Ibla, which have the cirri functionless, that the
palpi are rudimentary.

The _Mandibles_ (Pl. X, figs. 1-5) have from two to ten strong teeth in
a single row; where the number exceeds five, several of the teeth are
small; the inferior angle is generally pectinated with fine spines; in
Lithotrya (fig. 2), the interspaces between the teeth are also
pectinated. In the same individual there is not unfrequently one tooth,
more or less, on opposite sides of the mouth. Internally, the mandibles
are furnished on their outer and inner sides with several ligamentous
apodemes, in Lithotrya roughened with points (Pl. X, fig. 2), for the
attachment of the muscles; of these (fig. 1), there is a chief depressor
and elevator, attached at their lower ends to near the basal fold of the
mouth, and a lateral muscle, attached to the broad basal end of the
palpi, and serving, apparently, to oppose the edge of mandible to
mandible. The _Maxillæ_ in the different genera (Pl. X, figs. 9 to 15)
differ considerably in outline; they are generally about half the size
of the mandibles; at the upper corner, there are always two or three
spines larger than the others, and often separated from them by a notch;
the rest of the spinose edge is straight, or irregular, or step-formed,
or with the lowest part projecting, or with one or two narrow
prominences bearing fine spines. All these spines, quite differently
from the teeth of the mandibles, are articulated on the edge of the
organ, and stand in a double row. At a point corresponding with the
upper articulation of the mandibles, a long, thin, narrow, rigid
apodeme, projects inwards (fig. 10), and running down nearly parallel
to the thin, outer, flexible membrane of the mouth, is attached to the
corium, and thus serves as a support to the whole organ. This apodeme is
embedded in muscles (Pl. X, fig. 10); there are other large muscles
attached to the inner side of the organ, and again others running
laterally towards the mandibles. The apodeme, of course, is moulted with
the integuments of the mouth. The _Outer Maxillæ_ (Pl. X, figs. 16, 17)
serve as a lower lip; they are thicker than the other trophi; they have
their inner surfaces clothed with spines, sometimes divided into an
upper and lower group, and occasionally separated by a deep notch: there
are often long bristles outside. They are furnished with at least two
muscles; in sessile Cirripedes I have seen that they are capable of a
rapid to and fro movement, and I have no doubt that their function is to
brush any small creature, caught by the cirri, towards the maxillæ,
which are well adapted to aid in securing the prey, and to hand it over
to the mandibles, by them to be forced down the oesophagus. On the
exterior face of the outer maxillæ, above a trace of an upper
articulation, either two small orifices or two large tubular projections
can always be discovered; and these, as will presently be mentioned, I
believe to be olfactory organs.

_Cirri._--The five posterior pair are seated close to each other and
equidistant; the first pair is generally seated at a little distance,
and sometimes at a considerable distance from the second pair. The first
pair is the shortest; the others, proceeding backwards, increase
gradually in length. The rami of each pair are either equal in length or
slightly unequal: those of the first pair are oftenest unequal. The
number of segments in the posterior cirri is sometimes very great; in
one species of Alepas, there were above sixty segments in one ramus, the
other ramus being in this unique case (Pl. X, fig. 28) small and
rudimentary. The pedicels consist of two segments, a lower, longer, and
upper short one (fig. 18, _c_, _d_.) In the usual arrangement of the
spines on the segments of the three posterior pair of cirri, there are
(figs. 26, 27) from three to six pair of long spines on the anterior
face, with generally some minute spines (occasionally forming a tuft)
intermediate between them: on the dorsal surface, in the uppermost part
of each segment, there is a tuft of short spines generally mingled with
some longer, finer ones: on the inner side of each segment, on the upper
rim, there are generally a few extremely minute and short spines. From
the increase of these latter and of the intermediate spines, the
antero-lateral faces of the segments of the first cirrus, and of the
lower segments of the anterior ramus of the second cirrus (Pl. X, fig.
25), are almost always thickly paved with brush-like masses of spines.
The lower segments of the anterior ramus of the third cirrus is
generally, though not always, thus paved: these paved segments are much
broader than the others. The posterior rami of the second and third
cirri are often in some slight degree paved, though in other cases they
resemble the three posterior pair of cirri. The two segments of the
pedicels have bristles on their anterior faces, essentially arranged on
the same plan as on the segments of the rami: the bristles are generally
not so symmetrically arranged on the pedicels of the second and third
cirri, as on the three posterior pair. There are some exceptions to the
foregoing general rules: in the posterior cirri of _Alepas cornuta_,
there is only one pair of long spines to each segment (fig. 28); in
_Dichelaspis Lowei_, there are eight pair; in _Lepas fascicularis_, in
old specimens, the segments are paved with a triangular brush of spines;
the upper segments in _Pæcilasma eburnea_ support small oblong brushes;
and, lastly, in _Pæcilasma fissa_ (fig. 29), and _crassa_, the spines
form a single circle round each segment, interrupted on the two sides.
These spines are often doubly serrated or plumose: many of them on the
protuberant segments of the first three pair of cirri, are sometimes
coarsely and doubly pectinated.

_Caudal Appendages._--These are present (Pl. X, figs. 18 to 24) seated
on each side of the anus, in all the genera, except in Conchoderma,
Anelasma, and _Scalpellum villosum_; they consist of a very small
single segment, destitute of spines in Lepas, and spinose in Pæcilasma,
Dichelaspis, Oxynaspis, Scalpellum, and some species of Pollicipes; they
consist of several segments in Alepas, Ibla, Lithotrya, and in some
species of Pollicipes. In the latter genus, some species have their
caudal appendages multiarticulate, though so obscurely articulated, that
the passage (fig. 22) from several to one segment is seen to be easily
effected. When the appendage consists of many articulations, it is
generally about as long as the pedicel of the sixth cirrus; but in _Ibla
quadrivalvis_, it is four times as long. The segments are narrow,
slightly flattened, much tapering; each (fig. 24) is surmounted by a
ring of short spines, which are generally longest on the apex of the
terminal segment. I could never trace muscles into these appendages.

_Alimentary Canal._--The oesophagus is of considerable length: it is
formed of strong, transparent, much folded membrane, continuous with the
outer integuments, and moulted with them: it is surrounded by corium,
and as already stated, by numerous muscles: at its lower end it expands
into a bell, with the edges reflexed, and sometimes sinuous: this bell
lies within the stomach, and keeps the upper broad end expanded.
According to the less or greater distance of the mouth from the adductor
muscle, the oesophagus runs in a more or less parallel course to the
abdominal surface between the first and succeeding pairs of cirri, and
enters the stomach more or less obliquely. In Ibla alone, it passes
exteriorly to, and over the adductor scutorum muscle. The stomach lies
in a much curved, almost doubled course; it is often a little
constricted where most bent; it is broadest at the upper end, and here,
in Lepas and Conchoderma, there are some deep branching cæca; in the
latter of these two genera, the whole surface is, in addition, pitted in
transverse lines. The stomach is coated by small, opaque, pulpy,
slightly arborescent glands, believed to be hepatic; these are arranged
in longitudinal lines, in all the genera, except in Alepas, in which
they are transverse and reticulated: the whole stomach is thus coated.
There is, also, a coating of excessively delicate, longitudinal and
transverse muscles without striæ. The rectum varies in length, extending
inwards from the anus to between the bases of the second and fifth pair
of cirri: it is narrow, and formed of much folded transparent membrane,
resembling the oesophagus, continuous with the outer integuments, with
which it is periodically moulted. The anus is a small longitudinal slit,
in the triangular piece of membrane representing the abdomen, let in
between the last thoracic tergal arches, as already mentioned under the
head of the Metamorphoses; it lies almost between the caudal appendages,
and opens on the dorsal surface. Within the stomach, there can generally
be plainly seen, in accordance with the period of digestion when the
specimen was taken, a thin, yet strong, perfectly transparent epithelial
membrane, not exhibiting under the highest power of the microscope any
structure: it enters the branching cæca, and extends from the edge of
the bell of the oesophagus to the commencement of the closed rectum, and
consequently terminates in a point: it consists of chitine, like the
outer integuments of the animal, and by placing the whole body in
caustic potash, I have dissolved the outer coats of the stomach, and
seen the bag open at its upper end, perfectly preserved, floating in the
middle of the body, and full of the debris of the food. In most of the
specimens which I have examined, preserved in spirits of wine, this
epithelial lining was some little way distant and separate from the
coats of the stomach; and hence was thought by M. Martin St. Ange to be
a distinct organ, like the closed tube in certain Annelids.
Occasionally, I have seen one imperfect epithelial bag or tube within
another and later-formed one. Digestion seems to go on at the same rate
throughout the whole length of the stomach; if there be any difference,
the least digested portions lie in the lower and narrower part. The
prey, consisting generally of crustacea, infusoria, minute spiral
univalves, and often of the larvæ of Cirripedes, is not triturated: when
the nutritious juices have been absorbed, the rejectamenta are cast out
through the anus, all kept together in the epithelial bag, which is
excluded like a model of the whole stomach, with the exception of that
part coated by the bell of the oesophagus. I have sometimes thought that
the bag was formed so strong, for the sake of thus carrying out the
excrement entire, so as not to befoul the sack. I believe Lepas can
throw up food by its oesophagus; at least, I found in one case, many
_half-digested_ small Crustaceans in the sack, and others of the same
kind in the stomach.

_Circulatory System._--I can add hardly anything to what little has been
given by M. Martin St. Ange: like others, I have failed, as yet, in
discovering a heart. The whole body is permeated by channels, which have
not any proper coat: there is one main channel along the ventral surface
of the thorax, dividing and surrounding the mouth, and giving out
branches which enter the inner of the two channels in each cirrus: as
Burmeister has shown, there are also two channels in the penis. There
are two dorso-lateral channels in the prosoma, which are in direct
connection with the great main channel, running down the rostral (_i.
e._, ventral) side of the peduncle. This latter main channel branches
out in the lower part, and transmits the fluid through the ovarian
tubes, whence, I believe, it flows upwards and round the sack,
re-entering the body near the sides of the adductor scutorum muscle. The
main rostral channel (or artery?) in the uppermost part of the peduncle,
has a depending curtain, which, I think, must act as a valve, so as to
prevent the circulating fluid regurgitating into the animal's body
during the contractions of the peduncle.

_Nervous System and Organs of Sense._--In most of the genera, there are
six _main_ ganglia, namely, the supra-oesophageal, and five thoracic
ganglia; but in _Pollicipes mitella_ there are only four thoracic
ganglia. Of these, the first thoracic or infra-oesophageal ganglion is
considerably the largest and most massive; it is squarish, or oval, or
heart-shaped; it presents no trace of being formed by the union of two
lateral ganglia. Two great nerves spring from its under side (A),
represented in the woodcut on page 49, by dotted lines, and run straight
down amongst the viscera in the prosoma: these nerves are about as large
as those forming the collar and those running to the second ganglion;
hence, six great nerves meet here, two in front, two behind, and two on
the under side. At the anterior end, over the junction with the collar
chord, three equal-sized nerves rise on each side, with a fourth,
smaller one, outside; these go to the trophi and to the two olfactory
sacks. At the posterior end, on each side, a pair of nerves branch out
rectangularly, one of which (_a_,) goes to the first cirrus, and there
divides into two branches; of these, the upper runs up the cirrus, and
the lower one downwards. The other nerve (_b_), proceeding on each side
from this first thoracic ganglion, runs to the muscles beneath the basal
articulation of the first cirrus. The collar surrounding the oesophagus
is generally very long, sometimes equalling the whole thoracic chord; at
a middle point, a small branch is sent off, and at the anterior end
(_e_, _e_), close to the supra-oesophageal ganglia, double or treble
fine branches run to the true ovaria, lying close to the upper end of
the stomach. The four (or only three) other thoracic ganglia, when
viewed as transparent bodies, are seen to be solid; but in some of the
genera, as in Conchoderma, the outline plainly shows, that each consists
of a lateral pair fused together. The second thoracic ganglion (B) is
rather small; it is either close to the first, as in _Pollicipes
mitella_ and _Lepas fascicularis_, or far distant, as in Ibla. The third
(C) and fourth are of about the same size with the second: these three
ganglia send large branches to the second, third, and fourth pair of
cirri: other minute branches spring from their under sides, and from the
intermediate double chords. The fifth ganglion is larger and longer than
the three preceding ones, and gives off nerves to the fifth and sixth
pair of cirri; it is clearly formed by the union of the fifth, with what
ought to have formed a sixth ganglion. The two nerves going to the sixth
cirrus give off on their inner sides, each a great branch to the penis.
In _Pollicipes mitella_, in which there are only four instead of five
thoracic ganglia, it is evident from the outline and position of the
nerves going to the fourth pair of cirri, that the fourth ganglion is
fused into the fifth, itself, as we have just seen, normally composed of
two consecutive ganglia. In this Pollicipes there is other evidence of
concentration in the nervous system, for none of the ganglia show signs
of being formed of lateral pairs; the second is close to the first; and
the abdominal double chord is in part separated by a mere cleft; lastly,
as we shall immediately see, the same remark is applicable to the
supra-oesophageal ganglia.

The latter (D) alone remain to be described; they present far more
diversity in shape than do the thoracic ganglia; they are almost always
seen in outline to be laterally distinct, and usually resemble two pears
with their tapering ends cut off and united; in a transverse line they
are as long as the infra-oesophageal ganglion, but are much less
massive. In _Lepas fascicularis_ (D), they are pear-shaped; in
_Pollicipes mitella_ they are globular, and separated by a third
globular ganglion, which I believe is the ophthalmic ganglion, presently
to be described; in _Pollicipes spinosus_, however, the ophthalmic
ganglion is, as usual, placed in advance of the supra-oesophageal
ganglion, which latter, in this one species, shows no sign of being
formed of a lateral pair fused together. In _Alepas cornuta_ the
supra-oesophageal ganglion consists of two quite distinct ganglia,
elongated in the longitudinal axis of the body, and separated from each
other by the whole width of the mouth; the chord which unites them is of
the same thickness as the rest of the collar. In all the genera, from
the front of each of the two supra-oesophageal ganglia, a pair of
nerves, (_f_, _f_,) united and together as large as the collar nerve,
rises, and can be traced running unbranched, in a nearly straight line,
for a length equalling the whole rest of the nervous chord, so as to
supply the peduncle and the inside of the capitulum or sack. At the
inner ends of these two same ganglia, from a central point where they
are united, a little central branch runs in front to the adductor
scutorum and other adjoining muscles; and still smaller fibrils run
behind to the oesophageal muscles.

[Illustration: Diagram of the anterior portion of the nervous system in
_Lepas fascicularis_. A. First thoracic or infra-oesophageal ganglion.
B. Second thoracic. C. Third thoracic ganglion. D. Supra-oesophageal
ganglion. E. The two ophthalmic ganglia. F. Double eye. _a_. Nerve going
to first cirrus; _b_, to the muscles below the first cirrus; _c_, to the
second cirrus; _d_, to the third; _e_, nerves running to the ovaria;
_f_, double nerves supplying the sack and peduncle.]

_Ophthalmic Ganglia and Eyes._--Owing to Professor Leidy's[16] discovery
of eyes in a Balanus, I was led to look for them in the Lepadidæ.
Extending from the front of the two supra-oesophageal ganglia, two
chords may be seen in _Lepas fascicularis_ (of which a rude diagram is
here given), to run into two small, perfectly distinct oval ganglia
(E), which are not united by any transverse commissure. From the
opposite ends of these two ganglia smaller nerves run, and, bending
inwards at right angles, enter, beyond the middle, an elongated (F),
almost black, eye, composed of two eyes united together. Although in
outline the eye appears single, two lenses can be distinctly seen at the
end, directed upwards and towards the ganglia; two pigment-capsules can
also be distinguished; these are deep and cup-formed, and of a dark
reddish-purple. The following measurements will show the proportions of
the parts in a specimen of the _Lepas fascicularis_ having a capitulum
4/10ths of an inch in length.

  Double eye { length                         26/6000
             { width                          13/6000

  Diameter of single lens                      6/6000

  Ophthalmic ganglion { length                16/6000
                      { breadth               11/6000

  Supra-oesophageal ganglion, }
  transverse or longest axis    }            126/6000
  of both together              }

  Supra-oesophageal ganglion, }
  longitudinal axis of          }             45/6000

  Infra-oesophageal ganglion, }
  transverse axis of            }            120/6000

  Infra-oesophageal ganglion, }
  longitudinal axis of          }            114/6000

   [16] Proceedings of the Academy of Natural Sciences,
   Philadelphia. No. i, vol. iv, Jan. 1848.

In _Conchoderma aurita_ the ophthalmic ganglia are much smaller, and
nearer to the supra-oesophageal ganglion, than in _L. fascicularis_. In
_Alepas cornuta_ the ophthalmic chords run towards each other from the
two distant and separate supra-oesophageal ganglia; and the ophthalmic
ganglia, (instead of being quite separate, as in _L. fascicularis_,) are
united by their front ends, and the two eyes instead of standing some
way in front, with nerves running to them, are embedded on the double
ophthalmic ganglion; the pigment-capsules here, also, have the shape of
mere saucers, and are joined back to back, with the two lenses
projecting far out of them. In neither sex of Ibla could I perceive that
the eye was double. In _Pollicipes spinosus_ the ophthalmic ganglion
stands in front of the single supra-oesophageal ganglion, and shows no
signs of being formed of a lateral pair; the eyes themselves, however,
differently from, in all the foregoing cases, are, though approximate,
quite distinct. In _Pollicipes mitella_ I did not see the eyes; but the
ophthalmic ganglion consists, as I believe, of a single globular one,
placed exactly between the two globular, supra-oesophageal ganglia, all
three being of nearly equal size. Professor Leidy does not mention the
ophthalmic ganglia; hence I infer that in Balanus, which is a more
highly organised Cirripede, they are fused into the supra-oesophageal
ganglion.

In all the genera, the double eye is seated deep within the body; it is
attached by fibrous tissue to the radiating muscles of the lowest part
of the oesophagus, and lies actually on the upper part of the stomach;
consequently, a ray of light, to reach the eye, has to pass through the
exterior membrane and underlying corium connecting the two scuta, and to
penetrate deeply into the body. In living sessile Cirripedes, vision
seems confined to the perception of the shadow of an object passing
between them and the light; they instantly perceived a hand passed
quickly at the distance of several feet between a candle and the basin
in which they were placed.

As the infra-oesophageal ganglion sends nerves to the trophi and to the
first pair of cirri, it must correspond to the segments, from the fourth
to the ninth inclusive, of the archetype crustacean. The state of the
supra-oesophageal and ophthalmic ganglia appears to me very interesting:
I do not believe that in any _mature_ ordinary crustacean, the first or
ophthalmic ganglion can be shown to be distinct from the two succeeding
ganglia, or to be itself composed of a pair laterally distinct. The
ganglia, corresponding with the second and third segments of the body,
which should normally support two pair of antennæ, are in the Lepadidæ
united together; but laterally they are generally distinct in outline,
and are actually separate in Alepas: the supra-oesophageal ganglion
shows also its double nature, by giving rise to a pair of large double
nerves, evidently corresponding with the two pair of antennular nerves
in ordinary crustaceans. The embryonic condition of the whole
supra-oesophageal portion of the nervous system in the Lepadidæ,
corresponds with the rudimentary state of the only organ of sense
supplied by it, namely, the eye, which in size and general appearance
has retrograded to the state in which it was in, during the first stage
of development of the larva;--I have used the term embryonic, because,
in the embryos of ordinary crustacea, all the ganglia are at first
longitudinally distinct, and laterally quite separate. The conclusion at
which we before arrived from studying the metamorphoses, namely, that
the whole peduncle and capitulum consisted of the first three segments
of the head, is beautifully supported by the structure of the nervous
system, in which these parts are seen to be supplied with nerves
exclusively from the supra-oesophageal ganglion: now in ordinary
crustacea the supra-oesophageal ganglion sends nerves to the eyes and
the two pair of antennæ corresponding, as is known by embryological
dissections, to the first three segments of the body. Moreover, it is
asserted that the carapace which covers the thorax in crustacea, is not
formed by the development of the first segment; and this, likewise, may
be inferred to be the case with the peduncle and capitulum in the
Lepadidæ, as the nerves of the ophthalmic ganglia go exclusively to the
eyes. Finally, I may remark that in Pollicipes, looking to the whole
nervous system, the state of concentration nearly equals that in certain
macrourous decapod crustaceans, for instance the _Astacus marinus_, of
which a figure is given by Milne Edwards.

_Olfactory Organs._--In the outer maxillæ, at their bases where united
together, but above the basal fold separating the mouth from the body,
there are, in all the genera, a pair of orifices (Pl. X, fig. 16); these
are sometimes seated on a slight prominence, as in Lithotrya, or on the
summit of flattened tubes (Pl. X, fig. 17), projecting upwards and
towards each other, as in Ibla, Scalpellum, and Pollicipes. In Ibla
these tubular projections rise from almost between the outer and inner
maxillæ. It is impossible to behold these organs, and doubt that they
are of high functional importance to the animal. The orifice leads into
a deep sack lined by pulpy corium, and closed at the bottom. The outer
integument is inflected inwards, (hence periodically moulted,) and
becoming of excessive tenuity, runs to near the bottom of the sack,
where it ends in an open tube: so excessively thin is this inflected
membrane, that, until examining Anelasma, I was not quite certain that I
was right in believing that the outer integument did not extend over the
whole bottom. I several times saw a nerve of considerable size entering
and blending into a pulpy layer at the bottom of the sack of corium; but
I failed in tracing to which of the three pair of nerves, springing from
the front end of the infra-oesophageal ganglion, it joined. I can hardly
avoid concluding, that this _closed_ sack, with its naked bottom, is an
organ of sense; and, considering that the outer maxillæ serve to carry
the prey entangled by the cirri towards the maxillæ and mandibles, the
position seems so admirably adapted for an olfactory organ, whereby the
animal could at once perceive the nature of any floating object thus
caught, that I have ventured provisionally to designate the two orifices
and sacks as olfactory.

_Acoustic_ (?) _Organs._--A little way beneath the basal articulation of
the first cirrus (Pl. IX, fig. 4 _d_, and Pl. IV, fig. 2 _e_), on each
side, there may be seen a slight swelling, and on the under side of
this, a transverse slit-like orifice, 1/20th of an inch in length in
Conchoderma, but often only half that size. In Ibla this orifice is
seated lower down (Pl. IV, fig. 8 _a´_, _e_), between the bases of the
first and second cirri, which are here far apart: in _Alepas cornuta_ it
is placed rather nearer to the adductor scutorum muscle, namely, beneath
the mandibles. The orifice leads into a rather deep and wide meatus; the
external integument is turned in for a short distance, widening a
little, and then ends abruptly. The meatus, enlarging upwards, is lined
by thick pulpy corium, and is closed at the upper end; from its summit
is suspended a flattened sack of singular and different shapes in the
different genera. This, the so-called acoustic sack of _Conchoderma
virgata_, is figured Pl. IX, fig. 6. The deep and wide notch faces
towards the posterior end of the animal; the inferior lobe, thus almost
cut off, is flattened in a different plane from the upper part; the lobe
is lodged in a little pouch of corresponding form, leading from the open
meatus in which the upper part is included. In _Conchoderma aurita_, the
top of the acoustic sack is narrower and more constricted, the whole
more rounded, and the lobe more turned down. In _Lepas fascicularis_ the
notch is not so deep or wide, and the lobe larger. In _Ibla Cumingii_
the sack is of the shape of a vase, with one corner folded over. In
_Scalpellum vulgare_ it is small, oval, with the lower end much pushed
in, and furnished with a little crest. Lastly, in _Pollicipes mitella_
it is simply oval. In all cases the sack is empty, or contains only a
little pulpy matter: it consists of brownish, thick, and remarkably
elastic tissue, formed, apparently, of transverse little pillars,
becoming fibrous on the outside, and with their inner ends appearing
like hyaline points. The mouth of the acoustic sack (removed in the
drawing) is closed by a tender diaphragm, through which I saw what I
believe was a moderately-sized nerve enter; I have not yet succeeded in
tracing this nerve. The first pair of cirri seem, to a certain extent,
to serve as antennæ, and therefore the position of an acoustic organ at
their bases, is analogous to what takes place in crustacea; but there
are not here any otolites, or the siliceous particles and hairs, as
described by Dr. Farre, in that class. Nevertheless, the sack is so
highly elastic, and its suspension in a meatus freely open to the water,
seems so well adapted for an acoustic organ, that I have provisionally
thus called it. In the larva, as I have shown, a pouch, certainly
serving for some sense, I believe for hearing, is seated in quite a
different position at the anterior end of the carapace. I may mention
that I found sessile Cirripedes very sensitive of vibrations in objects
adjoining them, though not, apparently, of noises in the air or water.
In a group of specimens, I could not touch one even most delicately
with a needle, without all the adjoining ones instantly withdrawing
their cirri; it made no difference if the one touched had its operculum
already closed and motionless.

_Reproductive System_,--_Male Organs._--All the Cirripedia which I have
hitherto examined, with the exception of certain species of Ibla and
Scalpellum, are hermaphrodite or bisexual.[17] I shall so fully describe
the sexual relations of the several species of these two genera, under
their respective headings, and at the end of the genus of Scalpellum,
that I will not here give even an abstract of the grounds on which my
firm belief is based, that the masculine power of certain hermaphrodite
species of Ibla and Scalpellum, is rendered more efficient by certain
parasitic males, which, from their not pairing, as in all hitherto known
cases, with females, but with hermaphrodites, I have designated
_Complemental Males_.

   [17] I am compelled to differ greatly from the account given by
   Prof. Steenstrup of the reproductive system in the Cirripedia, in
   his 'Untersuchungen über das Vorkommen des Hermaphroditismus, ch.
   v, 1846;--a translation of which I have seen, owing to the great
   kindness of Mr. Busk. Mr. Goodsir has described ('Edin. New Phil.
   Journal,' July 1843,) what he considers the male of Balanus; but
   I have seen this same parasitic creature charged with ova,
   including larvæ! From the resemblance of the larvæ to the little
   crustacean described by Mr. Goodsir, in the same paper, as a
   distinct parasite, I believe the latter to be the male of his
   so-called male Balanus, and that all belong to the same species,
   allied to Bopyrus. This genus, as is well known, is parasitic on
   other crustacea; and it is a rather interesting fact thus to
   find, that this new parasite which is allied to Bopyrus, in
   structure, is likewise allied to it in habits, living attached to
   Cirripedia, a sub-class of the crustacea.

The male organs have been well described by M. Martin St. Ange, whose
observations have since been confirmed by R. Wagner.[18] The testes are
small, often leaden-coloured, either pear or finger-shaped, or branched
like club-moss,--these several forms sometimes occurring in the same
individual; they coat the stomach, enter the pedicels, and even the
basal segments of the rami of the cirri, and in some genera occupy
certain swellings on the thorax and prosoma, and in others the
filamentary appendages: the testes seen in the apex in one of these
appendages in Conchoderma, is represented in Pl. IX, fig. 5. The two
vesiculæ seminales are very large; they lie along the abdominal surface
of the thorax, and generally (but not in some species of Scalpellum)
enter the prosoma, where their broad ends are often reflexed; here the
branched vessels leading from the testes enter. The membrane of the
vesiculæ seminales is formed of circular fibres; and is, I presume,
contractile, for I have seen the spermatozoa expelled with force from
the cut end of a living specimen. The two canals leading from the
vesiculæ generally unite in a single duct at the base of the penis; but
in _Conchoderma aurita_, half-way up it. The probosciformed penis,
except in certain species of Scalpellum, is very long; it is capable of
the most varied movements; it is generally hairy, especially at the end;
it is supported on a straight unarticulated basis, which in _Ibla
quadrivalvis_ alone (Pl. IV, fig. 9 _a_), is of considerable length; in
this species, the upper part is seen to be as plainly articulated as one
of the cirri; in Alepas, the articulations are somewhat less plain, and
in the other genera, the organ can be said only to be finely ringed, but
these rings no doubt are in fact obscure articulations. In the females
of _Ibla Cumingii_ and _Scalpellum ornatum_, there is, of course, no
penis.

   [18] In 'Müller's Archiv,' 1834, p. 467. I have already several
   times referred to M. Martin St. Ange's excellent Memoir, read
   before the Academy of Sciences, and subsequently, in 1835,
   published separately.

_Female Organs._--M. Martin St. Ange has described how the peduncle[19]
is gorged with an inextricable mass of branching ovarian tubes, filled
with granular matter and immature ova. In Conchoderma and Alepas, the
ovarian tubes run up in a single plane (Pl. IX, fig. 3,) between the two
folds of corium round the sack. Here the development of the ova can be
well followed: a minute point first branches out from one of the tubes;
its head then enlarges, like the bud of a tulip on a footstalk; becomes
globular; shows traces of dividing, and at last splits into three, four,
or five egg-shaped balls, which finally separate as perfect ova. Within
the peduncle, the ovarian tubes branch out in all directions, and within
the footstalks of the branches (differently from what takes place round
the sack), ova are developed, as well as at their ends. Close together,
along the rostral (_i. e._, ventral) edge of the peduncle, two nearly
straight, main ovarian tubes or ducts may be detected, which do not give
out any branches till about half way down the peduncle, where they
subdivide into branches, which inosculate together, and give rise to the
mass filling the peduncle, and sometimes, as we have just seen, sending
up branches round the sack. These two main unbranched ovarian ducts,
followed up the peduncle, are seen to enter the body of the Cirripede
(close along side the great double peduncular nerves), and then
separating, they sweep in a large curve along each flank of the prosoma,
under the superficial muscles, towards the bases of the first pair of
cirri; and then rising up, they run into two glandular masses. These
latter rest on the upper edge of the stomach, and touch the cæca where
such exist; they were thought by Cuvier to be salivary glands. They are
of an orange colour, and form two, parallel, gut-formed masses, having,
in Conchoderma, a great flexure, and generally dividing at the end near
the mouth into a few blunt branches. I was not able to ascertain whether
the two main ducts, coming from the peduncle, expanded to envelope them,
or what the precise connection was. The state of these two masses varied
much; sometimes they were hollow, with only their walls spotted with a
few cellular little masses; at other times they contained or rather were
formed of, more or less globular or finger-shaped aggregations of pulpy
matter; and lastly, the whole consisted of separate pointed little
balls, each with a large inner cell, and this again with two or three
included granules. These so closely resembled, in general appearance
and size, the ovigerms with their germinal vesicles and spots, which I
have often seen at the first commencement of the formation of the ova in
the ovarian tubes in the peduncle, that I cannot doubt that such is
their nature. Hence I conclude, that these two gut-formed masses are the
true ovaria. I may add, that several times I have seen in the two long,
unbranched ducts, connecting the true ovaria and the ovarian tubes in
the peduncle, pellets of orange-coloured cellular matter (_i. e._,
ovigerms) forming at short intervals little enlargements in the ducts,
and apparently travelling into the peduncle.

   [19] I may here mention, that in all sessile Cirripedes, the
   ovarian branching tubes lie between the calcareous or membranous
   basis and the inner basal lining of the sack, and to a certain
   height upwards round the sack: the true ovaria and the two ducts
   occupy the same position as in the Lepadidæ.

The structure here described is quite conformable with that which we
have seen in the larva; in the latter, two gut-formed masses of equal
thickness extended from the cæca of the stomach to within the future
peduncle, where the cement-ducts entered them, and where, after a short
period, they were seen to expand into a mass of ovarian tubes. In the
mature Cirripede, the cement-ducts can still be found united to the
ovarian tubes in the middle of peduncle; and the cause of the wide
separation of the true ovaria and ovarian tubes, can be simply accounted
for by the internal, almost complete intersection of the animal, which
takes place during the last metamorphosis.

The ova, when excluded, remain in the sack of the animal until the larvæ
are hatched; they are very numerous, and generally form two concave,
nearly circular, leaves, which I have called after Steenstrup and other
authors, the _ovigerous lamellæ_ (Pl. IV, fig. 2 _b_). These lamellæ lie
low down on each side of the sack: in _Conchoderma virgata_, however,
there is often only a single lamella, forming a deeply concave cup: in
_C. aurita_ there are generally on each side four lamellæ, one under the
other. The ova lie in a layer from two to four deep; and all are held
together by a most delicate transparent membrane, which separately
enfolds each ovum: this membrane is often thicker and stronger round the
margins of the lamellæ, where they are united, in a peculiar manner,
presently to be described, to a fold of skin, on each side of the sack:
these two folds, I have called the _ovigerous fræna_ (Pl. IV, fig. 2
_f_).

M. Martin St. Ange, describes an orifice under the carina, by which he
supposes the ova to enter the sack; this, after repeated and most
careful examinations, I venture to affirm does not exist; on the
contrary, I have every reason to believe that the ova enter the sack in
the following curious manner. Immediately before one of the periods of
exuviation, the ova burst forth from the the ovarian tubes in the
peduncle and round the sack, and, carried along the open circulatory
channels, are collected (by means unknown to me) beneath the
chitine-tunic of the sack, in the corium, which is at this period
remarkably spongy and full of cavities. The corium then forms or rather
(as I believe) resolves itself into the very delicate membrane
separately enveloping each ovum, and uniting them together into two
lamellæ; the corium having thus far retreated, then forms under the
lamellæ the chitine-tunic of the sack, which will of course be of larger
size than the last-formed one, now immediately to be moulted with the
other integuments of the body. As soon as this exuviation is effected,
the tender ova, united into two lamellæ, and adhering, as yet, to the
bottom of the sack, are exposed: as the membranes harden, the lamellæ
become detached from the bottom of the sack, and are attached to the
ovigerous fræna. To demonstrate this view, an individual should have
been found, with both the old and new chitine tunic of the sack, and
with the lamellæ lying between them; this, I believe, I have seen, but
it was before I understood the full importance of the fact: a great
number of specimens would have to be examined in order to succeed again,
for the changes connected with exuviation supervene very quickly. I
have, however, several times found the ova so loose under the sack, as
to be detached with a touch from the ovarian tubes; and I have twice
carefully examined specimens, which had just moulted, as shown by even
the mandibles being flexible, in which the lamellæ had not become united
to the fræna, but still adhered to the newly-formed chitine tunic of
the sack; in these, the ova were so tender, that they broke into pieces
rather than be separated from the membrane of the lamella, itself hardly
perfectly developed, for pulpy cellular matter adhered outside some of
the ova. These and other facts are quite inexplicable on any other view
than that advanced.

As the lamellæ are formed without organic union with the parent, they
would be liable to be washed out of the widely open sack of the
Lepadidæ, if they had not been specially attached to the _fræna_. These
fræna consist of a pair of more or less semicircular folds of skin,
depending inside the sack, on each side of the point of attachment of
the body. The fræna are often of considerable size, but in Ibla, they
are very minute; they are formed of chitine tunic with underlying
corium, like the rest of the sack; on their crests, there is a row, or a
set of circular groups, or a broad surface, covered, either with minute,
pointed, bead-like bodies mounted on long hair-like footstalks, or with
staff-formed bodies on very short footstalks. I measured some of the
bead-like bodies, in _Lepas anserifera_, and they were 1/2000th of an
inch in diameter, and the footstalks three or four times as long as the
elongated heads. These heads, of whatever shape they may be, have an
opaque, and, I believe, glandular centre; I could not make out with
certainty an aperture at their ends, but, I believe, such exists, and
they seem to secrete a substance, which hardens into a strong membrane,
serving to unite the crest of the frænum to the edges of the lamellæ. In
one case, this bit of membrane seemed formed of a woven mass of threads.
These little glandular bodies, with the membrane formed by them, are
cast off at each exuviation, and new glands formed on the crest of the
frænum underneath. In some species of Pollicipes, (viz., _P. cornucopia_
and _elegans_,) the fræna, though present and large, are functionless
and destitute of the glands: I believe, they exist in this same
functionless condition, and in rather a different position in the
sessile Cirripedes, and that in this family they serve as Branchiæ.

The above-described method by which Cirripedia lay their eggs, namely,
united together in a common membrane, placed between their old outer and
new inner integuments, and the manner in which the lamellæ, when thus
formed, are retained for a time fastened to the fræna, and are then cast
off, appears to me very curious. In some of the lower Crustacea, it is
known, that the ova escape by rupturing the ovisacs formed by the
protruded ovarian tubes, and this is the nearest analogy with which I am
acquainted. The ova are impregnated (as I infer from the state of the
vesiculæ seminales), when first brought into the sack, and whilst the
membrane of the lamellæ is very tender: the long probosciformed penis
seems well adapted for this end. In the male of _Ibla Cumingii_, which
has not a probosciformed penis, the whole flexible body, probably,
performs the function of the penis: in _Scalpellum ornatum_, however,
the spermatozoa must be brought in by the action of the cirri, or of the
currents produced by them. That cross impregnation may and sometimes
does take place, I infer from the singular case of an individual, in a
group of Balani, in which the penis had been cut off, and had healed
without any perforation; notwithstanding which fact, larvæ were included
in the ova.

_Exuviation; Rate of Growth; Size._--I have had occasion repeatedly to
allude to the exuviation of the Lepadidæ: with the exception of the
genus Lithotrya,[20] in which the calcareous scales on the peduncle,
together with the membrane connecting them, is cast off, neither the
valves nor the membrane uniting them, nor that forming the peduncle with
its scales and styles, are moulted; but the surface gradually
disintegrates and is removed, perhaps sometimes in flakes, whilst new
and larger layers are formed beneath. In Scalpellum, I ascertained that
the new membrane, connecting together the newly-formed calcified rims
under the valves of the capitulum, was formed as a fold, with the
articulated spines which it bears, all adpressed in certain definite
directions. This fold of new membrane, when the old membrane splits and
yields, of course expands, and thus the size of the capitulum is
increased. In the peduncle, lines of splitting can seldom be perceived,
except, indeed, in the sub-globular, embedded, downward-growing peduncle
of Anelasma, as described under that genus. I do not understand what
determines the complicated lines of splitting of the old membrane
between the several valves of the capitulum,--without it be simply, that
along these lines alone, the old membrane is not strengthened by the new
membrane being closely applied under it, the new being formed, as we
have just said, in a fold, in order to allow of increase in size.
Although, as I believe, there is strictly no exuviation in the outer
membranes of mature Lepadidæ, it seems that narrow strips of membrane
are cast off from between the valves, for the few first moults, after
the final metamorphosis of the larva. I may here remark that, in most
sessile Cirripedes, the outside membrane connecting the operculum and
shell, is regularly moulted.

   [20] The external integuments being moulted in Crustacea, but not
   in the Cirripedia, may appear, at first, an important difference:
   but we here see that non-exuviation is not universal amongst the
   Lepadidæ, and, on the other hand, according to M. Joly, ('Annales
   des Sciences Naturelles,' 2d series, Zoolog.), there is one true
   crustacean, the _Isaura cycladoides_, which has a persistent
   bivalve shell.

The delicate tunic lining the sack, (a mere duplicature of that thick
one, forming the outside of the capitulum, and generally transformed
into valves,) and the integuments of the whole body, are regularly
moulted. With these integuments, the membrane lining the oesophagus, the
rectum, and the deep olfactory pouches, and the horny apodemes of the
maxillæ, are all cast together. I have seen a specimen of Lepas, in
which, from some morbid adhesion, the old membrane lining one of the
olfactory pouches had not been moulted, but remained projecting from the
orifice as a brown shrivelled scroll. The new spines on the cirri (and
on the maxillæ) are formed within the old ones; but as they have to be a
little longer than the latter, and as they cannot enter these up to
their very points, their basal portions are not thus included, but are
formed, running obliquely across the segments of the cirri; and what is
curious, these same basal portions are turned inside out, like the
fingers of a glove when hastily drawn off. After the exuviation of the
old spines, the new spines have their inverted basal portions drawn out
from within the segments, and turned outside in, so as to assume their
proper positions.

All Cirripedia grow rapidly: the yawl of H. M. S. _Beagle_ was lowered
into the water, at the Galapagos Archipelago, on the 15th of September,
and, after an interval of exactly thirty-three days, was hauled in: I
found on her bottom, a specimen of _Conchoderma virgata_ with the
capitulum and peduncle, each half an inch in length, and the former
7/20ths in width: this is half the size of the largest specimen I have
seen of this species: several other individuals, not half the size of
the above, contained numerous ova in their lamellæ, ready to burst
forth. Supposing the larva of the largest specimen became attached the
first day the boat was put into the water, we have the metamorphosis, an
increase of length from about .05, the size of the larva, to an whole
inch, and the laying of probably several sets of eggs, all effected in
thirty-three days. From this rapid growth, repeated exuviations must be
requisite. Mr. W. Thompson, of Belfast, kept twenty specimens of
_Balanus balanoides_, a form of much slower growth, alive, and on the
twelfth day he found the twenty-first integument, showing that all had
moulted once, and one individual twice within this period. I may here
add, that the pedunculated Cirripedes never attain so large a bulk as
the sessile; _Lepas anatifera_ is sometimes sixteen inches in length,
but of this, the far greater portion consists of the peduncle.
_Pollicipes mitella_ is the most massive kind; I have seen a specimen
with a capitulum 2.3 of an inch in width.

_Affinities._--Considering the close affinity between the several
genera, there are, I conceive, no grounds for dividing the Lepadidæ into
sub-families, as has been proposed by some authors, who have trusted
exclusively to external characters. In establishing the eleven genera in
the Lepadidæ, no one part or set of organs affords sufficient diagnostic
characters: the number of the valves is the most obvious, and one of the
most useful characters, but it fails when the valves are nearly
rudimentary, and when they are numerous: the direction of their lines of
growth is more important, and fails to be characteristic only in
Scalpellum: with the same exception, the presence or abscence of
calcified or horny scales on the peduncle is a good generic character.
For this same end, the shape of the scuta and carina, but not of the
other valves, comes into play. In three genera, the presence of
filamentary appendages on the animal's body is generic; in Pollicipes,
however, they are found only on three out of the six species. The number
of teeth in the mandibles, and the shape of the maxillæ, often prove
serviceable for this end; as does more generally the presence of caudal
appendages, and whether they be naked or spinose, uniarticulate or
multiarticulate; in Pollicipes alone this part is variable, being
uni-and multi-articulate; and in one species of Scalpellum they are
absent, though present in all the others. The shape of the body, the
absence or presence of teeth on the labrum, the inner edge of the outer
maxillæ being notched or straight, the prominence of the olfactory
orifices, the arrangement of the spines on the cirri, and the number and
form of their segments, are only of specific value.

Comparing the pedunculated and sessile Cirripedes, it is, I think,
impossible to assign them a higher rank than that of Families. The chief
difference between them consists, in the Lepadidæ, in the presence of
three layers of striæ-less muscles, longitudinal, transverse and
oblique, continuously surrounding the peduncle, but not specially
attached to the scuta and terga; and on the other hand, in the
Balanidæ, of five longitudinal bundles of voluntary muscles, with
transverse striæ, fixed to the scuta and terga, and giving them powers
of independent movement. In the Lepadidæ, the lower valves, or when such
are absent, the membranous walls of the capitulum, move with the scuta
and terga when opened or shut; and the lower part of the capitulum is
separated by a moveable peduncle from the surface of attachment; in the
sessile Cirripedes, the lower valves are firmly united together into an
immovable ring, fixed immovably on the surface of attachment. I will not
compare the softer parts, such as the cirri and trophi, of the Lepadidæ
with those of the Balanidæ, as my examination of this latter family is
not fully completed: I will only remark, that there is a very close
general resemblance, more especially with the sub-family Chthamalinæ.

_Geographical Range; Habitats._--The Pedunculated Cirripedes extend over
the whole world; and most of the individual species have large ranges,
more especially, as might have been expected, those attached to floating
objects; excepting these latter, the greater number inhabit the warmer
temperate, and tropical seas. Of those attached to fixed objects, or to
littoral animals, it is rare to find more than three or four species in
the same locality. On the shores of Europe I know of only three, viz., a
Scalpellum, Pollicipes, and Alepas. At Madeira (owing to the admirable
researches of the Rev. R. T. Lowe), two Pæcilasmas, a Dichelaspis, and
an Oxynaspis are known. In New Zealand, there are two Pollicipes and an
Alepas, and, perhaps, a fourth form. From the Philippine Archipelago, in
the great collection made by Mr. Cuming, there are a Pæcilasma, an Ibla,
a Scalpellum, Pollicipes, and Lithotrya. Of all the Lepadidæ, nearly
half are attached to floating objects, or to animals which are able to
change their positions; the other half are generally attached to fixed
organic or inorganic bodies, and more frequently to the former than to
the latter. Most of the species of Scalpellum are inhabitants of deep
water; on the other hand, most of Pollicipes,[21] of Ibla, and Lithotrya
are littoral forms. The species of Lithotrya have the power of
excavating burrows in calcareous rocks, shells, and corals; and the
singular manner in which this is effected, is described under that
genus. Anelasma has its sub-globular peduncle deeply embedded in the
flesh of Northern Sharks; and I have seen instances of the basal end of
the peduncle of _Conchoderma aurita_, being sunk into the skin of
Cetacea; in the same way the point of the peduncle in the male of Ibla,
is generally deeply embedded in the sack of the female. I believe in all
these cases, the cementing substance affects and injures the corium or
true skin of the animal on which the creature is parasitic, whilst the
surrounding parts, being not injured, continue to grow upwards, thus
causing the partial embedment of the Cirripede. In the case of Anelasma,
we have growth at the end of the peduncle, and consequently downward
pressure, and this may possibly cause absorption to take place in the
skin of the shark at the spot pressed on.

   [21] I am informed by Mr. L. Reeve that _Pollicipes mitella_ is
   eaten on the coast of China; and Ellis states ('Phil. Trans.,'
   1758) that this is the case with _P. cornucopia_ on the shores of
   Brittany. It is well known that the gigantic _Balanus psittacus_
   on the Chilian coast, is sought after as a delicacy; and I am
   assured, by Mr. Cuming, that it deserves its reputation.

_Geological History._--Having treated this subject at length, in the
volume of the Palæontographical Society for 1851, I will not here enter
on it: I will only remark, that the Lepadidæ or Pedunculated Cirripedes
are much more ancient, according to our present state of knowledge, than
the Balanidæ. The former seem to have been at their culminant point
during the Cretaceous Period, when many species of Scalpellum and
Pollicipes, and a singular new genus, Loricula, existed; Pollicipes is
the oldest genus, having been found in the Lower Oolite, and, perhaps,
even in the Lias. The fossil species do not appear to have differed
widely from existing forms.


_Genus_--LEPAS. Plate I.

  LEPAS. _Linnæus._[22] Systema Naturæ, 1767.

  ANATIFA. _Brugière._[23] Encyclop. Method. (des Vers), 1789.

  ANATIFERA. (_Lister_) et plerumque Auctorum Anglicorum.

  PENTALASMIS. (_Hill._) _Leach._ Journal de Physique, July, 1817.

  PENTALEPAS. _De Blainville._ Dict. des Sci. Nat., 1824.

  DOSIMA. _J. E. Gray._ Annals of Philosophy, vol. x, 1825.

   [22] Linnæus, as is well known, included under this genus both
   the pedunculated and sessile Cirripedes. According to the rules
   of the British Association, the name Lepas must be retained for
   part of the genus; and as the sessile division was named Balanus,
   by Lister and Hill, even before the invention of the binomial
   system, and subsequently, in 1778, by Da Costa, and again, in
   1789, by Brugière, there can be no question that Lepas must be
   applied to the pedunculated section of the genus. In this
   instance it is particularly desirable to recur to the Linnean
   name, as no other name has been _generally_ adopted. Had not
   Lister and Sir J. Hill published before the binomial system,
   their names of Anatifera and Pentalasmis would have had prior
   claims to Lepas.

   [23] The date of this publication is almost universally given as
   1792, apparently caused by an error in the title-page of the
   First Part, which has consequently been cancelled. The First Part
   contains Anatifa and Balanus, and was published in 1789. The
   Second Part was published in 1792, and has a corrected title-page
   for the whole _volume_.

_Valvæ 5, approximatæ: carina sursùm inter terga extensa, deorsùm aut
furcâ infossâ aut disco externo terminata: scuta subtriangula, umbonibus
ad angulum rostralem positis._

Valves 5, approximate: carina extending up between the terga,
terminating downwards in an embedded fork, or in an external disc: scuta
sub-triangular, with their umbones at the rostral angle.

Filaments seated beneath the basal articulation of the first cirri;
mandibles with five teeth; maxillæ step-formed; caudal appendages
uniarticulate, smooth.

    _Distribution._--Mundane; attached to floating objects.

_Description._--Capitulum flattened, sub-triangular, composed of five
approximate valves. The valves are either moderately thick and
translucent, or very thin and transparent; and hence, though themselves
colourless, they are often coloured by the underlying corium. Their
surfaces are either smooth and polished, or striated, or furrowed, and
sometimes pectinated. They are not subject to disintegration; they are
generally naked, except on the borders, where they are coated, and held
together by membrane; in _L. fascicularis_, however, the valves are
covered with thin membrane, bearing very minute spines. The manner of
growth of the valves will be best described under each. All the valves,
even in the same species, are subject to considerable variation in
shape, more especially the terga.

_Scuta._--These valves are sub-triangular in outline, with the basal
margin straight and rather short; and with occludent and tergo-carinal
margins more or less protuberant; in _L. fascicularis_, however, the
basal (Pl. I, fig. 6), and occludent margins are slightly reflexed and
prominent. A ridge, generally runs from the umbo to the upper point.
Internally, there is no conspicuous pit for the adductor muscle; under
the umbones, there is generally either on both valves, or only on the
right-hand side (Pl. I, fig. 1 _c_), a small calcareous projection or
tooth, of variable size and shape, even in the same species; it is
generally largest on the right-hand valve; these teeth at first sight
appear to form a hinge, uniting the opposite scuta at their umbones, but
this is not really the case, and their use appears to be only to give
attachment to the membrane uniting the valves together, and to the
peduncle. The basal margin is internally strengthened by a calcified
rim, more or less developed. The umbones (and primordial valves when
distinguishable,) are seated at the rostral angles; during growth the
basal margin is not added to, and the occludent margin only to small
extent; hence the main growth of the valve is at the upper end, and
along the carina-tergal margin. In _L. fascicularis_, however, the basal
reflexed margin is slightly added to beneath the umbo.

_Terga_,--flat, small compared with the scuta, usually of an irregular
quadrilateral figure, with the two upper or occludent margins very
short, in proportion to the two (carinal and scutal) lower margins; all
the margins are nearly straight. The two occludent margins, generally
meet each other at about right angles, forming a small triangular
projection; in _L. fascicularis_, however, the occludent margin is
formed by a single, slightly curved line. The umbones (and primordial
valves when distinguishable) are not seated at the uppermost point, but
at the angle where the carinal margin unites to the upper of the two
occludent margins: during growth the terga are added to, both on the
occludent and on the scutal margins, and slightly along the carinal
margin; hence their growth is unequally _quaqua-versal_, except at one
angle of the irregular quadrilateral figure.

_Carina._--This is always very narrow and curved, concave within, often
carinated and barbed exteriorly; it extends upwards between the terga
for one half or two thirds of their length: at the lower extremity it
ends (with the exception of _L. fascicularis_), in a small fork (Pl. I,
fig. 1, _a_, _b_) rectangularly inflected and embedded in the membrane,
beneath the basal margin of the scuta. From comparing this lower part of
the carina in _L. australis_ (fig. 5 _a_), with the same part in some of
the species of the allied genus Pæcilasma, it would appear that the fork
is formed by an oblong disc, more and more notched at the end, and with
the rim between the two points more or less folded backwards:
conformably with this view, in very young specimens of _L. australis_,
instead of a large and sharp fork, there is a small disc. The only use
of the fork appears to be to give firm attachment to the membrane
uniting the valves and peduncle. In _L. fascicularis_, instead of a
fork, there is a broad, oblong disc (figs. 6, 6 _a_), rectangularly
inflected; it is much longer than the fork, in proportion to the upper
part of the carina; the disc is not more deeply embedded than the upper
part. The umbo (and primordial valve when distinguishable,) of the
carina is seated just above the embedded fork (or disc in _L.
fascicularis_), at the point where the inflection takes place; hence the
main growth of the carina is upwards,--the fork, however, being of
course, likewise added to at its point: in _L. fascicularis_, the growth
is both upwards and downwards.

_Peduncle and Attachment._--The peduncle is generally quite smooth:
though with a high power its surface may be seen to be studded with
minute beads, or larger discs, of yellowish and hard chitine; in the
young of _L. australis_, and I suspect of some other species, it is
covered with very minute spines. The peduncle in this genus attains its
greatest development. The cement-tissue debouches, I believe, only
through the functionless larval antennæ, except in one species, _L.
fascicularis_, in which a ball of this substance is formed in a most
peculiar manner round the peduncle (Pl. I, fig. 6), apparently for the
purpose of serving as a float, as will be presently described.

_Size and Colour._--The species of this genus are the largest of the
Pedunculata, with the exception of some Pollicipes: even in the smallest
species (_L. pectinata_), the capitulum sometimes attains a length of
about half an inch. The peduncle varies much in length in the same
species: in _L. anatifera_, it is occasionally above a foot long. The
colours of _L. anatifera_, _L. Hillii_, and _L. anserifera_, are very
bright and striking; the membrane bordering the valves and that round
the top of peduncle in two of the species, is of the brightest
scarlet-orange; the valves, owing to the underlying corium, are pale
blueish-grey, and the interspaces between them dark leaden-purple. The
cirri and trophi are generally dark purple or lead-colour.

_Filamentary Appendages._--These are attached to beneath the basal
articulation of first pair of cirri; they vary in the several species,
from one to five or six on each side, the lowest being always the
longest. Several of them are occupied by testes. In _L. pectinata_,
generally, not even one is developed. They are subject to great
variation in their proportional lengths, and in number, in the same
species. These organs have generally been considered to serve as
branchiæ; I see no reason to believe that they are more especially
designed for this end, than is the general surface of the body.

_Mouth._--The labrum is moderately bullate, the longitudinal diameter of
this part equalling about one third, or half of that of the rest of the
mouth. The palpi are moderately developed. The mandibles (Pl. X, fig. 5)
have five teeth with the inferior point either broad, or very narrow and
tooth-like. The maxillæ are step-formed (Pl. X, fig. 9); the first step
is sometimes indistinct and curved; and in _L. pectinata_, all the steps
vary much, and are more or less blended together. The outer maxillæ
(like those at Pl. X, fig. 16), are internally clothed continuously with
spines. The olfactory orifices are not at all prominent.

_Cirri._--The first pair is placed near the second pair, and is of
considerable length; the second has the anterior ramus thicker than the
posterior ramus, and the segments brush-like; the segments (Pl. X, fig.
26) of the four posterior cirri bear from four to six pair of long
spines, with a row of small intermediate spines: in the posterior cirri
of _L. australis_ the lateral rim spines are much developed; and in
those of _L. fascicularis_, the usual pairs of large spines are lost in
a broad triangular brush, formed by the increase of the lateral
marginal, and intermediate spines.

_Caudal Appendages_ (Pl. X, fig. 18 _b_), very small, either blunt or
pointed, and quite destitute of spines.

The prosoma is well developed. The stomach is surrounded in the upper
part by a circle of large branching cæca. The generative system is
highly developed; the testes coating the whole of the stomach, entering
the filamentary appendages and the pedicels of the cirri; the two
ovigerous lamellæ contain a vast number of ova; they are united to
rather large fræna, of which the sinuous margin supports either a
continuous row or separate tufts of glands.

_Distribution._--The species abound over the arctic, temperate and
tropical parts of the Atlantic, Indian and Pacific Oceans, and are
always, or nearly always, attached to floating objects, dead or alive.
The same species have enormous ranges; in proof of which I may mention
that of the six known species, five are found nearly all over the world,
including the British coast; and the one not found on our shores, the
_L. australis_, apparently inhabits the whole circumference of the
southern ocean.

_General Remarks and Affinities._--The first five species form a most
natural genus; they are often sufficiently difficult to be
distinguished, owing to their great variability. The sixth species (_L.
fascicularis_) differs to a slight extent in many respects from the
other species, and has considerable claims to be generically separated,
as has been proposed by Mr. Gray, under the name of Dosima; but as it is
identical in structure in all the more essential parts, I have not
thought fit to separate it. As far as external characters go, some of
the species of Pæcilasma have not stronger claims, than has _L.
fascicularis_, to be generically separated; and I at first retained them
altogether, but in drawing up this generic description, I found scarcely
a single observation applicable to both halves of the genus; hence I was
led to separate Lepas and Pæcilasma. If I had retained these two genera
together, I should have had, also, to include the species of Dichelaspis
and Oxynaspis; and even Scalpellum would have been separable only by the
number of its valves; this would obviously have been highly
inconvenient. Although some of the species of Pæcilasma so closely
resemble externally the species of Lepas, yet if we consider their
entire structure, we shall find that they are sufficiently distinct; as
indirect evidence of this, I may remark that Conchoderma (as defined in
this volume), includes two genera of most authors, and yet certainly
comes, if judged by its whole organisation, nearer to Lepas than does
Pæcilasma.


1. LEPAS ANATIFERA. Tab. I. fig. 1. (_var._)

  L. ANATIFERA. _Linnæus._ Systema Naturæ, 1767.

  ANATIFA vel ANATIFERA vel PENTALASMIS lævis[24], plerumque
        auctorum.

  ---- ENGONATA (!).[25] _Conrad._ Journal Acad. Nat. Sc.
        Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 15.

  ---- DENTATA (var.) _Brugière._ Encyclop. Meth. (des Vers), 1789.

  PENTALASMIS DENTATUS (var.) _Brown._ Illust. Conch., Pl. lii, fig.
        5.

  ANATIFA . . . . . _Martin St. Ange._ Mem. sur l'organisation des
        Cirripedes, 1835.

   [24] As this, though the commonest species, has never been
   defined, I give only a few synonyms and references, it being
   quite impossible to distinguish, in any published description,
   this species from _A. Hillii_ of Leach; this latter species I
   recognise under this name only from having authentic specimens
   from the British Museum, as Leach overlooked every one of the
   real diagnostic characters.

   [25] I have used, in conformity with botanists, the mark of
   interjection, to show that I have seen an authentic specimen.

_L. valvis aut lævibus aut delicate striatis: è duobus scutis, dextro
solùm dente interno umbonali instructo; pedunculi parte superiore
fuscâ._

Valves smooth, or delicately striated. Right-hand scutum alone furnished
with an internal umbonal tooth: uppermost part of peduncle
dark-coloured.

Filaments, two on each side.

Var. (_a_). Fig. 1. Scuta and terga with one or more diagonal lines of
dark greenish-brown, square, slightly depressed marks.

Var. (_b_). (Fig. 1 _b._) Carina strongly barbed.

    Extremely common; attached to floating timber, vessels,
    sea-weed, bottles, &c., and to each other, in the Atlantic
    Ocean, Mediterranean, West Indies, Indian Ocean, Philippine
    Archipelago, Sandwich Islands, Bass's Straits, Van Diemen's
    Land.

_General Appearance._--Valves white, more or less translucent and thick,
with a tinge of blueish-grey, from the underlying corium; sometimes
brownish cream-coloured, rarely with a tint of purple. Surfaces smooth,
with traces of very fine lines radiating from the umbones, sometimes
rather plain on the basal part of the scuta. Length in proportion to the
breadth of the capitulum variable, owing to the varying degree to which
the scuta and terga have their apices produced. _Scuta_ with the
occludent margin either considerably curved or nearly straight. The
internal tooth of the right-hand scutum, close to the umbo, varies in
size and form, being either pointed, square, or obliquely truncated on
either side, or it has a notch on the summit; internal basal rim of the
scuta either plainly developed or nearly absent. In many specimens (Pl.
I, fig. 1), on the scuta, or on the scuta and terga, (and sometimes more
on one side of the individual than on the other,) a nearly straight
line, running diagonally across the capitulum, of slight, quadrilateral
depressions, of a dirty greenish colour, with the edges blending away,
is either conspicuously developed, or can only just be discerned. These
marks increase in size from the umbones to the margins of the valves.
There are sometimes two or even three rows on the scuta. They are formed
by the retention of a portion of the chitine membrane, which is cast off
the rest of the surface; the margins of the valves are occasionally
notched slightly on the line of marks; there is no difference along this
line in the underlying corium. Specimens both with and without a barbed
carina are thus characterised. _Carina_; the interspace between the
carina and the scuta and terga is not wide. The carina exteriorly, is
either convex and smooth, or furnished with knobs or with extremely
sharp, long teeth (Pl. I, fig. 1 _b_); small specimens, with the
capitulum under half an inch in length, are generally most strongly
barbed.[26] Apex more or less acuminated; width and thickness variable;
sides strongly furrowed. Fork (fig. 1 _a_) generally less wide than the
widest upper part of the valve, with the two prongs diverging from each
other at less than a right angle; their sharpness and precise form
variable; rim between them reflexed (figs. 1 _a_ and _b_), making a
slight notch behind. _Peduncle_ smooth, wrinkled, length in proportion
to that of the capitulum varying, from barely equalling it, to six or
seven times as long. I have noticed a specimen including mature ova,
with a capitulum under half an inch long.

   [26] Mr. W. Thompson found that 15 specimens, out of about 200,
   attached to a vessel which came from New Orleans into Belfast,
   had their carinas barbed.

_Filamentary Appendages_;--never more than two on each side, with
sometimes only one developed; of variable length; one seated on the
flank of the prosoma, under the first cirrus; the second close under the
basal articulation of this cirrus, on the posterior face of a slight
swelling: these appendages correspond with _g_ and _h_ in Fig. 4, Pl.
IX.

_Mouth._--Mandibles (Pl. IX, fig. 5), with, as usual, five teeth, all
pointing downwards. Maxillæ (Pl. IX, fig. 9), with the lower step of
variable width compared to the two upper steps. _Cirri_; posterior cirri
with segments (fig. 26) bearing six pair of spines; intermediate fine
spines rather long; first cirrus, anterior ramus longer by only about
two segments than the posterior ramus; second cirrus with anterior
ramus, with very broad transverse rows of bristles; spine-bearing
surfaces considerably protuberant; caudal prominences smooth, rounded.

_Size._--The largest specimen which I have seen had a capitulum two
inches in length; the longest, including the peduncle, was sixteen
inches.

_Colours._--Calcareous valves already described. Edges of the orifice
bright scarlet orange; basal edges of the scuta, and sometimes of all
the valves, with a torn border of orange membrane. Interspaces between
the valves dull orange-brown. Peduncle darkish purplish-brown, with the
lower part sometimes pale; chitine membrane itself tinted orange; in
young specimens, peduncle pale, the colour first appearing in the
uppermost part, close under the capitulum; this upper part is often
darker than the other parts, and never orange-coloured, as in _L.
Hillii_ and _L. anserifera_. _Sack_ internally dark purplish
lead-colour, sometimes with a tinge of orange, darkest under the
growing edges of the valves; body of animal pale purplish lead-colour.
The four posterior cirri blackish purple; the second, and often the
third cirrus, appear as if the colour had been laterally abraded off;
these latter cirri have sometimes a tinge of orange. In very young
specimens, the cirri are only barred with purple. The ova and the
contents of the ovarian tubes are of a beautiful azure blue, becoming
yellow in spirits.

In museums a vast amount of difference is seen in the colours of this
species, caused by the method of preparation: if dried without having
been in spirits, and subsequently kept dry, the orange tint round the
orifice is preserved; if kept long in spirits, this is quite lost; but
sometimes in specimens in spirits the colour of the membrane of peduncle
is preserved and rendered pinker. The colours of the sack and animal are
either quite discharged or rendered extremely dark. The valves
themselves also often become more opaque. In some specimens well
preserved in spirits, the sack and cirri were purplish-brown or
lead-colour, tinted with dirty green, or orange, or bright yellow, or
brick-red.

_General Remarks._--From the foregoing description it will be seen how
extremely variable almost every part of this species is. I find, in the
British Museum, ten distinct specific names given by Dr. Leach to
different varieties, or rather to different specimens, for some of them
are undistinguishable. A specimen from the Sandwich Islands, sent by Mr.
Conrad to Mr. Cuming, is marked _A. engonata_.

In looking over a large collection of specimens in a museum, the most
distinctive characters appear at first to be the colours, the dentation
or barbed condition of the carina, the row of square marks on the scuta
and terga, and the more or less produced form of the whole capitulum:
all these characters are absolutely worthless as distinctive characters,
and blend into each other. In a fresh condition, the colours of this
species, and of _L. anserifera_ and _L. Hillii_ are surprisingly alike,
though in _L. anatifera_ alone, the uppermost part of the peduncle is
dark. As far as I have seen, the smoothness of the valves, together with
the presence of a tooth beneath the umbo, on the right-hand scutum, and
its entire absence on the left side, (in other species it is smaller on
this, than on the right-hand side,) is an unfailing diagnostic mark. I
believe this species is always attached to floating objects, though
there are some very young specimens in the British Museum, collected by
Sir G. Grey, adhering to sandstone, but this may have been buoyed up by
some large sea-weed. Mr. Peach has given me the particulars of two
instances, in which, after gales of wind, this species, of nearly full
size, adhering to _apparently_ freshly broken-off Laminariæ, has been
cast upon the coast of England and Scotland.


2. LEPAS HILLII. (Pl. I, fig. 2).

  ANATIFA vel PENTALASMIS LÆVIS (!) plerumque auctorum.

  PENTALASMIS HILLII (!). _Leach._ Tuckey's Congo Expedit. p. 413,
        1818.

  ---- CHELONIÆ (!) Ib. Ib.

  ANATIFA TRICOLOR (?). _Quoy_ et _Gaimard_. Ann. des Sc. Nat., 1st
        series, tom. x, 1827, Pl. vii, fig. 7, et Voyage de
        l'Astrolabe, Pl. xciii, fig. 4.

  ---- SUBSTRIATA (!). _Conrad._ Journal Acad. Nat. Sc.,
        Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 14.

_L. valvis lævibus; scutorum dentibus internis umbonalibus nullis;
carinâ à cæteris valvis, furcâ etiam a scutorum basali margine, paululum
distante; pedunculi parte superiore aut pallidâ aut aurantiacâ._

Valves smooth; scuta destitute of internal umbonal teeth; carina
standing a little separate from the other valves, with the fork not
close to the basal margin of the scuta; uppermost part of peduncle
either pale or orange-coloured.

Filaments three on each side.

    Extremely common; attached to ships' bottoms, from all parts of
    the world; on floating timber; associated with _L. anatifera_
    and _L. anserifera_. Mediterranean. Attached to turtles, in the
    Atlantic, lat. 30° north. West Indies. Falkland Islands. "South
    Seas," collected by A. Menzies. Port Stephen, Australia.

_General Appearance._--Capitulum laterally flat; length varies in
proportion to the breadth; valves white, somewhat translucent,
moderately thick, very smooth, but with faint traces of radiating lines;
in some varieties, surface rather irregular along the zones of growth.
_Scuta_ without any internal teeth, and with scarcely any trace of the
internal basal rim; upper angle little acuminated; the occludent margins
of the two scuta stand rather separate from each other, showing a wide
space of corium between them: these margins are arched and protuberant,
but with the lower part a little hollowed out; basal margin a little
curved. In one specimen alone, I saw a trace of a diagonal line of
square coloured marks, like those common in _L. anatifera_. _Terga_
rather broad, with the basal angle not much acuminated. The degree of
prominence and outline of the double occludent margin varies very much.
_Carina_, separated by a rather wide space from the scuta and terga; of
very varying shape, the upper part not much acuminated, generally very
flat, sometimes exteriorly marked by a central depressed line; never
barbed; occasionally, (in a specimen from Australia,) middle part so
wide as almost to become spoon-shaped; on the other hand occasionally of
nearly the same width throughout; somewhat constricted above the fork.
Fork deeply embedded as usual; situated, in fresh specimens, a little
way beneath the basal margins of the scuta, instead of touching them, as
in the other species; forks of varying width, not so abruptly inflected
as in many species; sometimes much narrower than the upper widest part
of the valve, sometimes nearly twice as wide; prongs of fork not very
sharp, diverging at about a right angle, with the rim between them
reflexed. The apex of the carina extends up between the terga for barely
half their length, instead of up fully three fourths of their length,
as in _L. anatifera_.

The chitine membrane at the base of the capitulum, especially at the
anterior and posterior ends, is covered with beautiful, little,
embedded, yellowish beads, about 3/2000th of an inch in diameter; above
this, on each side of the carina, there is a space with similar but
smaller little spheres, and still higher up still minuter ones; others
occur on different parts of the capitulum; these spaces are seen to be
distinctly separated from each other, and present a beautiful appearance
under a high power.

_Peduncle_, as long as, or rather longer than, the capitulum: in one set
of specimens, however, it was thrice or four times as long as the
capitulum. The peduncle, in some specimens, was conspicuously covered
with transverse plates of yellowish hard chitine.

_Filamentary Appendages._--Three on each side; one on the flank of the
prosoma, with a pair beneath the basal articulation of the first cirrus;
relative lengths various, but the posterior filament of the pair under
the cirrus, is the shortest. _Mouth_; palpi not much acuminated; maxillæ
step-formed, but with the upper or first step in some specimens
indistinct, or forming a curve. _Cirri_; the segments of the first
cirrus and of the posterior arm of the second cirrus are highly
protuberant, the protuberances sometimes equalling half the thickness of
the segments themselves. Caudal appendages smooth, rounded.

_Size._--The largest specimen which I have seen, in the collection of
Mr. Cuming, had a capitulum 1-1/10th of an inch long, and 1-1/4 wide;
therefore not quite equalling in size the largest specimens of _L.
anatifera_.

_Colours._--When fresh, valves blueish-grey from the underlying corium,
edges of all the valves and round the orifice, and round the top of the
peduncle, bright orange-yellow, passing into the finest scarlet, and
varying slightly in tint in different specimens. Space between the
carina and the other valves, and between the occludent margins of the
scuta, rich purplish-brown; peduncle either pale or purplish-brown, or
only clouded on the sides with the same. In young specimens, peduncle
nearly colourless; and in those under a quarter of an inch long in the
capitulum, the top of the peduncle has not acquired its orange tint.
Sack pale, leaden-purple, body the same, but paler and more reddish;
cirri (but only the tips of first pair) tinted with fine golden orange.
Immature ova in peduncle beautiful blue. After being long kept in
spirits, the colours are changed, weakened, or discharged, as in _L.
anatifera_ and _L. anserifera_, and the valves become opaque. In some
long-kept specimens the corium everywhere had become pale brown; more
usually it assumes a dirty purplish lead-colour.

_Monstrous Variety._--Amongst a set of ordinary specimens from a ship
from Genoa, sent me by Mr. Stutchbury, there were three, one full-grown
and two very young, with the whole capitulum, (and likewise with the
scuta and terga taken separately,) not above half the usual length in
proportion to the breadth. Neither the colours nor animal in this
variety presented any difference.

_General Remarks._--This species is almost universally confounded with
_L. anatifera_. Quoy and Gaimard, however, appear to have distinguished
it, under the name of _A. tricolor_, from its colours. Leach named it
accidentally, for he specifies not one distinctive character, and
besides his two published names, he has appended two other names to
specimens in the British Museum. A specimen, from the Sandwich Islands,
sent by Mr. Conrad to Mr. Cuming, is marked _A. substriata_. In a dry
state, from the shrinking of the membranes, and consequent approach of
the carina to the other valves, and of the fork to the basal margin of
the scuta, it is most difficult to distinguish this species, though so
decidedly distinct, from _L. anatifera_; the absence, however, of a
tooth on the under side of the right-hand scutum is at once
characteristic. Even in specimens kept in spirits, in which there has
been no shrinking, but in which the colours have changed, and taking
into account the variation in the carina and upper part of the terga,
this species is not always readily distinguished from _L. anatifera_,
without opening the valves and looking for the right-hand tooth of the
latter. In fresh specimens, the orange ring at the top of the peduncle,
and the broad purplish interspace between the carina and other valves,
are characteristic. In all states, the filamentary appendages offer a
good character.


3. LEPAS ANSERIFERA. Pl. I, fig. 4.

  L. ANSERIFERA. _Linnæus._ Syst. Naturæ, 1767.

  ANATIFA STRIATA. _Brug._ Encyclop. Meth. (des vers), Pl. clxvi,
        fig. 3.

  PENTALASMIS DILATATA! (young). _Leach._ Tuckey's Congo Expedit.,
        p. 413, 1818.

  ANATIFA SESSILIS (?). _Quoy et Gaimard._ Voyage de l'Astrolabe,
        Pl. xciii, fig. 11.

  LEPAS NAUTA.[27] _Macgillivray._ Edin. New Phil. Journ., vol.
        xxxviii, p. 300.

  PENTALASMIS ANSERIFERUS. _Brown._ Illust. Conch., 1844, Pl. li,
        fig. 1.

   [27] Professor Macgillivray does not consider the species, which
   he has described under _L. nauta_, and which I cannot doubt is
   the same with the present species, as the _L. anserifera_ of
   Linnæus; but I find it so named in all old collections, and it
   seems to agree very well with Linnæus's description. There has
   been much groundless confusion about this species; I have no
   hesitation in giving _A. striata_, of Brugière, as a synonym,
   though I have received from Paris the _Lepas pectinata_ of this
   volume, named as the _A. striata_; and on the other hand, Poli
   has incorrectly called a common variety of _L. pectinata_ by the
   name of _L. anserifera_.

_L. valvis approximatis leviter sulcatis (tergis præcipuè); scuto dextro
dente forti interno umbonali, lævo aut dente exiguo, aut merâ cristâ
instructo; margine occludente arcuato, prominente: pedunculi parte
superiore aurantiacâ._

Valves approximate, slightly furrowed, especially the terga; right-hand
scutum with a strong internal umbonal tooth; left-hand with a small
tooth, or mere ridge; occludent margin arched, protuberant: uppermost
part of peduncle orange-coloured.

Filaments five or six on each side.

Var. (_dilatata_, young); valves rather thin, finely furrowed, often
strongly pectinated; scuta broad, with the occludent margins much
arched, making the space wide between this margin and the ridge
connecting the umbo and the apex: carina often barbed.

    Common on ships' bottoms from the Mediterranean, West Indies,
    South America, Mauritius, Coast of Africa and the East-Indian
    Archipelago. Central Pacific Ocean. China Sea. Chusan. Sydney.
    Attached to pumice, various species of fuci, Janthinæ, Spirulæ;
    often associated with _L. anatifera_ and _L. Hillii_, and, in a
    young state, with _L. fascicularis_.

_General Appearance._--Capitulum more or less elongated relatively to
its breadth; in two specimens, with scuta of equal width, one was longer
than the other by the whole of the occludent margin of the terga. Valves
white, thick, (in young specimens sometimes diaphanous and thin,)
closely approximate to each other; surfaces furrowed to a very variable
amount. Terga generally more plainly furrowed than the scuta, of which
the basal portion is generally less furrowed than the upper part;
ridges, often rough, generally much narrower than the furrows: in
half-grown specimens (var., _dilatata_ of Leach,) the ridges are
frequently denticulated, and there is even sometimes a row of bead-like
teeth along the basal margins of the scuta. The ridges vary much,
sometimes alternately wide and narrow; in two specimens of equal size,
there were, in one, thirty-two ridges, and in the other only eighteen,
on the scutum.

_Scuta_, with the occludent margin rounded and protuberant to a variable
degree, but always leaving a rather wide space between the margin, and
the ridge which runs from the umbo to the apex; apex pointed. Right-hand
internal tooth considerably larger than that on the left, which is often
reduced to a mere ridge; internal basal rim thick, sometimes furrowed
along its upper edge, but of variable thickness, sometimes not extending
as far as the baso-carinal angle. _Terga_, sometimes equalling,
sometimes only two-thirds of, the length of the scuta; in young
specimens, the two occludent margins form a right-angle with each other;
in older specimens they form less than a right-angle, and hence the
portion of valve thus bounded is unusually protuberant. _Carina_, within
deeply concave; exterior sides finely furrowed longitudinally, generally
denticulated; valve only slightly narrowed in above the fork, of which
the prongs diverge at an angle of 90°, or rather more, and are wider
than the widest upper part of the valve; rim between the prongs
reflexed; the heel or external angle, just above the fork, sometimes
considerably prominent. I have seen only a single large specimen with
its carina barbed. In half-grown specimens, (var. _dilatata_, Leach,)
the carina is often strongly barbed, with the upper point much
acuminated, the fork about twice as wide as the widest upper part, and
the prongs diverging at rather more than a right-angle. In some
specimens, especially very young ones, there are at the base of the
carina, above the fork, some strong, downward-pointed, inwardly-hooked,
calcareous teeth; such occur also in some specimens along the basal
margins of the scuta, two of these hooked teeth under the umbones of the
scuta being larger than the rest: specimens conspicuously thus
characterised came from the Navigator Islands; in these, I may add, the
acutely triangular primordial valves were quite plain.

_Peduncle_, generally about as long as the capitulum; in young specimens
generally short.

_Filamentary Appendages_, generally five, sometimes six, on each side;
one is seated on the side of the prosoma, and the four others placed in
pairs beneath the basal articulation of the first cirrus; the lowest
posterior filament of the four generally is the largest. In young
specimens, having a capitulum only half an inch long, the upper pair of
the four often is not developed, or is represented by mere knobs. The
mouth presents no distinctive characters. _Cirri_, with the longer ramus
of the first pair almost equal to the shorter arms of the second pair;
spine-bearing surfaces only slightly protuberant. Caudal appendages
smooth, curved, pointed.

_Size._--The largest specimen which I have seen, had a capitulum one
inch and a half in length.

_Colours._--The white valves are edged with bright orange membrane; and
are so close to each other that no interspaces, coloured from the
underlying corium, are left. Peduncle, dark orange-brown, with the
uppermost part under the capitulum bright orange all round; the chitine
membrane itself being thus coloured. Sack, internally, dark purplish
lead-colour. Body and cirri, either nearly white or pale purplish-lead
colour, with the arms of the second, third, and fourth cirri, and
pedicels of the fifth and sixth, more or less tinted with orange. A
specimen preserved during fourteen months in good spirits had only a
tinge of orange left round the orifice and round the upper part of
peduncle, and on the cirri. In some other specimens, badly preserved,
the chitine membrane was quite colourless, and sack and cirri dirty
lead-colour. Fresh ova, peach-blossom-red; immature ova, in ovarian
tubes, pale pink.

_Monstrous Variety._--In Mr. Stutchbury's collection, there was a
specimen, with the scuta, broad, smooth, thin, and fragile, without any
ridge running from the umbo to the apex, and with the occludent margin
reflexed. This seemed caused by the shell having been attacked by some
boring animal, and from having supported Balani. In the same specimen
the first cirrus on one side was monstrously thick and curled; the
second cirrus had its posterior ramus in a rudimentary condition. In Mr.
Cuming's Collection, there are small specimens with the zones of growth
overlapping each other, with thick irregular margins, and with the
carina distorted.

This species has cost me much trouble: I have examined vast numbers of
specimens, from a tenth to half an inch in length, attached to light
floating objects, such as Janthinæ and Spirulæ from the tropical oceans,
which all resembled each other, and slightly differed from the common
appearance of _L. anserifera_: this variety is the _Pentalasmis
dilatata_ of Leach; and for a long time I considered it as a distinct
species. It differs from _L. anserifera_, in the less thickness of the
valves, in their being more finely and yet plainly furrowed; in the
greater width of the scuta; and more especially, of that part of the
valve lying between the occludent margin, and the ridge running from the
umbo to the apex; in the less elongation of the area in the terga,
bounded by the two occludent margins; and, lastly, in the less size of
the whole individual. The trophi and cirri are absolutely identical.
Lately, however, in carefully going over a great suite of specimens, all
the above few distinctive characters broke down and insensibly graduated
away; and I am convinced that this form is only a variety of _L.
anserifera_; its different aspect being caused partly by youth, but
chiefly, I suspect, from being attached to light objects floating close
to the surface of the sea.

The _Lepas anserifera_ can be distinguished by the slight furrows on its
valves from all the other species, excepting _L. pectinata_: this latter
species can be readily known, by the close proximity in the scuta of the
occludent margin, and the ridge extending from the umbo to the apex; by
its carina being very narrow above the fork; by the prongs of the fork
diverging at an angle of from 135° to 180°; by the thinness of its
valves; by the coarseness of the furrows on them; and lastly, by there
being at most in _L. pectinata_ only one filamentary appendage beneath
the first cirrus.


4. LEPAS PECTINATA. Pl. I, fig. 3.

  LEPAS PECTINATA. _Spengler._ Skrifter Naturhist. Selbskabet, 2,
        B. 2, H., 1793, Tab. X, fig. 2.

  ---- MURICATA (var.) _Poli._ Test. Utriusque Scicil., vol. i, Pl.
        vi, figs. 23, 29, 1795.

  LEPAS ANSERIFERA. _Poli._ Test. Utriusque Scicil., vol. i, Pl. vi,
        figs. 25-27.

  ---- SULCATA. _Montagu._ Test. Brit., Pl. i, fig. 6, 1803.

  PENTALASMIS SULCATA. _Leach._ Encyclop. Brit. Suppl., tom. iii,
        Pl. lvii, 1824.

  ---- spirulæ (!) (var.) _Leach._ Tuckey's Congo Expedit. Appendix,
        1818.

  ---- RADULA (var.) et SULCATUS. _Brown._ Illust. of Conchology,
        Pl. li, figs. 3-6, 1844.

  ---- INVERSUS. _Chenu._ Illust. Conchy., Pl. i, fig. 14.

  ANATIFA SULCATA. _Quoy et Gaimard._ Voyage de l'Astrolabe, Pl.
        xciii, figs. 18, 20.[28]

   [28] I may add, that I have received many specimens incorrectly
   labelled _A. striata_, which is properly a synonym of _L.
   anserifera_.

_L. valvis tenuibus, crassè sulcatis, sæpe pectinatis; scutorum cristâ
prominente ab umbone ad apicem juxta marginem occludentem pertinente:
furcæ carinalis cruribus inter angulos 135° et 180° divergentibus._

Valves thin, coarsely furrowed, often pectinated. Scuta with a prominent
ridge extending, from the umbo to the apex, close to the occludent
margin; fork of the carina with the prongs diverging at an angle of from
135° to 180°.

Filaments absent, or only one on each side.

Var. (Pl. I, fig. 3 _a_), upper part of the terga (bounded by the two
occludent margins) produced and sharp; surface of all the valves often
coarsely pectinated, and with the carina barbed.

    Atlantic Ocean, from the North of Ireland to off Cape Horn;
    common, under the tropics; Mediterranean: attached to wood,
    cork, charcoal, sea-weed, a reed-like leaf, spirulæ, cuttle-fish
    bones, to a bottle together with _L. anatifera_; to a ship's
    bottom, Belfast, (W. Thompson.) Often associated with _L.
    fascicularis_. Montagu states ('Test. Brit.,' p. 18) that this
    species is sometimes attached to the fixed _Gorgonia flabellum_.

_General Appearance._--The capitulum varies considerably in length
compared to its breadth, caused chiefly by the greater or less
production of the occludent portion of the terga; valves thin, brittle;
the furrowed surface varies much in character, narrow and broad ridges
often alternating; frequently each ridge (but more especially the ridge
running from the umbo to the apex of each scutum, and sometimes that
alone,) is covered with prominent, curled, flat, calcareous spines,
giving the shell an appearance like that of many mollusca. Other
specimens show no trace of these calcified projections. From the
thinness of the valves and the depth of the furrows, the margins of the
valves are sinuous. _Scuta:_ the ridge running from the umbo to the apex
is unusually prominent and curved; it runs very close to the occludent
margin, so that, differently from in all the other species, only a very
narrow space is left between this margin and the ridge. Internal teeth,
under the umbones, either sharp and prominent, or mere knobs; sometimes
that on the right side is much larger than that on the left; sometimes
they are nearly equal; sometimes that on the left is scarcely
distinguishable. Internal basal rim absent, or barely developed.

_Terga:_ these valves have a conspicuous notch to receive the apex of
the scuta; the two occludent margins either meet each other at a
rectangle, or at a much smaller angle, causing the portion thus bounded
to vary much in outline, area, and degree of prominence. This at first
led me to think that the _P. spirulæ_ of Leach, in which the point is
very sharp and prominent, was a distinct species; but there are so many
intermediate forms, that the idea must be given up. I may remark, that
in all the species of Lepas, the upper part of the tergum seems
particularly variable. The degree of acumination of the basal portion of
the tergum also varies; the internal surface sometimes has small crests
radiating from the umbo.

_Carina_, broad, within deeply concave; edges sinuous, externally
sometimes strongly barbed; narrow above the fork, which latter is wider
than the widest upper part of the valve; prongs sharp, thin, diverging
at an angle of from 135° to 180°; the rim connecting the prongs not, or
only slightly, reflexed.

_Peduncle_, narrow, shorter than the capitulum.

_Filamentary Appendages_, none, or only one, short, obtuse projection on
each side, on the posterior face of the swelling under the first cirrus.

_Mouth._--Mandibles, with the inferior point produced into a single
pectinated tooth, rarely into two pectinated teeth; on one side of one
specimen, there were only four instead of five teeth. Palpi very narrow.
Maxillæ highly variable; they may be described as formed of five steps,
of which the two lower ones are generally united into a single one,
divided by a mere trace of a notch; or with the three lower steps
blended into an irregular, projecting surface, and with even the fourth
step indistinct. I have seen these two extreme forms on opposite sides
of the mouth of the same individual,--on one side the maxillæ being
regularly step-form, on the other the whole inferior part forming an
almost straight edge, standing high up above the first notch or step
which bears the two upper great spines.

_Cirri._--First pair rather far removed from the second pair, with the
longer ramus about three-fourths of the length of shorter ramus of
second cirrus; spine-bearing surfaces, hardly at all protuberant;
lateral marginal spines on the posterior cirri rather long; caudal
appendages smooth, rounded, extremely minute: penis very spinose.

_Size._--Capitulum in the largest specimen, six-tenths of an inch long;
only a few arrive at this size.

_Colours_, after having been kept in spirits,--sack and cirri,
especially first cirrus, clouded with pale purple; peduncle brownish;
valves appear blueish in specimens not long preserved, but in specimens
kept longer they become perfectly and delicately white.

_General Remarks._--Under the head of _L. anserifera_, I have made some
remarks on the diagnostic characters of this species. In the thinness of
the valves,--form of the carina, with the rim connecting the prongs
being not, or scarcely, reflexed,--and in the shortness and narrowness
of the peduncle, there is some approach to _L. australis_, and thence to
_L. fascicularis_. In the form of the maxillæ,--in one specimen having
the mandible on one side bearing only four teeth,--and in the frequent
absence of filamentary appendages, there is some approach to the genus
_Pæcilasma_; but there is no such approach in the characters derived
from the capitulum. We have seen that, as in so many other species of
this genus, most of the parts are variable, and this is the case to a
most unusual extent in the form of the maxillæ. Dr. Leach has attached
eight specific names to the specimens preserved in the British Museum.


5. LEPAS AUSTRALIS. Pl. I, fig. 5.

_L. valvis glabris, tenuibus, fragilibus; scutorum dentibus umbonalibus
utrinque internis; carinæ parte superiore latâ, planâ, suprâ furcam
valdè constrictâ; furcæ cruribus latis, planis, tenuibus, acuminatis,
intermedio margine non relexo._

Valves smooth, thin, brittle; scuta with internal umbonal teeth on both
sides. Carina with the upper part broad, flat; much constricted above
the fork, which has wide, flat, thin, pointed prongs, with the
intermediate rim not reflexed.

Filaments, two on each side.

    Common on Laminariæ in the whole Antarctic Ocean: Bass's
    Straits, Van Diemen's Land: Bay of Islands, New Zealand, lat.
    35° S.: lat. 50° S., 172° W.: coast of Patagonia, lat. 45° S.:
    attached to bottom of H. M. S. Beagle, lat. 50° S., Patagonia:
    attached to a Nullipora, (I presume a drift piece,) British
    Museum.

_General Appearance._--Capitulum rather obtuse and thick; valves thin,
brittle, approximate, either white and transparent, or dirty-brown and
opaque; or sometimes tinted internally with purple (perhaps the effects
of being preserved in spirits); surface plainly marked by lines of
growth, rarely marked with traces of lines radiating from the umbones.
_Scuta_ with teeth on both sides, nearly equal; internal basal rim
rather wide, sometimes furrowed; basal margin considerably curved
inwards. _Terga_ rather wide; basal angle blunt; angle formed by the two
occludent margins blunt and rounded. _Carina_ (fig. 5 _a_) with the apex
blunt, flat; the middle part generally very broad; much constricted
above the fork, where it is internally deeply concave, and externally
carinated; fork twice as broad as the broadest upper part of the valve;
with the prongs flat, broad, thin, pointed, diverging at about an angle
of 75°, with the intermediate rim not at all reflexed; the fork
generally not deeply imbedded in the chitine membrane of the peduncle,
so as to be quite easily visible externally; sometimes there is an
internal, transverse, depressed line on the fork. In young specimens,
with the capitulum about a quarter of an inch long, the fork of the
carina is not developed, the lower slightly inflected portion consisting
simply of an oval plate, twice as wide as the upper part. Until I had
carefully examined a perfect series, showing the gradual changes in this
part, I did not doubt that the young specimens formed a distinct
species, and named it accordingly: the shortness of the penis first made
me perceive that the specimens were immature. At this early age, I may
add, the filamentary appendages were not developed. _Peduncle_ either
quite short, or as long as the capitulum, close under which it is
considerably constricted all round.

_Filamentary Appendages._--Two on each side; one long, tapering, placed
on the prosoma (in one specimen represented by a mere knob), and the
second shorter, situated on the posterior margin of the swelling beneath
the first cirrus.

_Mouth._--Maxillæ, with three large spines at the upper angle, and with
the first step distinct, but narrow; mandibles with five teeth; in young
specimens the inferior point ends in a single spine; sides of the
supra-oral cavity very hairy; the membrane, forming the inner fold of
the labrum, yellow and thickened in the form of a spoon.

_Cirri._--In the posterior cirri there are, at the upper lateral edges
of the segments on _both_ sides, small spines; the segments in the first
cirrus, and in the broad anterior ramus of the second cirrus, are
hemispherically and considerably protuberant. Caudal appendages smooth.

_Size._--The largest specimen had a capitulum one inch long.

The _Colours_ (after having been long in spirit) of the valves have
already been given; sack and peduncle dirty yellowish-brown, with the
parts corresponding to the margins of the valves much darker brown, or
almost black; segments of the cirri clouded with dark brown; body and
pedicels of the cirri dirty yellowish. I have reason to believe that the
colours are totally different in living specimens.

_Monstrous Varieties._--Most of the specimens from lat. 50° S., on the
coast of Patagonia, were more or less deformed, with the successive
zones of growth overlapping each other, and forming coarse concentric
ridges. The carina in several specimens was laterally distorted.

I have already remarked that this species has some affinity to _L.
pectinata_; but it is much more closely related to _L. fascicularis_,
the affinity being clearly shown by the thinness and translucency of the
valves, their convexity, by the width and little acumination of the
upper part of the carina, by the width of the fork, and by its not being
deeply imbedded. In young specimens, moreover, before the fork is fully
developed, there is a remarkable similarity between the two species, in
the form of this lower part of the carina. Again, the narrowness and
inflection of the peduncle under the capitulum in _L. australis_, and
lastly, the lateral marginal spines on both sides of the segments of the
posterior cirri, all clearly indicate this same affinity to _L.
fascicularis_.

I believe this species is confined to the southern ocean; and perhaps
there represents _L. fascicularis_ of the northern and tropical seas. It
must, judging from the number of specimens brought home by Captain Sir
J. Ross, and from those previously in the British Museum, and from those
collected by myself, be a very common species.


6. LEPAS FASCICULARIS. Pl. I, fig. 6.

  LEPAS FASCICULARIS. _Ellis_ and _Solander_. Zoophytes, 1786, Tab.
        xv, fig. 5.

  ---- ---- _Montagu._ Test. Brit. Suppl., 1808, pp. 5, 164.

  ---- CYGNEA. _Spengler._ Skrifter Naturhist. Selbskabet, Bd. i,
        1790, Tab. vi, fig. 8.

  ---- DILATA. _Donovan._ British Shells, 1804.

  PENTALASMIS FASCICULARIS. _Brown._ Illust. Conch., 1844, Pl. li,
        fig. 2.

  ---- SPIRULICOLA (!) et DONOVANI (!) _Leach._ Tuckey's Congo
        Expedit., p. 413, 1818.

  ANATIFA VITREA. _Lamarck._ Animaux sans Vertebres.

  DOSIMA FASCICULARIS. (!) _J. E. Gray._ Annals of Philosophy, vol.
        x, 1825.

  PENTALEPAS VITREA. _Lesson._ Voyage de la Coquille. Mollusca, Pl.
        xvi, fig. 7, 1830.

  ANATIFA OCEANICA (!) _Quoy_ et _Gaimard_. Voyage de l'Astrolabe,
        Pl. xciii.

_L. valvis glabris, tenuibus, pellucidis; carinâ rectangulè flexâ, parte
inferiore in discum planum oblongum expansâ._

Valves smooth, thin, transparent; carina rectangularly bent, with the
lower part expanded into a flat oblong disc.

Filaments, five on each side; segments of the three posterior cirri with
triangular brushes of spines.

Var. (_Donovani_, of Leach.) Carina with the upper part flat,
spear-shaped, externally with a narrow central ridge.

Var. (_Villosa._ Pl. I, figs. 6 _b_, _c_.) Valves placed rather distant
from each other; carina extremely narrow, with the upper part of nearly
the same width throughout; terga with the lower part much acuminated;
body of animal finely villose.

    Coasts of Great Britain and France; Baltic Sea, according to
    Montagu Southern United States (from Agassiz); tropical Atlantic
    Ocean; East-Indian Archipelago, off Borneo and Celebes; Pacific
    Ocean, between the Sandwich and Mariana Archipelagos; New
    Zealand: attached to fuci, Spirulæ Janthinæ, Velellas, often to
    feathers and cork; often associated with the young of _L.
    anserifera_, (var. _dilatata_,) and _L. pectinata_.

_General Appearance._--Capitulum highly variable in all its characters;
thick and broad in proportion to its length, but the breadth is
variable,--in some specimens, the capitulum being longer by one-fifth of
its total length than broad; in others, one-fifth broader than long.
Valves generally approximate; in some varieties, however, from the
narrowness of the carina and terga, the valves stand far apart, there
being an interval between the carina and scuta of nearly half the
breadth of the latter. Valves excessively thin, brittle, transparent,
colourless, smooth, but generally sinuous along the zones of growth,
which are conspicuous: valves generally covered throughout by thin
chitine membrane, which is thickly clothed, especially in the
interspaces between the valves, with minute spines, barely visible to
the naked eye. _Scuta_ with the lower part of the tergo-carinal margin
extremely protuberant; occludent margin, more or less, but slightly
reflexed, with a depressed line running from the umbo to the apex; basal
margin much reflexed, but to a variable extent and at a varying angle,
even up to a right angle,--an external rim or collar being thus formed.
There are no distinct _internal_ teeth, but the basal margin under the
umbones, is more or less distinctly produced into a rounded disc or
projection, which is generally not so much outwardly reflexed as the
rest of the basal margin: there is no distinct internal basal rim. The
primordial valves are generally visible, but they do not lie, as in all
other species, close to the basal margin, but a little above it,--the
lower reflexed portion having been subsequently developed. _Terga_ flat,
with the occludent margin slightly arched, and not, as in the foregoing
species, formed of two sides; apex bent towards the carina; width of the
lower half highly variable, owing to the varying extent to which the
scutal margin is hollowed out; in some specimens, the whole lower half
beneath the apex of the scuta is of nearly the same width throughout; in
other specimens this lower part is spear-shaped. The widest part of the
tergum either equals in width, or is only two-thirds of the width of the
widest part of the carina beneath its umbo. _Carina_ (Pl. I, fig. 6 _a_)
highly variable in shape, with the part above the umbo either
spear-shaped and slightly concave within, or nearly flat and furnished
with a central external ridge; or the upper part (fig. 6 _c_) is of
equal and extreme narrowness throughout, and deeply concave within,
appearing as if only the central ridge had been developed. The part
below the umbo, (answering to the fork in the foregoing species,) is
about one-third of the length of the whole valve, and generally twice as
wide as the upper part, but in the variety with the upper part of the
carina equally narrow throughout, the lower part is thrice as wide as
the upper; the disc, or lower part, is generally slightly concave
within, exteriorly either with or without a central ridge; basal margin
rounded; lateral margin more or less curved, according to the form of
the upper part. The disc is not more deeply imbedded in membrane than is
the upper part of the valve. The heel or umbo is either angular and
prominent, or rounded. In very young specimens the carina is simply
bowed, instead of being rectangularly bent.

_Peduncle_,--short, narrow, being abruptly inflected all round under the
basal edges of the capitulum; lower part of very variable shape, being
often suddenly contracted into a mere thread (fig. 6 _b_), which
sometimes widens again at the extreme end. The external membrane is very
thin, and is penetrated by the usual fine tubuli leading to the corium;
its surface is wrinkled and destitute of spines, or with extremely few.
The peduncle is often completely surrounded by a yellowish ball, (of
which I have seen specimens from the coast of England, and from off
Borneo,) sometimes half as wide as the capitulum, composed of very
tender, vesicular, structureless membrane, and of a pulpy substance:
perhaps the yellow colour may be owing to long immersion in spirits.
Some authors have supposed that the ball was the ovisac of the animal;
and for the first few minutes, deceived by the numerous included spores
of, as I believe, Bacillariæ, I thought that this was the case; others
have supposed that it consisted of some encrusting algæ or other foreign
organism; but it is, in reality, a most singular development of the
cement-tissue, which ordinarily serves to attach Cirripedes by their
bases to some extraneous object, but here surrounding that object and
the peduncle, gives buoyancy, by its vesicular structure, to the whole.
The membrane of the ball falls to pieces in caustic potash, differently
from the chitine membrane of the enclosed peduncle, and this shows that
there is some difference in composition from ordinary cement. The ball,
when cut in two, exhibits an obscure concentric structure. The whole is
excreted by the two cement-ducts, through two rows of orifices, one on
each side of the surrounded portion of the peduncle; and I actually
traced, in one case, the yellow pulpy substance coming out of the
cement-ducts. The upper apertures are in gradation larger than those
below them, and they stand a little further apart from each other; these
are figured as seen from the outside, much magnified, at Pl. I, fig. 6
_d_. I did not succeed in finding the cement-glands, but I followed the
ducts, of rather large size, running for a considerable distance as
usual along and within the longitudinal muscles of the peduncle. Nearly
opposite the uppermost aperture, on each side, the duct passes out
through the corium, and becomes laterally attached to the outer membrane
of the peduncle, at which point an aperture is formed (as in other
cases, by some unknown process), thus giving exit to the contents of the
duct. Beneath this upper aperture the duct runs down the peduncle,
between the corium and the outer membrane, till it comes to the next
aperture, to which it is also attached, and so on to all the lower ones;
but I believe no cement tissue continues to pass out through these
lower apertures. Beneath the lowest aperture the two ducts run into the
two prehensile antennæ of the larva, which, as usual, terminate the
peduncle. The antennæ are attached to some small foreign body in the
centre of the vesicular ball, by the usual tough, light brown,
transparent cement. The two upper apertures are nearly on a level with
the outside surface of the ball; and it was evident that as the animal
grows, new apertures are formed higher and higher up on the sides of the
peduncle, and that out of these, fresh vesicular membrane proceeds, and
grows over the old ball in a continuous layer. It appears that the
growth of the vesicular ball is not regular,--that it is not always
formed,--and that when formed the whole, or the lower part, sometimes
disintegrates and is washed away. As that portion of the peduncle which
is enclosed ceases to grow, and has its muscles absorbed, retaining only
the underlying corium, whereas the upper unenclosed portion, and
likewise, (as it appears) lower portions once enclosed but since
denuded, continue to increase in diameter, the peduncle, when the
vesicular ball is removed, often has the most irregular outline,
contracting suddenly into a mere thread, and then occasionally expanding
again at the basal point.

Frequently two or three specimens have their peduncles imbedded in one
common ball, of which there is a fine specimen in the College of
Surgeons (Pl. I, fig. 6), the ball being about one inch and a quarter in
diameter, with a slice cut off. In this specimen, it is seen that the
vesicular membrane proceeding from several individuals, unites to form
one more or less symmetrical whole, and that the original common object
of attachment is entirely hidden. Dr. Coates[29] gives a curious account
of the infinite number of specimens, through which he sailed during
several days, in the Southern Atlantic Ocean: the balls appeared like
bird's eggs, and were mistaken for some fucus, which was supposed to
have encrusted the scales of the Velellæ, to which the Cirripede had
originally become attached. Several individuals had their peduncles
imbedded in the same ball, "which floated like a cork on the water." As
this species grows into an unusually bulky animal, we here see a
beautiful and unique contrivance, in the cement forming a vesicular
membranous mass, serving as a buoy to float the individuals, which, when
young and light, were supported on the small objects to which they
originally had been cemented in the usual manner.

   [29] Journal of the Acad. Nat. Sc., Philadelphia, vol. vi, p.
   138, 1829.

_Filamentary Appendages._--Five on each side, of which four lie in pairs
at the base of the first cirrus (of these, only three are sometimes
developed), and one on the flank of the prosoma.

_Mouth._--Palpi much acuminated. Mandibles with five teeth; the first
not far remote from the second; inferior point rather broad and finely
pectinated. Maxillæ with two large, unequal, upper spines, and four
regular steps.

_Cirri._--Posterior cirri, with the upper parts of the segments slightly
protuberant; in young specimens, the spines can be seen to consist of
five pairs, placed in two converging lines in the upper half of each
segment, with numerous minute, latero-marginal, and intermediate little
bristles: in large specimens, all these latter have so increased in
number, that the normal five pair cannot be distinguished, and the front
of each segment is covered by a triangular thick brush of bristles, all
pointing in the same direction, thus giving a very unusual character to
the posterior cirri: the dorsal tuft on each segment consists of six or
seven large spines, with from one to three dozen fine ones. First cirrus
and anterior ramus of second cirrus with broad brushes of bristles. The
pedicels of all the cirri are thickly covered with bristles. _Caudal_
appendages smooth, with rounded summits.

_Penis_ very hairy: vesiculæ seminales purple, much convoluted, lying
within the prosoma; testes dendritic, scarcely enlarged at their
terminal points, purplish; ovigerous fræna large with sinuous margins,
the glandular beads being arranged in groups.

_Size._--The largest specimen (from the coast of Devonshire) had a
capitulum 1.6 of an inch long, and 1.2 broad, and of unusual thickness.

_Colours_, after having been in spirits: front surfaces of the segments
of the cirri and of the pedicels purple. In some specimens from off
Borneo, parts of the sack and the interspaces between the two scuta,
were of a fine purple. Montagu states, that the whole shell and body of
animal, when fresh, are pale blue, with the cirri spotted with brown.

_General Remarks._--The extreme variability of this species is
remarkable. In the College of Surgeons, there is a group of specimens
collected by Mr. Bennett, I believe, in the Atlantic, in which the
extreme narrowness of the carina and of the terga (Pl. I, fig. 6, _b_,
_c_) (with consequent wide spaces of membrane left between these
valves), led me, at first, to entertain no doubt, that it was quite a
distinct species, which was strengthened by finding that the whole
surface of the cirri were villose, with very minute spines; hence I
called this variety, _villosa_. On the closest examination, however, I
could detect no other differences, and the narrowness of the carina and
terga varied very considerably: moreover, in one of the specimens, which
was about intermediate in the form of its valves between this variety
and the common form, the surfaces of the cirri were not in the least
degree villose. Again, in some other specimens, the terga were as narrow
as in Mr. Bennett's, whilst the carina had its usual outline.

In a var. (called by Leach, _P. Donovani_,) from the Atlantic, under the
Equator, the carina is remarkable from the extreme flatness of the upper
part, and from the presence of an exterior, narrow, central ridge. In
one specimen from Jersey, in the British Museum, the carina made an
extremely near approach to this same form.

_Affinities._--This species is certainly much the most distinct of any
in the genus, and Mr. Gray has proposed to separate it under the name of
Dosima; but considering the close similarity of the whole organisation
of the internal parts, together with the transitional characters
afforded by _L. australis_, I think the grounds for this separation are
not quite sufficient. I have remarked, under _L. australis_, on the
affinity between that and the present species. In the carina terminating
in a disc (though here not imbedded), there is some slight affinity to
_Pæcilasma eburnea_ and _crassa_, and markedly so in the arrangement of
the bristles on the posterior cirri. In the valves being covered with
villose membrane, and to a certain extent in the form of the carina and
of the occludent margin of the terga, and especially in the two rows of
cement-orifices in the peduncle, there is some affinity to Scalpellum.


PÆCILASMA. _Nov. Genus._[30] Plate II.

  ANATIFA. _J. E. Gray._ Proc. Zoolog. Soc., 1848, p. 44.

  TRILASMIS. _Hinds._ Voyage of the Sulphur. Mollusca, 1844.

   [30] [Greek: Pokilos], various, and [Greek: elasma], plate or
   valve. I have not been able to adopt Mr. Hinds' name for this
   genus, as it would be too glaringly incorrect to call a
   five-valved species, a _Trilasmis_.

_Valvæ, 3, 5, aut 7, approximatæ: carina solùm ad basales apices
tergorum extensa, termino basali aut truncato aut in discum profunde
infossum producto: scuta pænè ovalia, umbonibus ad angulum rostralem
positis._

Valves, 3, 5, or 7, approximate: carina extending only to the basal
points of the terga; with its lower end either truncated or produced
into a deeply imbedded disc. Scuta nearly oval, with their umbones at
the rostral angle.

Mandibles with four teeth; maxillæ notched, with the lower part of edge
prominent; anterior ramus of the second cirrus not thicker than the
posterior ramus; caudal appendages uniarticulate, spinose.

    Generally attached to Crustacea.

I have already given my reasons for instituting and separating this
genus from Lepas; as far as the capitulum is concerned, the differences
between these genera certainly appear trivial; they consist in the
carina not extending up between the terga, and in the lower end being
either truncated, or produced into an imbedded disc: the terga have a
single occludent margin. The included animal's body differs in more
important respects; for both mandibles and maxillæ are very distinct;
the cirri of some of the species also differ; and the caudal appendages
are here always spinose: there are no filamentary appendages: and
lastly, the habits are different.

The genus may be divided into two sections, firstly, _P. Kæmpferi_ and
_P. aurantia_, which have their carinæ basally truncated, the basal
angles of their terga cut off, and the anterior rami of their second
cirri shorter than the posterior rami; and, secondly, _P. crassa_, _P.
fissa_, and _P. eburnea_, which in these several respects are otherwise
characterised. The _P. eburnea_, however, differs rather more from _P.
crassa_ and _P. fissa_, than these two do from each other; but certainly
not enough to allow of the retention of Mr. Hinds' genus of Trilasmis.
_P. crassa_, in an especial degree, connects together all the forms.

_General Appearance._--Capitulum oval, more or less produced, flat or
gibbous; formed of three, five, or seven approximate valves; the lesser
number arising from the abortion of the terga, and the greater number
from the scuta being divided into two segments. Valves moderately thick,
either white or reddish, smooth or striated, and sometimes partly
covered by membrane, bearing minute spines. _Scuta_ oval, of varying
proportions; the basal margin is generally narrow, and blends into the
carina-tergal margin; the internal basal rim generally is well
developed, sometimes with, and sometimes without internal teeth beneath
the umbones. In _P. eburnea_, and sometimes in _P. crassa_, there is a
line of apparent fissure, and in _P. fissa_ of actual disseverment,
running from the umbo to the apex of each scutum, nearly in the line in
which a ridge extends in Lepas: the primordial valves of the scuta in
these three species, are seated at the basal angles of the lateral and
larger segments. The positions of the primordial valves, and the
direction of growth in the calcified valves, are, in all the species,
the same as in Lepas. In several of the species attached to Crustacea,
the two scuta are unequally convex, which is caused, as was pointed out
to me by Mr. Gray, by that valve which lies close and nearly parallel to
the body of the crab, being least developed. The _Terga_ are either
quite absent, or rudimentary as in _P. crassa_, or pretty well developed
as in the other species: the occludent margin is single, and not double
as generally in Lepas; the basal angle is either pointed or truncated.
The _Carina_ varies considerably in shape, but never extends up between
the terga, nor ends downwards in a fork; in the first two species it is
truncated; in the others, it terminates in a deeply-imbedded oblong
disc, which in _P. eburnea_ seems almost entirely (but of course not
quite) to separate the inside of the capitulum from the peduncle; a
similar separation is effected in _P. fissa_, where the imbedded disc is
small, by two large teeth on the internal basal rims of the two scuta.
The carina is always narrow, and either solid internally or very
slightly concave.

_Peduncle_, is very short and narrow; the membrane is generally ringed
with thicker, yellower portions, and often bears very minute spines.

_Size._--All the species are small, with a capitulum not exceeding half
an inch in length.

_Filamentary Appendages._--None.

_Mouth._--Labrum generally considerably bullate in the upper part, with
a row of teeth on the crest. The _mandibles_ have four teeth, with the
inferior point narrow and spine-like, or rudimentary and absent. The
_maxillæ_ have, under the two or three upper great spines, a deep notch
itself bearing spines; beneath this, the lower part is straight and
considerably prominent, Pl. X, fig. 15. Outer maxillæ are covered on
their inner sides continuously with spines.

_Cirri._--The first pair is sometimes seated very distant from the
second. The arrangement of the spines on the posterior cirri varies, to
an unusual degree within the limits of the same genus. We have either
the ordinary structure of anterior pairs, with single fine intermediate
spines (as in _P. Kæmpferi_ and _aurantia_), or we have the pairs
increased by one or two additional longitudinal lateral rows, as in _P.
eburnea_; or we have the front spines forming a single transverse row,
as in _P. crassa_ and _P. fissa_, Pl. X, fig. 29, _a_. The segments in
none of the species are protuberant; the anterior ramus of the second
cirrus does not seem to be thicker than the posterior ramus, as is
usually the case. The rami of the second, and of most of the other
cirri, are unequal in length,--the anterior ramus, contrary to the
ordinary rule, being longer in _P. eburnea_, _P. fissa_, and _P.
crassa_, than the posterior ramus by several segments; I have hitherto
observed this inequality only in the sessile genus Chthamalus.

The _Caudal Appendages_ are small, uniarticulate, and always furnished
with bristles.

    _Distribution._--Four out of the five species live attached to
    Crustacea in the European and Eastern warmer temperate and
    tropical oceans; the fifth species was found attached to the
    dead spines of an Echinus, off New Guinea. It is probable that
    several more species will be hereafter discovered.


1. PÆCILASMA KÆMPFERI. Pl. II, Fig. 1.

_P. valvis 5; carinæ basi truncatâ et cristatâ: scutorum dentibus
internis umbonalibus fortibus: tergorum acumine basali truncato,
margini occludenti pæne parallelo._

Valves 5; carina with a truncated and crested base; scuta with strong
internal umbonal teeth; terga with the basal point truncated, almost
parallel to the occludent margin.

Maxillæ with short thick spines in the notch under the two upper great
spines; caudal appendages with scattered bristles on their summits, and
along their whole outer margins.

    Japan; attached, in great numbers, to the upper and under sides
    of the _Inachus Kæmpferi_ of De Haan, a slow-moving brachyourous
    crab, probably from deep water. British Museum.

_General Appearance._--Capitulum rather compressed, narrow, and
produced. Valves white, tinged with orange, smooth, moderately thin,
occasionally with faint traces of striæ radiating from the umbones.
_Scuta_, apex pointed, with a very slight ridge running to the umbo;
basal margin equalling two thirds of the length of the terga, with an
internal basal rim; on the under side of each valve, beneath the umbo,
there is a strong tooth. Out of the numerous specimens, all excepting
one had their scuta unequally convex, with their occludent margins
unequally curved, that of the more convex valve at the umbo, curling
beyond the medial line. The basal end of the carina is, likewise,
slightly curved laterally, and always turns towards the more convex
valve. This inequality, as Mr. Gray pointed out to me, depends on the
position of the specimens; the flatter side lying close to the carapace
of the crab. _Terga_, flat, oblong, nearly rectangular; occludent margin
straight; basal angle, truncated, almost parallel to the occludent
margin; in width, three or four times as wide as the carina. _Carina_,
(fig. 1, _a_) short, narrow, slightly curved, upper part broadest, with
the apex rounded, only just passing up between the basal broad ends of
the terga; externally carinated, internally very slightly concave; basal
end abruptly truncated, crested, not deeply imbedded in the membrane of
the peduncle.

_Peduncle_, barely as long as the capitulum, apparently (for specimens
dry and much shrunk) narrow, surrounded by rings or folds of thicker
yellowish membrane, of which the upper ones retain moderately long
spines; low down these rings become confluent; whole surface finely
dotted, dots largest on the rings.

_Mouth._--Labrum highly bullate in the upper part, with a row of teeth
on the crest; mandibles with four teeth, the fourth close to the
inferior apex, which is very little developed, sometimes making the
fourth tooth appear simply bifid. Maxillæ with two large spines on the
upper angle, beneath which there is a large depression, bearing one
rather long and thick, and four short and thick, spines; inferior
upraised part with a double row of longer and thinner spines.

_Cirri._--Posterior cirri with segments bearing five pairs of spines, of
which the lowest pair is very minute; intermediate spines minute; spines
of the dorsal tuft thin, of nearly equal size; segments not at all
protuberant, elongated. First cirrus, standing far separated from the
second (as in Scalpellum), with its nearly equal rami rather above half
as long as those of the second cirrus. Second cirrus with anterior ramus
not thicker, and scarcely more thickly clothed with spines, than the
posterior ramus, but shorter than it by three or four segments; the
spines not forming a very thick brush on the anterior ramus. Both rami
of third cirrus with a longitudinal row of minute spines, parallel to
the main pairs. Between the bases of the pedicels of the first pair of
cirri, there are two closely approximate, conical flattened
protuberances, like the single one to be described in Ibla.

_Caudal Appendages_, about one third of the length of the pedicel of the
sixth cirrus, with some moderately long and strong spines at the end,
and down the whole outer sides.

_Ova_, much pointed. _Penis_, hairy.

_Size._--Capitulum in largest specimens half an inch long.


2. PÆCILASMA AURANTIA. Pl. II, Fig. 2.

_P. valvis 5; carinæ basi truncatâ: scutis ovatis, margine basali
perbrevi, dentibus parvis, internis, umbonalibus instructo: tergorum
acumine basali perobliquè truncato._

Valves 5; carina with a truncated base; scuta oval, with the basal
margin very short, furnished with small internal umbonal teeth; terga,
with the basal point very obliquely truncated.

Maxillæ with fine spines in the notch under the three great upper
spines; caudal appendages with scattered bristles on their summits, and
along only the upper part of their outer margins.

    Madeira; found by the Rev. R. T. Lowe, attached to the rare
    _Homola Cuvierii_, probably a deep-water crab. British Museum.

_General Appearance._--This species so closely resembles _P. Kæmpferi_,
that it is superfluous to describe it in detail; and I will indicate
only the points of difference. When the valves have been well preserved,
they are of fine pale orange colour, and hence the name above given,
which was proposed by the Rev. R. T. Lowe.

_Scuta_, with the internal umbonal teeth small; basal internal marginal
rim very prominent, furrowed within; basal margin short, (only equalling
half the length of terga), owing to the great curvature of the lower
part of the carino-tergal margin; hence, the outline of the scuta is
almost pointed oval. I saw no appearance of inequality in the two sides.

_Terga_, rather smaller in proportion to the scuta, than in _P.
Kæmpferi_, with the basal end very obliquely truncated, so as to appear
at first simply pointed, not parallel to the occludent margin; apex
considerably more pointed and produced than in the foregoing species.

_Carina_, almost of equal narrowness throughout, barely concave within;
lower end triangular, abruptly truncated, and not crested.

_Primordial valves_ very plain, with the usual hexagonal structure:
those of the terga, rounded at both ends, instead of being square, as in
the mature calcified valves.

_Peduncle_ short, narrow, not half as long as the capitulum; paved with
minute equal beads, as in the genus Dichelaspis.

_Mouth._--Mandibles with the fourth tooth very small; inferior angle
rudimentary. Maxillæ, with three great upper spines, beneath which there
is a deep notch bearing some delicate spines; inferior upraised part, as
in _P. Kæmpferi_.

_Cirri._--Rami of first cirrus hardly more than one third as long as the
rami of the second cirrus, which latter rami are unequal in length by
only two segments; the posterior ramus being the longer one.

_Caudal Appendages_, with only two or three lateral bristles, besides
those on the summit.

_Size._--Capitulum, three to four tenths of an inch long.

_General Remarks._--This species has the closest general resemblance to
_P. Kæmpferi_, and is evidently a representative of it. On close
examination, however, almost every part differs slightly; the chief
points being the narrowness of the basal margin of the scuta; the
obliqueness of the truncated basal end of the terga and the sharpness of
the upper end; the rudimentary state of the inferior angle of the
mandibles; the character of the spines on the maxillæ; the proportional
lengths of the cirri, and the fewness of the spines on the outer sides
of the caudal appendages. The fact of Madeira having this Pæcilasma, a
representative both in structure and habits of a Japan species, is
interesting, inasmuch, as I am informed by Mr. Lowe, that some of the
Madeira fishes are analogues of those of Japan.


3. PÆCILASMA CRASSA. Pl. II. Fig. 3.

  ANATIFA CRASSA. _J. E. Gray._ Proc. Zoolog. Soc., 1848, p. 44,
        Annulosa, Tab. iii, figs. 5, 6.

_P. valvis 5; carinæ termino basali in discum parvum infossum producto:
scutis convexis, dentibus internis umbonalibus nullis: tergis pæne
rudimentalibus, vix carinâ latioribus._

Valves 5; carina with the basal end produced into a small imbedded disc;
scuta convex, without internal umbonal teeth; terga almost rudimentary,
scarcely broader than the carina.

Spines on the segments of the posterior cirri arranged in single
transverse rows.

    Madeira; attached to the _Homola Cuvierii_, Rev. R. T. Lowe.
    British Museum.[31]

_General Appearance._--Capitulum highly bullate, or thick. Valves rather
thick, opaque, either pale or dark flesh-red, smooth, yet rather plainly
striated from the umbones. There are a few very minute spines on the
membranous borders of the valves.

_Scuta_ highly convex, broadly oval, apex broad rounded; basal margin
narrow, much curved; no internal, umbonal teeth; basal internal rim
strong, running up part of the occludent margin. A slightly prominent
ridge, either rounded or angular, but in one specimen a narrow depressed
fissure-like line, runs parallel to the occludent margin and ends near
the apex in a slight notch; this fact is of interest in relation to the
structure of the scuta in _P. eburnea_ and _P. fissa_. The scuta are
either equally or very unequally convex; in the latter case, the
occludent margin of one valve is curled, so that its umbo is not quite
medial.

   [31] It is stated, in 'Zoolog. Proc.,' (1848, p. 44,) that this
   species was attached to a gorgonia, from Madeira; I cannot but
   suspect that there has been some confusion with the _Oxynaspis
   celata_ from Madeira, which is thus attached.

_Terga_, minute, almost rudimentary, scarcely broader than the carina,
and half as long as the chord of its arc; carinal margin slightly
curved; scutal margin straight, with a slight prominence fitting into a
notch in the scuta; basal end bluntly pointed.

_Carina_, (fig. 3, _a_) rather shorter than the scuta, extending up only
to the basal ends of the terga; moderately curved; apex moderately
sharp; middle part broadest, externally carinated; internally not
concave, with the inner lamina of shell, at the basal end, produced into
a very small oblong disc or tooth, which is only as wide as the
narrowest upper part of the valve. The exterior keel does not extend on
to this disc, which is slightly constricted at its origin.

_Peduncle_ very short, narrow, ringed, and apparently without spines.

_Size._--Capitulum four tenths of an inch long.

The following parts of the animal are described from some small and not
well preserved specimens from Madeira, which I owe to the kindness of
Mr. Lowe.

_Mouth._--Labrum highly bullate in the upper part, with large, inwardly
pointed, unequal teeth. Mandibles, with four large, pointed, equal-sized
teeth, with the inferior angle very narrow, acuminated like a single
spine. Maxillæ, with three (?) large upper spines, of which the middle
one is extremely strong and long, beneath which, there is a deep notch
with a single strong spine, and with the whole inferior part square and
much upraised, so as to stand on a level almost with the tips of the
great upper spines.

_Cirri_ in a miserable state of preservation; first cirrus short, second
cirrus with rami unequal, and I suspect the anterior one the longest;
some of the other cirri also have unequal rami. The segments of the
posterior cirri are not protuberant, they have on their anterior faces a
single transverse row of bristles: in the upper segments, some of the
spines in each dorsal tuft (which is much spread out), are _much_
thicker, though rather shorter than those on the anterior face. This
peculiar structure is common to all five posterior cirri.

_Caudal Appendages._--I can only say that they are spinose on their
summits.

_Affinities._--This species is allied to _P. eburnea_ in the rudimentary
condition of its terga; in the disc-shaped basal end of its carina; and
in the presence in some specimens, of a fissure-like line on the scuta
parallel to their occludent margins. Its affinity, however, is closer to
_P. fissa_, as is more especially shown by the remarkable arrangement of
the spines on the five posterior cirri.


4. PÆCILASMA FISSA. Pl. II, Fig. 4.

_P. valvis 7; scuto utroque è duobus juxtapositis segmentis formato;
segmento altero intus dentato: tergis brevibus, ter aut quater carinâ
latioribus: carinæ termino basali in discum parvum angustum infossum
producto._

Valves 7; each scutum being formed of two closely approximate segments;
of which one is internally toothed: terga short, three or four times as
wide as the carina: carina with the basal end produced into a small,
narrow, imbedded disc.

Spines on the segments of the posterior cirri arranged in single
transverse rows.

    Philippine Archipelago; Island of Bohol; parasitic on a spinose
    crab, found under a stone at low water; single specimen, in
    Mus., Cuming.

_General Appearance._--Capitulum gibbous, broadly oval, nearly a quarter
of an inch long. Valves white, smooth, moderately thick, marked by the
lines of growth. The occludent segments of the scuta, and nearly the
whole of the terga, and the whole of the carina, enveloped in
lemon-yellow membrane, tinged with orange, but the specimen had long
been kept dry.

_Scuta_ formed of two, apparently always separate, segments, closely
united, so that externally their separation is hardly visible, and does
not allow of movement; the fissure thus formed runs almost in the line
connecting the umbo and apex, (where in most species a ridge extends,)
but a little on the carinal side of it. The occludent segment is
narrowly bow-shaped, pointed at both ends, with the upper end projecting
slightly beyond the apex of the lateral segment, and with the occludent
margin regularly curved from end to end. The lateral segment is large,
of an oval shape, with a narrow strip cut off on one side. Primordial
valves very plain at the umbones of the lateral segments, but none are
visible on the occludent segments; and this makes me believe that these
two pieces are normally parts of a single valve; having only one
specimen of _P. fissa_, I was not able to make out quite certainly
whether the two segments are continuously united at their umbones by a
non-calcified portion of valve, as is certainly the case with
Dichelaspis. The basal margin of the lateral segment is narrow,
inflected, and blends with the carino-tergal margin; it has an internal,
prominent, basal rim, and towards the occludent margin a large,
prominent, internal tooth. This internal basal rim is not parallel to
the outer basal margin, but rises to a point a little way up the
occludent margin, in the same manner as in _P. eburnea_, but in a lesser
degree; in this latter species the peduncle is internally almost cut off
by the large disc of its carina; here, on the other hand, it is
internally almost cut off by these rims and the two large teeth of the
lateral segments of the scuta.

_Terga_ sub-triangular, short, nearly half as broad as long; three or
four times as wide as the carina, and rather wider than the occludent
segment of the scuta; occludent margin single, arched; carinal margin
slightly arched; basal angle bluntly pointed.

_Carina_ very narrow, much arched, running up just between the basal
ends of the terga; exterior ridge enveloped in membrane; heel blunt,
prominent; internally, not concave, even slightly convex, produced at
the lower end into a very narrow, short, imbedded disc, (or rather
tooth,) which is itself a little curved downwards and blunt at the end.

_Peduncle_ very narrow, about half as long as the capitulum; yellow,
finely beaded, plainly ringed, without spines.

_Mouth._--Labrum, with a row of minute teeth; palpi narrow. Mandibles
with all the lower part narrow; of the four teeth, the second and third
are narrow, the fourth is pectinated and placed very close to the
inferior angle, which is produced into a long thin tooth. Maxillæ
unknown.

_Cirri._--First pair lost. The arrangement of the spines on all is most
abnormal, Pl. X, fig. 29: dorsal tuft long, arranged in a transverse
line and seated in a deep notch; in the sixth cirrus, the spines on the
lower segments are fine, those on the upper segments are thick and
claw-like, mingled with some fine spines; in the four anterior cirri the
spines of the dorsal tufts are even thicker and more claw-like. On the
anterior faces, also, of all the segments the spines form a single row;
they are shorter than those composing the dorsal tuft; hence the spines
on each segment are arranged in a circle, interrupted widely on the two
sides: this arrangement is common to all five posterior cirri. Second
cirrus, with the _anterior_ ramus one third longer and thinner than the
posterior ramus (this is the reverse of the usual arrangement); this
longer ramus equals in length the sixth cirrus. Third cirrus, with the
anterior ramus considerably longer than the posterior ramus; in the
three posterior pair of cirri, also, the anterior rami are a little
longer than the posterior: except in length, there is little difference
of any kind between the five posterior pair of cirri. Pedicels of the
cirri long; rami rather short; segments elongated, not protuberant.

_Caudal Appendages_ nearly as long as the pedicels of the sixth cirrus,
thickly clothed with very fine bristles, like a camel's-hair pencil
brush.

_Affinities._--In the structure of the carina, and more especially of
the scuta, there is a strong affinity between the present and following
species; for we shall immediately see that in _P. eburnea_ there is
evidence of the scuta being composed of two segments fused together; and
the larger segment is furnished with an internal oblique, strong, basal
rim. To this same species there is an evident affinity in the form of
the mandibles and of the caudal appendages, and in the anterior rami of
the cirri being longer than the posterior rami. Notwithstanding these
points of affinity, I consider that _P. fissa_ is more closely related
in its whole organisation, as more particularly shown in the arrangement
of the spines on the cirri and in the presence of terga, to _P. crassa_
than to _P. eburnea_. Although in Dichelaspis, the scuta are invariably
composed of two almost separate segments, yet _P. fissa_ shows no
special affinity to this genus.


5. PÆCILASMA EBURNEA. Pl. II, Fig. 5.

  TRILASMIS EBURNEA. _Hinds._ Voyage of Sulphur, 1844, vol. i,
        Mollusca, Pl. xxi, fig. 5.

_P. valvis 3; scutis acuminatis, ovatis; ad pedunculum pæne transversè
spectantibus; dentibus internis umbonalibus fortibus: tergis nullis:
carinæ termino basali in discum amplum oblongum infossum producto._

Valves 3; scuta pointed, oval, placed almost transversely to the
peduncle; internal umbonal teeth strong: terga absent: carina with the
basal end produced into a large, oblong, imbedded disc.

Spines on the upper segments of the posterior cirri, arranged in three
or four approximate longitudinal rows, making small brushes.

    _Habitat._--New Guinea, attached to the spines of a dead
    Echinus. Brit. Mus., and Cuming.

_General Appearance._--Capitulum flat, pear-shaped, placed almost
transversely to the peduncle. Valves white, smooth, moderately thick.

_Scuta:_ the basal margin, as seen externally, is narrow, and can hardly
be separated from the carinal margin; but an internal basal rim, (fig.
5, _b_) (along which the imbedded disc of the carina runs,) shows where,
in the other species, the basal and carinal margins are separated. This
basal internal rim is not parallel to the external basal margin, but
runs upwards to the occludent margin, leaving beneath it a large
triangular space, to which the membrane of the peduncle is attached; and
this makes it appear as if the rostral umbones of these valves had grown
downwards; but, judging from the allied species, _P. fissa_, I have no
doubt that the primordial valves really lie on the umbones, and that the
growth has been in the usual direction, that is, exclusively upwards.
The occludent margin is curved, and blends by a regular sweep into the
carinal margin, so that there is no acute upper angle. A distinct line
can be seen, as if two calcareous valves had been united, running from
the umbo to the upper end of the valve, thus in appearance separating a
slip of the occludent margin; internally this appearance is more
conspicuous; this structure is important in relation to that of _P.
fissa_. The pointed umbones are divergent, and internally under each,
there is a large tooth. The two valves are equally convex.

_Terga_, entirely absent.

The _Carina_ (Tab. II, fig. 5, _a_, _c_), including the disc, is three
fourths as long as the scuta; it is placed almost transversely to the
longitudinal axis of the peduncle; it is narrow and internally convex;
the imbedded disc is very large, forming a continuous curve with the
upper part of the carina; this disc runs along the internal basal rim of
the scuta, and hence almost separates, internally, the peduncle from the
capitulum; it equals one fourth of the total length of the valve, and is
thrice as wide as the upper part; it is oval, externally marked by a
central line, and with a slight notch at the end, giving a divided
appearance to the whole, and indicating how easily a fork might be
formed from it. The carina is thick, measured from the inner convex to
the exterior surface, which is carinated; heel prominent.

_Peduncle_, narrow, very short, not nearly so long as the capitulum.

_Mouth._--Labrum considerably bullate, with the lower part much produced
towards the adductor muscle; crest with small bead-like teeth; palpi
small, pointed; mandibles, with the first tooth standing rather distant
from the second; inferior angle spine-like and bifid; maxillæ (Pl. X,
fig. 15), with two considerable spines (only one is shown in the Plate)
beneath the upper large pair; the inferior upraised part bears seven or
eight pair of spines, and its edge is not quite straight; close to the
main notch, lying under the four upper spines, there are two minute
notches, with the interspace bearing a tuft of fine spines and a pair of
larger ones.

_Cirri._--The rami in all are rather unequal in length, the anterior
rami being rather the longest; the anterior rami of the second and third
cirri are not thicker than the posterior rami. The segments in the three
posterior cirri are not protuberant; the upper segments bear three or
four pair of spines, with some minute intermediate ones, and with the
lateral marginal spines unusually large and long, so as to form, with
the ordinary pairs, a third or fourth longitudinal row; hence a small
brush is formed on each segment. The dorsal tuft is large and wide, so
as to contain even fourteen spines, of which some are as long as those
in front. In the lower segments of these same posterior cirri, the
lateral marginal spines are not so much developed (nor is the dorsal
tuft), and hence the segments can hardly be said to be brush-like. The
first cirrus is placed rather distant from the second pair. The second
and third cirri differ from the three posterior pair, only in the
bristles being slightly more numerous, and in the dorsal tufts being
more spread out.

_Caudal Appendages_ about half the length of the lower segments of the
pedicels of the sixth cirrus; truncated and rounded at their ends;
thickly clothed with long excessively fine bristles, so as to resemble
camel-hair pencils.

The _Stomach_, I believe, is destitute of cæca; in it was a small
crustacean.

_General Remarks._--I was at first unwilling to sacrifice Mr. Hind's
genus, Trilasmis, which is so neatly characterised by its three valves;
moreover, the present species does differ, in some slight respects, from
the other species of Pæcilasma; but under the head of _P. fissa_ I have
shown how that species, _P. crassa_ and _P. eburnea_ are tied together.
The absence of terga, which are rudimentary in _P. crassa_, (and we
shall hereafter see, in _Conchoderma_, how worthless a character their
entire absence is,) and the arrangement of the spines in the upper
segments of the posterior cirri, are the only characters which could be
used for a generic separation.


_Genus_--DICHELASPIS. Plate II.

  OCTOLASMIS.[32] _J. E. Gray._ Annals of Philosophy, vol. x, new
        series, p. 100, August 1825.

  HEPTALASMIS. _Agassiz._ Nomenclator Zoologicus.

_Valvæ 5, quæ ferè pro septem haberi possent, scuto in segmenta planè
duo, ad angulum autem rostralem conjuncta, diviso: carina plerumque
sursum inter terga extensa, deorsum aut disco infosso aut furcâ aut
calyce terminata._

   [32] From [Greek: dichêlos], bifid, and [Greek: aspis], a shield,
   or scutum. The name Octolasmis was given by Mr. Gray under the
   belief that there were eight valves. Leach (as stated in the
   'Annals of Philosophy,') had proposed, in MS., the name
   Heptalasmis, and this is now used in the British Museum by Mr.
   Gray, and thus appears in Agassiz's 'Nomenclator Zoologicus.'
   Although, strictly, there are only five valves, I continued to
   use, in my MS., the term Heptalasmis, until I examined the _D.
   orthogonia_, where it was so apparent to the naked eye that there
   were only five valves, the scuta in this species being less
   deeply bifid, that I was compelled to give up a name so
   manifestly conveying a wrong impression, and hence adopted the
   one here used.

Valves 5, generally appearing like 7, from each scutum being divided
into two distinct segments, united at the rostral angle; carina
generally extending up between the terga terminating downwards in an
imbedded disc, or fork, or cup.

Mandibles, with three or four teeth; maxillæ notched, with the lower
part of edge generally not prominent; anterior ramus of the second
cirrus not thicker than the posterior ramus, not very thickly clothed
with spines; caudal appendages uniarticulate, spinose.

    _Distribution._--Eastern and Western warmer oceans in the
    Northern hemisphere, attached to crustacea, sea-snakes, &c.

_Description._--The capitulum appears to contain seven valves; but, on
examination, it is found that two of the valves on each side, are merely
segments of the scutum; these are united at the umbo, in three of the
species, by a narrow, non-calcified portion of valve, where the
primordial valve is situated; in _D. orthogonia_, however, the junction
of the two segments is perfectly calcified, and of the same width as the
whole of the basal segment. The capitulum is much compressed, broad at
the base, and extends a little beneath the basal segments of the scuta.
The valves are very thin, often imperfectly calcified, and generally
covered with membrane. They are not placed very close together, and in
all the species a considerable interspace is left between the carina and
the two other valves: in the _D. Grayii_ the valves are so narrow that
they form merely a calcified border round the capitulum. The membrane
between the valves and over them, is very thin, and is thickly studded,
in some of the species, with minute blunt conical points, apparently
representing spines. The valves in the same species present considerable
variations in shape; in their manner or direction of growth, and in the
position of their primordial valves, they agree with Lepas and
Pæcilasma.

_Scuta._--In three of the species the two segments, named the occludent
and basal, appear like separate valves, but these, by dissection, can be
most distinctly seen to be united at the rostral angle. The primordial
valve, formed of the usual hexagonal tissue, is elliptic, elongated, and
placed in the direction of the occludent segment; calcification
commences at its upper point, so as to form the occludent segment, and
afterwards at its lower point, but rectangularly outwards, to form the
basal segment; in the minute space between these two points of the
primordial valve, there is, in four of the species, no calcification; so
that the two segments are united by what may be called a flexible hinge;
in _D. orthogonia_ the two calcareous segments are absolutely
continuous. The occludent segment is longer than the basal segment; it
either runs close along the orifice, or in the upper part bends inwards;
both segments are narrow, except in _D. Warwickii_, in which the basal
segment is moderately broad; the two segments are placed at an angle,
varying from 45° to 90°, to each other. The capitulum generally extends
for a little space beneath the basal segments of the scuta, where it
contracts to form the peduncle.

The _Terga_ present singular differences in shape, and are described
under the head of each species; scarcely any point can be predicated of
them in common, except that they are flat and thin.

The _Carina_ is much bowed, narrow, and internally either slightly
concave or convex and solid; the upper end extends far up between the
terga; the lower end is formed by a rectangularly inflected, imbedded,
triangular or oblong disc, deeply notched at the end, or as in _H.
Lowei_, of a fork, the base, however, of which is wider than the rest of
the carina, so as to present some traces of the disc-like structure of
the other two species; or lastly, as in _D. orthogonia_, it terminates
in a crescent-formed cup.

_Peduncle._--This is narrow, compressed, and about as long, or twice as
long, as the capitulum; in _D. Warwickii_ it is studded with minute
beads of yellowish chitine.

_Size._--Small, with a capitulum scarcely exceeding a quarter of a inch
in length.

_Filamentary Appendages._--None. There are two small ovigerous fræna,
which, in _D. Warwickii_, had the glands collected in seven or eight
little groups on their margins.

_Mouth._--Labrum highly bullate, with small teeth on the crest; palpi
small, not thickly covered with spines. _Mandibles_ narrow, with three
or four teeth. Maxillæ small, with a notch beneath the two or three
great upper spines; lower part bearing only a few pair of spines,
generally not projecting, but in _D. orthogonia_ largely projecting.
Outer maxillæ, with their inner edges continuously covered with
bristles.

_Cirri._--First pair short, situated rather far from the second pair;
second pair with the anterior ramus not thicker than the posterior
ramus, and hardly more thickly clothed with spines than it, excepting
sometimes the few basal segments. All the five posterior pair of cirri
resemble each other more closely than is usual. In _D. Lowei_, the
segments of the posterior cirri bear the unusual number of eight pair of
main spines.

_Caudal Appendages._--Uni-articulate, spinose; in D. pellucida they are
twice as long as the pedicels of the sixth cirrus, but I could not
perceive in them any distinct articulations.

    _Distribution._--Attached to crabs at Madeira, and off Borneo;
    to sea-snakes in the Indian Ocean. The individuals of all the
    species appear to be rare.

_General Remarks._--Four of the five species, forming this genus, though
certainly distinct, are closely allied. I have already shown, that
although the characters separating Lepas, Pæcilasma, and Dichelaspis are
not very important, yet if they be neglected these three natural little
groups must be confounded together. Dichelaspis is much more closely
united to Pæcilasma than to Lepas, and, as far as the more important
characters of the animal's body are concerned, there is no important
difference between them. Consequently, I at first united Pæcilasma and
Dichelaspis, but the latter forms so natural a genus, and is so easily
distinguished externally, that I have thought it a pity to sacrifice it.
The carina, (which seems to afford better characters than the other
valves in Dichelaspis,) from generally running up between the terga and
in ending downwards, in three of the species, in a deeply notched disc
or fork, more resembles that in Lepas than in Pæcilasma; in the manner,
however, in which the imbedded disc, in _D. Warwickii_ and _D. Grayii_,
nearly cuts off the inside of the capitulum from the peduncle, there is
a resemblance to _Pæcilasma eburnea_. In the extent to which the valves
are separated from each other, in the bilobed form of the scuta, (the
two segments in Dichelaspis, perhaps, answering to the upper and lateral
projections in the scuta of _Conchoderma virgata_,) and in the basal
half of the scuta not descending to the base of the capitulum, there is
a considerable resemblance to Conchoderma; in both genera the adductor
muscle is attached under the umbones of the scuta; but the structure of
the mouth and cirri and caudal appendages shows that the affinity is not
stronger to Conchoderma than to Lepas. It appears at first probable,
that Dichelaspis would present a much closer affinity to _Pæcilasma
fissa_, in which, owing to the scuta being formed of two segments, there
are seven valves, than to any other species of that genus; but in _P.
fissa_ the primordial valve is triangular and is situated on the basal
segment, whereas, in Dichelaspis, it is elliptic and is seated between
the two segments, and is more in connection with the occludent than with
the basal segment; and this I cannot but think is an important
difference: in other respects, _P. fissa_ shows no more affinity to
Dichelaspis than do the other species of the genus. Finally, I may add
that Dichelaspis bears nearly the same relation to Pæcilasma, as
Conchoderma does to Lepas.


1. DICHELASPIS WARWICKII. Pl. II, figs. 6, 6 _a_, _b_.

  OCTOLASMIS WARWICKII. _J. E. Gray._ Annals of Philosophy, vol. x,
        p. 100, 1825; Spicilegia Zoologica. t. vi, fig. 16, 1830.

_D. scutorum segmento basali duplo latiore quam segmentum occludens:
tergorum parte inferiore paulò latiore quam occludens scutorum
segmentum._

Scuta, with the basal segment twice as wide as the occludent segment;
terga, with the lower part slightly wider than the occludent segment of
the scuta.

Mandibles, generally with four teeth.

    Off Borneo, attached to a crab (Belcher): China Sea. British
    Museum.

_General Appearance._--Capitulum much compressed, elongated, with the
valves not very close together, the carina being separated by a rather
wide space from the scuta and terga. Valves variable in shape, very thin
and translucent, covered by thin membrane, which, over the whole
capitulum, is studded with minute blunt points.

_Scuta._--Segments without internal teeth or an internal basal rim; the
occludent segment long, narrow, pointed, not quite flat, sometimes
slightly wider in the upper part; about one third of its own length
longer than the basal segment; occludent margin slightly arched; basal
segment about twice as wide as the occludent segment, triangular,
slightly convex; in young specimens (Pl. II, fig. 6 _b_), the carinal
margin of the basal segment is protuberant, and the occludent margin
hollowed out; in old specimens the occludent margin of the basal segment
is straight, and the carinal margin much hollowed out. In very young
specimens the basal segment is very small compared to the occludent.

_Terga_, variable in shape; flat, lower part wider than the occludent
segment of the scuta; occludent margin double, forming a considerable
rectangular projection, as in the terga of Lepas; scutal margin deeply
excised at a point corresponding with the apex of the scuta, a flat
tooth or projection being thus formed; there is sometimes a second tooth
(fig. 6 _b_) a little above the basal point. The terga, in the first
variety, somewhat resemble in shape the scuta of _Conchoderma aurita_.

_Carina_, much bowed, narrow, slightly concave within, (in the Borneo
specimen, rather wider and more concave,) extending up between the terga
for half their length, terminating downwards in a rectangularly
inflected, deeply imbedded, oblong, rather wide, flat disc, at its
extremity more or less deeply notched. This disc is externally smooth;
internally it sometimes has two divergent ridges on it; it extends
across about two-thirds of the base of the capitulum (fig. 6 _a_, as
seen from beneath, when the peduncle is cut off), to under the middle of
the basal segments of the scuta.

_Peduncle_, narrow, flattened; united to the capitulum some little way
below the scuta; about as long as the capitulum; the membrane of which
it is composed is thin, externally studded with bluntly conical beads of
yellowish chitine, of which the largest were 1/2000 of an inch in
diameter; on their internal surfaces these are furnished with a small
central, circular depression, apparently for a tubulus; the arrangement
of the beads varied in concentric zones. Similar conical points on the
capitulum have an internal concave surface about 1/3000 in diameter,
with a central circle 1/12000 in diameter, for the insertion, as I
believe, of a tubulus.

_Size._--The largest specimen had a capitulum a quarter of an inch long.

_Mouth._--Labrum highly bullate; crest with not very minute, blunt
teeth, which towards the middle lie closer and closer to each other, so
as to touch. Palpi rather small, with a few very long bristles at the
apex.

_Mandibles_, narrow, produced, with four teeth, and the inferior angle
tooth-like and acuminated; in one specimen, on one side of the mouth,
the mandible had only three teeth.

_Maxillæ_, small; at the upper angle there are two large spines and a
single small one, beneath which there is a deep notch, and beneath this
a straight but projecting edge, bearing a few moderately large and some
smaller spines. Outer maxillæ sparingly covered with bristles along the
inner margin.

_Cirri._--First pair far removed from the second pair, and not above
half their length; segments rather broad, with transverse rows of
bristles not very thickly crowded together; terminal segments very
obtuse, and furnished with thick spines. The segments of the three
posterior pair have each three or four pair of spines, with a few minute
spines scattered in an exterior, parallel, longitudinal row; dorsal
tufts, with four or five long spines. The second cirrus has its anterior
ramus not thicker, but rather shorter than the posterior ramus; the
former is only a little more thickly clothed with spines, owing to those
in the longitudinal lateral row being longer and more numerous, than is
the sixth pair of cirri. Bristles not serrated.

_Caudal Appendages_, narrow, thin, slightly curved, about half as long
as the pedicels of the sixth cirrus; in young specimens, the appendage
bore seven or eight pair of long bristles rectangularly projecting; in
some older specimens, there was a tuft of bristles on the summit, and
two other tufts on the sides.

I at first thought that the Borneo specimen was a distinct species, but
after careful comparison of the external and internal parts, the only
difference which I can detect is, that the terga are slightly larger,
and that the carina, to a more evident degree, is wider, more especially
in the middle and lower portions.


2. DICHELASPIS GRAYII. Pl. II, fig. 9.

_D. scutorum segmento basali angustiore quam segmentum occludens;
longitudine pæne dimidiâ: tergis bipenniformibus, margine crenato, spinâ
posticâ, manubrio angustiore quam occludens scutorum segmentum._

Scuta, with the basal segment narrower than the occludent segment, and
about half as long as it. Terga like a battle-axe, with the edge
crenated and a spike behind; the handle narrower than the occludent
segment of the scuta.

Mandibles with three teeth; cirri unknown.

    Attached to the skin of a sea-snake, believed to have been the
    _Hydeus_ or _Pelamis bicolor_, and therefore from the Tropical,
    Indian or Pacific Oceans; associated with the _Conchoderma
    Hunteri_; single specimen, in a very bad condition, in the Royal
    College of Surgeons.

_General Appearance._--Capitulum much compressed, elongated, formed of
very thin membrane, with the valves forming round it a mere border.
Valves thin, imperfectly calcified, covered with membrane.

_Scuta_ formed of two narrow plates at very nearly right-angles to each
other, one extending along the occludent, and the other along the basal
margin; both become very narrow at the point of junction, and are there
not calcified, but are evidently continuous and form part of the same
valve; the basal segment is about half as long and narrower than the
occludent segment, flat and bluntly pointed at the end; occludent
segment slightly curled, and therefore the whole does not lie quite in
the same plane; narrow close to the umbo, with a very minute tooth on
the under side; apex rounded. In the upper part, the occludent segments
leave the membranous margin of the orifice, and run in near to the
terga, bending towards them at an angle of 45° with their lower part. I
was unable to distinguish the primordial valves.

_Terga._--These valves are of the most singular shape, resembling a
battle-axe, with a flat and rather broad handle; the upper part consists
of an axe, with a broad cutting crenated edge, behind which is a short
blunt spike. The spike and cutting edge together answer to the double
occludent margin of the tergum in Lepas. The whole valve is flat, thin,
and lies in the same plane; the carinal margin is nearly straight; the
scutal margin bulges out a little, and at a short distance above the
blunt basal point is suddenly narrowed in, making the lowermost portion
very narrow; the widest part of the handle of the battle-axe, is
narrower than the occludent segment of the scuta. The two spikes behind
the cutting and crenated edges of the two terga, are blunt and almost
touch each other; above their point of juncture, the membrane of the
orifice forms a slight central protuberance.

_Carina_, very narrow throughout, concave within, much bowed; upper
point broken and lost, but it must have run up between the terga for
more than half their length; basal portion inflected at nearly right
angles, and running in between, and close below, the linear basal
segments of the scuta, so as almost entirely to cut off internally the
peduncle and capitulum. This lower inflected and imbedded portion, or
disc, gradually widens towards its further end, which is, at least, four
times as wide as the upper part of the carina, and is deeply excised,
but to what exact extent I cannot state, as the specimen was much
broken. On each side of this elongated triangular disc, there is a
slight shoulder corresponding to the ends of the basal segments of the
scuta; and on the upper surface of each shoulder, there is a small tooth
or projection. The middle part of the disc is barely calcified, and is
transparent.

_Peduncle_, rather longer than, and not above half as wide as, the
capitulum; the latter being nearly 2/10ths of an inch in length: the
membrane of the peduncle is thin, naked and structureless.

_Mouth._--Labrum highly protuberant in the upper part, with a row of
beads on the crest. Palpi small, with few bristles. _Mandibles_, with
the whole inferior part, very narrow; three teeth very sharp, with a
slight projection, perhaps, marking the place of a fourth tooth;
inferior angle ending in the minutest point; first tooth as far from the
second, as the latter from the inferior angle. _Maxillæ_ with a _broad_
shallow notch; inferior angle much rounded, bearing only four or five
pair of spines.

_Cirri._--First pair apparently remote from the second pair; all five
posterior pair lost; first pair short, with the rami unequal by about
two segments; segments clothed with several transverse rows of bristles;
terminal segments blunt.


3. DICHELASPIS PELLUCIDA. Pl. II, fig. 7.

_D. valvarum singularum acuminibus superioribus et inferioribus vix
intersecantibus: scutorum segmento basali multo angustiore quam
segmentum occludens; longitudine ferè dimidiâ: tergis bipenniformibus,
margine integro, manubrii acumine ad carinam flexo._

Valves with the upper and lower points of the several valves only just
crossing each other. Scuta with the basal segment much narrower than the
occludent segment, and about half as long as it. Terga like a
battle-axe, with the edge smooth, and the point of the handle bent
towards the carina.

Mandibles with four teeth; caudal appendages twice as long as the
pedicels of the sixth cirrus.

    Indian Ocean; attached to a sea-snake.

This species comes very close to the _D. Grayii_, which likewise was
attached to a snake; but I cannot persuade myself, without seeing a
graduated series, that the differences immediately to be pointed out can
be due to ordinary variation. I am much indebted for specimens to the
kindness of Mr. Busk.

_General Appearance._--The membrane of the capitulum and peduncle is
surprisingly thin and pellucid, so that the ovarian tubes within the
peduncle can be traced with the greatest ease. The valves are small, the
apices only just crossing each other, and are composed of yellow
chitine, with mere traces of calcification. The capitulum is pointed,
oval, .15 of an inch long; the peduncle is narrow, and fully twice as
long as the capitulum.

_Scuta._--The two segments stand at right-angles to each other; the
basal segment is linear and pointed, fully half as long, but only one
third as wide, as the occludent segment. The point of junction of the
two segments is wider than the rest of the basal segment. This latter
segment lies some little way above the top of the peduncle. The
occludent segment is bluntly pointed; it is directed a little inwards
from the edge of the orifice towards the terga; the apex reaches up just
above the slightly reflexed lower point of the terga. The adductor
muscle is fixed under the point of junction of the two segments.

The _Terga_ are battle axe-shaped, with the blade part very prominent,
smooth-edged; behind the blade there is a short upwardly-turned
prominence. The lower point of the handle of the axe, is bent towards
the carina. The tergum, measured in a straight line, equals in length
two thirds of the occludent segment of the scutum, the handle being
rather narrower than this same segment.

The _Carina_ is extremely narrow and much bowed; the apex reaches up
only to just above the lower bent points of the terga. The basal end is
rectangularly inflected, and stretches internally nearly across the
peduncle; it consists (fig. 7 _a_) of a triangular disc of yellow thin
membrane, four or five times as wide as the upper part of the valve; the
end of this disc is hollowed out; its edges are thickened and calcified,
and hence, at first, instead of a disc, this lower part of the carina
appears like a wide fork; the tips of the prongs stretch just under the
tips of the basal segments of the scuta.

_Peduncle._--Its narrowness and transparency are its only two remarkable
characters.

_Mouth._--All the parts closely resemble those of _D. Grayii_, but being
in a better state of preservation I will describe them. The labrum is
highly bullate, with a row of minute teeth on the crest, placed very
close together in the middle. Palpi small, thinly clothed with spines;
mandibles extremely narrow, hairy, with four teeth, but the lower tooth
is so close to the inferior angle, as only to make the latter look
double. Maxillæ, with a very deep broad notch, dividing the whole into
two almost equal halves; in the upper part there are three main spines.

_Cirri._--The first pair are placed at a considerable distance from the
second pair; they are short with equal rami, and rather broad segments
furnished with a few transverse rows of bristles. The five posterior
cirri have singularly few, but much elongated segments, bearing four
pair of spines: the two rami of the second pair are alike, and differ
only from the posterior cirri in a few of the basal segments having a
few more spines.

The _Caudal Appendages_ are twice as long as the pedicels, and nearly
half as long as the whole of the sixth cirrus; they have a small tuft of
long thin spines at their ends, and a few in pairs, or single, along
their whole length; at first I thought that they were multi-articulate,
but after careful examination I can perceive no distinct articulations;
I have seen no other instance of so long an appendage without
articulations.

_Diagnosis._--This species differs from _D. Grayii_ in all the valves
being shorter, so that their points only just cross each other; but
this, I conceive, is an unimportant character. In the scuta, the basal
segment is here narrower, but the point of junction of the two segments
wider than in that species; in the terga, the edge of the axe is smooth
instead of being crenated, and the handle and the point behind are of a
rather different shape; in the carina the imbedded basal disc has not
shoulders and small teeth, as in _D. Grayii_. Notwithstanding these
differences, I should not be much surprised if the present form were to
turn out to be a mere variety.


4. DICHELASPIS LOWEI. Pl. II, fig. 8.

_D. scutorum segmento basali angustiore quam occludens segmentum,
longitudine ferè 4/5: tergorum parte inferiori duplo latiore quam
occludens scutorum segmentum._

Scuta with the basal segment narrower than the occludent segment, and
about four-fifths as long as it. Terga with the lower part twice as wide
as the occludent segment of the scuta.

Mandibles with four teeth; segments of the three posterior cirri with
eight pair of main spines.

    _Hab._--Madeira; attached to a rare Brachyourous Crab,
    discovered by the Rev R. T. Lowe. Very rare.

_General Appearance._--Capitulum much compressed, sub-triangular, formed
of very thin membrane; valves imperfectly calcified, and thin.

_Scuta_ formed of two narrow plates placed at about an angle of 50° to
each other, and united at the umbo by a non-calcified flexible portion.
The primordial valve is situated at this point, but chiefly on the
occludent segment. The occludent segment is about twice as wide and
about one fifth longer than the basal segment, which latter is rather
sharply pointed at its end. The occludent segment is slightly arched, a
little narrowed in on the occludent margin close to the umbo; its upper
end is broad and blunt; it runs throughout close to the edge of the
orifice of the sack, and its longer axis is in the same line with that
of the terga. Close to the umbones, on the under side of the basal
segment, there is, on each valve, a longitudinal calcified fold, serving
as a tooth.

_Terga_ broad, with a deep notch corresponding to the apex of the
occludent segment of the scuta; the part beneath the notch is of nearly
the same width throughout, and is twice as broad as the occludent
segment of the scuta; it has its basal angle very broad and blunt. The
entire length of the terga equals two thirds of that of the occludent
segment of the scuta; occludent margin simply and slightly curved.

The _Carina_ is of nearly the same width throughout, with the upper part
rather the widest, and the apex blunt; within _convex_; it extends up
between three fourths of the length of the terga, terminating downwards
in a fork with very sharp prongs, standing at right-angles to each other
(fig. 8 _a_.) The fork, measured from point to point, is thrice as wide
as, and measured across at the bottom of the prongs it is wider than,
the widest upper part of the valve,--a resemblance being thus shown with
the triangular notched disc in _D. Grayii_. The points of the prong
extend under about one fourth of the length of the basal segments of the
scuta.

_Peduncle_ rather longer than the capitulum, which, in the largest
specimen, was 2/10ths of an inch in length; peduncle narrow, close under
the capitulum; membrane thin and structureless. The larger specimen had
almost mature ova in the lamellæ.

_Mouth._--Labrum with a few bead-like teeth on the crest, distant from
each other even in the central part; palpi rather small, moderately
clothed with bristles.

_Mandibles_, with four teeth; the inferior angle blunt and broad,
showing, apparently, a rudiment of a fifth tooth; the first tooth is as
far from the second, as is this from the inferior angle; second, third,
and fourth teeth very blunt, whole inferior part of mandible not much
narrowed. Maxillæ small, with a small notch under the three upper
spines, which are followed by five or six pair, nearly as large as the
upper spines.

_Cirri._--First pair remote from the second; their rami nearly equal,
and about one third of the length of the rami of the second cirrus;
thickly clothed with bristles: rami of the second cirrus of equal
thickness, but little shorter than those of the sixth cirrus; the three
or four basal segments of the anterior ramus are thickly clothed with
spines; the other segments, and all the segments on the third pair,
resemble the segments of the three posterior pair. These latter are
elongated, not protuberant, and support eight pairs of spines with very
minute intermediate spines; those in the dorsal tufts are numerous and
long.

_Caudal Appendages_ nearly as long as the pedicels of the sixth cirrus;
oval, moderately pointed, with their sides, for one fourth of their
length, thickly clothed with long very thin spines.

_Affinities._--In the form of the scuta and of the carina this species
is most nearly allied to _D. Grayii_ or _D. pellucida_, in the form of
the terga to _D. Warwickii_.


5. DICHELASPIS ORTHOGONIA. Pl. II, fig. 10.

_D. scutorum basali segmento angustiore quam occludens segmentum;
longitudine ferè dimidiâ; duorum segmentorum junctione calcareâ:
tergorum prominentiis marginalibus inæqualibus quinque: carinâ deorsum
in parvo calyce lunato terminatâ._

Scuta with the basal segment narrower than the occludent segment, and
about half as long as it; junction of the two segments calcified. Terga
with five unequal marginal projections. Carina terminating downwards in
a small crescent-formed cup.

Maxillæ with the inferior part of edge much upraised.

    Hab. unknown; associated with _Scalpellum rutilum_, apparently
    attached to a horny coralline. British Museum.

The specimens are in a bad condition, not one with all the valves in
their proper positions, and most of them broken; animal's body much
decayed and fragile.

_General Appearance._--Capitulum apparently much flattened; valves
naked, coloured reddish, separated from each other by thin structureless
membrane.

The _Scuta_ consist of two bars placed at right-angles to each other,
with the point of junction fully as wide as any part of the basal
segment, and perfectly calcified; the primordial valve lies at the
bottom of the occludent segment. The basal segment is equally narrow
throughout, and very slightly concave within; the occludent segment
widens a little above the junction or umbo, and then keeps of the same
width to the apex, which is obliquely truncated; internally this segment
is concave; externally it has a central ridge running along it; the
occludent segment is twice as long and twice as broad as the basal
segment. Both segments are a little bowed from their junction to their
apices.

_Terga._--These are of a singular shape; they are about three-fourths as
long as the occludent segment of the scuta, and in their widest part, of
greater width than it. They consist of four prominent ridges proceeding
from the umbo, and united together for part only of their length, and,
therefore, ending in four prominences; one of these, the longest, has
the same width throughout, and forms the basal point; a second, very
small one, is seated high up on the carinal margin just above the apex
of the carina; the third and fourth, are nearly equal in length, and
project one above the other on the scutal margin. There are two
occludent margins, meeting each other at right angles, and forming a
prominence, as in Lepas; and this gives to the margin of the valve the
five prominences. The whole valve internally is flat; externally, it is
ridged as described.

_Carina_ (fig. 10, _a_, _b_), much bowed, narrow, long; externally, the
central ridge is quite flattened; internally, slightly concave, but
scarcely so towards the lower part, which is narrow; the upper part
widens gradually, and the apex is rounded. The basal embedded portion is
as wide as the uppermost part, and forms a cup, unlike anything else
known: the outline of this cup is semi-oval and crescent-formed; it is
moderately deep; it is formed by the external lamina of the carina
bending rectangularly downwards and a little outwards, whereas the inner
lamina of the lower part (which is slightly concave), is continued with
the same curve as just above, and forms the concave chord to the
semi-oval rim of the cup. This cup, I believe, lies under the points of
the basal segments of the scuta.

_Peduncle_ unknown, probably short.

_Length_ of capitulum, above 2/10ths of an inch.

_Mouth._--Labrum with the upper part highly bullate, and produced into a
large overhanging projection; crest with a row of rather large bead-like
teeth; _palpi_ small, their two sides parallel, very sparingly covered
with long bristles.

_Mandibles_, narrow, produced, with four teeth, and the inferior angle
produced into a single strong spine: the distance between the tips of
the first and second teeth almost equals that between the tip of the
second tooth and of the inferior angle.

_Maxillæ_ with three large upper unequal spines, beneath which, there is
a deep and wide notch (bearing one spine), and the inferior part
projects highly, bearing three or four pairs of spines, and is, itself,
obscurely divided into two steps.

_Outer Maxillæ_, very sparingly covered with bristles; outline,
hemispherical.

_Cirri._--The rami of the five posterior pair are extremely long, as are
the pedicels; the segments are much elongated, with their anterior faces
not at all protuberant; each bears five pair of very long and thin
spines, with an excessively minute one between each pair; the dorsal
tuft consists of very fine and thin spines. The second cirrus has its
anterior ramus not at all thicker than the posterior ramus; but has an
exterior third longitudinal row of small bristles. First cirrus,
separated by a wide interval from the second pair; very short with the
two rami slightly unequal in length; the segments are broad, and are
paved moderately thickly with spines; the terminal spines not
particularly thick.

_Caudal Appendages_ consist of very small and narrow plates, about half
the length of the pedicels of the sixth cirrus, with a few long spines
at their ends.

This well-marked species, I think, has not more affinity to one than to
another of the previous species: it differs from all, in the junction
between the two segments of the scuta being perfectly calcified; in the
peculiar cup, forming the base of the carina; and lastly, in the
inferior part of the maxillæ projecting.


OXYNASPIS.[33] _Gen. Nov._ Pl. III.

_Valvæ 5, approximatæ: scutorum umbones in medio marginis occludentis
positi: carina rectangulè flexa, sursùm inter terga extensa, termino
basali simpliciter concavo._

Valves 5, approximate; scuta with their umbones in the middle of the
occludent margin; carina rectangularly bent, extending up between the
terga, with the basal end simply concave.

   [33] From [Greek: oxunô], to sharpen, and [Greek: aspis], a
   shield or scutum.

Mandibles with four teeth; maxillæ notched, with the lower part of edge
nearly straight, prominent; anterior ramus of the second cirrus thicker
than the posterior ramus; caudal appendages, uniarticulate, spinose.

    Attached to horny corallines.

I have most unwillingly instituted this genus; but it will be seen by
the following description, that the one known species could not have
been introduced into Lepas or Pæcilasma, without destroying these
genera, although it has a close general resemblance with both. As far as
the valves are concerned, it is more nearly related to Lepas than to
Pæcilasma; but taking the entire animal, its relation is much closer to
the latter genus than to Lepas: it differs from both these genera in the
manner of growth of the scuta, which is both upwards and downwards, the
primordial valve being situated in nearly the middle of the occludent
margin. In this respect, and in the shape of the carina and terga, there
is an almost absolute identity with Scalpellum; I may, however, remark
that in Scalpellum, the scuta first grow downwards, and afterwards in
most of the species upwards, whereas here from the beginning, the growth
is both upwards and downwards. In the mouth and cirri, there is rather
more resemblance to Scalpellum than to Pæcilasma and Lepas: in habits,
also, this genus agrees with Scalpellum, and if it had possessed a lower
whorl of valves, it would have quite naturally entered that genus. It is
unfortunate, that so insignificant and poorly characterised a form
should require a generic appellation. In natural position, it appears to
lead from Scalpellum through Pæcilasma to Lepas.


1. OXYNASPIS CELATA. Pl. III, fig. 1.

    Madeira; attached in numbers to an Antipathes; Rev. R. T. Lowe.
    Mus., Hancock.

_General Appearance._--The capitulum is rather thin, and broad in
proportion to its length; it seems always entirely covered by the horny
muricated bark of the Antipathes, and hence externally is coloured rich
brown and covered with little horny spines. The membrane over the valves
is very thin, and is with difficulty separated from the Antipathes; it
has, I believe, no spines of its own. The corium lining the peduncle is
a fine purple. All the individuals are attached to the coralline, with
their capitulums upwards in the direction of the branches, and in this
respect fig. 1. is erroneous.

The valves, when cleared of the bark, are white, or are strongly tinged
with pinkish-orange. The upper parts of the scuta and terga are plainly
furrowed in lines radiating from their umbones; hence their margins are
serrated with blunt teeth; their surfaces, moreover, are sparingly
studded with small calcareous points.

_Scuta_ (fig. 1, _a_), sub-triangular, with the lower part rounded and
protuberant, the upper produced and pointed. The umbo is situated in the
middle of the occludent margin, instead of at the rostral angle, as in
the foregoing genera. The occludent margin is straight, and is bordered
by a narrow step or ledge, formed of transverse growth-ridges, and
therefore has its edge serrated: the rostral angle is often slightly
produced into a small projection. The basal margin is short, and forms
an angle above a rectangle with the occludent margin: the tergal margin
is straight; the carinal margin is rounded, protuberant, and of unusual
length compared to the basal margin. The surface of the valve is convex
near the umbo; and beneath there is a large deep hollow for the adductor
muscle.

_Terga_ (fig. 1, _b_) large, flat, triangular, as long as the scuta or
the carina, all three valves being nearly equal in length; occludent
margin straight, or slightly arched, basal angle broad, not very sharp.

_Carina_ short (fig. 1, _c_, drawn rather too long), deeply concave,
rectangularly bent, with the lower part not quite as long as the upper,
and a little wider: the basal margin is truncated, rounded, and slightly
sinuous. The umbo is situated at the angle, and therefore nearly
central. The umbo of the terga, I may add, is in the same place, as in
Lepas.

The _peduncle_ is very short and narrow, and is, I believe, without
spines; it is enveloped by the bark of the Antipathes. The capitulum in
the largest specimens was .2 of an inch in length.

_Filamentary Appendages_, apparently none.

_Mouth_, with the orifice rather inclined abdominally.

_Labrum_, with the upper part extremely protuberant, forming a
projecting horn; no teeth on the crest. Palpi rather small, with only a
few bristles at the end.

_Mandibles_, with four teeth and the inferior angle pointed: first
tooth as far from the second, as is the latter from the inferior angle;
in one specimen, on one side, there were five teeth.

_Maxillæ_ with three great spines at the upper angle, beneath which a
deep notch, and with the inferior part much upraised; this lower part
rather rounded at both corners, with the upper spines longer than the
lower.

_Outer Maxillæ_, with the bristles continuous in front; externally,
slightly protuberant, with a tuft of bristles longer than those on the
front side. Olfactory orifices apparently not protuberant; but all the
specimens were in a bad state.

_Cirri._--Prosoma very little developed. First cirrus very far removed
from the second. The three posterior cirri are straight and long; the
segments are elongated and bear four or five pairs of very long spines,
with a single minute intermediate spine between each pair; dorsal tufts,
with long spines. First cirrus, rami unequal by two or three segments,
and thickly covered with spines; the first cirrus is short compared to
the second, owing to the length of the pedicel of the latter, though the
longer ramus of the first, nearly equals the shorter ramus of the second
pair. Second cirrus, with its anterior ramus shorter by two or three
segments than the posterior ramus, and thicker than it, with the
segments covered like brushes with bristles; posterior ramus, and both
rami of the third cirrus, a little more thickly clothed with bristles
than are the three posterior cirri.

_Caudal Appendages_, minute, broadly oval, with six or seven long
bristles on their summits.


_Genus_--CONCHODERMA. Plate III.

  CONCHODERMA. _Olfers._ Magaz. der Gesellsch. Natuforsch. Freunde
        zu Berlin, Drittes Quartel, 1814.[34]

  LEPAS. _Linnæus._ Systema Naturæ, 1767.

  BRANTA. _Oken._ Lehrbuch der Naturgeschichte, Th. 2, p. 362, 1815.

  MALACOTTA et SENOCLITA. _Schumacher._ Essai d'un Nouveau Syst. des
        Habitations des Vers., 1817.

  OTION et CINERAS. _Leach._ Journal de Phys., vol. lxxxv, p. 67,
        July, 1817.

  GYMNOLEPAS. _De Blainville._ Dict. des Sci. Nat., Art. Mollusca,
        1824.

  PAMINA. _J. E. Gray._ Annals of Philosophy, vol. x, (Second
        Series,) August, 1825.[35]

   [34] The general title to the volume, containing four Quarterly
   parts, is dated 1818; but as in the 'Journal de Physique,' for
   July, 1817, the editor refers to Conchoderma, the Quarterly Part
   containing this genus must have appeared before 1818: Lamarck
   gives the year 1814 as the date of the paper in question, and I
   have accordingly followed him. From a similar reference by the
   editor, it appears that Schumacher's volume appeared before the
   number of the 'Journal de Physique' containing Leach's Paper.

   [35] Under these nine generic names, the two common species of
   Conchoderma have received thirty-three different specific
   denominations, caused partly by changes of nomenclature, and
   partly from varieties having ranked as species.

_Valvæ 2 ad 5, minutæ, inter se remotæ: scuta bi-aut tri-lobata,
umbonibus in medio marginis occludentis positis: carina arcuata,
terminis utrinque pæne similibus._

Valves 2 to 5, minute, remote from each other: scuta with two or three
lobes, with their umbones in the middle of the occludent margin: carina
arched, upper and lower ends nearly alike.

Filaments seated beneath the basal articulations of the first pair of
cirri, and on the pedicels of four or five anterior pairs; mandibles,
with five teeth, finely pectinated; maxillæ step-formed; caudal
appendages, none.

    _Distribution._--Mundane, throughout the equatorial, temperate,
    and cold seas; attached to floating objects, living or
    inorganic.

The _Capitulum_ is formed of smooth membrane, including five small
valves, of which the terga and carina are often quite rudimentary or
absent. Valves minute, thin, generally more or less linear, placed far
distant from each other; sometimes imperfectly calcified and covered by
chitine membrane, or imbedded in it. The umbones of the valves
(together with the primordial valves) are nearly central, so that they
are added to at their upper and lower ends; hence their manner of growth
is considerably different from that of the valves in Lepas. The adductor
muscle is attached to a slight concavity on the under side of each
scutum, at the point whence the lobes diverge.

The _Terga_ are placed almost transversely to the scuta; at their lower
ends, there is either a very slight prominence in the capitulum, or
there is a large tubular, folded appendage, opening into the sack, and
apparently serving for respiratory purposes.

_Peduncle_, smooth, moderately long; attachment effected by the
cement-stuff being poured out exclusively, as it appears, from the
larval antennæ. These antennæ in _C. aurita_ and _C. virgata_, resemble,
in the form of the disc and in the long feathered spines on the ultimate
segment, those in Lepas.

The _Filamentary Appendages_ are highly developed; there are six or
seven on each side; two are attached beneath the basal articulation of
the first cirrus (as is usual in Lepas), and near them there are one or
two small pap-formed projections of apparently similar nature; the rest
of the filaments are attached to the posterior edges low down, on the
lower segments of the pedicels of the cirri. I believe, in all cases,
these appendages are occupied by testes.

_Prosoma_, moderately developed.

_Mouth_, situated not far from the adductor muscle; labrum considerably
bullate, with the crest hairy and pectinated with inwardly pointing,
approximate, flattened teeth: inner fold of the supra-oesophageal cavity
slightly thickened and yellowish, villose on the sides.

_Palpi_ of the usual shape, not meeting, moderately broad.

_Mandibles_, with five teeth, graduated in size, nearly equidistant,
finely pectinated either on one or both sides towards their bases;
inferior angle narrow, either produced into a fine tooth, or almost
rudimentary.

_Maxillæ_, about 3/4ths of the size of the mandibles, step-formed, with
five steps generally distinct; at the upper angle there are two large
unequal spines, of which the lower one is the largest, with a third long
thin one on the first step; lower spines doubly serrated. Apodeme
directed inwards and backwards.

_Outer Maxillæ_ (Pl. X, fig. 16) simply arched; the membrane of the
supra-oesophageal cavity under these maxillæ is highly bullate and
villose. Olfactory orifices not prominent.

_Cirri._--First pair not seated far distant from the second pair. The
three posterior pair have the anterior faces of their segments
considerably protuberant, supporting four or five pairs of long
bristles; between which, there is a row of minute, fine, upwardly
pointing bristles: on the lateral upper margins of each segment, there
are a few very minute spines; dorsal tuft short, with thick and thin
spines intermingled. In the first cirrus (of which the rami are nearly
equal in length), and in the anterior ramus of the second cirrus, the
faces of the segments are highly protuberant, and clothed with thick
transverse rows of finely and doubly serrated spines: the anterior ramus
of the second cirrus is considerably thicker than the posterior ramus,
which latter, together with both rami of the third cirrus, differ from
the three posterior cirri only in the intermediate and in the lateral
marginal spines being slightly more developed.

_Caudal Appendages_, absent.

_Alimentary Canal._--The upper part of the stomach has four large cæca,
of which the posterior one is the largest; the whole surface, also, is
covered with minute pits, arranged in transverse rows.

_Generative System_, developed to an extraordinary degree. The testes
run into all the filamentary appendages, as well as more or less, into
the pedicels of the cirri: the two vesiculæ seminales unite _within_ the
penis, either just beyond its basal constriction, or up one third of its
length. Penis short, hairy. The ovarian tubes not only fill the
peduncle, but extend in a thin sheet between the two folds of corium all
round the sack, close up to the terga. The two ovigerous fræna are
present in the usual position; the ovigerous lamellæ either form several
layers, in pairs, one under the other, or are united in a single large
cup-formed sheet enclosing the whole animal.

_Colours._--The prevailing tint is a dark purplish-brown, which forms,
or tends to form, broad longitudinal bands on the peduncle and
capitulum.

_General Remarks._--This genus is intimately related, as has been
remarked by Professor Macgillivray,[36] to Lepas: if we look to the body
of the animal, which from being less exposed to external influences
must, in the Cirripedia, offer the most trustworthy characters, we find
that in Conchoderma there are additional filamentary appendages attached
to the cirri, that there are no caudal appendages, that the teeth of the
mandibles are finely pectinated, and that the ovarian tubes run higher
up round the sack; in every other respect, there is the closest
similarity, even to the arrangement of the bristles on the cirri. In the
capitulum, the difference consists chiefly, though not exclusively, in
the less development of the valves, and their consequent wide
separation: the scuta, however, in Conchoderma, are added to beneath
their umbones, or original centres of growth, which is never the case,
or only to a very slight degree, in Lepas. Conchoderma has no very close
affinity to any other genus. As the majority of authors have ranked the
two common species under two distinct genera (Otion and Cineras), I may
observe, that there is no good ground for this separation; in the above
few specified points in which Conchoderma differs from the genus most
closely allied to it, the two species essentially agree together. If we
take the nearest varieties of _C. virgata_ and _C. aurita_, there is but
a very slight difference even in the form of their valves, and these
hold the same relative positions to each other; the carina, however, is
always less developed in _C. aurita_; even the colouring in both tends
to follow the same arrangement. The only obvious distinction between the
two species, are the ear-like appendages of _C. aurita_, which, however,
are not developed in its early age, are subject to considerable
variation, are of no high functional signification, and are indicated in
_C. virgata_ by two prominences on the same exact spots. On these
grounds I conclude, that the generic separation of the two species is
quite inadmissible.

   [36] Remarks on the Cirripedia, &c.; 'Edin. New Phil. Journal,'
   vol. xxxix, p. 171.


1. CONCHODERMA AURITA. Pl. III, fig. 4.

  LEPAS AURITA. _Linn._[37] Systema Naturæ, 1767.

  OTION CUVIERANUS (!) BLAINVILLIANUS (!) BELLIANUS (!)
        DUMERILLIANUS (!) RISSOANUS. _Leach._ Encyclop. Brit., vol.
        iii, Supp., 1824, and Zoological Journal, vol. ii, p. 208,
        July 1825.

  OTION DEPRESSA et SACCUTIFERA. _Coates._ Journal Acad. Nat. Sci.
        of Philadelphia, vol. vi, p. 132, 1829.

  OTION AURITUS. _Macgillivray._ Edinburgh New Phil. Journal, vol.
        xxxviii, 1845.

  LEPAS LEPORINA. _Poli._ Test. utriusq. Sicil., pl. vi, fig. 21,
        1795.

  LEPAS CORNUTA. _Montagu._ Linn. Trans., vol. xi, p. 179, 1815.

  CONCHODERMA AURITUM et LEPORINUM. _Olfers._ Magaz. der Gesell.
        Freunde zu Berlin, 3d Quartel., p. 177, 1814.

  BRANTA AURITA. _Oken._ Lehrbuch der Naturgesch., Th. 11, p. 362,
        1815.

  MALACOTTA BIVALVIS. _Schumacher._ Essai d'un Nouveau Syst., &c.,
        1817.

  GYMNOLEPAS CUVIERII. _De Blainville._ Dict. des Sc. Nat., Art.
        Mollusc., Plate, fig. 1, 1824.

   [37] Many authors (Poli, Montagu, &c.,) have doubted from the
   strangely mistaken description, viz., "ore octovalvi dentato,"
   whether this species could be the _Lepas aurita_ of Linnæus. But
   in the Linnean Society, there is a proof plate from Ellis's
   "Account of several rare Species of Barnacles," in 'Phil.
   Trans.,' 1758, with an excellent figure of the _C. aurita_, and
   on the margin in Linnæus's handwriting is the name _Lepas
   aurita_.

_C. capitulo duobus tubularibus quasi-auribus instructo, pone terga
rudimentalia (sæpe nulla) positis: scutis bilobatis: carinâ nullâ, aut
omnino rudimentali: pedunculo longo, a capitulo distincte separato._

Capitulum with two tubular ear-like appendages, seated behind the
rudimentary and often absent terga; scuta bilobed; carina absent, or
quite rudimentary; peduncle long, distinctly separated from the
capitulum.

Filaments attached to the pedicels of the second cirrus; two upper
spines of the maxillæ pectinated.

    _Hab._--Mundane; extremely common. On ships' bottoms from all
    parts of the world. Arctic Sea. Greenland. Pacific Ocean. Often
    attached to Coronulæ on Whales. On slow-moving fish, according
    to Dr. A. Gould. Often associated with _C. virgata_, and _Lepas
    anatifera_, _L. Hillii_, and _L. anserifera_.

_General Appearance._--The capitulum (seen from above in Pl. III, fig. 4
_a_) is slightly compressed, almost globular, composed of thick
membrane, with two large, ear-like, flexible, tubular, folded
appendages, at the upper end, opening into the sack. These appendages
are seated behind the rudimentary terga when such are present, or behind
the spots which they would have held if not aborted. In a young
condition they are tubular, but not folded; and often, according to
Prof. Macgillivray, either one or both are at first imperforate. They
are formed externally of the outer membrane of the capitulum (rendered
thin where folded), and internally of a prolongation of the inner tunic
of the sack; between the two, there is, as around the whole sack, a
double layer of corium. A section across both appendages, near their
bases, is given in Pl. III, fig. 4 _b_, showing how they are
folded,--the chief fold being directed from below upwards, with a
smaller fold, not always present, from between the two, outwards. The
folds sometimes do not exactly correspond on opposite sides of the same
individual; they are almost confined to the lower part, the orifice
itself being often simply tubular. These appendages are sometimes very
nearly as long as the whole capitulum: a section near their bases is
sub-triangular. I shall presently make some remarks on their functions
and manner of formation.

The _Scuta_, as well as the other valves, are imperfectly calcified:
shape, variable. They usually consist of two lobes or plates, placed at
above a right angle to each other, and rarely (fig. 4 _c_) almost in a
straight line; the lower lobe is more pointed and narrower than the
upper; the two correspond to the lower and middle lobes in the scuta of
_C. virgata_, the upper one being here absent.

The _Terga_ are developed in an extremely variable degree; they are
often entirely cast off and absent. In very young specimens, they are of
the same length with the carina, but after the carina has ceased to
grow, the terga always increase a little, and sometimes to such a degree
as to be even thirty or forty times as long as carina. When most
developed (fig. 4 _a_) they are not above one third as long as the
scuta, to which they lie at nearly right angles; they consist of
imperfectly calcified plates, square at both ends, slightly broader and
thinner at the end towards the carina, where they are a little curled
inwards, than at the opposite end; they are not quite flat in any one
plane; internally they are slightly concave; finally, I may add, they
nearly resemble in miniature the terga of _C. virgata_. In full grown
specimens, the terga almost invariably drop out and are lost; but even
in this case, a long brownish cleft in the membrane of the capitulum,
marks their former position. The orifice of the capitulum is usually
notched between the terga, or between the clefts left by them; on each
side of the notch there is a slight prominence. In some few cases,
however, there is no trace of this notch. Behind the terga or the
clefts, the great ear-like appendages, as we have seen, are situated.

_Carina_, rudimentary (fig. 4) and often absent; it is
pointed-elliptical, and is rarely above the 1/40th of an inch long.
After arriving at this full size, calcareous matter is added to the
under surface over a less and less area, so that it becomes internally
pointed, and finally, in place of calcareous matter, continuous sheets
of chitine are spread out beneath it; hence, during the disintegration
of the outer surface, the carina comes to project more and more, and at
last drops out; subsequently, even the little hole in which it was
imbedded, disintegrates and disappears.

_Peduncle_, cylindrical, distinctly separated from the capitulum, and
generally twice or thrice as long as it: the thickness of the outer
membrane generally great, but variable: surface of attachment variable,
either pointed, or widely expanded, or formed into divergent
projections.

_Filamentary Appendages_, seven on each side, highly developed, long and
tapering; there are two beneath the basal articulation of the first
cirrus, and one on the posterior margin of the pedicel of each cirrus,
excepting the sixth pair; the filaments on the pedicels are nearly twice
as long as the cirri themselves.

_Mouth_,--mandibles, with the five teeth nearly equidistant, and towards
their bases finely pectinated on both sides; inferior angle rudimentary,
often represented by a single minute spine: in one specimen, there were
only four teeth on one side. Maxillæ, with five steps, not very distinct
from each other, with the first step much curved. The larger of the two
upper great unequal spines is pectinated, like the teeth of the
mandibles; there is a third long finer spine beneath the upper large
pair.

_Cirri_ rather short, broad, with the anterior faces of the segments
protuberant, especially those of the first cirrus and of the anterior
ramus of the second pair: spines on the anterior cirri doubly serrated.
Posterior cirri, with the intermediate spines between the pairs, long;
dorsal tufts, minute. On the lower segment of the pedicels of the four
posterior cirri, there are two separate tufts of bristles.

_Colours_ extremely variable; sometimes five longitudinal bands of dark
purple can be distinctly seen (as in _C. virgata_) on the peduncle,
these bands becoming more or less confluent on the capitulum; at other
times, the capitulum is more or less spotted, or often nearly uniformly
purple: the sack, cirri and trophi are, also, purple.

_Size._--The largest specimen which I have seen was, including the
peduncle and ears, five inches in length, the capitulum itself being
rather above one inch in length, and 7/10ths of an inch in breadth.

_General Remarks._--I have come to the same conclusion with Prof.
Macgillivray, concerning the variability of this form, and I believe
there is only one true species. With respect to Dr. Coates's species,
viz., _Otion depressa_ and _O. saccutifera_, though I have not seen
specimens, I can hardly doubt, from the insufficient characters given,
that they are mere varieties.

With respect to the ear-like appendages, we shall presently see in _C.
virgata_, that at corresponding points on the capitulum (Tab. III, fig.
2 _b_), there are two slight, closed prominences. According to Professor
Macgillivray, in _C. aurita_, every gradation can be followed by which
the appendages, at first closed, become tubular and open. The opening
would ensue, if the corium became absorbed at the bottom of the
appendages whilst still imperforate, for then the inner tunic would be
cast off at the next moult and would not be re-formed, whilst the outer
membrane would gradually disintegrate together with the other external
parts of the capitulum, and not being re-formed at this point, an
aperture would at last be left. These appendages have no relation to the
generative system: the ovarian tubes, which surround the sack do not
extend into them; nor do the ovigerous lamellæ. I believe, that their
function is respiratory: the corium lining them is traversed by
river-like circulatory channels, and their much-folded, tubular and open
structure must freely expose a large surface to the circumambient water.
Why this species should require larger respiratory organs than any
other, I know not. In this species, moreover, the filamentary appendages
are developed to a greater extent than in any other cirripede; in most
genera, the surface of the body and of the sack suffices for
respiration.


2. CONCHODERMA VIRGATA. Pl. III, fig. 2. Pl. IX, fig. 4.

  LEPAS VIRGATA. _Spengler._ Skrifter Naturhist. Selbskabet., B. i,
        1790, Tab. vi, fig. 9.

  ---- CORIACEA. _Poli._ Test. utriusque Sicil., Pl. vi, fig. 20,
        1795.

  ---- MEMBRANACEA. _Montagu._ Test. Brit. Supp., p. 164, 1808, et
        Linn. Trans., vol. xi, Tab. xii, fig. 2.

  CONCHODERMA VIRGATUM. _Olfers._ Magaz. Gesells. Naturfor. Freunde,
        Berlin, 1814, p. 177, (3d Quartel).[38]

  BRANTA VIRGATA. _Oken._ Lehrbuch der Gesell., Th. ii, p. 362,
        1815.

  SENOCLITA FASCIATA. _Schumacher._ Essai d'un Nouveau Syst., 1817.

  CINERAS VITTATA. _Leach._ Encyclop. Brit. Supp., Tom. iii, Plate.
        1824.

  ---- CRANCHII (!) CHELONOPHILUS (!) OLFERSII (!). _Leach._
        Tuckey's Congo Expedition, p. 412, 1818.

  ---- MEGALEPIS (!) MONTAGUI (!) RISSOANUS. _Leach._ Zool. Journal,
        vol. ii, p. 208, 1825.

  ---- MEMBRANACEA. _Macgillivray._ Edin. New Phil. Journal, vol.
        xxxix, p. 171, 1845.

  ---- BICOLOR. _Risso._ Hist. Nat. des Productions, &c., 1826, Tom.
        iv, p. 383.

  ---- VITTATUS. _Brown._ Illust. of Conch., 1844, Pl. li, figs.
        16-18.

  GYMNOLEPAS CRANCHII. _De Blainville._ Dict. des Sci. Nat. Hist.,
        1824.

  PAMINA TRILINEATA (!) (Var. Monstr.). _J. E. Gray._ Annals of
        Phil., vol. x, 1825.

   [38] See page 136 respecting this date.

_C. Scutis trilobatis: tergis intùs concavis, apicibus introrsùm leviter
curvatis: carinâ modicâ, leviter curvatâ: pedunculo in capitulum
coalescente._

Scuta three-lobed: terga concave internally, with their apices slightly
curved inwards: carina moderately developed, slightly curved: peduncle
blending into the capitulum.

No filament attached to the pedicel of the second cirrus.

_Var. chelonophilus_ (Pl. III, fig. 2 _c_). Terga, minute, nearly
straight, solid, acuminated at both ends, placed far distant from the
other valves: carina, either minute and acuminated at both ends, or
moderately developed and slightly arched and blunt at both ends: lateral
lobes of the scuta broad: valves imperfectly calcified.

    _Hab._--Mundane: extremely common on ships' bottoms from all
    parts of the world. Falkland Islands. Galapagos Islands, Pacific
    Ocean. Attached to sea-weed, turtle and other objects. Often
    associated with _Conchoderma aurita_, _Lepas anatifera_, _L.
    Hillii_, and _L. anserifera_.

_General Appearance._ Capitulum, flattened, gradually blending into the
peduncle; summit square, rarely obtusely pointed. Membrane, thin.
Valves, thin, small, sometimes imperfectly calcified, very variable in
shape and in proportional length, and therefore, situated at variable
distances from each other, but always remote and imbedded in membrane.

_Scuta_, trilobed, consisting of an upper and lower lobe (the latter
generally the broadest), united into a straight flat disc, with a third
lobe standing out from the middle of the exterior margin, generally at
an angle of from 50° to 70° (rarely at right angles) to the upper part,
and generally (but not always) bending a little inwards. The shape of
the lateral lobe varies from rounded oblong to an equilateral triangle;
as it approaches this latter form, it becomes much wider than the upper
or lower lobes. In one specimen, and only on one side, the scutum (fig.
2 _d_) presented five points or projections. In some specimens, the
scuta are very imperfectly calcified, and consist of several quite
separate beads of calcareous matter of irregular shape, held together by
tough brown membrane.

_Terga_, extremely variable in shape, placed at nearly right angles to
the scuta: beyond their carinal ends (fig. 2 _b_), the capitulum
presents two small prominences, which are important as indicating the
position of the homologous, ear-like appendages in _C. aurita_.[39] The
upper ends of the terga are imbedded in membrane, and project freely
like little horns for about one third of their length: this free portion
exactly answers to the projecting portion, bounded by the two occludent
margins, in the terga of Lepas. The freely projecting portion is
generally curled inwards, and the carinal portion more or less
outwards,--the form of the letter =S= being thus approached; but the
curvatures are not exactly in the same plane. The whole valve is
generally of nearly equal width throughout, the carinal part being a
very little (but in some specimens considerably) wider; internally, it
is deeply concave; both points generally are blunt and rounded. In some
rare varieties (_Cineras chelonophilus_ of Leach, fig. 2 _c_), the terga
are much smaller and flat, with both points sharp, the whole upper
portion being much and abruptly attenuated, and internally, without a
trace of a concavity. Generally, the terga are about two thirds of the
length of the scuta, rarely only half their length; generally, they are
separated from the apices of the scuta by about their own length, rarely
by twice their own length. Generally, the terga are shorter than the
carina, but sometimes a very little longer than it: generally they are
distant by one third or one fourth of their own length from the apex of
the carina, rarely by their entire length.

   [39] These have also been observed by Dr. Coates; see 'Journal of
   Acad. Nat. Sci. Philadelphia,' vol. vi, p. 134, 1829.

_Carina_ (fig. 2 _a_), lying nearly parallel to the scuta, concave
within, very slightly bowed, of nearly the same width throughout, but
with the lower third beneath the umbo, generally a trace wider than the
upper part. Length, variable, generally rather longer (sometimes by even
one third of its own length) than the scuta, but sometimes equalling
only three fourths of the length of the scuta; generally longer than the
terga. Upper and lower points rounded; in rare varieties, both ends are
sharply acuminated. The carina and terga are generally most acuminated
where they are smallest and least perfectly calcified; and consequently,
in this same state, the valves stand furthest apart.

_Peduncle_, flattened, gradually widening as it joins the capitulum, to
which it is generally about equal in length, or a little longer.

_Filamentary Appendages._--Six on each side (Pl. IX, fig. 4), of which
one (_h_) is seated on the posterior margin of a swelling, beneath the
basal articulation of the first cirrus, and this is the longest; the
second (_g_) is short and thick, and is seated a little lower on the
side of the prosoma, (near to this, there are also two little pap-like
eminences;) the third (_i_) is seated on the posterior margin of the
pedicel of the first cirrus, above the basal articulation; the fourth,
fifth, and sixth (_j_, _k_, _l_) in similar positions on the pedicels of
the third, fourth, and fifth cirri. These three latter filaments are
shorter and smaller than the first three. At the base of the second
cirrus, which has no proper filament, there is a swelling as if one had
been united to it.

_Mouth._--_Mandibles_, with the basal edges of the five teeth pectinated
by minute, short, strong spines on one side; inferior angle extremely
short. In one specimen, there was a minute pectinated tooth between the
first and second; in another, the second tooth was bifid on its summit;
in another, the fourth was rudimentary.

_Maxillæ_, with five steps: sometimes each step commences with a spine
rather larger than the others; at the upper angle, there are two large
unequal spines (neither pectinated,) with a third longer and thinner,
seated a little below. _Outer maxillæ_ (Pl. X, fig. 16), simple.

_Cirri_, with twice as many segments in the sixth cirrus as in first;
spines on the first and second cirri doubly serrated.

_Colours_ (when alive).--Capitulum and peduncle grey, with a tinge of
blue, with six black bands, tinged with purplish brown. The two bands
near the carina become confluent on the peduncle, and sometimes
disappear; the carina is edged, and the interspace between the two
scuta, coloured with the same dark tint. The whole body and the pedicels
of the cirri are dark lead-colour, with the segments of the cirri almost
black: in some specimens, the colour seems laterally abraded from the
cirri. Ova white, becoming in spirits pinkish, and then yellow. The dark
bands on the capitulum and peduncle become in spirits purple; but are
sometimes discharged; the general grey tint disappears. Professor
Macgillivray states that many individuals are light-brown or
yellowish-grey, with irregular brown streaks, or crowded dots: he states
that in very young specimens the colours are paler, and the valves
spicular.

_Size._--The largest specimen which I have seen, had a capitulum rather
above one inch long and three fourths of an inch wide: growth very
rapid.

_Monstrous Variety._--In the British Museum, there is a dried and
somewhat injured specimen of a monstrous variety, the _Pamina
trilineata_ of J. E. Gray: it differs from the common form only in
having a tubular projection, just behind the notch separating the upper
points of the terga; this tube springs from over the terga, and is,
therefore, in a different position from the ear-like appendages in
_Conchoderma aurita_. It does not open into the sack: the membrane
composing it appears to have been double in the upper part, and to have
been lined with corium: in short, this tube seems to have been an
excrescence or tumour, of a cup or tubular form.

_General Remarks._--It will have been seen how much subject to variation
the valves of this species are. When I first examined the _Cineras
chelonophilus_ of Leach, from 36° N. lat., Atlantic Ocean, and found in
many specimens, both old and young, that the terga were very small,
flat, acuminated at both ends, with a projecting shoulder on the carinal
margin, and situated at about their own length from the apex of the
carina, and at twice their own length from the scuta; and when I found
the carina acuminated at both ends, and the scuta very imperfectly
calcified, with the lateral lobe broad, flat, and standing out at right
angles; and lastly, when I found the whole capitulum bluntly pointed,
instead of being square on the summit, I had not the least doubt, that
it was a quite distinct species. Afterwards, I found in the _Cineras
Olfersii_ of Leach, from the South Atlantic, the same form of terga; but
within slightly more concave or furrowed, and not nearly so small, and
therefore not placed at above half so great a distance from the other
valves; and here, the carina had its usual outline, as had nearly the
scutum on one side, whereas, on the other side, it presented a new and
peculiar form, having five ridges or points, and was imperfectly
calcified; seeing this, it was impossible to place much weight in the
precise form or size (and therefore, relative separation,) of the
calcified valves; and on close examination, I found every part of the
mouth and cirri identical in Leach's _Cineras chelonophilus_ and _C.
Olfersii_, and in the common form. Therefore, I conclude, that _C.
chelonophilus_, and still more _C. Olfersii_, are only varieties; the
terga presenting the greatest, yet variable, amount of difference,
namely, in their acumination and flatness. We know, also, that in the
species of the closely allied genus of Lepas, the terga are very
variable in shape, and this is the case, even in a still more marked
degree, in _Conchoderma aurita_. Professor Macgillivray, I may add, has
come to a similar conclusion regarding the extreme variability of the
valves of this species.

As the varieties here mentioned are very remarkable, and may perhaps
turn out to be true species, I think they are worth describing in some
detail: I will only further add, that we must either make several new
species, or consider, as I have done, several forms as mere varieties.


C. VIRGATA, var. CHELONOPHILUS of _Leach_. Pl. III, fig. 2 _c_.

    Atlantic Ocean, 35° 15´ N., 16° 32´ W. On the Testudo caretta.

Capitulum not above half an inch long, composed of very thin membrane,
with six bands (as stated by Leach) of faint colour; summit bluntly
pointed; valves very small, far distant from each other; the scuta are
imperfectly calcified, the central part of the umbo consisting of thick,
brown chitine, with imbedded shelly beads; terga and carina perfectly
calcified.

_Scuta_ trilobed, flat, within slightly concave, upper lobe rather more
acuminated than the lower; lateral lobe triangular in outline, twice as
wide as either the upper or lower lobes; lying in the same plane with
them and standing out at almost exactly right angle.

_Terga_, flat; placed obliquely to the scuta, and barely half as long;
separated from them by nearly twice their own length; upper and lower
points acuminated; the umbo on the carinal margin forms a projecting
shoulder; the scutal margin is straight, they are separated by nearly
their own length from the apex of the carina.

_Carina_ narrow, very slightly arched, within slightly concave, both
points acuminated; lower third rather wider than the upper part; in
length equalling three fourths of the scuta, and longer by one third
than the terga; about as wide as the latter.

_Filaments, Cirri, and Mouth_ exactly as before.

In some specimens sent to me by the Rev. R. T. Lowe from off the
_Testudo caretta_, taken near Madeira, the scuta have their lateral
lobes broad and nearly rectangular: the carina extends nearly to between
the terga: the terga are nearly straight, somewhat pointed at both ends,
distant from the scuta, almost solid within, with their upper points
bowed outwards: the whole capitulum is bluntly pointed, as in the _var.
chenophilus_, to which form this makes a rather near approach.


C. VIRGATA, var. OLFERSII.

  CINERAS OLFERSII. _Leach._ Tuckey's Congo Expedition.

    _Hab._ South Atlantic Ocean.

_Scuta_, unlike on the opposite sides of the same individual, on one
side with a single lateral lobe as usual, but this very narrow, on the
other (fig. 2 _d_), with five lobes or projections.

_Terga_ slightly concave within, separated by a little more than their
own length from the tips of the scuta, and by one third of their own
length from the tip of the carina.

_Carina_ longer than the scuta by about one fifth or one sixth of its
own length, blunt at both ends, considerably bowed.

Again, I possess a group of remarkably fine specimens given me by Mr. L.
Reeve, from the southern ocean, (as I infer from a young _Lepas
australis_ adhering to them,) in which all the individuals, young and
old, are characterised as follows:--Scuta, with the lateral lobe
generally broad, but to a very varying extent, with the upper and lower
lobes extremely sharp. Terga separated from the scuta, by one and a
fourth of their own length, and by their own length from the carina;
somewhat acuminated at both ends, nearly straight, with a very slight
shoulder near the umbo. Carina equalling the terga in length, and about
three fourths of the length of the scuta; neither the upper nor lower
point much acuminated. All the valves most imperfectly calcified: in one
specimen, the scutum on one side was simply horny, without a particle of
calcareous matter. The summit of the capitulum nearly intermediate in
outline between the common square, and bluntly-pointed form of _var.
chelonophilus_. I compared the cirri and trophi with those of a common
variety, and could detect not the smallest difference. This variety
differs from _var. Olfersii_, in the less development of its carina, and
from _chelonophilus_, in the greater development of its carina, and
especially of its terga. It would appear as if the great variability of
the valves was connected with the absence of calcareous matter.


3. CONCHODERMA HUNTERI. Pl. III, fig. 3.

  CINERAS HUNTERI. _R. Owen._ Cat. Mus. Coll. of Surgeons, (1830),
        Invert. Part I., p. 71.

_C. valvis angustis: scutis trilobatis, prominentiâ laterali non latiore
quam inferior: tergorum parte superiore pæne rectangulè secundùm
aperturæ marginem flexâ: carinâ valde arcuatâ: pedunculo brevi, in
capitulum coalescente._

Valves, narrow: scuta, trilobed, with the lateral lobe not wider than
the lower one: terga, with the upper part bent almost rectangularly
along the margin of the orifice: carina considerably arched: peduncle
short, blending into the capitulum.

No filament attached to the pedicel of the second cirrus.

_Var._--Carina absent; scuta, with the upper lobe absent; terga, with
the rectangular projection little developed.

    Attached to the skin of a snake, probably the Hydeus or Pelamis
    bicolor, and therefore from the tropical Indian or Pacific
    Oceans. Mus. Coll. of Surgeons.[40]

   [40] I owe to the kindness of Professor Owen, an examination of
   these specimens, and information regarding them.

_Capitulum_, with the membrane very thin; summit obtusely pointed.
Valves linear and thin.

_Scuta_, elongated, flat, with the upper projecting lobe rather more
acuminated than the lower, and equalling it in length; lateral lobe not
wider than the lower, and about as long as it, forming an angle of about
55° with the upper one.

_Terga_, of somewhat variable length, generally about half as long as
the carina, narrow, and of nearly equal width throughout; lower point
sharp; externally convex; internally solid, with a trace of a central
depressed line; the upper fourth part generally a little bowed out of
the plane of the lower part, and abruptly bent at rather above a right
angle along the occludent margin of the orifice. These valves are
situated at about half their own length from the upper points of the
scuta.

_Carina_ considerably arched, extending to the lower points of the
terga, or running up between them for even half their length; equally
narrow throughout; scarcely broader than the terga; both points rounded;
internally concave; the lower point does not extend as far down as that
of the lower lobe of the scuta.

_Peduncle_, narrow, shorter than the capitulum, which, in the largest
specimen was 4/10ths of an inch long. Longitudinal purple bands appear
to have originally existed on the peduncle.

_Filamentary Appendages, trophi and cirri_ all similar to the same parts
in _C. virgata_; but perhaps the anterior faces of the segments in the
posterior cirri are rather less protuberant; perhaps also the first
cirrus is rather shorter in proportion to the sixth cirrus.

_Variety_ (_monstrous_).--Amongst the specimens, I found one very young
one, in which the scuta had not upper lobes, so that in outline they
exactly resembled the scuta in the quite distinct _C. aurita_: there was
not even a rudiment of a carina: the tergum, _on one side_, was
externally bordered by a projecting, semicircular, calcified disc; and
the upper points of both terga showed only traces of the rectangular
projection, which is the chief characteristic of _C. Hunteri_. From
these traces alone, and from the specimen being mingled with the others,
do I here include this variety.

_General Remarks._--I have very great doubts whether I have acted
rightly in considering this as a species; but as there were many
specimens, old and young, all differing remarkably from the common
species, this form anyhow deserves description. The points by which it
can be distinguished from _C. virgata_, are--the almost rectangular
manner in which the upper portion of the tergum is bent outwards and
along the orifice of the sack--the narrowness of all the valves, and
especially of the lateral lobes of the scuta,--and lastly, the greater
curvature of the carina, which in some specimens runs up far between the
terga; had this last character been constant, it would have been an
important one, but such is far from being the case. Great as are these
differences in the valves, and though common to many specimens, they are
not sufficient to convince me that it is a true species, and I should
not be at all surprised at varieties, intermediate between it and the
common form, being hereafter found;--had a name not been already
attached to it, I should not have given one. In the monstrous variety
described, we see to what an extent the valves may vary. The _C.
Hunteri_ approaches nearest to the var. of _C. virgata_, called by Leach
_Cineras chelonophilus_, for in both, the top of the capitulum is
bluntly pointed and the terga are solid within; in the _Var.
chelonophilus_, the terga and carina are minute, whereas here, though
very narrow, they are much elongated. Certainly _C. chelonophilus_ has
almost as strong a claim to rank as a species as _C. Hunteri_; but, in
the former, by the aid of other varieties, the differences were almost
reduced to the peculiarities in the terga--the valves, the most subject
to variation. In _C. Hunteri_ we have other differences, and the form of
the terga is even still more peculiar. I have, therefore, provisionally
attached to it the specific name by which it is designated in the Museum
of the College of Surgeons. From having been long kept in spirits, all
aid from colour is lost.


_Genus_--ALEPAS. Pl. III.

  ALEPAS. _Sander Rang._ Manuel des Mollusques, 1829.

  ANATIFA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, 1834.

  TRITON. _Lesson._ Voyage de la Coquille, 1830.

  CINERAS. _Lesson._ Secundum Sander Rang.

_Capitulum aut sine valvis, aut scutis corneis, pæne abditis._

Capitulum without valves,[41] or with horny, almost hidden, scuta.

   [41] Any one not attending to the characters derived from the
   softer parts of the Balanidæ and Lepadidæ, might easily confound
   with Alepas the genus Siphonicella (genus nov.), which,
   undoubtedly, though having the external appearance of a
   pedunculated cirripede, belongs to the Balaninæ, and is closely
   related to Coronula.

Filaments seated beneath the basal articulations of the first pair of
cirri; mandibles, with two or three teeth; maxillæ notched, with the
lower part irregular, projecting; caudal appendages multi-articulate.

    Attached to various living objects, fixed or floating.

_Capitulum_ either entirely destitute of valves, or with transparent
horny scuta, not containing any calcareous matter, and almost hidden in
membrane. These scuta are formed of a lower and a lateral lobe, placed
at above right angles to each other; they are added to by successive
layers, and closely resemble in shape the scuta of the _Conchoderma
aurita_. The orifice in _A. tubulosa_ projects so much as to be almost
tubular. In _A. parasita_ and _A. minuta_ it does not project, and is
either moderately large, or very small in proportion to the length of
the capitulum; from contraction it is much wrinkled. The membrane
forming the capitulum is smooth and very transparent; it contains very
few tubuli, except under certain irregular projections in _A. cornuta_.

The _Peduncle_ is rather short and narrow; it blends into the capitulum,
and is not, in some of the species, separated from it by any distinct
line; the surface of attachment is rather wide. Within the peduncle we
have the three usual layers of striæ-less muscles; namely, the innermost
and longitudinal, which run lower down than the others; the middle and
transverse; and, lastly, the exterior, oblique muscles, which cross each
other (becoming transparent) on the rostral central line. These several
muscles run up from the peduncle and surround the capitulum; from the
transparency of the membranes they can be seen from the outside: they
are particularly conspicuous round the orifice, which they probably
serve to close. There is, in all cases, the usual adductor scutorum
muscle (with transverse striæ), which is attached under the horny scuta,
where such exist. The fact of the striæ-less muscles of the peduncle
surrounding the whole capitulum, has been observed only in one other
genus, namely Anelasma. In consequence of this structure, the capitulum
must possess considerable powers of contraction.

The antennæ of the larva in the _Alepas cornuta_ and _A. minuta_ have
the sucking disc nearly circular, with the spines unusually plain on the
distal as well as proximal margin. Basal segment broad, much constricted
where united to the disc. The ultimate segment has on the middle of the
outer margin, in _A. cornuta_, two minute spines, which I have not
observed in any other cirripede: on the summit there are the usual
spines.

_Size._--Three of the species are small.

_Filamentary Appendages._--These are rather small; there is only one on
each side, situated on the posterior margin of a slight swelling,
beneath the basal articulation of the first cirrus; and therefore in the
position in which the filaments are most constant in Lepas, and where
they likewise occur in Conchoderma.

_Body._--The prosoma is either pretty well developed or is small,
according as the first cirrus is placed near to, or far from the second
cirrus.

_Mouth._--Labrum moderately bullate, with the lower part more or less
produced; crest with blunt, bead-like teeth, and short hairs.

_Palpi_ (Pl. X, fig. 8), acuminated and narrow to an unusual degree.

_Mandibles_, with two or three teeth, and the inferior angle acuminated;
the lateral bristles unusually strong, so as to give the main teeth the
_appearance_ of being pectinated.

_Maxillæ_, widely notched, with three great upper spines; the part
beneath the notch projecting, and either straight or irregular.

_Outer Maxillæ_, with the inner bristles either continuous or divided
into two groups: exteriorly there is a smaller or larger prominence,
with long bristles. The olfactory orifices are either slightly, or not
at all protuberant.

_Cirri._--In the three posterior pair, the segments have their bristles
arranged in a transverse row, either in the form of a narrow brush, or
consisting only of a single pair with two or three minute, intermediate,
and lateral marginal spines. The anterior ramus of the second cirrus is
thicker, and more thickly clothed with spines than is the posterior
ramus: this latter ramus, however, and both rami of the third cirrus,
are rather more thickly clothed with spines than are the three posterior
pair. The unique case in _A. cornuta_ of the inner rami of the fifth and
sixth cirri being rudimentary (Pl. X, fig. 28) will be minutely
described under that species.

_Caudal Appendages_, thin, tapering, multi-articulate, about as long as
the pedicels of the sixth cirrus.

_Stomach._--The oesophagus runs in a somewhat sinuous course, and enters
the top of the stomach obliquely. There are no cæca. The biliary
envelope presents a reticulated structure, instead of the usual
longitudinal folds.

_Generative System._--The penis is hairy, not very long, and ringed or
articulated in an unusually plain manner; the space between each ring
being about one fourth of the diameter of the penis: the unarticulated
basal portion or support is here remarkably long. The vesiculæ seminales
are long, tortuous, and enter the prosoma. The ovarian tubes are of wide
diameter: in _A. cornuta_ they surround the whole capitulum. The
ovigerous fræna are small, constricted at the base, and square on the
free margin, which is studded with minute glandular beads, borne on the
finest footstalks.

    _Range._--Southern shores of England, Mediterranean, Atlantic,
    West Indies, New Zealand, attached to various objects. _A.
    parasita_ has been always taken on Medusæ.[42]

   [42] It appears that Solander (Dillwyn Des. Cat., vol. i, p. 34)
   observed a species of this genus adhering to a Medusa on the
   coast of Brazil. Mr. Cocks informs me that an Alepas, apparently
   _A. parasita_, has been cast on shore near Falmouth, attached to
   a Cyanæa; and that two other specimens adhered to the bottom of a
   vessel arriving at that port from Odessa.

_Affinities._--This genus differs from all, except Anelasma, in the
manner in which the striæ-less muscles of the peduncle run up and
surround the capitulum, and likewise in the reticulated character of
the biliary envelope of the stomach. To Conchoderma, especially to _C.
aurita_, there is manifest affinity in the form of the horny scuta:
there is also some affinity to this same genus in the presence of
filamentary appendages though here little developed, and in the circular
form of the disc of the larval antennæ, and, lastly, in the ovarian
tubes in _A. cornuta_ surrounding the capitulum. There is quite as
close, if not closer affinity to Ibla, in the following
peculiarities,--in the curved oesophagus,--in the general character of
the cirri and trophi, with the olfactory orifices in one species in some
degree prominent,--in the multi-articulated caudal appendages,--and in
the plainly-articulated penis, with its elongated unarticulated support,
though both these characters are exaggerated in Ibla. Lastly, the scuta
in Ibla, though not at all resembling in shape those of _A. cornuta_,
are formed without calcareous matter; and again, in Ibla, the muscles of
the peduncle run up to the bases of the valves, and so almost surround
the space in which the animal's body is lodged.

The four species of Alepas appear to form two little groups; viz. _A.
parasita_ and _A. minuta_ on the one hand, and _A. cornuta_ and _A.
tubulosa_ on the other.


1. ALEPAS MINUTA. Tab. III, fig. 5.

  ALEPAS MINUTA. _Philippi._ Enumeratio Mollusc. Siciliæ, 1836,
        Tab. xii, fig. 23.

  ---- ---- _A. Costa._ Esercitazione Accadem., vol. ii, part I, Naples,
        1840, Pl. iii, fig. 5 (secundum Guerin in Revue Zoolog.,
        1841, p. 250.)

  ---- ---- _Chenu._ Illust. Conch., Pl. iii, figs. 8-10.

_A. aperturâ non prominente, capituli longitudinis vix tertiam partem
æquante: scutis corneis, pæne absconditis: longitudine totâ ad quartam
unciæ partem._

Orifice not protuberant, one third of the length of the capitulum:
scuta horny, almost hidden. Total length quarter of an inch.

Outer maxillæ, with the spines in front continuous; posterior cirri,
with several long spines arranged in a transverse row on each segment;
caudal appendages longer than the pedicels of the sixth cirrus.

    Sicily; attached to a Cidaris:[43] island of Capri (_A. Costa_).

   [43] I am greatly indebted to Professor J. Müller, of Berlin, for
   kindly lending me specimens.

Capitulum oval, blending insensibly into the peduncle; moderately
flattened; composed of thin structureless membrane, with the exception
of two horny, almost quite hidden scuta. Orifice situated near the
summit, and in a line, which is oblique to the longitudinal axis of the
peduncle; much wrinkled; barely one third of the length of the whole
capitulum.

The _Scuta_, consist of yellowish, transparent, horny, laminated
chitine, without any calcareous matter; externally covered by the common
integument of the capitulum; these valves are placed very near to each
other, close under the orifice, and therefore high up on the capitulum;
the membrane between them is smooth and unwrinkled; they are formed of
two rather acuminated lobes, joining each other at above a right angle;
one lobe (the longer one) stretching nearly transversely across the
capitulum, the other running down parallel to its rostral margin: in
shape and position they resemble the scuta of _Conchoderma aurita_; and
if another lobe had been developed it would have run along the orifice,
and then these valves would have resembled the scuta of _Conchoderma
virgata_. In a specimen with a capitulum 2/10ths of an inch long, the
scuta from point to point were 1/20th of an inch in length.

_Peduncle_, much wrinkled, about one third in diameter of the capitulum,
and shorter than it; at the base it is generally expanded into two or
three finger-like projections. _Length_ of the largest specimen, about
one fourth of an inch. _Colour_, according to A. Costa in the work above
cited, "rufo-flava vittatâ;" but after spirits the whole becomes
uniformly yellowish.

_Filamentary Appendages_, situated beneath the basal articulation of the
first cirrus, on the posterior edge of the usual enlargement;
acuminated, about two thirds of the length of the shorter ramus of the
first cirrus.

_Prosoma_ well developed.

_Mouth._--On each side there are two slight prominences; one under the
mandibles, the other transverse nearer to the adductor muscle.

_Labrum_, placed near the adductor muscle, with the upper part not more
bullate than the lower part; crest with a row of blunt teeth, and many
fine bristles growing chiefly outside the teeth; there are many fine
bristles on the inner or supra-oesophageal fold of the labrum.

_Palpi_ not nearly touching each other, pointing towards the adductor:
much hollowed out on their inner sides, hence narrow and acuminated,
with doubly serrated bristles.

_Mandibles_, with three teeth and the inferior angle ending in a single
sharp spine; whole inferior portion narrow; first tooth as far from the
second, as the latter from the inferior angle; owing to the presence of
short thick spines projecting from the sides of the jaw, the lower edges
of the second and third teeth appear pectinated.

_Maxillæ_, nearly two thirds of the width of the mandibles; beneath the
three larger upper spines there is a considerable notch, and the whole
lower part is very slightly upraised; edge irregular, with obscure
traces of either two projections, or perhaps of four steps.

_Outer Maxillæ_, with bristles in front continuous; exteriorly there is
a slight prominence near each olfactory orifice, with a tuft of long
bristles.

_Cirri_ not much elongated; first pair placed not quite close to the
second; five posterior cirri nearly equal in length; pedicels long, with
irregularly scattered spines,--those on the pedicel of the first cirrus
beautifully and conspicuously feathered. The segments of the three
posterior pair are _not_ very short or broad; very slightly protuberant,
each with a long transverse, crescentic, narrow brush of bristles, which
stand two or three deep in the middle, but on the sides are single:
dorsal tufts long, and in the upper segments the spines are thick and
claw-like. This structure is common to all the cirri. First cirrus with
the rami unequal in length by two segments; from the shortness of the
pedicel, this cirrus is much shorter than the second, but its rami are
about two thirds of the length of those of the second cirrus. Second
cirrus (and in a less degree the third cirrus), with the anterior ramus
a shade broader than the posterior ramus, and rather more thickly
covered with spines than are the three posterior cirri. Fifteen segments
in the sixth cirrus; nine in the longer ramus of the first cirrus.

_Caudal Appendages_, rather longer than the pedicels of the sixth
cirrus, composed of seven cylindrical, tapering segments, each with a
circle of very fine bristles on its summit.

The acoustic (?) sacks are situated some way below the basal
articulations of the first cirrus.


2. ALEPAS PARASITA.

  ALEPAS PARASITA. _Sander Rang._ Man. des Mollusq., p. 364, Pl.
        viii, fig. 5, 1829.[44]

  ANATIFA UNIVALVIS. _Quoy_ et _Gaimard_. Annales des Sciences,
        Nat., tom. x, p. 234, 1827, Pl. vii, fig. 8.

  ---- PARASITA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.
        xciii, 1834.

  TRITON (ALEPAS) FASCICULATUS. _Lesson._ Voyage de la Coquille.
        Mollusc. Pl. xvi, fig. 6, tom. ii, part I, 1830, p. 442.

   [44] M. Sander Rang rejects the specific name "_univalvis_," as
   signifying a generic character, and he has been followed in this
   by MM. Quoy and Gaimard themselves. This, according to the Rules
   of the British Association, would hardly have been a sufficient
   reason, but it appears that _A. parasita_, like _A. minuta_, has
   a pair of horny scuta or valves; and, therefore, the name
   _univalvis_ is too obviously false to be retained. With respect
   to the generic name Triton, I fully believe that it was applied
   by Linnæus to the cast-off exuviæ of sessile Cirripedes.

_A. aperturâ non prominente, capituli longitudinis 2/3 æquante: scutis
corneis: longitudine totâ ad 2 uncias._

Orifice not protuberant, equalling two thirds of the length of the
capitulum: scuta horny. Total length two inches.

Animal unknown.

    Parasitic on Medusæ, Mediterranean and Atlantic Oceans: south
    shore of England(?)[45]

I have not seen this species, and have drawn up the above specific
character from the Plates and brief descriptions in the Voyages of the
Coquille and Astrolabe. M. Lesson thinks that his species differs from
that of MM. Quoy and Gaimard; but as the peculiar yellow colour of the
capitulum, general shape, short cirri, habits and range, are all common
to both, I believe that they are identical. There is, however, one
singular difference, namely, that the cirri are coloured bright blue in
the Plate in the Voyage of the Astrolabe, and yellowish in that in the
Voyage of the Coquille: this possibly may have resulted from the drawing
in the latter case having been made from a specimen long kept in
spirits.

M. Lesson says that there are seven pair of cirri, from which I infer
that this species has a pair of long, articulated, caudal appendages: he
asserts that each cirrus has ten segments; the cirri are short and
little curled. M. Lesson remarks, that "deux languettes bifurques
occupent le bas de l'ouverture ovale:" I can hardly doubt but that these
are horny scuta of nearly the same shape as in _A. minuta_. The whole
animal seems to be extremely transparent, and of a "jaune-citron clair."
MM. Quoy and Gaimard, however, remark, that different specimens vary
from white to yellow. Entire length two inches, of which the capitulum
is fourteen French lines. The peduncle is narrow and short.

   [45] See Foot-note, p. 159.


3. ALEPAS CORNUTA. Pl. III, fig. 6.

_A. aperturâ parvâ, leviter prominente: scutis nullis: capitulo
plerumque tribus, parvis, compressis eminentiis secundum carinalem
marginem instructo._

Orifice small, slightly protuberant; capitulum without horny scuta;
generally with three small flattened projections along the carinal
margin.

Outer maxillæ with the inner bristles divided into two groups; segments
of the posterior cirri extremely numerous, each with one pair of main
spines; inner rami of the fifth and sixth cirri rudimentary.

    St. Vincent's, West Indies, attached to an Antipathes, collected
    by the Rev. L. Guilding.

_Capitulum_ globular, slightly flattened, smooth, translucent, entirely
destitute of valves; orifice slightly projecting or tubular, parallel to
the longitudinal axis of the peduncle, with the edges sinuous; it
appears more tubular than it really is, from the convexity of the part
of the capitulum immediately beneath the orifice. Three small, flexible,
horny, irregular prominences project from the carinal margin; one at the
bottom of the capitulum; a second about half-way up it; and a third
generally close to the orifice; but their positions vary a little, and
the prominences vary still more in shape and size, being either rounded
and very small, or much flattened and considerably prominent; they are
imperforate; in the membrane under them a few tubuli may be seen, which
are not elsewhere visible; their summits are roughened with very minute
points and beads of chitine; others, still minuter, are scattered over
the whole capitulum.

_Peduncle_ short, narrower than the capitulum, into which it insensibly
blends; strongly wrinkled; surface of attachment wide; position with
respect to the branches of the coralline, various.

_Size and Colour._--The largest specimen, including the peduncle, was
half an inch in length, and 3/10ths of an inch across the capitulum;
colour, after having been long in spirits, brownish-yellow.

_Filamentary Appendages_, one on each side, short, tapering and pointed;
seated on the posterior margin of a slight swelling beneath the basal
articulation of the first cirrus; they are about equal in length to the
pedicels of this cirrus.

The _Mouth_ is directed abdominally; labrum much produced downwards, so
as to be far separated from the adductor muscle; moderately bullate,
forming about one third of the longitudinal axis of the entire mouth;
upper part forming a slightly overhanging prominence; crest with a row
of blunt, bead-like teeth, and externally to them there are numerous
curved short bristles.

_Palpi_ (Pl. X, fig. 8,) unusually narrow, a little hollowed out along
their inner margins; pointing towards the adductor muscle; thickly
covered with doubly serrated bristles.

_Mandibles_, with either two or three teeth; inferior angle narrow and
tooth-like; both sides covered with strong bristles or spines,
projecting beyond the toothed edge.

_Maxillæ_, with two large upper spines, and a third rather distant from
them; beneath these, there is a wide notch or hollow; inferior part
square, projecting, bearing six pair of moderately long spines, (of
which the central one is the longest,) mingled with finer ones.

_Outer Maxillæ_, with a semicircular outline; the serrated bristles in
front are divided into two groups; externally there is a rounded and
very considerable projection covered with long bristles. Olfactory
orifices slightly prominent, approximate, seated within and just beneath
the rounded projections at the base of the maxillæ.

_Body._--Prosoma little developed; thorax small.

_Cirri_, extremely long, but slightly curled, capable of being protruded
so as almost to touch the base of the peduncle or the surface of
attachment; segments short, extraordinarily numerous. In the three
posterior cirri (excepting the rudimentary rami), each segment supports
two long, slightly serrated spines, with two or three minute
intermediate ones, and with one or two very short, thick spines on the
inner and upper lateral margins: dorsal tufts with only two or three
long, fine, unequal spines. All the segments are extremely flat, broad,
short, with their anterior faces not protuberant; the greater number of
the segments, especially the lower ones, have very obscure
articulations, to be seen only with a high power, and these can be
capable of little or no movement.

_First Cirrus_ placed far from the second, with the top of its pedicel
on a level with the top of the lower segment of the pedicel of the
second cirrus; rami short, barely half the length of those of the second
cirrus; unequal, the anterior ramus being only two thirds of the length
of the posterior one; the shorter ramus contains thirteen
inverted-conical segments, with one side rather protuberant; the longer
ramus contains twenty-three thinner segments; the segments on both rami
are clothed with bristles, arranged in two or three rows, forming narrow
transverse brushes.

_Second Cirrus_, with its pedicel long, and its rami nearly equalling in
length those of the sixth pair; the two rami of nearly equal length; the
anterior one rather thicker than the posterior one; this posterior ramus
has fifty-five segments! The bristles on the second and third cirri are
arranged on the same principle as on the three posterior pair; but from
an increase in size and number of the little intermediate bristles
between the main pairs, and of those on the lateral rims, the segments,
especially the basal ones, of the anterior ramus of the second cirrus,
are clothed with thin brushes of bristles; these same bristles, on the
posterior ramus of the second, and on both rami of the third cirrus, can
hardly be said to form brushes, though longer and more numerous than
those on the three posterior pair of cirri.

_Fifth and Sixth Cirri._--These resemble each other, and have their
inner or posterior rami in an almost rudimentary condition. In the sixth
cirrus (Pl. X, fig. 28) the outer ramus (_a_) has actually sixty-three
segments, whereas the rudimentary ramus (_k_) has only eleven, nearly
cylindrical segments. These are furnished with extremely minute spines,
of which those on the dorsal face are longer than those on the anterior
face; the spines on the summit of the terminal segment are the longest;
the segments are not half as thick as the normal ones in the outer
ramus. The rudimentary ramus is only one seventh part longer than the
pedicel which supports both it and the normal ramus. In the fifth
cirrus, the rudimentary ramus is rather longer, and has thirteen
segments, resembling those in the rudimentary ramus of the sixth. In the
fourth cirrus there is no trace of this peculiar structure, the rami
being equal in length and strength. The two rudimentary rami on each
side are nearly straight, and seem incapable of movement; they project
out behind the normal rami, and closely resemble in general appearance,
the two caudal appendages; hence this cirripede, at first sight, appears
to be six-tailed.

_Pedicels of Cirri._--The pedicel of the first pair is very short; that
of the second is the longest; those of the posterior cirri decreasing in
length. Upper segments short; lower segments in the second, third and
fourth cirri, irregularly and rather thickly clothed with bristles, but
in the fifth and sixth cirri, there is a regular double row of main
spines, with some minute intermediate ones: hence there is a difference,
both in the rami and in the pedicels, between the fourth cirrus and the
fifth and sixth, and this is a unique case. On the dorsal surface of the
pedicel of the second cirrus, there is a tuft of much feathered fine
spines.

_Caudal Appendages._--Each consists of eight much tapering, very thin
segments, furnished with a few short simple spines round their upper
margins, and with a longer tuft on the terminal short segment; basal
segments twice as thick as the middle ones. In length, these caudal
appendages equal the pedicels of the sixth pair of cirri, and are a
very little shorter than the rudimentary rami of these same cirri.

_General Remarks._--Having examined this species first in the genus, I
fully anticipated that the very remarkable character of the inner rami
of the fifth and sixth cirri being rudimentary, and serving the same
function (if any) with the caudal appendages, would have been generic;
but this is not the case, for _Alepas cornuta_ cannot be separated from
_A. minuta_ without violating a clear natural affinity.


4. ALEPAS TUBULOSA.

    Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, fig. 5, 1834.

_A. aperturâ parvâ prominente et tubulosâ: scutis et prominentiis
secundùm marginem carinalem, nullis._

Orifice small, tubular, protuberant; capitulum without horny scuta or
projections along the carinal margin.

Animal unknown.

    New Zealand, Tolaga Bay. Attached to a living Palinurus.

I have given the above brief character from the plate, and imperfect
description in the voyage of the Astrolabe. The small and distinctly
tubular orifice, and the smooth carinated edge of the globose capitulum,
appear sufficiently to distinguish this species from _A. cornuta_. The
colour is stated to have been white with violet tints. Length, two
(French) lines.


ANELASMA. _Gen. Nov._ Pl. IV.

  ALEPAS. _Lovén._ Ofversigt of Kongl. Vetenskaps-Akad.
        Fördhandlinger: Forsta Argangen. Stockholm, 1844, p. 192,
        Tab. 3.

_Capitulum sine valvis: aperturâ amplâ: pedunculus fimbriatus,
sub-globosus, infossus._

Capitulum without valves; aperture large; peduncle fimbriated,
sub-globular, imbedded.

Cirri without spines; outer maxillæ and palpi rudimentary, spineless;
mandibles minute, with several small teeth irregularly placed; maxillæ
minute, with very minute irregularly scattered spines. No caudal
appendages.

       *       *       *       *       *

I owe to the great kindness of Professor Steenstrup, an examination of
this very curious cirripede, well described and figured by Lovén, who
considered it an Alepas. It lives parasitic, with its peduncle imbedded
in the skin of sharks, in the North Sea. According to the principles of
classification which I have followed, this cirripede cannot possibly
remain in Alepas, and must form a new genus; for some time, indeed, I
thought that a new family or sub-family ought to have been instituted
for its reception; but when I considered that its highly peculiar
characters are all negative, as the non-articular, non-spinose structure
of the cirri, and that no new or greatly modified functional organ is
present, I concluded that it might properly remain amongst the Lepadidæ.
We shall, moreover, hereafter see that the male of Ibla, which, of
course, must remain in the same family with the female, is, in some
analogous respects, even more abnormal than Anelasma.


1. ANELASMA SQUALICOLA. Pl. IV, figs. 1-7.

  ALEPAS SQUALICOLA. _Lovén_, ut supra.

    North Sea. Parasitic on Squalus.

_Capitulum_, destitute of valves; oval, much flattened; the double
membrane composing it, thin, highly flexible, coloured externally and
internally, by the underlying corium, of a blackish purple; aperture,
extremely large, extending from the upper end of the capitulum, to close
above the peduncle, gaping, and not protecting (in the dead condition)
the cirri and mouth.

The _Peduncle_ is about half as long as the capitulum, but, according to
Lovén, this part varies in length; it is a little narrower than the
capitulum; colourless, from being imbedded in the shark's skin;
sub-globular; basal end almost hemispherical. Total length of animal
1.3; diameter of peduncle .4 of an inch.

The external membrane of the capitulum is not nearly so thick as is
usual in other Cirripedes, and is, therefore, unusually flexible. The
internal membrane, on the other hand, is very much thicker than is
usual, being only a little thinner than the outside coat; this
circumstance, as well as the similarity in colour on both sides, is
evidently due to the remarkable openness of the sack, and consequent
exposure of its inside. The inner membrane, when viewed under a high
power, is seen to be covered with the minutest spines; the external
membrane is structureless, except that there are a few rows of very
minute beads of hard chitine, like those which occur on the capitulum of
_Conchoderma aurita_. Lovén, however, states that there are imbedded in
the outer membrane, scattered, minute, dendritic, calcareous particles.
Of these, I could see no trace. There is a very thin muscular layer
between the two coats, all round the capitulum, and this layer becomes
rather thicker round the base, near the peduncle. The adductor muscle,
occupying its usual place close below the mouth, is thinner than in any
other Cirripede of the same size seen by me; nor does it end so abruptly
at each extremity, as is usual: where attached to the outer coat, no
impression is left. It is a singular fact, that in this Cirripede alone,
the fibres of the adductor, and of the muscles of the cirri, and of the
trophi of the mouth, are destitute of transverse striæ; but it is not
singular, that the muscles surrounding the capitulum should, also, be
destitute of striæ, for this is the case with the muscles which, running
up from the peduncle, surround the capitulum in Alepas, and partly
surround it in Conchoderma. It must not be inferred from the absence of
transverse striæ in the muscular fibres of the adductor and of the
cirri and trophi, that they are involuntary, but only that they are in
an embryonic condition, for I find in the natatory larva, that all the
muscles, with the exception of some connected with the eyes, are
similarly destitute, and yet perform voluntary movements.[46]

   [46] Dr. C. Schmidt in his Contribution to the comparative
   Anatomy of the Invertebrate animals, &c., (translated in Taylor's
   Scientific Memoirs, vol. v, p. 1,) says that in young Crustacea,
   "we find plain primitive fibres, which subsequently acquire the
   transversely striated aspect."

Although in the dead state, the aperture of the capitulum seems to be
always gaping, yet I have little doubt, that the living animal can fold
the flexible membrane, like a mantle, round its thorax and cirri, and
thus protect, though feebly compared with most Cirripedes, these organs.
I suspect that the mouth is always exposed.

_Peduncle._--The membrane of the peduncle is thin; the whole surface is
sparingly and quite irregularly studded with minute, much-branched
filaments (Pl. IV, fig. 3, highly magnified); these are occasionally as
much as l/5th of an inch in length; the degree of branching varies much,
but is generally highly complex; the ordinary diameter of the branches
is about 1/200th of an inch; their tips are rounded, and even a little
enlarged, and frequently torn off, as if they had been attached to or
buried in the flesh of the shark, in which the whole peduncle is
imbedded. These filaments are formed of, and are continuous with the
external transparent membrane of the peduncle, and they contain, up to
the tips of every sub-branch, a hollow thread of corium, prolonged from
the layer internally coating the whole peduncle. In all other Lepadidæ,
the peduncle increases in length, chiefly at the summit where joined to
the capitulum, and in diameter, throughout nearly its whole length,
except close to the base; but, owing to the constant disintegration of
the outer surface, the old outside coat does not split in defined lines,
like the membrane of the capitulum. In Anelasma, however, owing to the
imbedded position of the peduncle, the old outer coats are preserved,
the lines in which they have split during continued growth being thus
exhibited: those in the uppermost part almost symmetrically surround the
peduncle, showing that here, as in other Lepadidæ, has been one regular
line of growth; but in the lower part the lines are extremely irregular;
and what is almost unique, it appears that the blunt basal end is
constantly increasing in length and breadth, and, apparently, at a
greater rate than any other part. I judge of this latter fact, from the
whole bottom of the peduncle being covered with numerous curved, or
nearly circular, lines of natural splitting, the nature of which can be
best understood by examining the much-enlarged drawing (Pl. IV, fig. 3)
of a small portion (taken by chance) of the membrane of the base, seen
from the outside, and bearing some of the simplest branched filaments:
other branches, as may be seen, have been cut off. This manner of growth
explains the broad, blunt basal termination of the peduncle, so unlike
that in other Lepadidæ. New membrane is formed, not continuously as in
other cases, under the whole surface of the old membrane, but in
irregular patches; thus the portion marked (_a_) runs under (_b_), but
not under the little circles (_c_, _c_), for these are the last-formed
portions and underlie the membrane (_a_) and (_b_). I do not understand
how the splitting of the old membrane is effected; but no doubt it is by
the same process by which the membrane of the capitulum in other genera,
as in Scalpellum, splits symmetrically between the several valves. In
the branched filaments it is particularly difficult to understand their
growth, for it is not possible, after examining them, to doubt that they
continue to increase, and send off sub-branches, which it would appear
probable, penetrate the shark's flesh like roots. I may remark that one,
or more commonly two or three branched filaments stand nearly in the
centre of each circular line of exuviation or splitting. The branched
filaments first commence as mere little pustules, and these appear to be
most numerous at the bottom of the peduncle.

The final cause of the downward growth of the bottom of the peduncle, is
obviously to allow of the animal burying itself in the shark's body, in
the same way as Coronula and Tubicinella become imbedded by the downward
growth of their parietes in the skin of Cetacea. The only other genus of
Lepadidæ, in which the growth of the peduncle is at all analogous, is
Lithotrya, in this genus, however, the animal burrows mechanically into
soft rock or shells.

I looked in vain for cement, or for the cement-glands, (but the specimen
was in an extremely unfavorable state for finding the latter) or for the
prehensile antennæ of the larva. No doubt this Cirripede at first
becomes attached in the same way as others, but after early life, I
suspect it is retained in its place, by being so deeply imbedded in the
shark's body, and perhaps by the root-like branched filaments. The
irregular growth and splitting of the membrane at the base of the
peduncle, where the prehensile antennæ of the larva must originally have
been situated, would account for not finding them.

The inside of the peduncle (fig. 2 _g_) was gorged, in the specimen
examined by me, with immature ova. The innermost muscular layer consists
of longitudinal bundles of unusual size, but placed rather far apart
from each other; these do not extend to the very base of the peduncle,
and at the upper end they curve inwards, almost to the middle of the
under side of the diaphragm, separating the peduncle and capitulum.
Outside these longitudinal muscles, there are delicate transverse ones,
but apparently there are no oblique muscles in the upper part of the
peduncle, as in other Lepadidæ; near the bottom, the transverse muscles
form a thicker layer with many of the bundles running in oblique lines.

_Mouth._--uLovén has not described this part quite accurately, owing to
his not having used high enough magnifying powers. He states that the
trophi are soft and functionless, which is far from the case. The whole
mouth (fig. 2 _d_), is unusually small; it is, to a certain extent,
probosciformed, and being curved a little downwards, projects slightly
over the adductor muscle, to which it is closely placed. The labrum does
not project more beyond the general surface of the body, than in many
other Cirripedes, but the probosciformed structure is caused by the
elongation of the surface fronting the thorax. The summit of the mouth
stands above the level of the top of the pedicels of the first pair of
cirri. The labrum is slightly hollowed out in the middle of its upper
margin; it can scarcely be called bullate, in which it differs from all
other Lepadidæ; on the other hand, the outer and inner folds of the
labrum are not so close together as in Balanus. On each upper corner,
there is, as usual, a small rounded prominence, close to which there is
a second slight, rounded, spineless swelling; these latter represent the
quite rudimentary _Palpi_.

The _Mandibles_ (figs. 4, 5) are more highly developed than the other
trophi; they are, however, very minute, the toothed edge being only
about 16/1000th of an inch in length, measured in its longest direction;
the edge is unusually thick, with the teeth placed rather on one side;
this organ, when viewed on the labrum side (fig. 5), shows two large
teeth placed low down, with the inferior angle pectinated and broadly
truncated; but when viewed on the other or maxillæ side (fig. 4),
several large and small teeth, placed alternately and irregularly in
pairs, are seen extending along the whole edge. The mandibles are
furnished, as usual, with three principal sets of muscles attached to
the basal fold of the mouth.

The _Maxillæ_ (fig. 7) are still smaller than the mandibles; the spinose
edge being only the 1/100th of an inch in length; the edge, instead of
being square, and furnished with a double row of long spines, as in all
other Cirripedes, is rounded, thick, club-shaped, and with the side
facing the mandibles, thinly and irregularly strewed with short, thick,
very minute spines; there is a large broad apodeme (_a_), in the usual
place, but it is much more transparent and flexible than common: there
are also the usual muscles. In other cirripedes, the mandibles alone
seem to force the prey down the oesophagus; but here, the mandibles and
maxillæ equally stand over the orifice, and their adjoining spinose
faces and edges, seem excellently adapted to force, by their united
action, any minute living creature down the passage.

The _Outer Maxillæ_ are almost in as rudimentary a condition as the
palpi; they are quite spineless; viewed externally, they appear like two
smooth, blunt, very minute projecting points; but viewed internally, the
membrane forming the supra-oesophageal hollow seems to be united
actually to their tips, so that they do not project at all. I was
surprised to find that the longitudinal muscles going to these organs
were developed, in proportion to the other muscles, quite as fully as in
ordinary cirripedes: hence, these two little outer maxillæ, no doubt,
serve as an under lip, and possess the usual backward and forward
movement.

The surface of the probosciformed mouth facing the first pair of cirri,
has a deep central longitudinal fold, and rather more than half-way
down, a transverse fold; just above this latter fold, and therefore
quite below the outer maxillæ themselves, the two olfactory orifices are
seated; these are unusually large, and the sack into which they lead, is
most unusually large and deep. In this Cirripede, I was first enabled to
observe that the membrane lining the sack is tubular, and open at the
bottom.

_Cirri._--There are, as usual, six pair, and not of very small size;
they have a shapeless and rudimentary appearance; they are coloured,
like the rest of the body, blackish purple: they are quite spineless,
and not articulated, but their anterior faces are either obscurely or
very plainly lobed, so that in some (for instance in the third pair, Pl.
IV, fig. 6), nine or ten prominent steps could be counted, manifestly
representing so many segments. The rami are equal in length in the first
pair, and slightly unequal in the second and third pair; these two
latter are longer than either the first or three posterior pair. There
is a small interspace as usual between the first and second pair of
cirri. Internally, the cirri are occupied, even up to their tips, by
delicate striæ-less muscles. The external membrane of the thorax and
limbs, when examined under a very high power, is seen to be covered with
minute toothed scales, as in most Cirripedes.

The thorax is articulated as usual: the posterior part, however, is
smaller, and tapers more suddenly than in other species, and this
corresponds with the smaller size and more rudimentary condition, of the
three posterior pair of cirri, compared with the anterior pair. The
prosoma is hardly at all developed. The orifice (Pl. IV, fig. 2 _e_) of
the acoustic (?) sack, beneath the first cirrus, is unusually large.

There are no filamentary appendages.

_Alimentary Canal._--The membrane lining the oesophagus is unusually
thin: it is furnished with the ordinary constrictor muscles, and others
radiating from them like spokes of a wheel. The stomach is lined by
unusually prominent biliary folds, which in the duodenum are transverse,
sending forth, however, short folds at right angles; and these latter,
in the proper stomach, become so much developed that the folds appear
longitudinal. The rectum extends inwards, about as far as the base of
the fourth pair of cirri, but is very short, owing to the little
development of the three posterior segments of the thorax. The anus is
seated in its usual place, at the dorsal basis of the penis, and is
hidden by loose folds of skin; but there are no distinct caudal
appendages. The stomach, in the specimen examined, was quite empty.

_Reproductive Organ._--The penis (fig. 2, _c_) is thick, short (about
twice as long as the sixth cirrus), constricted at the base, ringed,
spineless, with the terminal aperture large; internally it is well
furnished with muscles. The two vesiculæ seminales, appeared to be
unusually small; and one was much smaller than the other; they do not (I
believe) become united into a common tube, till near the apex of the
penis. They were empty; and, I presume, from the state of the ova, that
their contents had lately been discharged. The whole thorax was filled
with a white, fibrous and cellular mass, consisting perhaps of the
testes in their undeveloped state. The individual dissected by me,
appeared to have been defective in its last act of reproduction, for
there were only two or three ova attached to the frænum on one side, and
not very many on the other. The ova are much less elongated than is
usual; they are of a remarkable size, namely 22/1000ths of an inch in
their longer diameter; the membrane by which they are united into a pair
of lamellæ is remarkably strong; the frænum (Pl. IV, fig. 2 _f_) on each
side is large, strong, with rounded edges, pale coloured and hence
conspicuous; on the side nearest the body, the whole surface is covered
with club-shaped glands, having very short footstalks, and being in
total length 5/6000ths of an inch; these glands secrete a reticulated
layer of gut-formed fibres, attached to the ovigerous lamellæ. In the
specimen described by Lovén, the lamellæ (fig. 1, and fig. 2, _b_, _b_)
appear to have been very large: and in that examined by myself, the
peduncle was gorged with immature ova, showing that the female
reproductive powers were ample, though at the foregoing period, only a
few eggs had been formed.

_Habits._--According to Lovén, this species lives imbedded in the skin
of _Squalus maximus_ and _spinax_, in the North Sea: I suspect that it
is not closely compressed in its cavity, otherwise, I do not see the use
of the two layers of muscles round the whole peduncle; it probably
adheres to the sides of the cavity by the tips of the branched,
root-like filaments; owing to the flexible nature of the capitulum, this
Cirripede can offer little resistance to the water, and, therefore, is
little likely to be torn out of its cavity. I have no doubt that it can
fold the membrane of the capitulum, like a cloak, round its thorax and
cirri; but it certainly can offer far less resistance, than other
Cirripedes, to any enemy. This creature must obtain its food, and
considering its productiveness much food must be required, in a manner
quite different from nearly every other member of its Order. As the
whole of the peduncle is imbedded, and as the mouth is probosciformed,
with the labrum a little curled over the adductor muscle, I conclude
that this Cirripede can reach minute animals crawling by on the surface
of the shark's body.

It must be borne in mind that the mouth, as in all Cirripedes, has the
power of independent movement, and that the mandibles and maxillæ are
here beautifully adapted to catch and force down any small living
creature into the muscular oesophagus; the rudimentary outer maxillæ,
moreover, no doubt have the power of scraping, like a lip, anything
towards these prehensile organs. It will hereafter be seen, that the
male of _Ibla Cumingii_, in which the cirri are quite rudimentary,
obtains its food in a somewhat analogous manner, though in this case the
whole peduncle moves, and not merely a probosciformed mouth: it deserves
attention, that in the male Ibla and in Anelasma, in neither of which
the cirri are prehensile, the palpi are rudimentary and useless. I am
tempted to believe, that the largely developed olfactory sacks, and
perhaps, likewise, acoustic (?) sacks, in Anelasma, replace, by giving
notice of the proximity of prey, the loss of tactile cirri. It should be
remembered that all Cirripedes subsist on animals which happen to swim
or float within reach of the cirri; but here it is only those which
happen to crawl within reach of the probosciformed mouth. It would,
however, be rash to assert that the cirri in Anelasma, considering their
muscular though feeble structure, may not be of some slight use, when
thrown over the prey, in preventing its escape.

Professor Steenstrup informs me that, from late observations, it appears
that this animal always adheres to the shark's body in pairs. I regret
extremely that I have not been able to examine a pair: that the
individual examined by me was bisexual, I can hardly doubt, though the
male organs certainly were feebly developed; it appears probable, that
the individual described by Lovén was likewise bisexual: but after the
facts presently to be revealed regarding the sexes in Ibla and
Scalpellum, it is quite possible that the male and female organs may be
developed in inverse degrees in different and adjoining individuals.

The genus Anelasma is, I think, properly placed between Alepas and Ibla.
In several of its characters, such as the absence of calcareous valves,
the broad blunt end of the peduncle, the spineless cirri, the small size
of the trophi, and more especially the absence of transverse striæ in
those muscles, which in mature cirripedes are thus furnished, we see
that this genus is in some degree in an embryonic condition.


_Genus_--IBLA. Pls. IV, V.

  IBLA. _Leach._ Zoolog. Journal. vol. ii, July, 1825.

  ANATIFA. _Cuvier._ Mem, pour servir, ... Mollusques, Art. Anatifa,
        1817.

  TETRALASMIS. _Cuvier._ Regne Animal, 1830.

(_Foem. et Herm._) _Valvæ 4, corneæ: pedunculus spinis corneis,
persistentibus vestitus._

(Fem. and Herm.) Valves four, horny: peduncle clothed with persistent,
horny spines.

Body partly lodged within the peduncle; mandibles with three teeth;
maxillæ with two obscure notches; outer maxillæ pointed; olfactory
orifices prominent; caudal appendages multiarticulate.

_Male and Complemented Male_, parasitic within the sack of the female or
hermaphrodite; mouth and thorax seated on a long tapering peduncle, but
not enclosed within a capitulum; mouth with normal trophi, but palpi
small and almost rudimental; cirri rudimental, reduced to two pairs;
penis reduced to a pore; caudal appendages rudimentary.

    Attached to fixed littoral objects: Eastern Hemisphere.

_General Remarks._--As there are only two species as yet known, and as
these resemble each other in every respect most closely, a generic
description would be a useless repetition of the full details given
under _Ibla Cumingii_. I have taken this latter species as the type,
from having, owing to the kindness of Mr. Cuming, better and more
numerous specimens. Ibla and Lithotrya are the only two recent genera in
which the body of the animal is lodged within the peduncle; but there is
no distinction of any importance, though useful for classification,
between the capitulum and peduncle; and these two parts, as we have
seen, tend to blend together in some species of Conchoderma and Alepas.
The entire absence of calcareous matter in the valves and spines of the
peduncle, at first appears very remarkable; but we have seen a similar
fact in Alepas, and there is an approach to it in some varieties of
_Conchoderma aurita_ and _C. virgata_. In all four valves of Ibla, the
umbones, or centres of growth, are at their upper points. The horny
spines on the peduncle, are the analogues of the calcareous scales in
Scalpellum and Pollicipes; and in this latter genus, two of the species
have their scales, almost cylindrical, placed irregularly, with new ones
forming over all parts of the surface, and not exclusively at the
summit,--in which several respects there is an agreement with Ibla. The
shape of the body (_i. e._ thorax and prosoma, Pl. IV, fig. 8 _a´_) is
peculiar; but it is only a slight exaggeration of what we have seen in
several genera, and shall meet again in some species of Scalpellum. The
presence of hairs on the outer membrane of the prosoma is a peculiarity
confined to this genus amongst the Lepadidæ, though observed in the
sessile genus, _Chthamalus_. The caudal appendages in the _I.
quadrivalvis_ attain a greater length than in any other species of the
family, being four times the length of the pedicels of the sixth cirrus.
A far more important peculiarity is the fact of the oesophagus, in both
species, running over or exteriorly to the adductor scutorum muscle,
instead of, as in every other species, close under this muscle. I took
great pains in ascertaining the truth of this singular anomaly: the
course of the oesophagus is approximately represented in Pl. IV, fig. 8
_a´_ by faint dotted lines. The stomach has no cæca; the biliary folds
are longitudinal; there is a marked constriction at the line
corresponding with the junction of the thorax and prosoma. There are no
filamentary appendages.

The generative system gives the chief interest to this genus. We here
first meet with Males and Females distinct; and, within the limits of
this same restricted genus, the far more wonderful fact of
hermaphrodites, whose masculine efficiency is aided by one or two
Complemental Males. The complemental and simple males closely resemble
each other, as do the female and hermaphrodite forms; but under the two
following species I enter into such full and minute details on these
remarkable facts, that I will not here dilate on them. I may add that,
at the end of the genus Scalpellum, I give a summary of the facts, and
discuss the whole question. The penis (Pl. IV, fig. 9 _a_) in the
hermaphrodite, _I. quadrivalvis_, is singular, from the length of its
unarticulated support, and from the distinctness of the segments in the
articulated portion.

As ovigerous fræna occur in the usual place in _I. quadrivalvis_, though
much smaller than in any other species, I have no doubt that they occur
in _I. Cumingii_, although I failed in observing them. The glands on the
margin, in _I. quadrivalvis_, are singular, from not being borne on a
long, hair-like footstalk.

_Affinities._--Ibla, though externally very different in appearance from
Scalpellum, is more nearly related to that genus than to any other; in
both genera some species have the sexes separate, the imperfect males
being parasitic on the female, and other species are bisexual or
hermaphrodite, but aided by parasitic complemental males. In Scalpellum,
again, the oesophagus pursues a sinuous course, resembling that in Ibla,
though it does not pass exteriorly to the adductor scutorum muscle. The
disc of the prehensile antennæ of the larva, in both genera, has an
unusual oblong form, like a mule's hoof; there is also an affinity
between the two genera in the size and form of the ova, in the prominent
orifices of the olfactory cavities, and in the peduncle not being naked;
though, in these two latter respects, in the structure of the cirri, and
in the multiarticulate caudal appendages, there is an equal affinity to
Pollicipes and Lithotrya. I have already shown that Alepas is likewise
related to Ibla.


1. IBLA CUMINGII. Pl. IV, fig. 8.

_I. (foem.) valvarum marginibus lateralibus, et superficie interiore,
cæruleis: pedunculi spinis plerumque annulis cæruleo-fuscis._

Fem.--Valves coloured, along the lateral margins and on the upper
interior surface, blue: spines on the peduncle, generally ringed with
blueish-brown.

Caudal appendages barely exceeding in length the pedicels of the sixth
cirrus: rami of the first cirrus unequal in length by about two
segments.

Male,--with scarcely a vestige of a capitulum: maxillæ with fewer spines
than in the female.

    _Hab._--Philippine Archipelago, Island of Guimavas; invariably
    attached to the peduncle of _Pollicipes mitella_, in groups of
    two or three together; Mus. Cuming. Tavoy, British Burmah
    Empire; Mus. A. Gould of Boston.


FEMALE.

The capitulum is formed of four valves, but is hardly distinct from the
peduncle. The latter includes, in its wide upper part, the animal's
body. The valves, namely, a pair of scuta and terga, are composed of an
extremely hard, horny substance, or properly chitine, and do not contain
any calcareous matter; they are extremely flat or thin, and both pairs
project freely, like curved horns, to a considerable height above the
sack enclosing the body: the terga project about twice as much as the
scuta, and their flat apices generally diverge a little. The tips of the
valves are frequently broken off; their surfaces are plainly marked or
ribbed by the layers of growth, which are wide apart. The bases of the
valves externally are hidden by the long spines of the peduncle.

_Scuta._--These are shorter and broader than the terga; their internal
(Pl. IV, fig. 8 _b´_) growing or corium-covered surfaces are slightly
concave, triangular, with the basal margin longer than the other margins
and slightly excised in the middle: there is no depression for the
strong adductor muscle: the internal surface of the free horn-like
portion, has a small central fold (formed by an oblique crest) running
from the summit of the triangular growing surface to the tip of the
valve: in perfect specimens, the growing and the free horn-like portions
(the latter represented much too long in fig. 8 _a´_ and _b´_) are about
equal in length: the basal portion of one side of the scutum overlaps
the tergum.

_Terga._--The internal glowing surface (fig. 8 _b´_) is almost
diamond-shaped, and less in area than the sputa: external surface
rounded; internal surface of the free horn-like portion, slightly
concave.

_Colour and Structure of Valves._--The external surfaces of the scuta
and terga are yellow along the middle, plainly marked by zones of
growth, and finely ribbed longitudinally: the internal surfaces and
sides of the horns of the two valves, are coloured fine blue or purple;
in the terga, however, the internal surface is mottled with yellow. In
some specimens, especially in one from Tavoy, each zone of growth was
only very narrowly edged with blue. When a thin layer is removed from
one of the valves, the dark blue or rather purple appears by transmitted
light a beautiful pale blue; and it is a very singular fact, that this
blue portion is permanently turned by very gentle into a fiery red; the
same singular effect is produced by muriatic and acetic acids. This blue
part is much harder than the yellow; the latter exhibits, under a high
power, a folded structure, and is penetrated by a few tubuli, whereas
the harder blue portion has a cellular or scaled appearance. The spines
of the peduncle exhibit, in a smaller degree, similar phenomena.

_Peduncle._--This, as already remarked, cannot be distinctly separated
from the capitulum; it is much compressed; it is composed of unusually
thin and delicate membrane, transversely wrinkled and thickly clothed
with long cylindrical horns or spines of chitine. These horns (fig. 8
_c´_) are not the analogues of the spines which are articulated on the
external membranes of many Pedunculated and Sessile Cirripedes, but of
the calcified scales on the peduncle of Scalpellum and Pollicipes; for
they pass through the membrane (the underlying corium being marked by
their bases) and are persistent, being added to, like the valves, during
each successive period of growth. Their bases are concave, so that a
section of the layers of growth exhibits a series of pointed cones, one
within another. Each spine is nearly cylindrical, irregularly curled,
and nodose or slightly enlarged at intervals: the apex smooth and
pointed; the exterior surface longitudinally and finely ribbed, like the
valves. The spines increase irregularly in size from the bottom to the
top of the peduncle, those at the carinal and rostral ends being
generally the longest; they point upwards and hide the bases of the
valves. They are not arranged symmetrically, and new ones are formed
over all parts of the peduncle. They are formed of the same substance as
the valves, and do not contain any calcareous matter. These horns are
yellowish, generally ringed with pale and dark blueish brown, which on
pressure becomes slightly opalescent with pale blue and fiery red:
sometimes only the upper horns are thus ringed, and in rare instances
all are simply yellowish. The muscles of the peduncle run up to the
bases of the four valves.

_Surface of Attachment._--The cement appears to proceed from only two
points. In some specimens, a considerable length of one side of the
peduncle was fastened to the surface of attachment, the horns or spines
being enveloped in the cement. The prehensile antennæ of the larva will
presently be described under the male.

The _length_ of an average specimen, including the peduncle and valves,
is about half an inch, and the width across the widest part one fifth of
an inch. Mr. Cuming has one specimen an inch in length, but this is
owing to the peduncle being unusually tapering. In a specimen kept some
years in spirits, the cirri, trophi, caudal appendages, and corium under
the membrane between the scuta, were all dark purple; the sack and
corium of peduncle clouded with purple, and the prosoma pale-coloured.

The _Body_ (Pl. IV, fig. 8 _a´_) is small compared with the capitulum
and peduncle; it is much flattened; the prosoma is of a very peculiar
shape, being square, the sides of equal length, and, in an average-sized
specimen, 75/1000th of an inch long. The peculiar shape arises from the
great distance between the first and second cirrus--from the mouth being
far removed from the adductor scutorum muscle--and lastly, from the
lower part of the prosoma being not at all protuberant. The thorax which
supports the cirri is also unusually small, plainly articulated, and
separated from the prosoma by a deep fold. The thin membrane of the
prosoma is studded with some fine, pointed hairs, about 3/400ths in
length, and articulated on little circular discs.

_Mouth_, placed at a considerable distance from the adductor, and
directed in an unusual manner towards the ventral surface of the thorax:
the trophi are arranged, in a curved line, facing the thorax (see Pl. V,
fig. 2, for this part in the male), and therefore less laterally than is
usual.

_Labrum_ (Pl. IV, fig. 8 _a´_ opposite _c_) highly bullate; the upper
part produced into a blunt point: on its crest there are no teeth.

_Palpi_ (fig. 8 _a´_ opposite _d_) small, blunt and rounded at their
ends; inner margins slightly concave.

_Mandibles_ (Pl. X, fig. 4), with three teeth, of which the first is
much larger than the second and third, and distant from them: inferior
angle produced and pectinated; upper edges of the second and third teeth
finely pectinated.

_Maxillæ_ (Pl. X, fig. 11) small, slightly but distinctly indented by
two notches, supporting, besides the three upper great spines, three
pairs of moderately long spines and some finer ones: apodeme short,
thick.

_Outer Maxillæ_, unusually pointed, with the inner bristles not very
numerous, continuously arranged; externally, the bristles are longer.
Olfactory orifices, tubular, projecting, flattened, square on the
summit, smooth: they point upwards and obliquely towards each other:
they arise more laterally than in the other genera, namely outside the
bases of the outer maxillæ, and between them and the inner maxillæ.

Between the bases of the first pair of cirri, there is a conical
prominence, clothed with bristles and coloured purple: it projects
nearly as high as the top of the lower segment of the pedicel of the
first cirrus: it lies over the infra-oesophageal ganglion, and serves, I
suspect, to fill up a little interval between the outer maxillæ.

_Cirri_ long, little curved: the first pair (Pl. IV, fig. 8 _a´_) is
situated at an extraordinary distance from the second; hence its basal
articulation is on a level with the upper articulation of the pedicel of
the second cirrus. In the three posterior cirri, the segments are
laterally very flat, with their anterior surfaces not protuberant; each
supports three pairs of thin, non-serrated bristles, of which the second
pair is much shorter than the upper, and the lowest pair minute; between
each pair there is a minute, rectangulary projecting bristle; dorsal
tufts consist of two or three spines, of which one is longer than the
others. The two bristles forming each pair, are not of equal length; for
in the rami of each cirrus, the inner row of bristles is much shorter
than the outer; and this seems to be connected with the flatness of the
whole animal, and the consequent little power of divergence in the rami
of the cirri. The first cirrus is rather short, with the rami unequal in
length by about two segments: the anterior ramus is shorter and thicker
than the other: segments numerous, each clothed with several rows of
bristles. The second cirrus has the anterior ramus thicker and more
thickly clothed with spines than the posterior ramus; this latter is
rather more thickly clothed with spines than are the three posterior
cirri; the third cirrus is in all these respects characterised like the
second cirrus, but in a lesser degree. The pedicels of the second and
third cirri are thickly and irregularly clothed with spines; in the
three posterior pairs, the spines are placed in two regular rows, with
some minute intermediate spines.

_Caudal Appendages_ (Pl. IV, fig. 8 _a´_, _f_), multiarticulate, thin,
tapering, in one specimen equalling, in another just exceeding, in
length the pedicels of the sixth cirrus. In the latter specimen there
were thirteen segments, of which the basal segments were broader and
shorter than the upper; these latter are slightly constricted round the
middle, so that they resemble, in a small degree, an hour-glass. Their
upper margins are surrounded by rings of bristles; the terminal segment
being surmounted by one or two very fine bristles much longer than the
others. The two appendages are closely approximate; each arises from a
narrow elongated slip, attached to the side of the pedicel of the sixth
cirrus.

_Nervous system._--I examined the upper part of the nervous chord, in
order to ascertain whether the infra-oesophagean ganglion, which is of a
globulo-oblong shape, was far separated from the second ganglion; and
this I found to be the case, in accordance with the distance of the
first cirrus from the second. I may here remark, that in _S.
quadrivalvis_ I discovered the eye, which, though in all probability
really double, appeared to be single; it was situated near to the
supra-oesophageal ganglion; and this ganglion was situated near to the
adductor scutorum muscle, and at a considerable distance from the
labrum. The aperture leading into the acoustic (?) sack, is situated
much lower down than is usual (Pl. IV, fig. 8 _a´_), namely, at the
length of the pedicel of the first cirrus beneath its basal
articulation.

_Generative system._--The specimens here described, of which I examined
six, are exclusively female; they have no trace of the external,
probosciformed penis, or of the two great vesiculæ seminales, or of the
testes: on the other hand, the ovarian tubes within the peduncle are
developed in the usual manner, and owing to the large size of the ova,
are of large diameter, and hence very distinct: I detected, also, the
true ovaria at the upper edge of the stomach.


MALE. Plate V, figs. 1-8.

Of the above-described _Ibla Cumingii_ I dissected six specimens, four
from the Philippine Archipelago,[47] and two from the Burmah Empire, and
none of them, as we have just seen, possessed the probosciformed penis,
the vesiculæ seminales, or the testes, so conspicuous in other
Cirripedes; on the other hand, all were furnished with the usual
branching ovarian tubes and sometimes with ova, and consequently were
unquestionably of the female sex. Within each of these specimens there
was attached within the sack, in a nearly central line, at the rostral
end, (Pl. IV, fig. 8 _a´_, _h_, magnified five times,) a flattened,
purplish, worm-like little body, projecting about the 1/20th of an inch:
in one of the six individuals, there was a second similar little
creature attached at the carinal end of the sack. Before giving the
reasons which I think conclusively prove that these little animals are
the Males of the ordinary form of the _Ibla Cumingii_, it will be
convenient to describe their structure in detail.

   [47] I am deeply indebted to the liberality and kindness of Mr.
   Cuming, in allowing me to cut up four specimens of this new
   species; and to Dr. Gould, of Boston, U. S., for the examination
   of the Burmese specimens.

The whole consists of a long, much flattened peduncle, separated from
the mouth and thorax by an oblique fold, (Pl. V, fig. 1 _h_, _b_), which
is conspicuous on the dorsal margin under the cirri, and can be traced
with difficulty to the ventral margin. The thorax, itself rudimentary,
and supporting rudimentary cirri, is in some individuals, as in the one
represented (fig. 1, _magnified 32 times_), covered by, or received in
the oblique fold _h_, just mentioned: in other individuals the thorax is
drawn out, and then the fold shows merely as a notch on the dorsal
margin, and the basal articulations of the cirri stand some little way
above it. The basal edge of the large, well-developed month can be
traced all round, and on the ventral margin (_b_), is generally marked
by a slight notch. The dimensions and proportions vary much: the longest
specimen, including the imbedded portion, was 8/100th, and the shortest
barely 5/100ths of an inch in length; the width of the widest portion
varied from 1 to 2/100ths of an inch: the specimen figured (Pl. IV, fig.
8 _a´_, and Pl. V, fig. 1,) is a broad, short individual. Generally, the
middle of the peduncle is rather wider than the upper part.

_Peduncle._--The main part of the animal, as may be seen in the drawing,
consists of the peduncle, of which the imbedded portion tapers more or
less suddenly in a very variable manner, and is of variable length,--in
one specimen being one fourth of the entire length, and in another
consisting of a mere minute blunt point. The free upper part of the
animal is bent in various directions, in relation to the imbedded
portion. The latter passes obliquely through the chitine membrane and
corium, lining the sack of the female, and running along amidst the
underlying muscles and inosculating fibrous tissue, is attached to them
by cement at the extremity. The peduncle is often, but not in the
individual represented, much constricted at the point where it passes
through the skin of the female, and generally at several other points,
especially towards the extremity (see fig. 1); the stages of its deeper
and deeper imbedment being thus marked. The constrictions are, I
believe, simply due to the continued growth of the male, whilst the hole
through the membrane of the female does not yield. The imbedment, which
is considerable only when the lower part of the peduncle is almost
parallel to the coats of the sack, seems caused by the growth and
repeated exuviations of the female; I believe, that the larva attaches
itself to the chitine tunic of the sack, and that the cement, by some
unknown means, affects the underlying corium, so that this particular
portion of the tunic is not moulted with the adjoining integuments, and
that the growth of the surrounding parts subsequently causes this
portion to be buried deeper and deeper: it is, I believe, in the same
way as the end of the peduncle in _Conchoderma aurita_, sometimes
becomes imbedded in the skin of the whale to which it is attached.

The outer tunic of the peduncle is thin and structureless: in the fold
(fig. 1 _h_) under the cirri, there is a central triangular gusset of
still thinner membrane, corresponding in position to the membrane
connecting the two terga in the female, and there subjected to much
movement. I may here remark, that this fold, in its office of slightly
protecting the thorax and in its position, evidently represents the
capitulum with its valves, enclosing the whole body of the female. The
outer tunic is lined by corium, mottled with purple, and within this
there are two layers of striæ-less muscles, transverse and longitudinal,
as in all pedunculated Cirripedes. The corium extends some way into the
imbedded portion of the peduncle, and consequently, the outer tunic
there continues to be added to layer under layer, and as it cannot be
periodically moulted, it becomes much thicker than in the upper free
part of the animal: the corium, however, does not extend to the extreme
point, so that in it growth of all kind ceases.

_Antennæ._--The peduncle terminates (Pl. V, fig. 1 _e_) in the two
usual, larval, prehensile antennæ, which it is very difficult to see
distinctly; they are tolerably well represented in fig. 5, greatly
magnified. Their extreme length, measured from the basal articulation to
the tip of the hoof-like disc, is 22/6000ths of an inch, the disc itself
being 7/6000ths of an inch. The disc is slightly narrower than the long
basal segment, from which it is divided by a broad conspicuous
articulation; its lower surface is flat and its upper convex, altogether
resembling in shape a mule's hoof; its apex is fuzzy with the finest
down; it bears a narrow ultimate segment, thrown, as usual, on one side;
this segment supports on its rounded irregular summit, at least five, I
believe, judging from the structure of the same part in the male larva
of _Ibla quadrivalvis_, six or seven spines, longer than the segment
itself: one long spine arises from the under side of the disc, near the
base of the ultimate segment, and points backward: there is also a
single curved spine on the outside, near the distal end of the basal
segment. These organs were imbedded in a heart-shaped ball or cylinder
of brown, transparent, finely laminated cement, and thus attached to the
fibrous tissue of the female. The two cement-ducts (fig. 1 _f_) were
very plain, each about 1/6000th of an inch in diameter, containing the
usual inner chord of opaque cellular matter. I traced them at the one
end into the prehensile antennæ as far as the disc; and at the other, up
the peduncle for about one fourth of its length, where I lost them, and
could not discover with certainty any cement glands. I may, however,
here mention, that I found in the lower half of the peduncle, numerous,
yellowish, transparent, excessively minute, pyramidal bodies, with
step-formed sides; of these two or three often cohered by their bases
like crystals; I have never seen anything like these in other
Cirripedes, but it has occurred to me that they may possibly be
connected with the formation of the cement: for in the last larval
condition of Lepas, the cement-ducts run up to the gut-formed ovaria,
filled at this period with yellowish, grape-like, cellular masses,
without the intervention of cement glands, and I can imagine that
similar masses, not being developed into functional ovaria, might give
rise to the yellow pyramidal bodies.

_Mouth._--The mouth is well developed; it is represented as seen
vertically from above, in Pl. V, fig. 2, magnified about 60 times; the
positions of the cirri and the outline of the thorax are accurately
shown by dotted lines; a lateral view is given in fig. 1. In the
specimen figured, the longitudinal diameter of the mouth, including the
labrum, was 5/400th of an inch. The muscles of the several trophi have
transverse striæ, and are the strongest and most conspicuous of any in
the body. The labrum is largely bullate, with its summit slightly
concave; the trophi are arranged in a remarkable manner, in a
semicircular line, so as to be opposed to the labrum rather than to each
other: there are no teeth or spines on the crest of the labrum, which
overhangs the oesophageal cavity.

The _Palpi_ (fig. 2 _b_ and fig. 3) are very small, dark purple, bluntly
pointed, with a few small bristles at the point; they do not extend
beyond the knob at each corner of the labrum, which is here present, as
in all other Lepadidæ; they are much smaller than in the female, though
of a similar shape, and consequently, their points are much further
apart: within their bases, the lateral muscles of the mandibles are, as
usual, attached; they are represented in fig. 3, as seen from the
inside, with the eye on a level with the concave summit of the labrum.
The rudimentary condition of the palpi is connected, as remarked under
the _Anelasma squalicola_, with the absence of efficient cirri.

The _Mandibles_ (fig. 7) are well developed; they so closely resemble
those of the female that it is superfluous to describe them: they are,
however, smoother, without any trace of the teeth being pectinated, and
with the inferior point smaller: measured in their longer direction,
they are 7/2000th of an inch in length, and, therefore, a little less
than one third of the size of those of the female. These organs have the
usual muscles well developed, and the usual articulations.

The _Maxillæ_ (fig. 8) have a rather rudimentary appearance; yet they
have the same size relatively to the mandibles, as in the female, the
spinose edge being 3/2000ths of an inch in length. These organs
resemble, to a certain extent, those of the female, differing from them
in being less prominent,--in the outline being more rounded, with the
notches even less distinct,--and in the spines being fewer. The apodeme
is short and broad.

The _Outer Maxillæ_ (fig. 6) are pointed, with a small tuft of bristles
at the apex; they are much less hairy than in the female, but have
nearly the same unusual shape. Outside their bases, and between them and
the inner maxillæ, the two well-developed, tubular, flattened,
square-topped, olfactory orifices, project in exactly the same
remarkable position as in the female; these are not represented in fig.
2, though sometimes they can be very distinctly seen, when the mouth is
viewed from vertically above.

_Thorax and Cirri._--The thorax is in a rudimentary condition: I did not
observe the usual articulations. The whole, as seen from vertically
above, is of small size, compared with the mouth; the outline is
accurately shown by dotted lines in Tab. 5, fig. 2, together with the
positions of the two pair of cirri, the caudal appendages, and anus. The
posterior end of the thorax does not rise to the level of the summit of
the mouth; and the thorax seems of no service, excepting perhaps as a
sort of outer lip to protect the mouth. The cirri are in an extreme
state of abortion, and evidently functionless; they are lined with
purplish corium, without the vestige of a muscle; they are usually
distorted and bent in different directions; they vary in size, and even
those on opposite sides of the same individual, sometimes do not
correspond, and do not arise from exactly corresponding points of the
thorax. There are always two pair of cirri, which, as I conclude from
the position of the excretory orifices, answer to the fifth and sixth
pair in other Cirripedes. Each cirrus (fig. 4) usually carries only one
ramus, placed on a large basal segment, evidently corresponding to the
pedicel of a normal cirrus. The posterior are larger than the anterior
cirri, which latter spring from points a little lower down on the
thorax. In the posterior cirrus figured, the great basal articulation
or pedicel, almost equals in length, and much exceeds in thickness, the
four segments of the ramus; these segments are furnished on their upper
dorsal edges with little brushes of spines, but have not even a trace of
the normally larger and far more important anterior spines. In one
specimen, the anterior cirrus had a large pedicel, carrying three
segments, like those of the posterior pair; but in another specimen, one
of the three segments showed traces of being divided into two, thus
making four imperfect segments; whilst on the corresponding side of this
same individual there were only two ill-formed segments, with their few
spines differently arranged. Again, in a third specimen, the great basal
segment of the anterior cirrus on one side, bore, exteriorly to the
usual ramus, a single segment furnished with bristles, and evidently
representing a second ramus; thus showing that the great basal segment
certainly answers to a pedicel. I may here add, that on the integuments
of these cirri, I observed with a high power, the serrated scale-like
appearance common in other Cirripedes. Directly between the bases of the
sixth cirrus, there is a very minute papillus, which, under the highest
power, can be seen to consist of two closely approximate, flattened
points; these, I have no doubt, are the caudal appendages in an
extremely rudimentary condition, for I traced the vesiculæ seminales to
this exact spot: close outside these rudimentary points, on a slight
swelling, is the anus. It will presently be seen that in the male of the
closely allied _Ibla quadrivalvis_, the nature of these caudal
appendages admits of no doubt, for in this species they consist of more
than one segment, are spinose, and close under them towards the mouth,
there is a perfectly distinct papillus, representing the usual
probosciformed penis.

_Alimentary Canal._--The oesophagus is very narrow, and of remarkable
length; from the orifice under the mandibles, it first runs back (in
this respect not well represented in Pl. V, fig. 1,) under the bullate
labrum, and then straight down the peduncle, where it terminates in the
usual bell-shaped expansion, entering one side of the small globular
stomach; the latter, at its lower end, is slightly constricted, and then
is rather abruptly upturned. The rectum is of unparalleled length, and
extremely narrow; it can be best detected after the dissolution by
caustic potash of the softer parts, when its inner coat of chitine can
be seen to be continuous, in the ordinary manner, with the outer
integuments of the thorax. The anus, as already stated, is seated on a
slight swelling, and consists of a small longitudinal slit (_f_, fig.
2), placed close outside the two very minute caudal appendages.

_Organ of Sight._--In all the specimens, a little below the fold
separating the mouth from the peduncle, and near the abdominal (or
rostral) edge, a black ball (_c_, fig. 1), about 1/1000th of an inch in
diameter, is conspicuous. When dissected out, it is somewhat conical in
form, and appears to consist of an outer coat, with a layer of
pigment-cells of a dark purple colour, surrounding a transparent, rather
hard lens, apparently leaving a circular orifice at the summit, and
forming a short tube at the base, surrounding what I believe to be a
nerve. I was not able to perceive that this eye consisted of two eyes
united, which the analogy of other Cirripedes makes me suppose probable,
although in the ordinary and hermaphrodite _Ibla quadrivalvis_, the eye
also appeared single. It is seated under the two transparent muscular
layers, close upon the upper end of the stomach, and this is the exact
position, as stated in the introductory discussion (p. 49), in which the
eyes of pedunculated Cirripedes are commonly situated.

_Generative System._--Within the muscular layer all round the upper part
of the peduncle, and surrounding the stomach, there are numerous,
little, rather irregular globular balls, with brown granular centres, so
closely resembling the testes in other Cirripedes, though of smaller
size, that I cannot doubt that this is their nature: they were much
plainer, larger, and more numerous in some specimens than in others. The
vesiculæ seminales can seldom be made distinctly out; but having cut
one specimen transversely across the thorax, they were as plain as could
be desired, lying parallel and close to each other above the rectum,
(the animal being in the position as drawn,) and therefore in their
normal situation. Each had a diameter four times as great as that of the
rectum. In this individual the contents seemed (whether from
decomposition or state of development, or from my not having used high
enough power, I know not,) merely pulpy; but I have since found, in
another specimen, masses of the most distinct spermatozoa, with the
usual little knots on them, associated with numerous cells, about as
large as and resembling those which I have examined in living
Cirripedes, and from which I have every reason to believe the
spermatozoa are developed. The vesiculæ seminales unite and terminate
under the two extremely minute caudal appendages, and here I think I saw
an orifice; but there is certainly no projecting, probosciformed penis.

Having dissected the six specimens with the utmost care, and having
scrupulously examined the ovaria in other Cirripedes during their early
stages of development, even before the exuviation of the larval
locomotive organs, and in specimens of smaller size than the male Ibla,
I am prepared to assert that there are no ovaria, and that these little
creatures are exclusively males. It should be borne in mind, that in
some of the specimens there were perfect spermatozoa in the vesiculæ
seminales (as likewise in some of the males of _I. quadrivalvis_), and,
therefore, if these individuals had been hermaphrodites, their ova would
have been, at this period, well developed, and ready for impregnation:
in this state it is almost impossible that they could have been
overlooked. Moreover, it is probable that such ova would not have been
very small, for the larvæ whence the parasitic males are derived, attain
(as might have been inferred from the known dimensions of their
prehensile antennæ, and as we shall show actually is the case in _I.
quadrivalvis_,) the size common amongst ordinary Cirripedia.

_Concluding Remarks._--That these animals are true Cirripedes, though
having so different an external appearance from others of the class,
admits of not the least doubt. The prehensile antennæ, enveloped in
cement and including the two cement-ducts, would have been amply
sufficient, without other parts--for instance, the mouth, by itself
perfectly characteristic with each organ, together with the whole
alimentary canal, constructed on the normal plan,--to have proved that
they were Cirripedia. Under the head of the closely-allied _Ibla
quadrivalvis_, we shall, moreover, see that the males are
developed from larvæ, having every point of structure--the peculiar
quasi-bivalve shell, the two compound eyes, the six natatory legs,
&c.,--characteristic of the Order. But in some respects, the males are
in an embryonic condition, though unquestionably mature, as shown by the
spermatozoa;--thus, in the thorax and mouth opening throughout their
whole width into the cavity of the peduncle, that is, homologically into
the anterior part of the head, and in the viscera being there lodged
instead of in the thorax and prosoma, there is a manifest resemblance to
the larva in its last stage of development: the absence of a
probosciformed penis, the spineless peduncle, the food being obtained
without the aid of cirri, and the length of the rectum, are likewise
embryonic characters. Not only are these males, as just remarked,
Cirripedia; but they manifestly belong to the Pedunculated Family. If a
specimen had been brought to me to class, without relation to its sexual
characters, I should have placed it, without any hesitation, next to the
genus Ibla; if the mouth alone had been brought, I should assuredly have
placed it actually in the genus Ibla: for let it be observed how nearly
all the parts resemble those of _Ibla Cumingii_, excepting only in size
and in being less hairy. The trophi are arranged in the same peculiar
position as in the female; the labrum is largely bullate, without teeth
on the crest; the palpi, though relatively smaller, are of the same
shape; so are the mandibles; the maxillæ are more rounded and less
prominent, but have the same exact size relatively to the mandibles;
the outer maxillæ have the same, quite peculiar pointed outline, and the
olfactory orifices are tubular, and hold the same unusual position. It
is most rare to find so close a resemblance in the parts of the mouth,
except in very closely allied genera, and often species of the same
natural genus differ more. Again, in the long oesophagus and constricted
stomach there is a resemblance to Ibla. In the male of _Ibla
quadrivalvis_, the caudal appendages are multi-articulate; now, this is
a character confined to four genera, namely, Ibla, Alepas, Pollicipes,
and Lithotrya. I may add, that large tubular olfactory orifices are
confined to the same genera, together with Scalpellum. Lastly, it
particularly deserves notice, that the prehensile antennæ, in having a
hoof-like and pointed disc, with a single spine on the heel, much more
closely resemble these organs in Scalpellum, certainly the nearest ally
of Ibla, than in any other genus; they differ from the antennæ in
Scalpellum, only in the ultimate segment not having a notch on one side.
These organs, unfortunately for the sake of comparison, were not found
in the female and ordinary form of Ibla. The full importance of the
above generic resemblance in the antennæ, will hereafter be more clearly
seen, when their classificatory value is shown in the final discussion
on the sexual relations of Ibla and Scalpellum.

Here, then, we have a pedunculated Cirripede _very much_ nearer in all
its essential characters to Ibla than to any other genus, and
exclusively of the male sex; and this Cirripede in six specimens, from
two distant localities, adhered to an Ibla exclusively of the female
sex. May we not, then, safely conclude that these parasites are the
males of the _Ibla Cumingii_? Considering that, in the same class with
the Cirripedia, there is a whole family of crustaceans, the Lerneidæ, in
which the males, compared with the females to which they cling, differ
as much in appearance as in Ibla, and are even relatively smaller, I
should not have added another remark, had there not been under the head
of the following species, and of the next genus Scalpellum, a class of
allied facts to be advanced, which in some respects support the view
here taken, but in others are so remarkable and so hard to be believed,
that I will call attention to the alternative, if the above view be
rejected. The ordinary _Ibla Cumingii_ must have a male, for that it is
not an hermaphrodite can hardly be questioned, seeing how easy it always
is to detect the male organs of generation; and we must consequently
believe in the visits of a locomotive male, though the existence of a
locomotive Cirripede is improbable in the highest degree. Again, as the
little animal, considered by me to be the male of _I. Cumingii_, is
exclusively a male, (for there were no traces of ova or ovaria, though
the spermatozoa were perfect,) we must believe in a locomotive Cirripede
of the opposite sex, though the existence in any class of a female
visiting a fixed male is unknown:[48] in short, we should have
hypothetically to make two locomotive Cirripedes, which, in all
probability, would differ as much from their fixed opposite sexes, as
does the Cirripede, considered by me to be the male of _I. Cumingii_,
from the ordinary form. This being the case, I conclude that the
evidence is amply sufficient to prove that the little parasitic
Cirripede here described, is the male of _Ibla Cumingii_.

   [48] It deserves notice, that in the class Crustacea, both in the
   Lerneidæ and in the Cirripedia, the males more closely resemble
   the larvæ, than do the females; whereas amongst insects, as in
   the case of the glow-worm in Coleoptera, and of certain nocturnal
   Lepidoptera, it is the female which retains an embryonic
   character, being worm-like or caterpillar-like, without wings.
   But in all these cases, the male is more locomotive than the
   female.

If we look for analogies to the facts here given, we shall find them in
the Lerneidæ already alluded to, but in these the males are not
permanently attached to the females, only cling, I believe, to them
voluntarily. The extraordinary case of the Hectocotyle, originally
described as a worm parasitic on certain Cephalopoda, but now shown by
Kölliker to be the male of the species to which it is attached, is
perhaps more strictly parallel. So again in the entozoic worm, the
_Heteroura androphora_ the sexes cohere, but are essentially distinct:
"this singular species, however," according to Professor Owen,[49]
"offers the transitional grade to that still more extraordinary
Entozoon, the _Syngamus trachealis_, in which the male is organically
blended by its caudal extremity with the female, immediately anterior to
the slit-shaped aperture of the vulva. By this union a kind of
hermaphroditism is produced; but the male apparatus is furnished with
its own peculiar nutrient system; and an individual animal is
constituted distinct in every respect, save in its terminal confluence
with the body of the female. This condition of animal life, which was
conceived by Hunter as within the circle of physiological possibilities,
has hitherto been exemplified only in the single species of Entozoon,
the discovery of the true nature of which, is due to the sagacity and
patient research of Dr. C. Th. Von Siebold." In Ibla, the males and
females are not organically united, but only permanently and immovably
attached to each other. We have in this genus the additional singularity
of occasionally two males parasitic on one female.

   [49] Cyclopædia of Anatomy and Physiology, p. 142.

I have used the term parasitic, which perhaps ought strictly to be
confined to cases where one creature derives its nutriment from another,
inasmuch as the male is invariably and permanently attached to and
imbedded in the female,--from its being protected by her capitulum, so
that its own capitulum is not developed--and from its feeding on minute
animals infesting her sack. The male Ibla must seize its prey, guided
probably by its well-developed olfactory organs, through the movement of
its long, flexible body, furnished with muscles, and with the mouth
seated on the summit. We have already seen one instance of a Cirripede,
the Anelasma, obtaining its food without the aid of cirri, by means of
its probosciformed, flexible mouth. The eye can serve only to announce
to the male when the female opens her valves, allowing occasionally some
minute prey to enter. In ordinary Cirripedes the penis is long,
articulated, and capable of varied movements, I presume for the purpose
of impregnating each separate ovum: the male Ibla has no such organ; and
no doubt the whole body, furnished like the penis with longitudinal and
transverse muscles, serves the same purpose! I may remark, that it seems
surprising that so small a male should secrete sufficient semen to
impregnate the ova of the female, but the ova are not nearly so numerous
in Ibla as in most genera of Cirripedes; and the smallness of the males
in some parasitic Crustacea has already been alluded to. The male must
always be younger than the female, for the latter must first grow large
enough for the larva of the male to crawl into her sack. Whether the
male lives as long as the female I know not, but he certainly lives for
a considerable period and increases in size, as shown by the depth to
which the end of the peduncle is imbedded. Moreover we shall see, under
the next species, that the male is metamorphosed from a larva, not one
sixth of its own size.

In the male Ibla, abortion has been carried to an extraordinary and, I
should think, almost unparalleled extent. Of the twenty-one segments
believed to be normally present in every Crustacean, or of the seventeen
known to be present in Cirripedes, the three anterior segments are here
well developed, forming the peduncle: the mouth consists as usual of
three small segments: the succeeding eight segments are represented by
the rudimentary and functionless thorax, supporting only two pair of
distorted, rudimentary and functionless cirri: the seven segments of the
abdomen have disappeared, with the exception of the excessively minute
caudal appendages; so that, of the twenty-one normal segments, fifteen
are more or less aborted. The state of the cirri is curious, and may be
compared to that of the anthers in a semi-double flower; for they are
not simply rudimentary in size and function, but they are monstrous, and
generally do not even correspond on opposite sides of the same
individual. As males in other classes of the animal kingdom often retain
some female characters, so here (though the case is not strictly
analogous[50]) the male possesses the cementing apparatus, which
homologically is part of an ovarian tube modified.

   [50] Certain plants offer a closer, though not perfect, analogy.
   Thus, in the florets of some compositous flowers, the pistil,
   besides its proper female functional end, serves to brush the
   pollen off the anthers; while, in the florets of some other
   compositæ (see the account of Silphium in 'Ch. K. Sprengel Das
   entdeckte Geheimniss der Natur'), the pistil is functionless for
   its proper end, the flower being exclusively male, but its style
   is developed, and still serves as a brush. So in the male Ibla,
   part of the ovaria, in a modified condition, is still present,
   and serves as a cementing apparatus.

The individuals in every other genus (with the exception of Scalpellum),
in the several families, in the three Orders of Cirripedia, are
hermaphrodite or bisexual. Why, then, is Ibla unisexual; yet, becoming,
in the most paradoxical manner, from its earliest youth, essentially
bisexual? Would food have been deficient, and was the seizure of
infusoria by another and differently constructed individual, necessary
for the support of the male and female organs? The orifice of the sack
of the female is unusually narrow; would the presence of testes and
vesiculæ seminales have rendered her thorax and prosoma inconveniently
thick? Seeing the analogous facts in the six, differently-constructed
species of the allied genus Scalpellum, I infer there must be some
profounder and more mysterious final cause.


2. IBLA QUADRIVALVIS. Pl. IV, fig. 9.

  ANATIFA QUADRIVALVIS. _Cuvier._ Mém. pour servir ... Mollusq.
        1817, Art. Anatifa, Plate, figs. 15, 16.

  IBLA CUVIERIANA. _J. E. Gray._ Annals of Philosophy, vol. x, New
        Series, Aug. 1825.

  ---- _J. E. Gray._ Spicilegia. Zoolog. Tab. iii, fig. 10.

  TETRALASMIS HIRSUTUS. _Cuvier._ Regne Animal, vol. iii, 1830.

  ANATIFA HIRSUTA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.
        xciii, figæ. 7-10, 1834.

_I. (Herm.), valvis et pedunculi spinis sub-flavis: basali tergorum
angulo, introrsùm spectanti, hebete, quia margo carinalis inferior
longiùs quam margo scutalis prominet._

_Hermaph._--Valves and spines on the peduncle yellowish: basal angle of
the terga, viewed internally, blunt, owing to the lower carinal margin
being more protuberant than the scutal margin.

Caudal appendages four times as long as the pedicels of the sixth
cirrus: rami of the first cirrus unequal in length by about six
segments.

_Complemental Male_, with a notched crest on the dorsal surface, forming
a rudiment of a capitulum: maxillæ well furnished with spines.

    Kangaroo Island, South Australia (Mus. Brit., given by Cuvier to
    Leach); Adelaide, South Australia (Mus. Stutchbury); King
    George's Sound, Voyage of Astrolabe; New South Wales, attached
    to a mass of the Galeolaria decumbens, (Mus. Hancock).


HERMAPHRODITE.

All the external parts so closely resemble those of _I. Cumingii_, that
it would be superfluous to describe more than the few points of
difference. The horny substance of both scuta and terga is uniformly
yellow; though in dryed specimens, from the underlying corium being seen
through the valves, these generally have a tinge of blue.

The _Scuta_, viewed internally, are less elongated transversely; they
have their basal margins slightly more hollowed out, and the fold on the
upper free and horn-like portion rather deeper.

The _Terga_, viewed internally, have the apex of the growing or
corium-covered surface higher relatively to the scuta than in _I.
Cumingii_; and the basal angle is much broader, owing to the lower
carinal margin being much more protuberant than the scutal margin. The
spines on the peduncle are all yellowish-brown, and are rather longer
than in _I. Cumingii_. I observed in three or four specimens, that the
lowest part of the peduncle had become _internally_ filled up with the
usual, brown, transparent, laminated cement, cone within cone, so that
this lower part was rendered rigid and stick-like; this latter effect, I
apprehend, is the object gained by the formation of cement within the
peduncle, of which I have not observed any other instance. The entire
length of the largest specimen was one inch; some other specimens were
only half this size.

The thorax and prosoma are of the same shape as in _I. Cumingii_, and in
the largest specimen, about one tenth of an inch square; the prosoma, as
in that species, is hairy. In the _Mouth_, all the parts are closely
similar to those of _I. Cumingii_, but one third larger; the crest of
the labrum is a little roughened with minute points: the palpi are
squarer and blunter at their extremities: the mandibles have their
second and third teeth nearly equal in size to the first, and they do
not appear pectinated: the maxillæ have their spinose edge very nearly
straight: the outer maxillæ are pointed. The olfactory orifices are
similarly situated, and of similar shape; they are dark coloured.

_Cirri._--These also are similar to those of _I. Cumingii_; the
segments, however, of the three posterior cirri have each four pair of
spines, placed very close together in a transverse direction. First
cirrus has its two rami unequal in length by about six segments. The
anterior rami of the second and third cirri are thicker, and more
thickly clothed with spines, than the posterior rami, to perhaps a
greater degree than in _I. Cumingii_. In the posterior cirri, the upper
segments of the pedicels are nearly as long as the lower segments.

_Caudal Appendages_, four times as long as the pedicel of the sixth
cirrus, and three fourths of the length of the rami of this same cirrus:
segments thirty-two in number, and therefore as many as those forming
the sixth cirrus: the upper segments are much thinner and longer than
the basal segments; each furnished with a circle of short bristles;
whole appendage excessively thin and tapering: the two closely
approximate.

_Colour._--From some well-preserved dryed specimens in Mr. Stutchbury's
possession, it appears that the sack, cirri and trophi, were dark blue,
as in _I. Cumingii_; after being long kept in spirits, these parts
become brown.

_Generative System._--The penis (Pl. IV, fig. 9 _a_) is very singular in
structure; it is of the ordinary length, but of small diameter; it
tapers but little; it consists of a moveable articulated, and a fixed
unarticulated portion; this latter is smooth, much flattened, not
divided into segments, and projects straight out under the caudal
appendages; it is about one third of the length of the entire penis; it
corresponds with a part present in all Cirripedes, but here surprisingly
elongated. The articulated portion consists of separate segments, twenty
in number, quite as distinct as those of the cirri; each one is oblong,
being longer by about a third part than broad; each has a few short
bristles round its upper margin; the terminal segment has a circular
brush of bristles. The vesiculæ seminales are easily seen, though they
are narrow; they are slightly tortuous; they enter the prosoma, and lie
on each side of the stomach; their outer case has a ringed structure,
but is not fibrous; the contents in the best specimen consisted of a
mass of spermatozoa, which I saw with perfect distinctness. The testes
are unusually large and egg-shaped.

_Ova_, spherical, 5/400ths of an inch in diameter, united as usual into
two ovigerous lamellæ. The ovigerous fræna are extraordinarily small,
and might be very easily overlooked; their length, in a full-sized
specimen, was only 7/400ths of an inch, and they projected only 2/400ths
from the inner surface of the sack. The glands on their margin, to which
the lamellæ adhere, are pointed oval, with an extremely short footstalk,
and that rather thick; the entire length of gland and footstalk, being
only 2/3000ths of an inch. The larvæ, in their first stage of
development, offer the usual characters, and closely resemble those of
Scalpellum; the probosciformed mouth, however, is remarkably prominent,
and the limbs unusually thick.

_Affinities._--This species most closely resembles _I. Cumingii_, and
cannot be distinguished externally, except by the absence of the blue
colour on the marginal and interior portions of the valves; and this can
hardly be ascertained without separating and cleaning them, owing to the
blueness of the underlying corium. Internally some slight differences
may be perceived in the form of the valves. Considering these so slight
differences, it is highly remarkable that this species should be
hermaphrodite, whilst _I. Cumingii_ is unisexual. There is a greater,
though still slight, difference in the included animal's body; the palpi
in _I. quadrivalvis_ are blunter, the mandibles smoother, the olfactory
orifices darker-coloured; the rami of the first cirrus more unequal, the
spines more numerous on the segments of the posterior cirri, and lastly
and most conspicuously, the caudal appendages are very much longer
relatively to the length of the sixth cirrus, than in _Ibla Cumingii_.


COMPLEMENTAL MALE.

I have examined one specimen of the hermaphrodite _I. quadrivalvis_,
preserved in spirits from Kangaroo Island, and one dry from Adelaide,
both places in South Australia, and four from an unknown locality,
purchased from Mr. Sowerby; and within five out of these six specimens,
males were attached. In one of them, two males of different ages were
included, one adhering to the peduncle of the other: in _I. Cumingii_,
also, it may be remembered, there was a case of two males parasitic on
one female. I may add that I opened another quite young specimen, from
Adelaide, not counted with the above, and it was without a male. The
males in the five specimens were attached low down, at the rostral end,
almost in a horizontal position, stretching across the bottom of the
sack; one of them, however, was placed considerably on one side. One
individual which I measured, was 16/100ths of an inch in length, and
5/100ths in width in the widest part, namely, about half down the
peduncle. I may state, for the sake of comparison, that the
hermaphrodite to which this individual was attached, was, including the
peduncle and capitulum, one inch in length, that is, six times as long
as the male, and one fifth of an inch in width, that is, four times as
wide. The above measurements show that the male of this species is
rather more than twice as large as that of _I. Cumingii_. In consequence
of this greater size, I dissected, with the utmost care, the one
specimen which was excellently preserved in spirits, and found every
part, with a few exceptions, so exactly the same as in the male of _I.
Cumingii_, only larger and more conspicuous, that it will be sufficient
to indicate the few points of difference.

The most conspicuous difference is, that the oblique fold separating the
thorax and peduncle is more plainly developed, projecting at the point
corresponding to _h_ in fig. 1, Pl. V, 8/1000ths of an inch; in the
middle the fold is notched; it can be traced more easily than in _I.
Cumingii_, running beneath and parallel to the basal edge of the mouth,
to the ventral margin of the body. In the mouth there is hardly any
difference; the maxillæ, however, have two notches even plainer than in
the hermaphrodite _I. quadrivalvis_, or than in the male _I. Cumingii_,
but the depth of such notches is always a variable character; there are
also more spines on the edge in the male of the present species, than in
_I. Cumingii_. Both mandibles and maxillæ in the male _I. quadrivalvis_,
are larger than in the male _I. Cumingii_, to a greater degree than the
larger proportional size of the body in the former will account for; and
this, likewise, is the case with these same organs in the hermaphrodite
_I. quadrivalvis_ compared with the female _I. Cumingii_. The tubular
olfactory orifices are situated in the same peculiar position as in the
hermaphrodite, and as in both sexes of _I. Cumingii_: they are 1/500th
of an inch in diameter, and about as thick as one of the lower segments
in the rami of the sixth cirrus.

The thorax, as in the male of _I. Cumingii_, is quite rudimentary, and
serves as a mere flap to protect the mouth. In the three specimens
carefully examined, the posterior cirri had each only one ramus, whilst
the anterior cirri generally had two: in one specimen, one of the rami
in the anterior cirrus was formed of five segments, and the other ramus
of three segments, both rami being supported on a uni-articulated
pedicel; but on the opposite side of the same individual, the anterior
cirrus was represented by a mere knob. The longer ramus of the anterior
cirrus, in the best-developed individual, barely exceeded in length the
mandibles measured along the line of the teeth! In one specimen between
the bases of the posterior cirri, there were two perfectly distinct
caudal appendages; these, like the cirri, are in a quite rudimentary
condition; one was 5/1000ths of an inch in length, and consisted of
three segments, the upper edges of which had short spines; the other was
shorter, uni-articulated, but spinose. In a second specimen, these
appendages were quite aborted. Close under them, on the inside or
towards the mouth, (that is, in the normal position,) there was a
rudimentary but quite distinct penis, with the apex projecting freely,
and with the sides distinguishable from the ventral surface of the
thorax, for the length of 1/1000th of an inch: the corium lining this
little penis made the terminal orifice plainly visible. The vesiculæ
seminales lie in the usual position, and are conspicuous; they are
slightly tortuous, with their ends blunt: in the specimen so well
preserved in spirits, they were filled with a mass of spermatozoa,
perfectly distinct; and the whole cavity of the body was lined with
globular and pear-shaped testes. Assuredly there was no vestige of
ovarian tubes. From the greater size and excellent preservation of this
specimen, which rendered the examination of the generative system so
easy, I was able to examine the contents of the stomach, in which I
found the delicate epithelial coat, separated as usual, and containing
cellular matter, on which the animal had preyed, but the nature of which
I was unable to make out. The anus was much plainer than in the male of
_I. Cumingii_. I saw the eye distinctly. I could not distinguish the
orifices of the acoustic (?) sacks; and I think I should have seen them,
if they had existed.

_Prehensile Antennæ._--I examined these in the larvæ presently to be
mentioned, and therefore they were in better condition than in the
mature animal when cemented. Their total length, measured along the
outside, from the basal articulation to the end of the disc, is
32/6000ths or 33/6000ths of an inch--that is, one third longer than in
_I. Cumingii_; whilst the hoof-like disc itself is 8/6000ths, or only
1/6000th of an inch longer than this same part in _I. Cumingii_: the
apex of the disc is downy, or bears some excessively minute spines. The
ultimate segment has its end irregularly rounded, with the spines
obscurely divided into two groups, the outer group consisting of two or
three longer and thinner spines, and the inner group of, as I believe,
five rather shorter spines: the longer spines equal in length the whole
ultimate segment. I could not perceive that they were plumose, as in
many other genera. A single, rather thicker and long spine, pointing
backwards, is attached to the under side of the disc, nearly opposite to
the point where the ultimate segment is articulated on the upper convex
surface. Another single, curved spine is attached on the outer side of
the basal segment, near its distal end.

_Development of the Male._--In the specimen before alluded to, which
included two males, one of these was only the 30/1000ths of an inch in
length, and therefore between one fifth and one sixth of the size of the
mature male. It had, probably, undergone only one exuviation since its
metamorphosis, for the larva is nearly as long, namely, 25/1000ths of an
inch. In this young male, the mouth formed one third of the entire
length: it was attached, not as in every other case to the sack of the
hermaphrodite, but low down to the peduncle of the other male.

In the sack with these two males, there were certainly four, I believe
five, larvæ, which in every main point of structure resembled the larvæ
of other pedunculated Cirripedes. From the peculiar form of their
prehensile antennæ, differing in no respect, except in the proportional
lengths of the segments, from the same organ in the male _I. Cumingii_,
I can feel no doubt that these were the larvæ of the male _I.
quadrivalvis_;--for a moment's reflection will show how excessively
improbable it is, that several larvæ of some other Cirripede, and that a
Cirripede intimately allied to the parasitic male Ibla, should have
forced themselves, without any apparent object, into the sack of the
hermaphrodite Ibla. The larvæ, though not yet attached, were on the
point of attachment, so that the single eye of the mature animal could
be distinctly seen, lying near to the two great compound eyes of the
larva. We have also just seen, that one male quite recently here had
undergone its metamorphosis. The larvæ are 25/1000ths of an inch in
length, and rather more than 10/1000ths in width in the widest part:
they are boat-shaped, the dorsal edge forming the keel of the boat; the
anterior end is only a little blunter than the posterior end; the
quasi-bivalve carapace is smooth. All the essential points of structure
in the larvæ of other Cirripedes at this stage, could be distinctly here
seen,--such as the two compound eyes, with the apodemes to which they
are attached, and the two oblong sternal plates whence the apodemes
spring,--the adductor muscle,--the six natatory legs, with long plumose
spines,--the abdomen, with its three small segments and the caudal
appendages,--the prehensile antennæ already described,--and, lastly, the
two little (auditory?) sacks at the antero-sternal edges of the
carapace, but not so near the anterior extremity as in Lepas. The four
or five larvæ, after having undergone in the open sea the several
preparatory metamorphoses common to the class, must have voluntarily
entered the sack of the hermaphrodite: ultimately would they, on finding
two males already attached there, have retired, and sought another
individual less well provided; or would they all have remained, and so
formed a polyandrous establishment, such as we shall presently see
occurs sometimes in Scalpellum? This must remain quite uncertain.

In this same hermaphrodite specimen of _I. quadrivalvis_, the two
ovigerous lamellæ contained some hundreds of larvæ in the first stage of
development, which were liberated from their enveloping membranes by a
touch of a needle: they were about the 16/1000ths of an inch in length,
and presented all the usual characters of larvæ at this period. What a
truly wonderful assemblage of beings of the same species, but how
marvellously unlike in appearance, did this individual hermaphrodite
present! We have the numerous, almost globular larvæ, with lateral horns
to their carapaces, with their three pair of legs, single eye,
probosciformed mouth and long tail:--we have the somewhat larger larvæ
in the last stage of development, much compressed, boat-formed, with
their two great compound eyes, curious prehensile antennæ, closed
rudimentary mouth and six natatory legs so different from those in the
first stage:--we have the two attached males, with their bodies reduced
almost to a mouth placed on the summit of a peduncle, with a minute,
apparently single eye shining through the integuments, without any
carapace or capitulum, and with the thorax as well as the legs or cirri
rudimentary and functionless:--lastly, we have the hermaphrodite, with
all its complicated organisation, its thorax supporting six pairs of
multi-articulated two-armed cirri, and its well-developed capitulum
furnished with horny valves, surrounding this wonderful assemblage of
beings. Unquestionably, without a rigid examination, these four forms
would have been ranked in different families, if not orders, of the
articulated kingdom.

_Concluding Remarks._--If the creature which I have considered as the
male of _Ibla Cumingii_ be really so, and the evidence formerly given
seems to me amply conclusive, then the animal just described, from its
close affinity in every point of structure with the former, assuredly is
the male of _Ibla quadrivalvis_. But feeling strongly how improbable it
is, that an additional or complemental male should be associated with an
hermaphrodite, I will make a few remarks on the only possible
hypothesis, if my view be rejected,--namely, that the two parasites
considered by me to be exclusively males, are not so, but are
independent hermaphrodite Cirripedes, the female organs and ova (which,
if present, would have been nearly mature, judging from the presence of
spermatozoa in both species) having been overlooked by me in every
specimen: and again, that in the animal described as the female _I.
Cumingii_, I have, though minutely dissecting several specimens, and
finding far smaller parts, such as the organs of sense and nervous
system, entirely overlooked all the conspicuous male organs, though when
I came to _I. quadrivalvis_, and naturally expected to find it likewise
exclusively female, a single glance showed me the great probosciformed
penis, and by the simplest dissection the vesiculæ seminales and testes
were exhibited. Such an oversight is scarcely credible; but even if
assumed, we have to believe in the extraordinary circumstance of the two
parasites being species of an independent genus, not only the very next
in alliance to the animals to which they are attached, but in certain
most important points, namely, the organs of the mouth, actually
deserving a place in the very same genus. Moreover, the two parasites
differ from each other, not only in about the same slight degree, but in
a corresponding manner, as do the two Iblas to which they are attached;
thus the mouths of _Ibla quadrivalvis_ and _I. Cumingii_ are closely
similar, (the difference being barely of specific value,) so are the
mouths of the two parasites; but the parts are larger in the
hermaphrodite _I. quadrivalvis_, than in _I. Cumingii_, so are they in
the parasites. Again, the most conspicuous character in _I.
quadrivalvis_, is the number of segments in the caudal appendages, far
exceeding those in the other species of Ibla, as well as of every other
pedunculated Cirripede, and the parasite of this species has articulated
spinose appendages, far larger than the barely visible, non-articulated
pair in _I. Cumingii_.

Considering the whole case, there seems no room to doubt the justness of
the conclusion arrived at, under the former as well as under the present
species, namely, that these little parasites are the males of the two
species of Ibla to which they are attached;--wonderful though the fact
be, that in one case, the male should pair with an hermaphrodite already
provided with efficient male organs. It is to bring this fact
prominently forward, that I have called such males, Complemental Males;
as they seem to form the complement to the male organs in the
hermaphrodite. We look in vain for any, as yet known, analogous facts in
the animal kingdom. In the genus Scalpellum, however, next in alliance
to Ibla, in which, consequently, if anywhere, we might expect to find
such facts, they occur; and until these are fully considered, I hope the
conclusions here arrived at, will not be summarily rejected. Although
the existence of Hermaphrodites and Males within the limits of the same
species, is a new fact amongst animals, it is far from rare in the
Vegetable Kingdom: the male flowers, moreover, are sometimes in a
rudimentary condition compared to the hermaphrodite flowers, exactly in
the same manner as are the male Iblas. If the final cause of the
existence of these Complemental Males be asked, no certain answer can be
given; the vesiculæ seminales in the hermaphrodite of _Ibla
quadrivalvis_, appeared to be of small diameter; but on the other hand,
the ova to be impregnated are fewer than in most Cirripedes. No
explanation, as we have seen, can be given of the much simpler case of
the mere separation of the sexes in _Ibla Cumingii_: nor can any
explanation, I believe, be given of the much more varied arrangement of
the parts of fructification in plants of the Linnean class, Polygamia.


_Genus_--SCALPELLUM. Pls. V, VI.

  SCALPELLUM. _Leach._ Journ. de Physique, t. lxxxv, July, 1817.

  LEPAS. _Linn._ Systema Naturæ, 1767.

  POLLICIPES. _Lamarck._ Animaux sans Vertebres, 1818.

  POLYLEPAS. _De Blainville._ Dict. des Sc. Nat., 1824.

  SMILIUM (pars generis). _Leach._ Zoolog. Journal, vol. 2, July,
        1825.

  CALANTICA (pars generis). _J. E. Gray._ Annals of Philosophy, vol.
        x, (new series,) Aug. 1825.

  THALIELLA (pars generis). _J. E. Gray._ Proc. Zoolog. Soc., 1848.

  ANATIFA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, 1826-34.

  XIPHIDIUM (pars generis). _Dixon._ Geology of Suffolk, 1850.

(_Herm. et Foem._) _Valvis 12 ad 15: lateribus verticilli inferioris
quatuor vel sex, lineis incrementi plerumque convergentibus: sub-rostrum
rarissime adest: pedunculo squamifero, rarissime nudo._

(Herm. and Fem.) Valves 12 to 15 in number: latera of the lower whorl,
four or six, with their lines of growth generally directed towards each
other: sub-rostrum very rarely present: peduncle squamiferous, most
rarely naked.

Filamentary appendages, none: labrum, with the upper part highly
bullate: trophi, various: olfactory orifices, more or less prominent:
caudal appendages, uniarticulate and spinose, or none.

_Males_, parasitic at or near the orifice of the sack of the female or
of the hermaphrodite: thorax enclosed within a capitulum, furnished with
three or four rudimentary valves, or with six perfect valves: peduncle
either short and distinct, or confounded with the capitulum: sometimes
mouth and stomach absent, and cirri non-prehensile; sometimes mouth and
cirri normal.

    Generally attached to horny corallines, in the warmer temperate
    seas over the whole world.

I have felt much doubt in limiting this genus: the six recent species
which it contains, differ more from each other than do the species in
the previous genera. Mr. Gray has proposed or adopted generic names for
four of the species, and a fifth certainly has equal claims to this same
rank. These genera have been founded almost exclusively on the number of
the valves; and oddly enough, the numbers have generally been given
wrongly, namely, in Scalpellum, Calantica, Thaliella, and Xiphidium.
Scalpellum blends through _S. villosum_ into Pollicipes; and this latter
genus has an equal right with Scalpellum, to be divided into sub-genera,
three in number. Hence, no less than eight genera might be made out of
the twelve recent species of Scalpellum and Pollicipes, and their
formation, in some degree, be justified; but, in my opinion, this
inordinate multiplication of genera destroys the main advantages of
classification. At one time, I even thought that it would be best to
follow Lamarck, and keep the twelve recent species in one genus; but
considering the number of fossil species, I believe the more prudent
course has been followed, in retaining the two genera Scalpellum and
Pollicipes; more especially as I can hardly doubt, that several other
species will be hereafter discovered.

Having so lately described in the Memoirs of the Palæontographical
Society, the fossil species, I will not here further allude to them,
than to state, that out of the fifteen species therein described, _S.
magnum_ comes very close to the recent _S. vulgare_, and that several
Eocene and Cretaceous species, such as _S. quadratum_, _S. fossula_, and
_S. maximum_, are allied to _S. rutilum_ and _S. ornatum_. _Scalpellum
villosum_, a recent species, has stronger claims than any other species
to be generically separated; and its habits, in not being attached to
horny corallines, are also different, but the identity of its
Complemental Male with that of _S. Peronii_, and its numerous points of
resemblance in structure with the other species, have determined me not
to separate it. _Scalpellum Peronii_, _villosum_, and _rostratum_, in
having a sub-carina,--in the rostrum being pretty well developed,--and
in the Complemental Male being pedunculated, and furnished with a
functional mouth and prehensile cirri, may be separated from _S.
vulgare_, _ornatum_ and _rutilum_; but even between these two little
groups, _S. rostratum_ is in some respects intermediate, namely, in
having three pairs of latera, and more especially in the rudimentary
condition of the valves of its Complemental Male, and in the position in
which the male is attached to the hermaphrodite. The three species in
the second little group, namely, _S. vulgare_, _S. ornatum_, and _S.
rutilum_, are more nearly allied to each other in all their characters,
especially in the characters drawn from their Males, than are the other
three species. _S. ornatum_ and _S. rutilum_ are considerably nearer to
each other than any other two of the species. Upon the whole I conclude
that the six species must be thrown either into five or into four genera
(the first three species making one genus), or all into one genus, and
this latter has appeared to me the preferable course. The separation
even of Scalpellum and Pollicipes, as already stated, is hardly natural.
The fact of these genera having existed from a remote epoch, and having
given rise during successive periods to many species now extinct, is
probably the cause that the few remaining species are so much more
distinct from each other, than is common in the other genera of
Lepadidæ. Whenever the structure of the whole capitulum in the fossil
species is well known, and as soon as more species, recent and fossil,
shall have been discovered, then probably the genus Scalpellum will have
to be divided into several smaller genera.

_Description._--The _Capitulum_ is much compressed, and generally
produced upwards; it is formed of from twelve to fifteen valves, which
are rather thin, and with the exception of _S. ornatum_, almost entirely
covered by membrane, bearing spines: the valves are seldom locked very
closely together. A sub-rostrum exists only in _S. villosum_, which
species leads on to Pollicipes; in _S. vulgare_ the rostrum is
rudimentary and hidden. The scuta, terga and carina, are much larger
than the other valves: these five valves seem to differ essentially
from the others in being at first developed under the form of the
so-called primordial valves: the other valves commence by a small
indistinct brown spot, very different from the hexagonal tissue of the
primordial valves: I saw this very clearly in young specimens of _S.
vulgare_. At first, the scuta, terga and carina, grow exclusively
downwards (and permanently so in most fossil species), and therefore the
growth of the scuta and carina is in an absolutely opposite direction to
what it is in Lepas, Pæcilasma and Dichelaspis. After a short period the
scuta are added to at their upper ends; the portion thus added, stands
at a rather lower level, and projects in a rather different direction
from the first-formed part of the valve, giving to it, in some respects,
the appearance of having been broken and mended. This structure is
common to _S. vulgare_, _S. rostratum_ and _S. Peronii_. The upper
Latera (except in _S. villosum_) grow in the same manner, namely, at
first exclusively downwards, and then both upwards and downwards. The
rostral and carinal latera (with the same exception of _S. villosum_)
have their umbones seated laterally, at opposite ends of the
capitulum,--the umbones of the rostral latera being close to the
rostrum, and those of the carinal pair close to the carina, and
consequently their chief growth is directed towards each other. The
carina in all the species, except _S. villosum_, is either bowed or
angularly bent; in the latter case the lower half is parallel to the
peduncle, and the upper half, extending far up between the terga, is
parallel to their longer axes. In some of the species the carina is
added to almost equally at both ends; in _S. ornatum_ it grows but
little at the upper end, and to a varying degree in different
individuals according to their age; in _S. rutilum_ the umbo is at the
apex, and there is consequently no upward growth; lastly, in _S.
villosum_ the carina widening much from the apex to the basal margin,
grows exclusively downwards, and a portion of the apex projects
freely,--characters all common to the carina in the genus Pollicipes.
The upper latera occur in all the species; in the lower whorl there are
either two or three pair of latera, in the former case the infra-median
pair being absent. The latera differ considerably in shape in the
different species.

The _Peduncle_ is generally rather short, and, with the exception of _S.
Peronii_, is covered with calcified scales. These scales are generally
small, and placed symmetrically in close whorls, in an imbricated order,
with each scale corresponding to the interspace between two scales in
the whorls above and below. In _S. ornatum_, the scales are so wide,
transversely, that there are only four in each whorl. In _S. villosum_,
the scales are spindle-shaped and arranged somewhat irregularly in
transverse rows, not very near to each other. New calcareous scales
originate only round the top of the peduncle, and they continue to grow
only in the few upper whorls; and as the peduncle itself continues to
increase in diameter by the formation of new inner membranous layers and
the disintegration of the old outer layers, the calcareous scales come
in the lower part of the peduncle to stand further and further apart. In
the earliest stage of growth there are no calcareous scales on the
peduncle in _S. vulgare_; they first appear under the carina. Spines are
articulated in great numbers on the surface of the peduncle in _S.
vulgare_, _S. Peronii_, and _S. villosum_, and very short ones on that
of _S. rostratum_.

_Attachment._--All the species, except _S. villosum_, are attached to
horny corallines: the singular means of attachment in _S. vulgare_ will
be described under that species, and is probably common to several of
the other species. The larva in most, or in all cases, when it proceeds
to attach itself, clings head downwards to the branch, and hence the
capitulum comes to be placed upwards, with its orifice fronting the
branch and the carina outwards. The sucking disc of the prehensile
antennæ of the larva, in the five species examined, was a little
pointed, and in shape resembled the hinder hoof of a mule: this may
perhaps be accounted for by the narrowness of the branches of the
corallines, to which it has to adhere: a large circular disc, as in
Lepas, would have been worse than useless: the ultimate segment in most
or all the species, has on its inner side (the segment being supposed to
be extended straight forward) a notch or step, bearing, I believe, two
spines.

_Size and Colour._--Some of the species attain a medium size, others are
small. The valves are generally clouded red or pink, but sometimes
white.

_Mouth._--The various parts vary far more than in any genus hitherto
described. The labrum is highly bullate, with the upper part forming a
rounded overhanging projection, and with the lower part much produced,
so that the mouth is placed far from the adductor scutorum muscle, and
consequently the orifice is directed more towards the ventral surface of
the thorax than in most other Cirripedes: on the crest of the labrum
there are some very small teeth in several of the species, but not in
all. The mandibles have either three or four main teeth, generally with
either one or two small teeth intermediate between the first and second
large teeth, and in the case of _S. Peronii_, with small teeth between
all the larger ones. The maxillæ have their edges furnished with many
spines, and are either straight or have the inferior part prominent and
step-formed. The outer maxillæ have the spines on their inner edges
either continuous or divided into two groups, of which latter structure
we have not hitherto had any very well characterised example. The
olfactory orifices are either highly or moderately protuberant.

In most of the species the prosoma is little developed, and the first
cirrus is placed far from the second. The _Cirri_ are generally but
little curled, and have elongated segments, with long, generally
serrated spines: the first cirrus varies in proportional length; the
second and third cirri have both their rami more thickly clothed with
spines than are the three posterior cirri, the spines being generally
arranged in three or four longitudinal rows: the cirri, however, of _S.
villosum_ in all respects resemble closely the cirri of _Pollicipes
sertus_ and _P. spinosus_.

The _Caudal Appendages_ are uniarticulate, small, and clothed with
spines: in _S. villosum_, however, differently from in all other allied
forms, there are no appendages.

The _Stomach_, in those species which I opened, is destitute of cæca.
There are no filamentary appendages.

_Generative System._ The ova are nearly spherical, and remarkably large,
as was stated to be the case in the introductory discussion, in which
the larva of _S. vulgare_, in the first stage of development, was
described: the ovigerous fræna are small. The testes are large, but the
vesiculæ seminales in some of the species extraordinarily small.
_Scalpellum ornatum_, and perhaps _S. rutilum_, are unisexual; the other
species are hermaphrodite, but most or at least some of the individuals,
are furnished with Complemental Males. These latter are fully described
under each species, so I will here only remark, that _S. ornatum_, which
alone (excepting perhaps _S. rutilum_) is unisexual, has less claim than
the other species to be generically separated: we have seen also, in
Ibla, that similar sexual differences occur in two most closely allied
species. It is very singular how much more some of the Males and
Complemental Males in Scalpellum differ from each other, than do the
female and hermaphrodite forms; this seems due to the different stages
of embryonic development at which the males have been arrested. In the
males, however, of _S. rostratum_, _S. Peronii_, and _S. villosum_,
compared one with another, but not with the males of the other species,
the parts of the mouth and apparently the cirri, resemble each other
more closely, than do the same organs in the hermaphrodites. At the end
of this genus I shall give a summary on the highly remarkable sexual
relations both in Scalpellum and Ibla.

    _Distribution._--The species seem distributed over the whole
    world, but as far as we can trust our present scanty materials,
    are most common in the warmer temperate regions. The _S.
    vulgare_ ranges from the Norwegian seas to Naples. Most of the
    species are inhabitants of deep water.

_Affinities._--In the preliminary remarks, we have seen how this genus
blends into Pollicipes; and under the head of Oxynaspis, I have shown
its close affinity to that genus. If, indeed, we take _Pollicipes
spinosus_, and destroy all but six of the already minute and almost
rudimentary latera, we shall, as far as the capitulum is concerned,
convert it into a Scalpellum, closely similar to _S. villosum_. If we
take any species of Scalpellum, (excepting _S. villosum_ and _S.
rutilum_,) and destroy all the valves, but the scuta, terga and carina,
we shall convert it into an Oxynaspis. Lastly, I have shown under Ibla,
that in several most remarkable peculiarities of structure, there is a
manifest affinity between Scalpellum and that genus.

_Geological History._--Full details on this subject have been given in
the Memoirs of the Palæontographical Society. I will here only state,
that the oldest known form of Scalpellum occurs in the Lower Green Sand.


[=T= SUB-CARINÂ NULLÂ.]

1. SCALPELLUM VULGARE. Pl. V, fig. 15.

  SCALPELLUM VULGARE. _Leach._ Encyclop. Brit. Suppl., vol. iii,
        1824.

  LEPAS SCALPELLUM. _Linn._ Systema Naturæ, 1767.

  ---- _Poli._ Test. utriusque Siciliæ, Pl. vi., fig. 16. 1795.

  POLLICIPES SCALPELLUM. _Lamarck._ An. sans Vertebres, 1818.

  POLYLEPAS VULGARE. _De Blainville._ Dict. Sc. Nat., Plate, fig. 4.
        1824.

  SCALPELLUM LÆVE, var. _Leach._ Zoolog. Journal, vol. ii, p. 215,
        1825.

  ---- SICILIÆ, var. _Chenu._ Illust. Conch. Pl. iv, fig. 9.

  SCALPELLUM VULGARE, (et var.) _Brown._ Illust. of Conch., 1844,
        Pl. li., figs. 7 to 20.

_S. (Herm.) valvis 14, si rostrum pæne rudimentale includatur: lateribus
superioribus inæqualiter ovatis._

(Herm.) Capitulum with 14 valves, including the rudimentary rostrum:
upper latera irregularly oval.

Mandibles, with four or five teeth: maxillæ, with the edge straight,
bearing numerous spines.

COMPLEMENTAL MALE flask-formed, with four rudimentary valves; no mouth;
cirri not prehensile; attached to the occludent margin of the scutum,
near the umbo.

    Great Britain, Ireland, France, Norway, Naples. Attached to
    horny corallines, at from twenty to thirty, sometimes even to
    fifty fathoms in depth, according to Forbes and MacAndrew.


HERMAPHRODITE.

_Description._--Capitulum much flattened with the apex produced, of a
pale brown colour, sometimes faintly tinted purple, composed of 14
valves, of which the rostrum is rudimentary and barely visible
externally; valves thin, white, translucent, smooth, slightly marked by
the lines of growth, separated from each other by rather wide
interspaces of colourless membrane, which is thickly clothed by small,
articulated spines of unequal length. The valves, excepting sometimes
their umbones, are also covered with membrane, bearing spines, placed in
rows parallel to the lines of growth; the spines are particularly
numerous round the orifice of the sack.

_Scuta_ slightly convex, thrice as long as broad; upper part much
acuminated; occludent margin almost straight; basal margin nearly at
right angles to the occludent margin; the tergal margin is separated
from the lateral margin by an angle more or less prominent; a slight
curved ridge runs from the umbo to this angle, and this deserves
especial notice, inasmuch as it indicates the outline which the valve
assumed in its earliest growth, and which is permanently retained in
most of the older fossil species. Along the occludent margin, there is a
trace of a ledge, developed in a variable degree, and which is noticed
only on account of the plainly visible ledge along this same margin, in
the allied genus Oxynaspis. The umbo, or centre of calcification, is
seated close to the occludent margin, and at about one fourth of the
length of the valve from the apex. Internally, (fig. 15, _a´_, Pl. V,)
the part above the umbo is flat; and beneath this upper part, there is a
large rounded hollow (_d_) for the adductor muscle: a fold or
indentation (_a_) running downwards from the umbo, extends in a very
oblique line across the occludent margin. This fold is of high interest
as giving lodgment to the Complemental Males, and will hereafter often
be referred to.

_Terga_, triangular, flat; occludent margin, very slightly arched.

_Carina_ much bent, with the umbo placed at barely one third of the
entire length of the valve from the apex. Two very slight ridges can be
perceived, one on each side, running from the umbo to the basal margin,
and separating the roof from the parietes of the valve; these ridges are
of great use in distinguishing the fossil carinæ of Scalpellum, from the
carinæ of Pollicipes. The part above the umbo is formed by the upward
production of a marginal slip along each side of the valve, which slips
in the fossil species (C in the woodcut, fig. 1, given in the
Introduction,) I have designated as the intra-parietes. The lower part
of the valve gradually widens from the umbo downwards; internally, the
whole is deeply concave, and continuously curved. The angle varies at
which the upper and lower portions externally meet each other; but is
never less than 135°. The upper part of the carina runs up between the
terga for three-quarters of their length; the basal margin does not
extend down low enough to pass between the carinal latera.

_Rostrum_, (fig. 15 _b´_, seen externally, and highly magnified,)
minute, almost hidden by the enveloping membrane and by the small
prominent umbones of the rostral latera; in area equalling about one
fourth of the rostral latera; externally pyramidal, with the upper side
rather longer than the lower; internally slightly concave, square, with
the upper margin and sometimes with the lower margin, slightly hollowed
out. Umbo of growth nearly central.

_Upper Latera_, flat, irregularly oval, with an almost rectangular
shoulder under the basal angle of the terga; in area, about one third
larger than the largest valve of the lower whorl; the exact degree of
elongation of the oval figure varies a little. Umbo seated a little
above the central point.

_Lower Whorl_,--_Rostral Latera_, nearly twice as long as broad, lying
under the basal margins of the scuta: umbo seated over the rostrum;
opposite end, towards which the valve widens either sensibly or but
little, is either square or rounded; in area, less than any of the other
valves, excepting the rostrum; in breadth, equalling either half or one
third of the height of the infra-median latera; growth, directed chiefly
towards the infra-median latera. The freely-projecting umbo is about one
sixth part of the entire length of the valve.

_Infra-median Latera_, rather larger than the carinal latera; their
shape varies from elongated pentagonal with the angles rounded, to oval,
with the longer axis directed upwards. The umbo is seated a little above
the middle of the basal margin, so that there is some little growth
downwards, but the main growth is upwards. The upper point generally
stands a little above that of the carinal latera.

_Carinal Latera_, flat, less in area than the infra-median latera; basal
margin nearly straight; carinal margin slightly hollowed out, terminal
margin arched and protuberant. The umbones of the two valves almost
touch each other under the middle of the carina; main growth towards the
infra-median latera and upwards; umbones projecting not above one fifth
of the entire length of the valve.

_Peduncle_, much flattened, rarely as long as the capitulum, with the
upper end nearly as wide as it; the lower end is either blunt, or tapers
to a very fine point. The calcareous scales are transversely elongated,
and are about four times as wide as high; their internal surfaces are
slightly concave, and their external, convex; the two ends are pointed.
Viewed internally, the scales approach in shape to rhomboids. There are,
in a medium-sized specimen, about twenty scales in each whorl, their
tips overlapping each other: the whorls are placed not very near each
other and at rather unequal distances, except round the uppermost part,
where, being in process of formation, they are packed closely together.
The membrane uniting the scales, supports numerous transverse rows of
articulated spines, varying from 1/100th to 1/500th of an inch in
length, and each furnished with a long sinuous tubulus, 1/10,000th of an
inch in diameter, running through the membrane to the underlying corium.

_Attachment._--Specimens are attached to various horny corallines, and
occasionally to the peduncles of each other.[51] In both cases,
supposing the coralline to be erect, the capitulum is placed upwards,
with its orifice towards the branch to which it is attached, and
consequently with its carina outwards. Where several are crowded in a
group, their peduncles often become twisted and their positions
irregular, with their orifices facing in any direction. This uniform
position is simply the consequence of the larva attaching itself
head-downwards, and from the position of the prehensile antennæ,
necessarily with its sternal surface parallel and close to the branch of
the coralline; hence the dorsal surface, which afterwards is converted
into the carina, faces outwards. The peduncle, as already stated, often
tapers, at its basal extremity, to a sharp point. In very young
specimens, for instance in one with a capitulum only 1/20th of an inch
in length, the method of attachment is the same as in Lepas and many
other genera, namely, by cement proceeding exclusively from the antennæ
of the larva; but in older and full-grown specimens, instead of the
whole bottom of the peduncle becoming flattened and broadly attached,
which would be here impossible, the cement is poured out through a
straight row of orifices along the rostral edge, thus causing, by an
excellent adaptation, a narrow margin to adhere firmly to the thin and
cylindrical branches of the coralline. These orifices are represented,
magnified seven times, in Pl. IX, fig. 7, in which the lower attached
portion of the peduncle is split open and exhibited; they are circular,
and stand at regular intervals, in a straight line; the higher orifices
are larger, but further apart from each other than the lower ones; in
one full-grown specimen, I counted ten of these orifices in a length of
exactly a quarter of an inch. At each period of growth, the corium
recedes a little from the attached portion of the peduncle; of which
portion, the greater part is thus left empty and as incapable of further
growth, as are the larval antennæ at the extreme point: in the specimen
figured, the corium extended a little below the upper orifice. The
prehensile antennæ, however, I must remark, do not strictly rise from
the extreme point of the peduncle, but at a little distance from it, on
the rostral surface; this simply ensues from the antennæ in the larva,
being situated on the sternal surface, close to, but not actually on the
front of the head. The two cement glands are seated high up on the sides
of the peduncle, and remote from each other; they are small, unusually
globular and transparent. The two cement-ducts (fig. 7 _a_ _a_)
proceeding from them, are 3/2000ths of an inch in diameter, and run in a
zig-zag line; at the point where they pass through the corium to enter
the lower attached portion of the peduncle, they become closely
approximated, and partially imbedded in the membrane of the peduncle.
Together they run along the rostral edge, giving out through each
orifice a little disc of brownish cement, and finally they enter the
larval antennæ. The peduncle, just above the attached portion, where
still lined by corium, no doubt increases in diameter at each period of
growth, and must, I presume, become pressed against the almost parallel
branch of the coralline. The corium, at this same period, shrinks, or is
absorbed, and the two cement-ducts come in contact with, and adhere to,
the inner surface of the outer membrane of the peduncle; and then, by a
process which I do not understand in this or any other Cirripede,
apertures are formed both in the ducts and through the membrane, so that
the cement passes through, firmly fastening the outer surface of the
peduncle with its calcareous scales and spines, to the coralline.

   [51] Mr. Peach, (Transact. Brit. Assoc., 1845, p. 65,) states
   that this is sometimes the case in Cornwall; and I have seen a
   similar instance in a fine group from Naples.

The structure of the larval prehensile antennæ will be most conveniently
described when we come to the Complemental male; and figures (10-12, Pl.
V) will be given.

_Size and Colours._--Montagu states ('Test. Brit.,' p. 18) that British
specimens rarely have a capitulum .62 of an inch in length; I have,
however, seen an Irish specimen, .7 long; and several specimens, from
the Bay of Naples, .8 long, and including the peduncle, 1.3 in length.
The valves in all the specimens are white, and the membrane connecting
them either nearly white, or dirty pale yellowish, or purplish-brown.
Within the sack the corium under the valves is tinted pale purple, and
two very faint bands of the same colour can generally be distinguished
running down the two sides of the peduncle. Body, coloured
yellowish-white, with the upper segments of the pedicels of the cirri,
tinted in front with purple.

_Body_, much flattened, the prosoma is very little developed; the mouth
placed far from the adductor muscle, and is directed in a remarkable
manner towards the ventral surface of the thorax: the first pair of
cirri stands far separated from the second pair.

_Mouth._--Labrum with the upper part highly bullate, forming an
overhanging projection equalling the longitudinal axis of the mouth;
basal margin much produced; crest with a row of bead-like teeth.

_Palpi_ rather small, with their external margin straight, and internal
margin oblique: the bristles on the two palpi just meet each other.

_Mandibles_, with five or six teeth, with the second, (or second and
third, when there are six teeth,) smaller than the others; in two
specimens, there were five teeth on one side and six on the other;
inferior angle rather broad and strongly pectinated.

_Maxillæ_ with the edge nearly straight, without any notch, but with the
inferior portion very slightly projecting; there are twelve or thirteen
pairs of unequal spines, of which some of the middle ones are rather
longer than the others, and almost as long as the two upper great
spines.

_Outer Maxillæ._--On the inner margin the bristles are divided into two
separate tufts; exteriorly, near the base, there is a distinct rounded
swelling with bristles. The olfactory orifices are highly protuberant,
approximate, flattened, scarcely tapering towards their upper ends.

_Cirri._--The five posterior pair are elongated, very little curled,
with short pedicels; their segments are long, not at all protuberant in
front, bearing five or six pairs of long, slightly serrated spines, with
a very minute tuft of bristles between each pair, and with some short
lateral spines on the inner side of each segment; on the fourth pair of
cirri, these lateral spines are considerably developed; dorsal tufts
consist of fine spines, with one much longer than the others. _First
pair_ short, separated by a wide interval from the second; rami unequal
in length, by between two and four segments; longer ramus having nine
segments, scarcely half as long as the rami of the second cirrus;
shorter ramus with seven segments; in the same individual there were
twenty segments in the sixth cirrus. The segments in the shorter ramus
of the first cirrus are oblong in a transverse direction, and may be
compared to a set of shields placed transversely and strung together; in
the longer ramus the segments are longitudinally oblong; in both they
are thickly covered with spines. _Second cirrus_; the anterior ramus is
a little broader than the posterior ramus, with the segments bearing
about five rows of bristles; fifteen segments in the shorter ramus.
_Third pair_, with the two rami equal in thickness, and with the
segments differing very little from those of the posterior cirri,
excepting that the serrated spines in the external lateral rows are
rather larger. The fourth pair is remarkable by having, on the inner
side of the upper edge of each segment, a little tuft of minute smooth
spines, flattened, and a little enlarged near their ends, so as to be
spear-shaped; I could not see these singular spines on the other cirri.
The lower segments of the pedicels of all the cirri, excepting the sixth
pair, are remarkable from having their inner edges, in the middle,
produced into a considerable, abrupt, rounded projection, irregularly
covered with spines.

_Caudal Appendages_, (Pl. X, fig. 21,) very small, flattened, of nearly
the same width throughout; in a medium-sized specimen, only 1/100th of
an inch in length; each bears from ten to twenty small bristles placed
distantly from each other, of which those on the rounded apex are the
longest.

_Generative System._--The penis is remarkably acuminated; the vesiculæ
seminales are unusually small, and enter only for a short distance into
the prosoma; the testes are large. The ovarian tubes are of large
diameter; the ova are nearly spherical and large, namely, 9/400ths of an
inch in diameter; they are not numerous, and lie in single layers in the
two lamellæ. The ovigerous fræna are well developed, and lie under the
scuta; one I measured was 5/100ths of an inch in length and 2/100ths in
width; the margin is obliquely truncated and slightly sinuous. This
species breeds late in the autumn, and even in mid-winter; I have
examined a specimen from Cornwall with ova containing larvæ, taken on
the 26th of October; again, in another specimen from Belfast, sent to me
by Mr. Thompson, taken in January, there were ova in the lamellæ, and
therefore no doubt impregnated; and on February the 12th I received from
Mr. Peach, from Cornwall, specimens so very young that they must have
become attached during the first days of the month.

_Varieties._--The specimens from near Naples, (which I owe to the
kindness of the Rev. F. W. Hope,) are somewhat larger, and differ
slightly from those of Britain: they form, I imagine, the _S. Siciliæ_
of Chenu. After carefully examining them internally and externally, I
think it is quite impossible to consider them specifically distinct, for
although in several specimens, the valves were placed a little further
apart from each other,--the upper latera a little more elongated,--the
carinal latera rather narrower in their upper half,--the infra-median
latera rather more rounded,--and, lastly, in the scuta, the tergal
margin extended almost in the same line with the lateral margin;
nevertheless in other specimens, I could perceive no difference
whatever. It is, however, remarkable that in several full-grown
Neapolitan specimens there were no Complemental males, whereas I have
never seen a single full-grown British specimen without such being
present. In some specimens in the British Museum, without any given
locality, I have observed considerable variation in the breadth of the
carinal and rostral latera.


COMPLEMENTAL MALE. Pl. V, figs. 9-14.

When first dissecting _Scalpellum vulgare_, I was surprised at the
almost constant presence of one or more very minute parasites, on the
margins of both scuta, close to the umbones: these are represented, but
rendered darker and therefore more conspicuous than in nature, in the
drawing, Pl. V, fig. 15, which is three times the natural size. I
carelessly dissected one or two specimens, and concluded that they
belonged to some new class or order amongst the Articulata; but did not
at that time even conjecture, that they were Cirripedes. Many months
afterwards, when I had seen in Ibla, that an hermaphrodite could have a
complemental male, I remembered that I had been surprised at the small
size of the vesiculæ seminales in the hermaphrodite _S. vulgare_, so
that I resolved to look with care at these parasites; on doing so, I
soon discovered that they were Cirripedes, for I found that they adhered
by cement, and were furnished with prehensile antennæ, which latter, I
observed with astonishment, agreed in every minute character, and in
size, with those of _S. vulgare_: the importance of this agreement will
not at present be fully appreciated. I also found, that these parasites
were destitute of a mouth and stomach; that consequently they were
short-lived, but that they reached maturity; and that all were males.
Subsequently the five other species of the genus Scalpellum were found
to present more or less closely analogous phenomena. These facts,
together with those given under Ibla (and had it not been for this
latter genus, I never probably should have even struck on the right
track in my investigation,) appear sufficient to justify me, in
provisionally considering the truly wonderful parasites of the several
species of Scalpellum, as Males and Complemental Males. When these
parasites are fully described, will be the proper time to discuss and
weigh the evidence on their sexual relations and nature. I will now
describe the parasite of _S. vulgare_.

_General Appearance._--Shape, flask-like, compressed (Pl. V, fig. 9,
magnified 36 times), with a short neck: the outline is usually
symmetrical, but sometimes is a little distorted on the under side. The
creature is imbedded more than half its length or depth in the
transparent, spine-bearing chitine border of the scutum of the
hermaphrodite. Its length, or longer axis, varies from 10 to 11/400ths;
its breadth, or transverse axis, is 6 to 7/400ths; and its thickness,
for it is much flattened, is only 4/400ths of an inch. On the summit,
there is a fimbriated orifice (_a_), the size of which can rarely be
made out quite distinctly, owing to the extreme thinness of the
membranous edges. A little way beneath the orifice, there are four
little blunt, bristly points (_b_), generally rather more than the
1/1000th of an inch in length; they are rather variable in size, and
seem to be of no functional importance; directly beneath them, there
are four little calcareous beads (as may be known by their dissolving
with effervescence in any acid, and breaking easily under the needle);
these are the 3/2000ths of an inch in their larger external diameter;
they are rather deeply imbedded in the outer integument, and taper a
little downwards ending in a concave terminal point, into which a minute
tubulus enters, like those passing into and through the valves of
ordinary Cirripedia: along the axis of imbedment, they are often
4/2000ths of an inch in length. These calcareous beads or rudimental
valves are seated in pairs, at the two ends of the flattened animal, so
that when the animal is laid on one side, the upper bead in each pair
exactly covers and hides the lower one. The outer integument is composed
of chitine, as may be inferred from boiling caustic potash having no
effect on it; the upper part is thicker than the imbedded portion and is
wrinkled transversely; it is covered with minute spines 4/10,000ths of
an inch in length, either single or in groups of two and three, (Pl. V,
fig. 14.) This outer tunic is lined by corium, sometimes slightly
mottled with dull purple; and this by delicate, longitudinal, striæ-less
muscles, running from the base up to the under edge of the orifice;
these longitudinal muscles are crossed, at least, in the upper part, by
still finer transverse muscles.

_Thorax and Abdomen._--When the external integument is cut open, the
thorax (Pl. V, fig. 13) is found lodged within an inner sack or rather
tube, extending from near the bottom of the animal, up to the external
orifice. The whole thorax is sometimes forced through the orifice, owing
perhaps to the action of the spirits of wine and consequent endosmose,
and is thus well displayed without dissection. The thorax tapers a
little, is much flattened and straight; its length, together with the
terminal abdominal lobe, is about 6/400ths of an inch; it is formed of
very thin, most finely hirsute membrane, transversely wrinkled and so
extensible, that when everted by the internal muscles being seized, it
stretches to twice its former length; in this condition, five transverse
articulations are displayed. The abdominal lobe is smooth, and cannot
be stretched, or turned inside out by pulling the above muscles. On the
thorax, corresponding with the interspaces between the five transverse
articulations, there are four pair of short limbs, but their bases, I
believe, are prolonged across the inner or ventral surface of the
thorax, so as almost to touch each other. These limbs, I believe, have
no articulations, except, perhaps, where united to the thorax. The
anterior or lowest limb, on each side, supports two or sometimes only a
single spine; this pair is rather smaller than the second, and is placed
a little more distant from it, than are the upper pairs from each other.
The second pair differs from the upper two, only in having its three
spines a very little shorter. The two upper or posterior pair exactly
resemble each other; each has two spines on the summit, and a third
seated lower down, on a little notch on the outer side, but with its
point on a level with the others. The points of the spines of the two
upper limbs, stand on a level with the external spines at the end of the
abdomen. All the spines are of excessive tenuity and sharpness; they are
straight, long, and not plumose.

The abdominal lobe is square, and from not being wrinkled, has a
different appearance from the thorax: on each of the posterior angles,
there are three moderately long, very sharp spines, with the tips of the
outer pair bent a little inwards; in the middle between them, there are
two little spines, and a little below and outside these latter, on the
ventral surface, there are two other longer spines with their tips bent
inwards; and again, lower down, two other pair, one beneath the other,
of short spines. Perhaps, the three pair of spines on the ventral
surface, mark the three segments, which are distinct on the abdomen of
the larva in the last stage of its development, in Lepas and other
genera. In the same way, it is probable that the lateral spine on the
notch in each limb, marks the point where, in the larva, there is an
articulation. Altogether, there are seven pairs of spines on the
abdomen, and eleven pairs on the thoracic limbs.

A little way beneath the lower or anterior pair of limbs, the thorax is
abruptly bent, and becomes confluent with the lower internal parts of
the whole animal. Here, the very delicate membrane of chitine which
lines the sack or tube, extending from the external orifice, can be seen
to be continuous, as in all Cirripedes, with the outer tunic of the
thorax. Within the thorax, there are some longitudinal muscles, without
transverse striæ, which, I believe, enter the short limbs, but not the
abdomen, as I infer from the latter not being everted when they are
pulled. At their lower ends these muscles terminate abruptly, and from
being contracted are often a little enlarged. They extend a short way
beneath the lower pair of limbs, and are, I suspect, attached to the
outer integument of the animal, near the base.

After the most careful dissection of very many specimens, and their
examination in many different methods (as by caustic potash, &c.), I can
venture positively to assert that there is no vestige of a mouth, or
masticatory organs, or stomach: I did not see any anus, but I will not
affirm that such does not exist.

In the upper part of the animal, lying under the superficial muscles,
and close beneath the upper line of their attachment, I found in all the
specimens, an eye, of a pointed oval form, rather less than 11/12,000ths
of an inch in diameter, formed of an outer capsule, lined with purple
pigment-cells, and surrounding, as it appeared, a lens. The eye is not
introduced in fig. 9, for I could not see it, except by dissection, and
therefore do not know its exact relative position.

_Generative System._--The contents of the animal, between the sack
containing the thorax and the outer integuments, and directly under the
thorax, varied much in condition: in young and lately attached specimens
the whole consisted of a pulpy mass with numerous oil-globules; in other
specimens, apparently more mature, there were vast numbers of cells,
sometimes cohering in sheets, about 3/10,000ths of an inch in diameter,
and having darkish granular centres; these I believe to be the testes,
for in a specimen presently to be mentioned, in which the vesicula
seminalis was gorged with spermatozoa, I found adhering to its outside,
a mass of cells of exactly the same diameter, but now empty and
transparent instead of having brownish centres. Lastly, in several other
specimens, at the very bottom of the sack-formed animal, there was a
brownish, pear-shaped bag, of different sizes in different individuals,
and occasionally broader even than the thorax. This bag contained either
pulpy matter, or a great mass of spermatozoa. Before being disturbed,
these spermatozoa lay parallel to each other in flocks, and they yielded
to the needle in a peculiar manner, so that I found (having had
experience with these bodies in living Cirripedia) I could almost tell
before examination under the compound microscope, whether or not I
should see spermatozoa. Many had distinct heads,[52] which were two or
three times as broad as the filamentary bodies; the latter when placed
between glass were the 1/20,000th of an inch in diameter. I compared
these spermatozoa with others taken out of the vesiculæ seminales of the
individual hermaphrodite _S. vulgare_, to which the parasite was
attached, and could not perceive the slightest difference in them. The
brownish pear-shaped bag, or vesicula seminalis, the coat of which seems
fibrous, could sometimes be distinctly traced, sending a chord or
prolongation far up the thorax: at the end of the abdominal lobe, no
doubt there is an orifice; and this, I believe, I once distinguished.
Owing to this chord, the bag often adheres to the thorax, when the
latter is dissected out of the general integuments; in this condition, I
twice clearly made out that it was single: in one other specimen,
however, there appeared to be two small vesiculæ seminales. By using a
condenser and very brilliant light, the outline of the vesicula
seminalis could sometimes be distinguished before dissection, at the
bottom of the sack-formed animal; and such was the case in the specimen
drawn in fig. 9.

   [52] I do not understand the development of the spermatozoa in
   Cirripedia: in a recent Chthamalus and Balanus, I found the
   greater number had a little filament in front of the head or
   nodular enlargement, which latter varied in size and in shape
   from globular to that of a spindle. The filament before the head,
   also, varied in proportional length; it did not project in
   exactly the same straight line with the hinder part, and some of
   the spermatozoa were entirely without this filament in
   front;--such is the case with the spermatozoa here described.

Although I have dissected, at least, thirty specimens, taken at
different times of the year, and from different localities, and when
many of the specimens were mature and ready for the impregnation of ova,
as clearly shown by the presence of innumerable spermatozoa, I have
never seen even a trace of an ovum or ovaria.

_Antennæ and Attachment._--The prehensile antennæ (Pl. V, fig. 10), are
seated a little above the very base of the sack-like animal; and this
might have been expected from the antennæ in the larva, being seated on
the ventral surface, not at the very extremity of the head. By a very
strong light, they can sometimes just be seen whilst the parasite is
attached to the hermaphrodite (the scutum of the latter having been
cleaned on the under side), and are thus represented in fig. 9. They are
formed of thicker membrane than the general integument of the body: the
second segment, or disc, is pointed and hoof-like; when seen in profile
(fig. 11), the upper convex surface has a uniform slope with the upper
surface of the basal segment; it is furnished with a single backward
pointing spine, attached, I believe, on the under side, nearly opposite
the articulation of the ultimate segment: at the apex, there are some
excessively minute hairs or down. The ultimate segment projects
rectangularly outwards as usual, and has on its inner side, rather
beneath the middle, a conspicuous notch (fig. 12), which bears two or
three long, non-plumose spines; on the summit there are three or four
rather shorter spines. On the outside of the great basal segment there
is a single spine curving backwards. The importance of the following
measurements (in fractions of an inch) will hereafter be seen.

  Length of whole organ, from end of disc to the further   }
  margin of the oblique basal articulation                 } 38-39/6000

  Length of whole organ, to the inner margin of the oblique}
  basal articulation                                       } 1/6000

  Breadth of basal segment, measured half-way between the  }
  basal and second articulations,--the limb being viewed   }
  from vertically above                                    } 8/6000

  Length of hoof-like disc, measured from the apex to the  }
  middle of the articulation with the basal segment        } 9-10/6000

  Breadth of ditto                                           5/6000

  Length of ultimate segment                                 6/6000

  Breadth of ultimate segment beneath the notch              7/20000

  Breadth of ultimate segment above the notch                5/20000

I did not see the cement-ducts, which, perhaps, was owing to the corium
extending from the inside of the whole animal some way into the antennæ,
thus rendering them rather less transparent than in common Cirripedes.
That the ducts and cement-glands exist, is certain, for the antennæ in
every case were enveloped in a little irregular mass or capsule of the
usual, brown, transparent, laminated cement. When several of these
parasites were attached close together, the cement ran up between them.

I may here state, that I found on one Scalpellum, three males very
lately attached, and not as yet imbedded in the chitine border; they
were white, opaque, pulpy, and full of oily globules; the lower part was
considerably more pointed, and extended further beyond the prehensile
antennæ, than in the older and imbedded specimens. There were distinct
remnants of two great reddish-brown eyes, showing that in this respect
the larvæ of the male in their last stage of development, are
characterised like the larvæ of other Lepadidæ. The male larva would,
probably, be a little larger than the male itself; but yet compared with
the larva in the earliest stage, there can have been unusually little
increase of size during the several intermediate metamorphoses; I judge
of this from the dimensions of the larva of the hermaphrodite in the
first stage, namely, 9/400ths of an inch, exactly the size of some of
the smaller males. In the allied genus Ibla, the increase is also less
than is usual, namely, from 15/1000ths of an inch, the diameter of the
ovum, to only 25/1000ths of an inch, the length of the boat-shaped
larva, just before its final metamorphosis.

_Habits and Concluding Remarks._--The males are imbedded in the spinose
chitine border of the occludent margin of the scuta, exactly over an
oblique fold or notch (fig. 15 _á_ _a_), close by the umbo. This fold
has no direct relation to the males, but being present is taken
advantage of by them; for it occurs in the young hermaphrodite, before
the attachment of the males, and in species of the genus in which the
males are attached to other parts. It occurs, also, in fossil species of
Pollicipes, and in these it seems caused by the upper inner part of the
valve being rendered more and more prominent during growth: in the
present species, I suspect, its origin is connected with the formation
of a ridge bounding the outer side of the pit for the adductor scutorum
muscle: we shall see in the next species, that this fold is of the
highest importance in relation to the position of the Males. The
transparent chitine border of the scuta is broad, and fills up the fold
in the shell, so that the outline of the occludent margin is not
affected by it: in the drawing (fig. 9) some of the inner layers of
chitine (_e_ _e_), which dipped into and filled up the fold, have been
removed, that the lower part of the animal might be more plainly
exhibited. The chitine bears numerous spines of various lengths, which
must afford some protection to the males, rudely arranged in lines,
parallel to the edge of the valve, indicating the successively-formed
layers of chitine; each spine has a fine, tortuous tubulus connecting
its base with the underlying corium. The extreme outer edge of the
border is thin, forming a kind of lip, close beneath which the delicate
tunic lining the sack is attached. During continued growth, the valve is
added to in thickness, and so is the chitine border, and likewise in
breadth. It appears that the larva of the male must attach itself on the
under side of this border, on the edge of the tunic of the sack, and
that by the action of the cement, the corium beneath is killed (as I
believe always is the case with other parasitic Cirripedia), whereas on
both sides, the chitine continues to be added to, so that the male,
excepting the upper and always projecting portion, becomes imbedded at
first laterally, and ultimately all round: I have seen specimens in
several different stages of imbedment. Hence, in old specimens, with a
thick and broad chitine border, it might and does come to pass that one
male is imbedded (the valve being laid flat) directly beneath another.

I have examined a great number of specimens from various localities,
taken at different times of the year,--some dozen specimens from
Cornwall,[53] and several from unknown localities in various
collections; some from Ireland, from the Shetland Islands, from Norway,
and from near Naples. Every one of these specimens, with the exception
of some of the Neapolitan ones, had parasitic males attached to them: I
must also except very young specimens, on which they never occur. On a
Cornish specimen, with a capitulum a little more than one fifth of an
inch in length, it may be mentioned as unusual that there were three
males. In young specimens there is generally one male on each scutum,
but sometimes there are two, and sometimes none on one side. In large
old Cornish specimens I have counted on the two sides together, six,
seven, and eight males, and in one Irish specimen no less than ten,
seven all close together on one valve and three on the other, but I do
not suppose that all these were alive at the same time. In the
Neapolitan specimens, however, which are the largest that I have seen,
there was in no case more than two; and out of seven or eight
specimens, four had not any male; so that it would appear there is
something in this locality hostile to the development of the parasitic
males. I have noticed only one instance (that given in fig. 9) in which
the males were imbedded a little way apart; generally they touch each
other, and are cemented together: where there are several males, they
occur at different levels, as measured from the under or upper surface
of the chitine border: in one instance of four males adhering to one
valve, I distinctly perceived that the lowest one was white, pulpy, and
recently attached; the two above, which were placed close together and
between the same laminæ of chitine, were mature; and the third still
higher up, was dead, empty, transparent, and half decayed: in some other
instances, I have found the uppermost parasites dead, and, together with
the surrounding chitine, partially worn away.

   [53] I am greatly indebted to Mr. Peach for his unwearied
   kindness in procuring me fresh specimens. Mr. W. Thompson allowed
   me to dissect one, possessing particular interest, out of his
   three Irish specimens. Professor Forbes procured me a specimen
   from the Shetland Islands, and Professor Steenstrup was so kind
   to take pains to send me some Scandinavian specimens.

The larva of the male must have a different instinct from the larva of
the hermaphrodite; for the latter attaches itself head downwards to a
coralline, whilst the male larva crawling on the scuta of the
hermaphrodite, discovers, I presume by eye-sight, the fold in the shell
beneath the translucent border of chitine, and there invariably attaches
itself. Its object in choosing this particular spot, I believe, simply
is that the depth or thickness of the chitine is there greater, and
sufficient for its imbedment, which would hardly be the case elsewhere.
This parasite has, as we have seen, no mouth or stomach, and indeed,
considering its fixed position and the non-prehensile condition of its
limbs or cirri, a mouth would have been of no service to it, without it
had been extraordinarily elongated. The male must live on the
nourishment acquired during its locomotive larval condition; and its
life no doubt is short, but yet not very short, as I infer from the
depth to which mature specimens are buried in the chitine border. The
full development of the spermatozoa consumes, I suppose, some
considerable lapse of time. The thorax and limbs, though furnished with
muscles, are obviously, as already remarked, of no use for prehension;
these parts serve, probably, to defend the little creature, when its eye
announces the passing shadow of some enemy, and for this purpose they
are well adapted from the extreme sharpness of the spines. The thorax,
into which I traced the vesicula seminalis, no doubt also serves for the
emission and first direction of the spermatozoa; and hence, perhaps, its
singularly extensible structure. I have already remarked, that in
specimens preserved in spirits, the thorax is often largely protruded,
and bent down at right angles to the orifice. I presume this is caused
by endosmose; nevertheless it deserves notice, that it was in these
protruded specimens that the vesicula seminalis was most conspicuously
gorged with spermatozoa. I suspect the longitudinal and transverse
muscles lining the upper part of the outer integuments of the whole
animal, can be of little use to the creature, without it be to aid in
the protrusion of the thorax, and perhaps in the violent expulsion of
the spermatozoa, thus causing them to reach the ovigerous lamellæ within
the sack of the hermaphrodite. It is also probable, that the action of
the cirri of the hermaphrodite, would tend to draw inwards the
spermatozoa in the right direction. In one specimen, the spermatozoa in
the hermaphrodite and in the male were mature at the same time; in
another this was not the case; and as the males, apparently, become
attached at all periods of the year, this want of coincidence in
maturity must often occur. Can the males retain their spermatozoa, till
told by some instinct, that the ova in the sack of the often fecundated
hermaphrodite are ready for impregnation; or are the spermatozoa
sometimes wasted, as must annually happen with such incalculable
quantities of the pollen of many dioecious plants?

This little Cirripede is, in many respects, in a partially embryonic
condition. There is no separation between the capitulum and peduncle;
there is no mouth; and the thorax, throughout its whole width, opens
into the anterior part of the animal: the limbs differ greatly from
those both of the mature Cirripede and of the larva, but come closest to
the latter: the preservation of the abdomen is a well-marked embryonic
character. On the other hand, the four rudimentary calcareous valves,
the narrow orifice, the hirsute outer integument, the two muscular
layers, the single eye, and male internal organs, are all characteristic
of the fully-developed condition. The four little valves, as I believe,
represent the scuta and terga, though they are placed considerably below
the orifice: the little bristly points have no homological
signification, and are absent in the male of the following closely
allied species. The four pairs of limbs answer to the four posterior
cirri, as may be inferred from their proximity to the abdominal lobe,
and from the three posterior pairs closely resembling each other, and
differing a little from the first pair; this latter pair corresponds
with the third pair in the hermaphrodite form of Scalpellum. If I am
right in believing that only a single vesicula seminalis is ordinarily
developed in the male, this is a special and singular character.

As stated in the beginning of this description, from the one great fact
of the absolute correspondence of the prehensile antennæ of the
parasite, with those of the hermaphrodite _Scalpellum vulgare_, together
with its fixed condition, its short existence, and exclusively male sex,
I have thought myself justified in provisionally considering it as the
Complemental Male of the Cirripede to which it is attached; but I hope
final judgment will not be passed on this view, until the whole case is
summed up at the end of the genus.[54]

   [54] I trust, before long, that some naturalist, with more skill
   than I possess, will examine these parasites on _Scalpellum
   vulgare_, which unfortunately is the only species of the genus
   that can be easily obtained. Fresh specimens, or those preserved
   in spirits of wine, are necessary. The action of boiling caustic
   potash is very useful in cleaning the prehensile antennæ. If
   these latter organs are sought in the hermaphrodite for the sake
   of comparison, young specimens, adhering to clean branches of a
   coralline, should be procured, and caustic potash used.


2. SCALPELLUM ORNATUM. Pl. VI, fig 1.

  THALIELLA ORNATA. _J. E. Gray._ Proc. Zoolog. Soc., 1848, p. 44,
        Annulosa, Plate.

_S. (Foem.) valvis 14, sub-rufis: lateribus superioribus
quadranti-formibus, arcu crenâ profundâ notato._

(Fem.) Capitulum with 14 reddish valves: upper latera quadrant-shaped,
with the arched side deeply notched.

Mandibles with three teeth; maxillæ narrow, bearing only four or five
pair of spines.

MALES, two, lodged in cavities on the under sides of the scuta;
pouch-formed, with four unequal, rudimentary valves: no mouth: cirri not
prehensile.

    Algoa Bay, South Africa. Attached to Sertularia and Plumularia.
    British Museum.[55]

   [55] I am greatly indebted to Mr. Bowerbank for specimens of this
   extremely interesting species; also to Mr. Morris, to whom Mr.
   Bowerbank had given some of the original specimens.


FEMALE.

_Capitulum_ oblong, with the upper portion much produced; valves, 14,
thick, naked, closely locked together, irregularly clouded with pale
crimson; the membrane connecting the valves is not furnished with
spines. On most of the valves there are furrows and ridges diverging
from the umbones, and the lines of growth are plainly marked: in the
valves of the lower whorl, the umbones are slightly protuberant.

_Scuta_, convex, unusually thick, oblong, quadrilateral, with the
occludent margin the longest; lateral margin slightly hollowed out. The
umbo (and primordial valve) is situated at the uppermost point of the
valve, and consequently the growth is exclusively downwards. On the
under side (Pl. VI, figs. 1 _b´_ and 1 _c´_), in about the middle of the
valve, there is a pit (_a_) for the adductor scutorum muscle, the depth
and distinctness of which varies a little; above the pit, and between
it and the apex, there is a transverse, oblong, deeper depression (_b_),
within which, the male is lodged. A small portion of the apex of the
valve projects over the terga.

_Terga_, large, nearly equalling the scuta in area, flat and
sub-triangular; the scutal margin is not quite straight. The apex of the
valve is thick and solid, and must have projected freely for a length
equalling one third of the occludent margin.

_Carina_, laterally broad, angularly bent; slightly widening from the
apex to the base; internally, deeply concave. The position of the umbo
varies, in young specimens it is seated at the uppermost point, and
consequently in such there is no upward growth; in older specimens, from
the junction and upward production of that part on each side of the
valve, which I have called in fossil specimens the intra-parietes, the
valve is added to above the umbo, but to a lesser degree than in _S.
vulgare_. Slight ridges separate the roof from the parietes, and the
parietes from the intra-parietes.

_Rostrum_, minute, narrow, widening a little from the apex downwards,
inserted like a wedge between the umbones of the rostral latera, and
hardly projecting above their upper margins, so as to be easily
overlooked: internally concave.

_Upper Latera_ (fig. 1 _á_), quadrant-shaped, with a deep square notch
cut out of the arched margin, which notch receives the upper point of
the carinal latera; the surface of the valve between the notch and the
umbo is depressed.[56]

_Rostral Latera_, small, gradually widening from the umbo to the
opposite end, which is obliquely rounded.

_Infra-median Latera_, approaching to diamond-shaped, placed obliquely
to the longer axis of the capitulum; or the upper part may be described
as spear-shaped.

   [56] The only valve which I have seen at all like this, is a
   fossil specimen from the Upper Chalk of Scania; this is described
   in my memoir on the Fossil Lepadidæ (Palæontographical Society),
   under the name of _Scalpellum solidulum_ (Tab. 1, fig. 8, _e_,
   _f_), and is perhaps erroneously there considered as a carinal
   latus.

_Carinal Latera_: these appear as if formed of two valves united
together; the upper portion, widening as it ascends in a curved line,
terminates in a rounded margin, which enters the deep notch in the upper
latera; the other and lower portion is shorter, and terminates in a
square margin abutting against the infra-median latera; the umbones of
the carinal latera project beyond the line of the carina.

_Direction of the Lines of Growth in the Valves._--This should always be
carefully observed, on account of the great diversity there is in this
respect between the different species, especially when the recent are
compared with the older fossil species; moreover one of the chief
characters between the genus Scalpellum and Pollicipes, depends on the
direction of the lines of growth. In the scuta, terga, rostrum, and
upper latera of the present species, the chief growth is downwards; in
the carina, in mature specimens, it is both upwards and downwards; in
the carinal latera, both upwards and towards the infra-median latera; in
the infra-median latera chiefly upwards; and, lastly, in the rostral
latera, towards the infra-median latera.

_Peduncle_, short, not half as long as the capitulum; calcareous scales
imbricated as usual, tinged red, almost crescent-shaped, acuminated at
both ends, of remarkable length, so that in each whorl there are only
four scales: a full-sized scale equals in length one of the rostral
latera. The tips of two scales, in one whorl, lie under the middle
points of the carina and rostrum; and in the whorl, both above and
below, a single much curved scale occupies this same medial position.
The peduncle does not seem to have been attached in any definite
position to the horny coralline, as is the case with _S. vulgare_.

Length of capitulum in the largest specimen .2 of an inch.

The _Mouth_ is directed towards the ventral surface of the thorax. The
_Labrum_ is far removed from the adductor muscle, with the upper part
forming an overhanging projection; I believe there are some very minute
bead-like teeth on the crest. _Palpi_, small, narrow, thinly clothed
with bristles.

_Mandibles_, with three teeth, of which the first is distant from the
second; inferior angle not much acuminated, pectinated on both edges.

_Maxillæ_, small, narrow, produced, without any notch, with two large
upper spines, of which one is much thicker than the other; on the convex
upper margin there are some minute tufts of very small hairs.

_Outer Maxillæ_, with few bristles, arranged in a continuous line on the
anterior surface; on the external surface there is a tuft of long
bristles. Olfactory orifices situated laterally, forming two flattened,
tubular projections.

_Cirri._--First pair placed not far from the second; the three posterior
pair not very long, with their segments elongated, not protuberant,
bearing four pair of non-serrated spines, with a single short bristle
between each pair; dorsal tufts small, with one spine longer than the
others. First cirrus rather short, segments not very broad; second
cirrus with the rami nearly equal in length, anterior ramus rather
thicker than the posterior ramus, with three longitudinal rows of
spines.

_Caudal Appendages._--These are minute, rather broad, not half as long
as the lower segments of the pedicels of the sixth cirrus, with four
very long spines at the tip.

_Penis._--There is no trace of a probosciformed penis in the four
specimens examined; and as this organ is present in every ordinary
cirripede, with the exception of _Ibla Cumingii_ which we know to be
exclusively female, so we may infer with some confidence that the form
here described is female, although it is impossible in specimens once
dried to demonstrate the absence of the vesiculæ seminales and testes.

_Affinities._--This is a very distinct species; it is, however, much
more nearly related to _S. rutilum_, than to any other species; and next
to this, to _S. vulgare_; from this latter species it chiefly differs in
the large scales of the peduncle, in the scuta not being added to at
their upper ends, and in the membrane covering and connecting the valves
being spineless; but there is a greater difference in the trophi and in
the cirri. The peduncle of _S. ornatum_ presents some resemblance to
that of the singular cretaceous genus, _Loricula_.


MALE.

All the specimens, as already stated, were dry, but in an excellent
state of preservation, so that after having been soaked in spirits, they
could be minutely examined. In the four which I opened, I found, in a
transverse pouch on the under side of each scutum, a male lodged; in a
fifth dead and bleached specimen, the cavities in the shell for the
reception of the males, were present; and in a sixth young specimen,
also dead, cavities were in process of formation. As compared with
plants, the relation of the sexes in this species may be briefly given,
by saying that it belongs to the class _Diandria monogynia_. I will
first describe the males themselves, and then the cavities in the shell
of the female. The males differ in every point of detail, from the
complemental males of _S. vulgare_, but yet present so close a general
resemblance, that a comparative description will be most convenient.

The general shape of the whole animal is rather more elongated, and I
suspect flatter, but this latter point could not be positively
ascertained in dry specimens. The entire length is greater, being in the
largest specimen 13/400 (instead of at most 11/400), and the width,
7/400 of an inch. The orifice is not fimbriated; the four bristly points
over the calcareous beads are absent. The whole outer integument is much
thinner, owing evidently to its protected position, and is not covered
by little bristles, but with an extremely high power, minute points
arranged in transverse lines can be distinguished. The calcareous beads,
or rudimentary valves, are thin and regularly oval. It is remarkable
that in all the specimens, two on one side were smaller than the two on
the other side,--the smaller beads being 16/6000, and the larger,
22/6000 of an inch in diameter; therefore more than twice the size of
one of the beads in _S. vulgare_, which are only 9/6000 externally in
diameter. From the position of the eye, close to one margin, near the
upper end of the flattened animal, and from the manner in which the
little limbs and spines lay between two of the beads at the opposite
end, it was manifest that these latter, one large and one small,
corresponded with the terga of the other cirripedes, and that the other
two, near the eye, answered to the scuta. The valves being of unequal
sizes on the right and left-hand sides of the animal, is probably
connected with one side being pressed against the hard, shelly valve of
the female; in the same way as the valves in certain Pæcilasmas; are
smaller and flatter on the side nearest to the crustacean to which they
are attached. The eye, in being slightly notched on the upper and lower
edge, shows signs of really consisting of two eyes, which I believe is
always normally the case; it is rather larger, in the proportion of 13
to 11, being 13/12,000 of an inch in diameter, than in _S. vulgare_; and
from the almost perfect transparency of the integuments, is far more
conspicuous than in that species. Hence when the valves of the female
are opened, the black little eye is the first part of the male which
catches the attention. No vestige of a mouth could be discovered.

_Thorax and Abdomen._--The thorax, as in _S. vulgare_, is highly
extensible, and when stretched exhibits the same five transverse folds
or articulations; when contracted, it is broader, so that even the
truncated end of the abdomen is wider than the lower (properly anterior)
end of the thorax in _S. vulgare_. Its thin outer integument is studded
with excessively minute points in transverse rows. The four pair of
limbs are longer than in _S. vulgare_, but the spines on them much
shorter and thicker; each limb (including the first) supports three
spines, of which one is seated on a notch low down on the outside, and
is longer than the other two; of these two, the one on the same side
with the notch, is a little longer than the other. The spines on the
first and second pair of limbs are considerably shorter than those on
the third pair, and these latter, are a little shorter than those on the
fourth or posterior pair. Hence, the spines on the thoracic limbs,
compared with those of _S. vulgare_, present considerable differences,
both in their relative and absolute dimensions. The abdominal lobe is in
proportion rather shorter; its end is less abruptly truncated, and
supports a row of, I believe, six moderately long, and basally thick
spines; these spines are not so long as those surmounting the fourth
pair of limbs. On both lateral margins of the abdomen, rather on the
ventral face, there is a row of, I believe, seven long spines, but it is
very difficult to count the spines in specimens which have been once
dried. I was able to distinguish that the two lower pair of spines on
the ventral surface, are seated a little way one below and within the
other, as in _S. vulgare_. The abdominal spines altogether form quite a
brush, and there are certainly several more than in _S. vulgare_, and
those on the two sides are much longer.

_Antennæ._--The disc is hoof-like, with the upper surface forming a
straight line with the upper edge of the basal segment; the apex is
pointed and clothed with some fine down; there is a single spine
pointing backwards, which rises from the lower flat surface. The
ultimate segment was hidden in laminæ of cement; and I was not able to
make out its structure. There is a single spine on the outer edge of the
basal segment, in the usual position. The entire length of the limb,
measured from the end of the disc to the further margin of the basal
articulation, is 36/6000ths of an inch; measured to the inner margin, it
is; 21/6000ths of an inch; the disc itself is 12/6000ths of an inch
long; these measurements differ a little both absolutely ad
proportionally, compared with those of the antennæ of _S. vulgare_.

_Cavities in the Scuta of the Female for the reception of the
Males._--These extend nearly parallel to the tergal margin, transversely
across the valves, for three fourths of their width; they are seated
above the depression for the adductor muscle, and are more conspicuous
than it; they are deep and well defined, and each exactly contains one
male. The males are placed with their orifices in a little notch in the
occludent margin, and their prehensile antennæ at the further end. The
distance to which the cavities extend across the valve, and their
distance from the upper or tergal margin, varies a little, but chiefly
in accordance with the age of the specimens; for the valve continues to
increase in width, whilst the size of the cavity remains the same. The
occludent margin of the scutum in the largest female, was .1 of an inch
in length; of another, in which there was a fully developed cavity,
.084; of a third, in which there was no cavity, only a slight concavity,
with a preparatory impression, the length of the occludent margin was
.062. The larger and smaller of these three valves, are drawn of their
proper proportional sizes, in Pl. VI, figs. 1 _b´_, 1 _c´_. The
preparatory impression (fig. 1 _c´_, _b_), consists of a narrow, not
quite straight, extremely slight furrow, of slightly irregular width,
bordered on each side by a very minute ridge, which is distinctly
continuous with the inner edge of the occludent margin, both above and
below the cavity. The furrow appears to have been formed by calcareous
matter not having been deposited along this line, during the thickening
or growth of the internal surface of the valve: I suspect, that it
originates at a single period of growth, for I could see no signs of
successively-formed transverse lines. I believe that it is strictly
homologous with the fold, over which the complemental male is attached
in _S. vulgare_, but carried, for a special purpose, much further across
the valve and rectangularly inwards, for in structure and position both
are identical. In comparing the internal views of the scuta in _S.
vulgare_ and _S. ornatum_ (Pl. V, fig. 15 _a´_, and Pl. VI, fig. 1
_c´_), it must be borne in mind, that the latter should be compared, as
clearly shown by the lines of growth, with that portion alone of the
scutum in _S. vulgare_, which lies under the curved ridge connecting the
umbo and tergo-lateral angle. The deep cavity in which the male is
lodged, is formed subsequently to the preparatory furrow, simply by the
gradual thickening of the surrounding surface of the valve, more
especially of a ridge just above the pit for the adductor muscle, and of
another broad ridge just beneath the tergal margin. The deepest part of
the cavity lies parallel to the tergal margin along the upper side, and
here, in the older valves, the preparatory furrow can by care be
distinctly traced. In conformity with the shape of the cavity, the
orifice or notch in the occludent margin of the scutum, is situated at
the point where the preparatory furrow sweeps round and enters. I
believe that the cavity is lined by membrane, and that between the
cavity and the body of the female, there is a complex membranous
layer,--a pouch or bag being thus formed. An imaginary section of this
pouch (with the thickness of all the parts extremely exaggerated and in
a reversed position) is given in Pl. VI, fig. 1 _d´_: _a_ is the shell;
_x_ the cavity, converted, as I believe, into a pouch by, firstly, the
delicate tunic (_c_) lining the sack of the female; secondly, a double
layer (_d_) of corium; and, thirdly, by a special, rather thick
membranous layer (_b_), which thinning out round the cavity coats only
part of the under surface of the scutum. This latter membrane I have not
seen in any other Cirripede, and I believe it is nothing but the tissue,
here not calcified, which, in a calcified condition, ordinarily forms
the valves. On this view, the males may be said to be lodged in pouches,
formed in the thickness of the valves.

_Concluding Remarks._--The males from the absence of a mouth (and no
doubt of a stomach), must necessarily be short-lived, and, I suppose,
are periodically replaced by fresh males.[57] In one instance, the
remnants of the two great compound eyes of the larva, could be seen at
the end of the pouch, opposite the orifice. The larvæ, I conclude, crawl
in at the orifice, one side of which is formed, as we have seen, of
yielding membrane, and scratch out the dead exuviæ of the former
occupant: certainly, the males are less firmly attached to their
pouches, though some small quantity of cement is excreted, than are
other Cirripedes to the objects to which they are attached. The small
size of the female, and her valves not being thickly edged with chitine,
accounts for the males having pouches specially formed for them, instead
of being, as in _S. vulgare_, laterally imbedded in the chitine-border
of the scuta. In hereafter weighing the evidence on the nature of the
parasites in Ibla and in Scalpellum, the fact of the valves of the
supposed female being here modified for the special purpose of lodging
the males, will be seen to be important. If we imagine the male
parasites to be extraneous animals, and that by adhering to the sack of
the Scalpellum, they injure the corium and thus prevent the growth of
the shell over an area exactly corresponding to their own size, and so
form for themselves cavities; yet what can be said regarding the
preparatory furrows? surely these narrow lines cannot have been produced
by the pressure of the much broader parasites. Must we not see in the
furrows, the first marking out, if such an expression may be used, of
the habitation for the male, which has to be specially formed by the
independent laws of growth of the female?

   [57] It is possible, though opposed to all analogy, that the
   females may be short-lived, and breed only once, in which case
   the males would not have to be periodically replaced.


3. SCALPELLUM RUTILUM. Pl. VI, fig. 2.

_S. (Foem. an Herm.) valvis 14 sub-rufis: carinæ tecto plano, utrinque
cristâ rotundatâ instructo; margine basali truncato: lateribus
superioribus latitudine duplo longioribus._

(Fem. or Herm.) Capitulum with 14 reddish valves: carina with the roof
flat, bordered on each side by a rounded ridge; basal margin truncated:
upper latera twice as long as broad.

Mandibles with three teeth: maxillæ narrow, bearing only four or five
pair of spines: segments of the second and third pair of cirri with one
side wholly covered with spines.

MALES, two, lodged in hollows, on the under sides of the scuta;
pouch-formed, with four (?) rudimentary valves; no mouth; cirri not
prehensile.

    Hab. unknown; associated with _Dichelaspis orthogonia_. British
    Museum.


FEMALE OR HERMAPHRODITE.

There is only a single specimen in the British Museum, and this had
nearly all its valves separated, and many of them in fragments: from its
state of decay, I think the specimen must have been dead, when
originally collected.

_Description._--The capitulum consists of fourteen valves, including
from analogy a rostrum.[58] Valves, apparently covered with membrane,
bearing some thin spines on the margins; clouded with a fine, though
pale, orange tint; surfaces plainly marked with lines of growth.

   [58] In my first, and as I thought careful examination of the
   separated valves (my only materials) of this species, I mistook
   one of the triangular rostral latera for the rostrum, and hence
   was unfortunately led into an error in my 'Monograph on the
   Fossil Lepadidæ of Great Britain,' in which I state that the
   present species has only twelve valves in the capitulum; and I
   inferred from this, that _S. quadratum_, _S. fossula_, &c., had
   only twelve valves; I still believe this to be correct, but the
   existence of fourteen valves in _S. rutilum_ and _S. ornatum_,
   the recent species to which the above fossils are most closely
   allied, no doubt is a strong argument in favour of this higher
   number.

_Scuta_, elongated, nearly three times as long as broad; apex, pointed;
basal margin extremely oblique, forming an acute angle with the
occludent margin; the lateral margin is slightly hollowed out, and is
separated from the tergal margin by a large rectangular projection or
shoulder. The occludent margin is nearly straight; externally, there is
a slight ridge running down the middle of the valve, from the apex to
the baso-lateral angle; and a second ridge running from the apex to the
tergo-lateral angle. The lines of growth do not end abruptly at the
tergo-lateral angle, as is the case with _S. ornatum_ and several fossil
species, but run up a little way along the tergal margin. The umbo is
seated at the uppermost point, and, therefore, the main growth is
downwards. There is a large rounded depression for the adductor muscle
(_a_, fig. 2 _a´_), and higher up, opposite the tergo-lateral angle,
there is another hollow (_b_), for the lodgment of the males; this
latter is of nearly the same shape as the hollow for the adductor
muscle, but rather more conspicuous than it. From the appearance of the
under surface of the scuta, it might readily have been thought, that
there had been two adductor muscles.

_Terga_, of large size, longer than the scuta, flat, triangular, with
the whole inferior part much produced and spear-like. A portion of the
apex, must have projected freely above the sack.

_Carina_ (Pl. VI, fig. 2 _b´_), simply bowed (_i. e._, not rectangularly
bent), with the umbo (and primordial valve) seated at the upper point;
rather massive, narrow, only slightly increasing in width from the upper
to the lower end; the two sides are flat, and at right angles to the
roof, which is bordered on each side by a rather broad, square-topped
ridge (_see section_ fig. 2 _c´_), or the roof may be said to have a
square-edged furrow running from the apex to the basal margin, and
widening downwards; these two ridges have their lines of growth oblique,
and hence have a twisted appearance; the central depressed portion of
the basal margin, which is square or truncated, descends lower down than
the two ridges. The sides of the valve close to the apex are broad, and
consist, as I believe, of intra-parietes, as well as of parietes, but
these parts are not separated from each other by ridges, as is commonly
the case, more especially with the fossil species. I have described the
carina in some detail, on account of its resemblance to that of the
cretaceous _S. fossula_, _S. trilineatum_, and _S. quadricarinatum_.

_Rostrum_, unknown; but one probably existed.

_Upper Latera_, of large size, elongated, quadrilateral, approaching to
diamond-shaped, with the angles rounded, nearly twice as long as broad;
almost flat; upper half acuminated, lying between the scuta and terga;
the lower half broad, forming a rectangular projection lying between two
latera of the lower whorl. The umbo is near the apex, the greater part
of the growth being downwards, but the valve is added to a little, round
the two sides of the apex; these additions do not take place in the
early stages of growth, (as explained under _S. vulgare_,) and,
therefore, they form a depressed rim.

_Rostral Latera_, almost exactly triangular, curved; basal margin
furnished with a just perceptible rim.

_Infra-median Latera_, quadrilateral, sides unequal in length; the
carino-basal margin being the longest; in area not quite twice double
the rostral latera; directed obliquely upwards.

_Carinal Latera_, sub-triangular, produced upwards, with the apex
rounded, and the two lateral margins hollowed out; the basal margin
exceeds a little in length the basal margin of the rostral latera. The
umbones of these two latera are seated at their basal outer angles, so
that the growth of the valves is towards each other and upwards. The
umbo of the infra-median latus is seated at the baso-rostral angle, and
hence the growth is obliquely upwards. The umbones of the rostral latera
must have been close together, over the unknown rostrum.

_Length_ of capitulum about 4/10th of an inch.

_Peduncle_, only small fragments are preserved; the calcified scales are
small, closely imbricated, several of them together only equalling in
length the basal margin of the rostral latera. Each scale is thin,
transversely elongated; basal imbedded portion straight; upper margin
rounded.

_Mouth._--Labrum with the upper part highly bullate, forming an
overhanging projection; palpi apparently small and narrow.

_Mandibles_, narrow, produced, with three teeth; inferior angle
pectinated, as is sometimes the third tooth; the distance between the
tips of the first and second teeth equals that between the second tooth
and the inferior angle.

_Maxillæ_, extremely narrow, produced, without any notch; spinose edge
exactly one third of the length of the mandibles: beneath the two upper
great spines there are only three or four pair of spines; on the convex
upper margin there are some minute tufts of the smallest hairs.

_Outer Maxillæ_, rounded with the inner margins very sparingly but
continuously covered with bristles. I could not ascertain whether the
olfactory orifices were tubular.

_Cirri._--These consisted, in the one specimen, of merely small
fragments. The segments of the posterior cirri are elongated, not
protuberant, and support, I believe, five pair of non-serrated spines,
and an exterior row of very minute spines: dorsal spines fine and long.
Either the second or third cirri, or probably both, are remarkable for
having the whole of one side of each segment covered with irregular rows
of long spines. Moreover, in the upper segments of these same cirri,
between each separate dorsal tuft, there is placed one or two long
bristles. The first cirrus appears to have had very broad segments, and
these are singular from the spines in the dorsal rows, being extremely
long. In some of the cirri, several of the basal segments are soldered
together.

_Caudal Appendages_, lost.

From the state of the specimen, it was quite impossible to ascertain
whether the individual here described was an hermaphrodite or female;
from the analogy of its nearest congener, _S. ornatum_, the latter is
the most probable; but the genus Ibla shows how the sexes may differ in
the most closely-allied forms.

_Affinities._--From the hollows on the under sides of the scuta, for the
lodgment of the males; from the umbones of the scuta and of the carina
being situated on the apices of these valves; and from all the
characters of the mouth, _S. rutilum_ is much more closely allied to _S.
ornatum_ than to any other species.


MALE, OR COMPLEMENTAL MALE.

In the concavity or hollow above the depression for the adductor muscle
(Pl. VI, fig. 2 _a´_), I found males, but in so extremely decayed a
condition, that they could hardly be examined. On one side, however, I
distinctly saw the larval prehensile antennæ, with pointed, hoof-like
discs; and part of the thorax, with its small limbs and long spines, as
in _S. vulgare_ or _S. ornatum_. I also saw clearly the eye. The four
calcified beads or rudimentary valves, I believe, were present; but in
removing the specimen, the whole fell to pieces and was lost. The outer
integument was covered with rather thick, very minute bristles, each
about, 2/10,000th of an inch in length, and therefore only half the
length of those on the complemental males of _S. vulgare_. The cavities
for the males are not formed, as in _S. ornatum_, by the thickening of
the internal surface of the valve round a defined space, but by the
scutum being externally convex and internally concave down the middle,
hollows being thus produced both for the lodgment of the males and for
the attachment of the adductor muscle. These hollows are separated from
each other by a slight transverse ridge. I do not know at which point of
the margin of the valve, the orifice of the male is situated, but I
presume close under the apex. In this species, as in _S. ornatum_, there
can be no question that the scuta of the female are specially modified
by their own growth for the reception of the males. It must be added
that, as it was not possible to ascertain whether the ordinary form of
_S. rutilum_ was hermaphrodite or female, so it must remain doubtful
whether the parasites are males or complemental males; but the former, I
think, is most probable.


[=TT= SUB-CARINÂ PRESENTE.]

4. SCALPELLUM ROSTRATUM. Pl. VI, fig. 7.

_S. (Herm.) valvis 15: rostro permagno: laterum paribus quatuor: pari
superiore pentagono._

(Herm.) Capitulum with 15 valves: rostrum very large: four pair of
latera; upper latera pentagonal.

Mandibles with four teeth; maxillæ with the inferior angle prominent.

_Complemental Male_, attached between the mouth and adductor scutorum
muscle; pedunculated; capitulum bearing a pair of elongated scuta and a
rudimentary carina; mouth and cirri prehensile.

    Philippine Archipelago; Island of Bantayan. Attached to a horny
    coralline: 20 fathoms. Mus. Cuming.


HERMAPHRODITE.

_Capitulum_, with the upper part narrow and produced.

_Valves_, 15 in number, placed close together, clouded pale red, covered
with membrane, which is thickly clothed with minute points.

_Scuta_ rather small, oval, with the upper end pointed; rather convex;
basal and lateral margins blending into each other; the upper produced
portion above the umbo is small; there is a deep pit for the adductor
muscle, and there is a fold on the occludent margin in the usual
position; occludent margin not straight.

_Terga_ large, one third of their own length longer than the scuta; fat,
sub-triangular; the three margins are not quite straight; the carinal
margin projects a little above the apex of the carina, and the scutal
margin is excised to fit the upper part of the scuta.

_Carina_ bowed, internally deeply concave; upper portion above the umbo,
about one fourth of the total length, extending between the terga for
two thirds of their length, up to the slight prominences on their
carinal margins: a ridge separates, on each side, the parietes from the
tectum.

_Rostrum_ (fig. 7 _a_) unusually large, about two thirds of the length
of the scuta, and twice as long as the rostral pair of latera;
internally concave, externally carinated; outline of the upper portion
acutely triangular, of the lower portion rounded; umbo seated at the
upper end.

_Upper Latera_ pentagonal, with the apex rounded.

_Rostral Latera_ flat, four-sided, with the basal margin the longest,
and the baso-carinal angle produced.

_Infra-median Latera_ nearly equalling in area the upper latera; not
descending so low down as the rostral and carinal latera; outline of
lower half semi-oval, of upper half rectangular.

_Carinal Latera_ flat, four-sided, with the basal margin the longest,
and slightly protuberant; baso-rostral angle produced; whole valve
larger than the rostral latus, but closely resembling it in form.

_Sub-carina_ minute, not above one third of the size of the rostral
latera, which are the smallest of the other valves; internally deeply
concave; externally solid, pyramidal, standing out beyond the surface of
the carina, with the umbo at the apex.

The umbones of the four pair of latera are seated a little above the
centre in each valve, on the summit of a raised triangular portion; this
arises from the valve at first growing only downwards, and when added to
at the upper end, the new part forms a ledge at a lower level round the
old part, which had already acquired some thickness.

_Peduncle_, short, about half the length of the capitulum; narrow;
thickly clothed with minute, longitudinally elongated, spindle-shaped,
calcareous scales or beads, which project but little.

_Length_ of the capitulum, rather under 3/10ths of an inch.

In a _Young Specimen_, with its capitulum, together with the peduncle,
only 1/10th of an inch long, the scuta, terga, and carina are very large
in proportion to the valves of the lower whorl. The latter project
more, and are externally more pointed, as in the genus Pollicipes. The
rostrum is well developed; the infra-median latera, in proportion, are
the least of all the valves. The carina is straight and pointed, and
not, relatively to the scuta, quite so long. The scuta are rather
broader in proportion to their length, which would naturally follow from
less having been added to their apices,--these valves at first growing
only downwards. The membrane covering and connecting the valves is
furnished with long thin spines.

_Mouth._--Labrum placed far from the adductor scutorum muscle, with the
upper part exceedingly prominent; apparently there are no teeth on the
crest. Palpi blunt.

_Mandibles_, narrow, with four teeth, of which the second is not smaller
than the others; inferior angle sharp and produced, barely pectinated.

_Maxillæ._--Under the two or three great upper spines, there is a tuft
of fine bristles; the inferior part of the edge is step-like, and much
upraised.

_Outer Maxillæ_, with the inner edge deeply notched, and the bristles
arranged in two quite distinct tufts; the bristles on the outer surface
are long. Olfactory orifices, thin, tubular, and projecting.

_Cirri._--The first pair is placed far from the second; the three
posterior pair are long and straight, with their segments much
elongated, not protuberant, bearing four or five pair of long spines,
with little intermediate tufts of minute spines, and with the minutest
spines on the lateral upper edges. Dorsal tufts with one spine extremely
long, equalling a segment and a half in length; the others very short.
Spines all serrated. First cirrus not very short; rami nearly equal,
with the four terminal segments of both tapering; all the basal segments
much thicker, and thickly covered with bristles. Second cirrus (as well
as the third in a less degree), with the anterior ramus thicker than the
posterior ramus, and with all the lower segments in both rami thickly
clothed with three or four longitudinal rows of spines.

_Caudal Appendages_, spinose, uni-articulate; but the specimen was
injured, and I could not exactly make out their shape: I believe it was
oval, and thickly fringed with fine spines.

_Penis_, very small, almost rudimentary, narrow, and hairy, scarcely
exceeding in length the pedicel of the sixth cirrus.


COMPLEMENTAL MALE. Pl. VI, fig. 5.

Before describing the parasite of the present species, which departs
entirely from the character of the males of the three preceding species,
it is proper to state that I consider it to be a Complemental Male
simply from analogy, as will hereafter be more fully shown at the end of
the genus. Had a specimen of the parasite been brought to me without any
information, I should have concluded that it was an immature individual
of a new genus of pedunculated Cirripedes, remarkable from the
rudimentary condition of the valves, and exhibiting, in one important
character, namely, in the form of the larval prehensile antennæ, an
alliance to Scalpellum. Had I been then told that three individuals in a
group, had been found attached to _S. rostratum_, not outside the
valves, but to the integument, in a central line, between the labrum and
the adductor scutorum muscle, in such a position that when the
Scalpellum closed its valves, these parasites were enclosed within the
capitulum, my surprise would have been great; for it is very improbable
that this singular and unparalleled position was accidental in this one
group of specimens, inasmuch as there seems to be a relation between the
naked condition of the capitulum of the parasite, and the protection
afforded to it by the capitulum of the Scalpellum. It further becomes
apparent on reflection, that these minute parasites, though having the
appearance of immaturity, can not increase in size, or but little, for
if they did grow, and acquired an ordinary size, they would either be
killed by the pressure of the scuta of the Scalpellum, or they would
destroy the latter, and in doing so soon lose their own support, and
thus necessarily perish!

The one full-grown specimen of _S. rostratum_, in Mr. Cuming's
collection, was in a good state of preservation, but dry. The three
parasites were attached, as stated, close under the labrum, between it
and the adductor muscle. They are constructed like ordinary Cirripedia,
and have a mouth, thorax and cirri, enclosed in a capitulum, supported
on a peduncle of moderate length and narrow. The entire length of the
capitulum and peduncle, as far as could be ascertained in the shrivelled
condition of the specimens, was 35/1000ths, and the greatest width of
the capitulum 11/1000ths of an inch. Both capitulum and peduncle are
hirsute with spines, nearly 1/1000th of an inch in length, mingled with
shorter hairs in little rows of three and four together. The figure (5)
in Pl. VI is merely a restoration, as accurate as could be made from the
much shrivelled specimens. There are only three valves,--namely, an oval
carina (_a_), seated rather high up on the capitulum, in a rudimentary
condition and only 1/1000th of an inch in length, and a pair of scuta;
these latter consist of a narrow, slightly curved plate, 8/1000ths in
length, broadest at the lower end, where the breadth is 2/1000ths of an
inch. The prehensile antennæ, at the end of the peduncle, have pointed
hoof-like discs: I was not able to make out the other parts. It deserves
notice, that in the young specimen of the ordinary form of _S.
rostratum_, 1/10th of an inch in length, and therefore only thrice as
long as the parasites, all the valves were perfect, and seemed to have
followed the ordinary law of development.

_Mouth._--The largely bullate labrum is placed far from the adductor, in
the same manner as in the hermaphrodite. The mandibles have three large
sharp teeth, with the inferior point very sharp and small, so that there
is one less tooth than in the hermaphrodite. The maxillæ have two or
three large upper spines, the others being very thin; I believe the
lower part is upraised and step-like, as in the hermaphrodite. The
outer maxillæ are bilobed in front, with a few short bristles on the
outer side near the bottom. I was not able, from the dried state of the
specimens, to discover whether the olfactory orifices were tubular.
Altogether it was apparent, from this imperfect examination, that there
was a close similarity between the mouth of the parasite and of the
hermaphrodite.

The _Thorax_ is unusually elongated.

_Cirri._--The first pair is very short, and is distant from the second.
All have the appearance of immaturity, with their pedicels very long in
proportion to their rami; the latter are slightly unequal in length,
even in the sixth pair. There appeared to be six segments in the rami of
the sixth pair, each segment bearing two or three pair of long spines.

_Caudal Appendages_, with two or three little spines on their summits.

_Penis_, short, blunt, thick at the apex, with one or two spines on it.
I did not see any ovaria, but this could hardly have been expected in
specimens in a dried condition, without they had happened to have been
in a gorged condition. Certainly there were no ova.

In the general summary at the end of the genus, I shall give my reasons
for believing this parasite to be the Complemental Male of the
_Scalpellum rostratum_.


5. SCALPELLUM PERONII. Pl. VI, fig. 6.

  SMILIUM PERONII. _J. E. Gray._ Annals of Philosoph., new series,
        tom. x, 1825.

  ---- ---- . . . . . Spicilegia Zoologica, tab. iii, fig. 10, 1830.

  ANATIFA OBLIQUA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.
        xciii, fig. 16, 1823-1834.

  POLLICIPES OBLIQUA. _Lamarck._ An. sans Vertebres (2d edition).

_S. (Herm.) valvis 13: laterum paribus tribus; pari superiore multùm
elongato: pedunculi squamis calcareis nullis._

(Herm.) Capitulum with 13 valves: three pair of latera; upper latera
much elongated: peduncle without calcareous scales.

Mandibles with 10 or 11 unequal teeth: maxillæ with the edge nearly
straight, bearing numerous spines.

COMPLEMENTAL MALE, attached externally, between the scuta and below the
adductor muscle; pedunculated; capitulum formed of six valves, with the
carina descending far beneath the basal angle of the terga; mouth and
cirri prehensile.

    Swan River, Australia, attached to a coralline; Mus. Cuming.
    Port Western, Bass's Straits, as stated in the Voyage of the
    Astrolabe. Mus. Brit.


HERMAPHRODITE.

_Capitulum_ formed of 13 valves; namely, two scuta, two terga, a carina
and sub-carina, a rostrum, a pair of upper latera, and two pair of lower
latera; these latter valves, with the sub-carina and the rostrum, make a
whorl of six pieces. The upper part of the capitulum is, as usual,
produced. The upper valves are separated (in specimens which have not
been dried) by rather wide interspaces of membrane; they are covered
(excepting, generally, their umbones,) by membrane, which in the
interspaces is clothed with fine spines. The spines, or the marks where
they were once articulated, are visible over nearly the entire surface
of the membrane covering the valves. The spines are particularly
numerous round the orifice of the sack. The whole capitulum, (in a dried
condition), is coloured dull purplish-red, which is only in part due to
the underlying corium, for the valves themselves are pale red. After
having been long kept in spirits, the whole capitulum becomes
colourless. The valves are smooth, faintly marked by lines of growth.
The umbones of the lower valves project outwards, giving a denticulated
appearance to the base of the capitulum.

_Scuta_, slightly convex, oblong, breadth about two thirds of the
length, almost quadrilateral, with the upper portion produced into a
flat projection; this projection is almost spear-shaped, being
constricted a little on each side below the apex. There is a deep pit
for the adductor muscle. The umbo is near the apex, the part above not
being above one fifth of the whole length of the valve. As in _S.
vulgare_, the growth is at first downwards, and subsequently a little
upwards and downwards, thus producing the upper, small, spear-like
projection, which lies at a lower level than the umbo. There is a fold
on the occludent margin.

_Terga_, large, flat, triangular; carinal margin slightly hollowed out;
occludent margin slightly arched, with a small portion protuberant to a
variable amount. The apex is slightly curved towards the carina.

_Carina_, long, internally deeply concave, angularly bent, the lower
portion slightly longer and wider than the upper part; the two halves
meet each other at about an angle of 135°; the upper half is parallel to
the longer axis of the terga, between which it extends for three fourths
of their length. The external surface is rounded, except near the umbo,
where the edge is carinated; growth almost equally upwards and
downwards; the parietes and tectum are not separated by ridges.

The _Sub-carina_ lies close under the carina, and is placed almost
transversely to the longer axis of the capitulum; external surface
arched and smooth, the whole having the shape of half of a cone, with
the apex a little curved outwards; seen internally, it may be said to be
formed of two triangular wings placed at right angles to each other;
basal margin straight; in size equalling the carinal latera.

_Rostrum_, lying almost transversely to the longer axis of the
capitulum, under the basal margins of the scuta; in shape (fig. 6 _a_)
closely resembling the sub-carina, but about one third larger than it;
larger also than either the rostral or carinal latera; seen externally,
appears like a half cone; seen internally, is formed of two triangular
wings (with curved edges), placed at right-angles to each other.

_Upper Latera_, internally flat, oblong, twice as long as broad; upper
end square, truncated; upper half rather wider than the lower half;
fully twice as large as either of the lower latera. The basal points
extend below the basal margins of the scuta. The umbo is placed a little
above the centre.

_Rostral Latera_, minute, scarcely exceeding one third of the size of
the carinal latera, and very much less than the rostrum; they are placed
transversely under the basal point of the upper latus, or rather between
it and the baso-lateral angle of the scutum; basal margin, as seen
internally, straight; upper margin arched; rostral angle produced;
internally flat; the whole valve is very thick and solid, so that the
umbo which lies at the rostral end, projects rectangularly outwards.

_Carinal Latera_, oblong, nearly quadrilateral, with the upper angle
produced; placed obliquely, parallel to the lower half of the upper
latera; umbo slightly prominent, seated near the apex, with three
rounded ridges proceeding from it; internal surface very slightly
concave.

_Peduncle and Attachment._--The peduncle is short, not equalling the
capitulum in length. The whole surface is most thickly clothed with
minute spines, which are not visible when the specimen is dry; I think
it probable that they may sometimes all drop off before a new period of
exuviation. The peduncle does not (at least in the specimens which I
have examined, which were grouped in a bunch) taper at the lower end to
a point; and after careful examination, I feel sure that the cement does
not debouch from several successively formed orifices, as in _S.
vulgare_ and as in some Pollicipes, but only from the two original
orifices in the prehensile antennæ of the larva. In these latter organs,
the sucking disc is hoof-like and pointed, and is narrower than the
basal segment. The ultimate segment has on its inner side (supposing
this segment stretched straight forwards,) a notch or step bearing at
least three spines. The proportions of the different parts differ
slightly from those in _S. vulgare_; but, as I shall hereafter have to
give all the measurements, I do not think them worth repeating here. In
the one large group of specimens examined by me, in Mr. Cuming's
possession, all were attached symmetrically to the coralline, as in the
case of _S. vulgare_, capitulum upwards, and their carinas outwards.

_Length_ of capitulum about three quarters of an inch; width about half
an inch; entire length, with peduncle, a little more than one inch.

The _Mouth_ is placed far from the adductor muscle.

_Labrum_, with its basal margin much produced; upper part highly
bullate, forming a rounded projection equalling the longitudinal axis of
the rest of the mouth; crest without any teeth.

_Palpi_, triangular, with the two margins, thickly clothed with
bristles; on each side of the mouth, near where the palpi are united to
the mandibles, there is a slight, orbicular, shield-like swelling.

The _Mandibles_ (Pl. X, fig. 3) have nine or ten very unequal teeth,
with the inferior angle rather broad and pectinated; of these, there are
four main teeth, of which the second is always the smallest, and between
the four, one or two small teeth are interpolated; so that the total
number is either nine or ten, and often varies on the two sides of the
same individual, as likewise does the shape of the inferior angle.

_Maxillæ_, with the edge nearly half as long as that of the mandibles,
supporting from seventeen to twenty pairs of spines; the upper pair is
only slightly larger than the others; a part near the inferior angle
projects slightly beyond the rest of the nearly straight edge. The
apodeme, at its base or point of origin, is unusually broad and flat.

_Outer Maxillæ_, large and triangular. The inner margin is slightly
concave, and continuously covered with short spines. The outer margin is
bilobed, as in _S. vulgare_, with the basal part supporting a great tuft
of long bristles, of which the greater number turn outwards, and almost
cover the olfactory orifices. The latter are slightly prominent, placed
some way apart from each other, with the above-mentioned tufts of
bristles between them. All the spines of the trophi are in some degree
doubly serrated.

_Cirri._--The first pair is seated rather far from the second pair, and
the prosoma being little developed, the shape of the body nearly
resembles that of _S. vulgare_. The posterior cirri are elongated, very
little curled, with the segments much flattened, not at all protuberant,
bearing from five to seven pair of long serrated spines, with a few
small spines in an exterior row; between each pair there is a very
minute tuft of small bristles; the upper lateral rim of each segment is
toothed with small spines; spines of the dorsal tufts, long, serrated.
_First pair_, elongated, having numerous segments, namely, seventeen,
whilst the sixth pair in the same individual had only twenty-one
segments; rami nearly equal; segments short, nearly cylindrical, thickly
clothed with long serrated spines. The _second_ and _third_ pair are
nearly equal in length; they have their anterior rami slightly thicker
than their posterior rami, both being much more thickly clothed with
spines, than are the three posterior pair of cirri. Pedicels, rather
short, with their inner edges not forming a projection, as in _S.
vulgare_.

_Caudal Appendages_ (Pl. X, fig. 20), uni-articulate, flat, rounded at
their ends and moderately long; clothed most thickly, like brushes, with
very fine bristles, which latter are serrated, and are longer than the
appendages themselves.

_Penis_, of small size, narrow, pointed, and thickly clothed with
delicate hairs; in length equalling only one fourth of the sixth cirrus.

_Ovigerous Fræna_, small, semicircular; entire edge thickly covered with
glands. Ovarian tubes, within the peduncle, fully developed as usual.

_Affinities._--This species differs from all the others in the absence
of calcareous scales on the peduncle; but it has no other character
which at all justifies its generic separation. In the shape of the scuta
and carina it comes nearest to _S. vulgare_. Taking all the characters
together, it is scarcely possible to say to which of the other species
it is most closely allied, having close affinities with all. In the
entire structure, however, of the Complemental Male, immediately to be
described, this species certainly comes nearer to _S. villosum_ than to
any other species. I may add, that in _S. villosum_ the latera are
almost rudimentary, and therefore tend to disappear, whereas in _S.
Peronii_ it is the calcareous scales on the peduncle which have actually
disappeared.


COMPLEMENTAL MALE. Pl. VI, fig. 3.

I examined, owing to the great kindness of Mr. Cunning, six dry
specimens of the hermaphrodite _S. Peronii_, from Swan River, and one in
spirits from another locality, in the British Museum. Out of these seven
specimens, only three appeared to have had parasites attached to them,
and these I infer, from reasons to be more fully given at the end of the
genus, are Complemental Males. One of the three specimens, however, had
two males close together. These parasites were firmly cemented to the
integument of the hermaphrodite, in a fold, in a central line between
the scuta, a little below (the animal being in the position in which it
is figured) the adductor scutorum muscle, and therefore some way below
the umbones of these valves. When the scuta are closed, the parasites,
from their small size, are enclosed and protected. In every detail of
structure, they are obviously pedunculated Cirripedia.

The _Capitulum_ (Pl. VI, fig. 3) has six valves; namely, a pair of scuta
and of terga, a carina, and a rostrum, all united by finely-villose
membrane, furnished near the orifice with some much longer and thicker
spines. The capitulum is truncated in a remarkable manner, the orifice
not being, as in the hermaphrodite, in the same line with the peduncle,
but almost transverse to it, and therefore almost parallel to the
surface of attachment. The largest specimen measured transversely,
through the scuta and terga, was 30/1000ths of an inch in breadth;
another was only 26/1000ths to 27/1000ths: this latter specimen,
measured longitudinally, from the base of the carina to the tips of the
terga, was 15/1000ths of an inch. A scutum of the largest specimen was
17/1000ths in length. The scuta and terga are broadly oval, with the
primordial valves very plain at their upper ends. I may here mention,
that in a central line between the scuta, I observed the _apparently_
single, minute, black eye, as in ordinary Cirripedia.

The _Carina_ is straight, triangular, and internally slightly concave;
its basal margin descends far below the basal points of the terga.

The _Rostrum_ is shorter, and internally more concave than the carina: I
believe it projects more abruptly outwards than is represented in the
figure.

The _Peduncle_ commences some little way below the scuta: it is narrow
and very short: it is finely villose: it is lined by delicate transverse
striæ-less muscles, within which there are the usual stronger,
longitudinal muscles. The base is flat and truncated. I examined, and
carefully compared, the prehensile antennæ with those of the
hermaphrodite, and found every part and every measurement the same. The
full importance of this identity will hereafter be more fully insisted
on. The antennæ are represented of their proper proportional size in
fig. 3.

_Mouth._--The labrum, as in the hermaphrodite, is highly bullate, and
far removed from the adductor scutorum muscle. The _Palpi_ are small and
triangular, with their blunt apices clothed with a very few scattered
bristles.

_Mandibles_, with only three teeth, and the lower angle minute, slightly
pectinated; the first tooth is distant from the second, and larger than
it. Width of the whole organ, .0021 of an inch.

_Maxillæ_, bearing only a few spines, furnished with a long apodeme;
beneath the upper large pair there is a notch, under which there are two
spines of considerable size and a small tuft of fine bristles; width
.001 of an inch, and therefore only 1/16th of the size of the same organ
in the hermaphrodite: the relative sizes of the maxillæ and mandibles
are the same in the male and hermaphrodite.

_Outer Maxillæ_ blunt, triangular, with a few thinly-scattered bristles
on the inner face; those on the outside being longer.

_Cirri._--The First pair is far removed from the second; the rami are
very short, barely exceeding the pedicel in length; they are formed of
only four segments, each bearing a pair of spines; but on the end of the
terminal segment, there are three spines, of which the central one is
very long. Second pair also short. In the sixth pair there are five or
six elongated segments, each bearing three pair of long spines; dorsal
tufts large. The cirri are furnished with transversely-striated muscles.

The _Caudal Appendages_ exist as two very minute plates, with a few
bristles at their apices.

The _Penis_ is not acuminated, with four bristles at the end; it is
short, equalling only the lower segment of the pedicel of the sixth
cirrus. In the one specimen preserved in spirits, I unfortunately
omitted to search for the vesiculæ seminales; I cannot doubt that such
existed, but it would have been important to have ascertained whether
they contained spermatozoa. I made out, most distinctly, that there was
no trace of ovarian tubes within the peduncle; and my assertion may be
believed when I state, that I traced the two much finer and more
transparent cement-ducts, from the prehensile antennæ up to the body of
the animal: in Lepas I have _repeatedly_ detected, with ease, the
ovarian tubes within the peduncle, before the calcification of the
valves had even commenced, and therefore at a much earlier period of
growth than in these parasites. Consequently I am prepared to affirm,
that these parasites are not females, but that, as far as can be judged,
from external organs, they are exclusively males.

_Concluding Remarks._--In comparing the capitulum of the hermaphrodite
with that of the complemental male (Pl. VI, figs. 6 and 3), we must be
struck with the differences in their shape, in the number, relative
sizes, and forms of the several valves. It should, however, be borne in
mind, that the scuta and carina in the hermaphrodite at first grow
exclusively downwards; so that if we remove the upper portions
subsequently added, the difference in shape in these valves is not so
great as it at first appears. The rostrum in the male is of much larger
relative size; whilst of the upper latera there is not a trace, although
in the hermaphrodite these valves are larger than the rostrum. The
terga, compared with those of the hermaphrodite, differ more essentially
than do the other valves; and the manner in which the primordial valves
project, shows that from the first commencement of calcification, the
lines of growth have followed an unusual course. The great breadth and
shortness of the terga is evidently related to the shortening of the
whole capitulum, and the transverse position of the orifice; and this
shortening of the capitulum, no doubt, is rendered necessary for its
reception and protection within the shallow furrow between the scuta of
the hermaphrodite. Finally, if we compare the internal parts of the
hermaphrodite and male, the differences are considerable, though partly
to be accounted for by the youth of the latter: the form and position of
the labrum, and the distance between the first and second pair of cirri,
is the same in both; but the mandibles and maxillæ differ considerably.

To put the case as I have before done, if a specimen of one of these
parasites had been brought to me to class without any information of its
habits,--the downward direction of growth in all the valves, the
presence of a rostrum, the villose outer integument, all the details of
the prehensile antennæ, the form of the animal's body, and the position
of the labrum, would have convinced me that, though a quite new genus,
it ought to have stood close to Scalpellum, and nearer to it than to
Ibla.


6. SCALPELLUM VILLOSUM. Pl. VI, fig. 8.

  POLLICIPES VILLOSUS on Plate (TOMENTOSUS in text). _Leach._
        Encyclop. Brit., Suppl., vol. iii, 1824, Pl. lvii.

  ---- VILLOSUS.[59] _G. B. Sowerby._ Genera of Shells, Pollicipes,
        fig. 3, 1826.

  CALANTICA HOMII. _J. E. Gray._ Annals of Phil., vol. x, p. 100,
        1825.

   [59] As Mr. Sowerby has adopted the name _villosus_, I have
   followed him; though as _tomentosus_ is used through some mistake
   by Leach in the text, both names have equal claims as far as
   priority is concerned.

   In Lamarck, 'Animaux Sans. Vert.,' the _P. villosus_ of Sowerby
   is made synonymous with _Anatifa villosa_ of Brugière, which is
   certainly incorrect, although the _A. villosa_ of this latter
   author is not positively known.

_S. (Herm.) valvis 14: sub-rostro præsente: carinâ pæne rectâ: laterum
paribus tribus; pari superiore triangulo._

(Herm.) Capitulum with 14 valves: sub-rostrum present: carina nearly
straight: three pair of latera; upper latera triangular.

_Mandibles_ with four teeth, of which the second is the smallest:
maxillæ with a projection near the inferior angle: no caudal appendage.

COMPLEMENTAL MALE, attached externally between the scuta, below the
adductor muscle; pedunculated; capitulum formed of six valves, with the
carina not descending much below the basal angles of the terga: mouth
and cirri prehensile.

    Eastern Seas[60] (?) attached to shells and rocks. Mus. Brit.;
    College of Surgeons; Cuming.

   [60] No habitat is attached to any of these specimens; but Mr.
   Sowerby informs me that he has seen specimens attached to the
   _Modiola albicostata_ of Lamarck, which shell is said by the
   latter author to be found in the seas of India, Timor, and New
   Holland.


HERMAPHRODITE.

_Capitulum_ with fourteen valves, consisting of a pair of scuta and of
terga, a carina, (which five valves are much larger than the others,) a
rostrum, sub-rostrum, sub-carina, and three pair of small latera. All
the valves are covered by membrane, as are the calcareous scales on the
peduncle; and this membrane everywhere is densely clothed with spines.
The upper valves are not very thick; they stand rather close together.
The eight valves of the lower whorl are more solid, and are placed far
apart; they are small, tending to become rudimentary. None of the valves
are added to at their upper ends, in which respect this species differs
remarkably from the others of the genus, and approaches in character to
Pollicipes.

_Scuta_, with a deep hollow for the adductor muscle, triangular, with
the basal margin elongated, and protuberant.

_Terga_, large, flat, triangular, basal point blunt, with the carinal
margin slightly hollowed out, and the scutal margin protuberant. Apex
solid.

_Carina_, rather longer than the terga, straight, gradually widening
from the upper to the basal end, deeply concave. In young specimens the
upper part is slightly bowed inwards. Apex solid.

_Sub-carina_, with the inner surface crescent-shaped; the umbo points
transversely outwards; in width it exceeds the largest of the latera.

_Rostrum_, triangular, internally (fig. 8 _a_) concave; basal margin
slightly hollowed out, and deeply notched; rather less in width than the
carina; short, with the umbo pointing upwards and outwards. In young
specimens the apex curves a little inwards.

_Sub-rostrum_, with the inner surface transversely elongated (fig. 8
_b_), slightly crescent-shaped, about two thirds as wide as the rostrum.
The apex points transversely outwards.

_Latera_, three pair; the middle pair apparently corresponds with the
upper latera of the other species of the genus. The two other pair of
latera, together with the rostrum and sub-carina, form a whorl. The
sub-rostrum lies by itself, a little beneath this whorl. The latera are
smaller than the rostrum or the sub-carina. They are placed far distant
from each other; their inner surfaces are triangular; their umbones
point upwards; the rostral pair is smaller than the other two pair,
which are of equal size. The exact position of the rostral latus
differed on the two sides of the specimen examined; apparently its
normal position is at the baso-lateral angle of the scuta.

_Peduncle_, wide at the summit, longer than the capitulum; calcified
scales small, not arranged very regularly; flattened, spindle-shaped,
rather far separated from each other; imbedded in membrane, so that even
their summits are rarely uncovered. The surface of the membrane is
thickly clothed with spines, which are strong, thick, yellow, pointed,
and furnished with large tubuli running to the underlying corium. These
spines are arranged in groups of from three or four, to five or six.
Besides these larger spines, the whole surface is villose with very
minute colourless spines, not above 1/20th of the length of the larger
ones. The surface of attachment is broad. This species, not being
symmetrically attached to a coralline, the peduncle does not curve, as
in most of the other species, towards the rostrum.

The capitulum is above half an inch in length.

_Mouth._--The labrum is much produced downwards, but yet the mouth is
not very far distant from the adductor muscle: the upper part is
bullate, forming a small overhanging point, and in longitudinal diameter
equals the rest of the mouth. _Palpi_ blunt.

_Mandibles_ with four teeth, strong, short, thick, the second tooth much
smaller than the others; inferior angle broad, pectinated.

_Maxillæ_ with a long, rather sinuous edge, which, near the inferior
angle, has a narrow projecting point, bearing rather finer spines; there
is, also, apparently, a very minute tuft of small spines close under the
two large upper spines: there are, altogether, about twenty pair of
spines, without counting the smaller ones.

_Outer Maxillæ_, with the inner edge slightly concave, continuously
covered with bristles; exteriorly, with a prominence covered with longer
bristles. Olfactory orifices prominent, protected by a slight punctured
swelling between the bases of the first pair of cirri.

_Cirri._--Prosoma moderately developed; first pair of cirri rather far
removed from the second pair. The segments of the three posterior pair
are not elongated, short, slightly protuberant in front, bearing four or
five pairs of strong spines; a little below each pair, there is an
intermediate tuft of very fine straight bristles, of which the upper
tuft is the largest; on the lateral upper rims there are some short,
strong spines; dorsal tufts rather small and thick; spines all more or
less serrated, especially on the broad basal segments of the three
anterior cirri. Pedicels of the cirri not particularly protuberant in
front. First cirrus with rami, slightly unequal in length; not short;
basal segments much thicker and more protuberant than the upper
segments. Second cirrus; anterior ramus with six or seven basal segments
highly protuberant, and crowded with spines; posterior ramus with about
six segments, similarly characterised. Third cirrus with the anterior
ramus having six, and the posterior ramus five segments, also similarly
characterised.

_Caudal Appendages_ absent, there being only a slight swelling on each
side of the anus.

The _oesophagus_ runs parallel to the labrum, and enters obliquely the
summit of the stomach, which is destitute of cæca: the biliary envelope
is longitudinally plicated.

There are no _Filamentary Appendages_.

_Testes_ large, branched like a stag's horns, attached in a sheet to the
ventral surface of the stomach: the vesiculæ seminales enter the
prosoma, and have their reflexed ends not very blunt. The _Penis_ is
rather narrow, with the terminal half plainly ringed, and bearing tufts
of fine bristles arranged in circles, one tuft below the other; on the
basal half there are only a few scattered minute bristles.

_Affinities._--In the downward growth of all the valves, in the presence
of a sub-rostrum, in the shape of the scuta, carina, and more especially
of the triangular latera, in the form of the peduncle, with its
irregularly-scattered calcified scales, in the shape of the animal's
body, in the structure both of the mandibles and maxillæ, in the
arrangement of the spines, both on the anterior and posterior cirri,
_Scalpellum villosum_ most closely resembles, or rather is identical
with, Pollicipes. Had it not been for the formation of the valves
forming the capitulum, and from the presence of Complemental Males, I
should have placed this species alongside of _Pollicipes spinosus_ and
_sertus_. In not having caudal appendages, _S. villosum_ differs from
all the species of Scalpellum and Pollicipes; but this organ is variable
to an unusual degree in Pollicipes.


COMPLEMENTAL MALE. Pl. VI, fig. 4.

From the kindness of Professor Owen, Mr. Gray, and Mr. Cuming, I have
been enabled to examine six specimens of this species; and on two of
them I found Complemental males. They were attached in the same position
as in _S. Peronii_; namely, beneath the adductor muscle, in the fold
between the scuta, so as to be protected by the latter when closed. This
parasite is six-valved, and has a close general resemblance with that of
_S. Peronii_, but differs in very many points of detail. It is
represented of the natural size at _á_ fig. 4. The capitulum is
43/1000ths of an inch, measured across the scuta and terga; and the same
measured from the base of the carina to the top of the capitulum; hence
it is broader, by a quarter of the above measurement, and considerably
higher than the male of _S. Peronii_. From the capitulum being higher,
that is, not so much truncated, the orifice is placed more obliquely.
The membrane connecting the valves is finely villose, and is besides
furnished with spines, conspicuously thicker and longer than those on
the male _S. Peronii_. The scuta and terga are much more elongated, a
scutum being here 35/1000ths of an inch in length. The carina descends
only just below the basal points of the terga, instead of far below
them. The rostrum is a little broader and more arched than the carina;
it is 2/1000ths in length, and therefore more than two thirds of the
length of the carina, the latter being 28/1000ths of an inch from the
apex to the basal margin. The primordial valves, with the usual
hexagonal tissue, are seated on the tips of the scuta, terga, and
carina, but not on the rostrum; so that these valves follow the same law
of development, as in the ordinary and hermaphrodite form of Scalpellum.
The scuta (_a_, fig. 4, greatly enlarged), the terga (_b_), and carina
(_c_) of the male, resemble the same valves in the hermaphrodite, much
more closely than do these valves in the male and hermaphrodite _S.
Peronii_. The rostrum has not its basal margin hollowed out, and is very
much larger relatively to the carina, than in the hermaphrodite. The
large relative size of the rostrum in the complemental male both of this
species and of _S. Peronii_, is a remarkable character, which I can in
no way account for.

The peduncle is narrow and short, but in a different degree in the two
specimens examined. It is naked. The prehensile antennæ were not in a
good state of preservation: the disc is narrower than the basal segment,
and only slightly pointed, in which important respect it differs from
the same part in the foregoing species; at its distal end, rather on the
inner side, there are two or three spines, apparently in place of the
excessively minute hairs, which are found at the same spot in some or in
all the other species of Scalpellum, and in Ibla: similar strong spines
occur in Pollicipes. Unfortunately, for the sake of comparison, I was
not able to find the prehensile antennæ in the hermaphrodite _S.
villosum_.

_Mouth._--Labrum bullate, with teeth on the crest. _Palpi_ blunt,
spinose.

_Mandibles_, with three teeth; inferior point rather strongly
pectinated.

_Maxillæ_, with a considerable notch under the upper pair of large
spines; inferior part of the edge not prominent.

_Outer Maxillæ_, with the spines on the inner edge arranged into two
groups. Olfactory orifices tubular and prominent, with some long
bristles near their bases. In the mandibles having only three teeth, in
the maxillæ being notched and in the lower part not being prominent,
and, lastly, in the bristles on the inner face of the outer maxillæ
being arranged in two groups, these several organs differ from those in
the hermaphrodite.

_Cirri._--First pair short, with only three or four segments in each
ramus: second cirrus, with the basal segments not very thickly clothed
with spines: sixth cirrus with seven segments, not protuberant in front,
each bearing four pairs of spines, without intermediate tufts.

_Caudal appendages_, none. This is an interesting fact, considering that
these organs are likewise absent in the hermaphrodite _S. villosum_,--an
absence highly remarkable, and confined to the genus Conchoderma and the
one species of Anelasma.

_Penis_ thick, not tapering, rather exceeding in length the pedicel of
the sixth cirrus, square at the end, and furnished with some spines. In
one specimen, I believe I distinguished the vesiculæ seminales: if so,
they contained only pulpy matter, and not spermatozoa. There were no
ovarian tubes within the peduncle, which was lined by the usual muscles;
I traced the two delicate cement-ducts, running from within the antennæ
close up to the animal's body. Hence in this case, as in that of _S.
Peronii_, I dare positively affirm that ovarian tubes do not occur; for
it is out of the question that I could have traced the cement-ducts,
and, at the same time, overlooked the far larger and more conspicuous
ovarian tubes, into which, moreover, the ducts, had they existed, would
have run. Consequently, these parasites are not females; but judging
from the probosciformed penis, and from the presence, as I believe, of
vesiculæ seminales, they are males.

The complemental males of the present species, and of _S. Peronii_, so
closely resemble each other, that what I have stated regarding the
affinities of the latter, are here quite applicable. It is singular how
much more alike the parts of the mouth and the cirri of these two
complemental males are, than the corresponding parts in the two
hermaphrodites: this no doubt is due to the two males having been
arrested in their development, at a corresponding early period of
growth. Several of the characters, by which the hermaphrodite _S.
villosum_ so closely approaches, and almost blends into the genus
Pollicipes,--such as the thicker cirri, with the intermediate tufts of
bristles, the small second tooth of the mandibles, and the little
brush-like prominence on the maxillæ,--are not in the least apparent in
the complemental male.


SUMMARY ON THE NATURE AND RELATIONS OF THE MALES AND COMPLEMENTAL MALES,
IN IBLA AND SCALPELLUM.

Had the question been, whether the parasites which I have now described,
were simply the males of the Cirripedes to which they are attached, the
present summary and discussion would perhaps have been superfluous; but
it is so novel a fact, that there should exist in the animal kingdom
hermaphrodites, aided in their sexual functions by independent and, as I
have called them, Complemental males, that a brief consideration of the
evidence already advanced, and of some fresh points, will not be
useless. These parasites are confined to the allied genera Ibla and
Scalpellum; but they do not occur in Pollicipes,--a genus still more
closely allied to Scalpellum; and it deserves notice, that their
presence is only occasional in those species of Scalpellum which come
nearest to Pollicipes. In the genera Ibla and Scalpellum, the facts
present a singular parallelism; in both we have the simpler case of a
female, with one or more males of an abnormal structure attached to her;
and in both the far more extraordinary case of an hermaphrodite, with
similarly attached Complemental males. In the two species of Ibla, the
complemental and ordinary males resemble each other, as closely as do
the corresponding hermaphrodite and female forms; so it is with two
sets of the species of Scalpellum. But the males of Ibla and the males
of Scalpellum certainly present no special relations to each other, as
might have been expected, had they been distinct parasites independent
of the animals to which they are attached, and considering that they are
all Cirripedes having the same most unusual habits. On the contrary, it
is certain that the animals which I consider to be the males and
complemental males of the two species of Ibla, if classed by their own
characters, would, from the reasons formerly assigned, form a new genus,
nearer to Ibla than to the parasites of Scalpellum: so, again, the
assumed males of the three latter species of Scalpellum would form two
new genera, both of which would be more closely allied to Scalpellum,
than to the parasites of Ibla. With respect to the parasites of the
first three species of Scalpellum, they are in such an extraordinarily
modified and embryonic condition, that they can hardly be compared with
other Cirripedes; but certainly they do not approach the parasites of
Ibla, more closely than the parasites of Scalpellum; and in the one
important character of the antennæ, they are identical both with the
parasitic and ordinary forms of Scalpellum. That two sets of parasites
having closely similar habits, and belonging to the same sub-class,
should be more closely related in their whole organisation to the
animals to which they are respectively attached, than to each other,
would, if the parasites were really distinct and independent creatures,
be a most singular phenomenon; but on the view that they differ only
sexually from the Cirripedes on which they are parasitic, this
relationship is obviously what might have been expected.

The two species of Ibla differ extremely little from each other, and so,
as above remarked, do the two males. In Scalpellum the species differ
more from each other, and so do the males. In this latter genus the
species may be divided into two groups, the first containing _S.
vulgare_, _S. ornatum_ and _S. rutilum_, characterised by not having a
sub-carina, by the rostrum being small, by the constant presence of four
pair of latera, and by the peculiar shape of the carinal latera; the
second group is characterised by having a sub-carina and a large
rostrum, and may be subdivided into two little groups; viz., _S.
rostratum_ having four pairs of latera, and _S. Peronii_ and _villosum_
having only three pairs of latera: now the males, if classed by
themselves, would inevitably be divided in exactly the same manner,
namely, into two main groups,--the one including the closely similar,
sack-formed males of _S. vulgare_, _ornatum_, and _rutilum_, the other
the pedunculated males of _S. rostratum_, _Peronii_, and _villosum_; but
this latter group would have to be subdivided into two little
sub-groups, the one containing the three-valved male of _S. rostratum_,
and the other the six-valved males of _S. Peronii_ and _S. villosum_. It
should not, however, be overlooked, that the two main groups of
parasites differ from each other, far more than do the two corresponding
groups of species to which they are attached; and, on the other hand,
that the parasitic males of _S. Peronii_ and _S. villosum_ resemble each
other more closely, than do the two hermaphrodite forms;--but it is very
difficult to weigh the value of the differences in the different parts
of species.

Besides these general, there are some closer relations between the
parasites and the animals to which they are attached; thus the most
conspicuous internal character by which _Ibla quadrivalvis_ is
distinguished from _I. Cumingii_, is the length of the caudal appendages
and the greater size of the parts of the mouth; in the parasites, we
have exactly corresponding differences. Out of the six species of
Scalpellum in their ordinary state, _S. ornatum_ is alone quite
destitute of spines on the membrane connecting the valves; and had it
not been for this circumstance, I should even have used the presence of
spines as a generic character; on the other hand, _S. villosum_, in
accordance with its specific name, has larger and more conspicuous
spines than any other species. In the parasites we have an exactly
parallel case; the parasite of _S. ornatum_ being the only one without
spines, and the spines on the parasite of _S. villosum_ being much the
largest! This latter species is highly singular in having no caudal
appendages, and the parasite is destitute of these same organs, though
present inn the parasites of _S. rostratum_ and _S. Peronii_. Again, _S.
villosum_ approaches, in all its characters, very closely to the genus
Pollicipes, and the parasite in having prehensile antennæ, with the disc
but little pointed, and with spines at the further end, departs from
Scalpellum and approaches Pollicipes! Will any one believe that these
several parallel differences, between the Cirripedial parasites and the
Cirripedes to which they are attached, are accidental, and without
signification? yet, this must be admitted, if my view of their male sex
and mature be rejected.

One more, and the most important special relation between the parasites
and the cirripedes to which they are attached, remains to be noticed,
namely that of their prehensile larval antennæ. I observed the antennæ
more or less perfectly in the males of all, and except in _S. villosum_,
in all the species, though so utterly different in general appearance
and structure, I found the peculiar, pointed, hoof-like discs, which are
confined, I believe, to the genera Ibla and Scalpellum. In the
hermaphrodite forms of Scalpellum, I was enabled to examine the antennæ
only in two species, _S. vulgare_ and _S. Peronii_, (belonging,
fortunately, to the two most distinct sections of the genus,) and after
the most careful measurements of every part, I can affirm that, in _S.
vulgare_, the antennæ of the male and of the hermaphrodite are
identical; but that they differ slightly in the proportional lengths of
their segments, and in no other respect, from these same organs in _S.
Peronii_,--in which again the antennæ of the male and of the
hermaphrodite are identical. The importance of this agreement will be
more fully appreciated, if the reader will consider the following table,
in which the generic and specific differences of the antennæ in the
Lepadidæ, as far as known to me, are given. These organs are of high
functional importance; they serve the larva for crawling, and being
furnished with long, sometimes plumose spines, they serve apparently as
organs of touch; and lastly, they are indispensable as a means of
permanent attachment, being adapted to the different objects, to which
the larva adheres. Hence the antennæ might, _à priori_, have been deemed
of high importance for classification. They are, moreover, embryonic in
their nature; and embryonic parts, as is well known, possess the highest
classificatory value. From these considerations, and looking to the
actual facts as exhibited in the following table, the improbability that
the parasites of _S. vulgare_ and _S. Peronii_, so utterly different in
external structure and habits one from the other, and from the
Cirripedes to which they are attached, should yet have absolutely
similar prehensile antennæ with these Cirripedes, appears to me, on the
supposition of the parasites being really independent creatures, and
not, as I fully believe, merely in a different state of sexual
development, insurmountably great.

The parasites of _S. vulgare_ take advantage of a pre-existing fold on
the edge of the scutum, where the chitine border is thicker; and in this
respect there is nothing different from what would naturally happen with
an independent parasite; but in _S. ornatum_ the case is very different,
for here the two scuta are specially modified, _before the attachment of
the parasites_, in a manner which it is impossible to believe can be of
any service to the species itself, irrespectively of the lodgment thus
afforded for the males. So again in _S. rutilum_, the shape of the
scutum seems adapted for the reception of the male, in a manner which
must be attributed to its own growth, and not to the pressure or
attachment of a foreign body. Now there is a strong and manifest
improbability in an animal being specially modified to favour the
parasitism of another, though there are innumerable instances in which
parasites take advantage of pre-existing structures in the animals to
which they are attached. On the other hand, there is no greater
improbability in the female being modified for the attachment of the
male, in a class in which all the individuals are attached to some
object, than in the mutual organs of copulation being adapted to each
other throughout the animal kingdom.

  Generic Characters of the larval prehensile ANTENNÆ, in the Lepadidæ,
  as far as known from their imperfect state of preservation, and the
  number of species examined.

      |Name of Species.
      |    |Length of, from end of disc to the further margin of the
      |    |oblique basal articulation: Scale, fractions of the 1/6000ths
      |    |of an inch.
      |    |    |Length of, from end of disc to the inner margin of the
      |    |    |basal articulation. Scale same.
      |    |    |    |Width of basal segment, in widest part. Scale same.
      |    |    |    |    |Disc, length of. Scale same.
      |    |    |    |    |    |Disc, width of. Scale same.
      |    |    |    |    |    |    |Ultimate segment, length of. Scale
      |    |    |    |    |    |    |same.
      |    |    |    |    |    |    |    |Ultimate segment, width of.
      |    |    |    |    |    |    |    |Scale, fractions of the
      |    |    |    |    |    |    |    |1/20,000ths of an inch.

  LEPAS: disc large, thin, almost _circular_, slightly elongated, with
  several long spines on the hinder margin; end segment with three very
  long, plumose spines on the upper _exterior_ angle.[61]

      |_L. anatifera_ (?)
      |    |62
      |    |    |--
      |    |    |    |20
      |    |    |    |    |23
      |    |    |    |    |    |22
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

      |_L. australis_,
      |    |111
      |    |    |--
      |    |    |    |40
      |    |    |    |    |42
      |    |    |    |    |    |39
      |    |    |    |    |    |    |18
      |    |    |    |    |    |    |    |30

      |_L. pectinata_,
      |    |51
      |    |    |--
      |    |    |    |23
      |    |    |    |    |16
      |    |    |    |    |    |14
      |    |    |    |    |    |    |9
      |    |    |    |    |    |    |    |16

      |_L. fascicularis_,
      |    |60
      |    |    |40
      |    |    |    |22
      |    |    |    |    |16
      |    |    |    |    |    |15
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

  DICHELASPIS: disc _small_, thin, circular, with several spines on the
  hinder margin; end segment, with two long spines on the upper _exterior_
  angle.

      |_D. Warwickii_,
      |    |54
      |    |    |--
      |    |    |    |11
      |    |    |    |    |7-8
      |    |    |    |    |    |7-8
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |13-14

  CONCHODERMA: disc large, thin, _transversely_ elongated, with several
  long spines on the hinder margin; end segment, with two excessively
  long, plumose spines on the upper _exterior_ corner.

      |_C. virgata_,
      |    |82
      |    |    |40
      |    |    |    |28
      |    |    |    |    |25
      |    |    |    |    |    |35
      |    |    |    |    |    |    |12
      |    |    |    |    |    |    |    |26

      |_C. aurita._
      |    |--
      |    |    |--
      |    |    |    |--
      |    |    |    |    |28
      |    |    |    |    |    |40
      |    |    |    |    |    |    |11
      |    |    |    |    |    |    |    |26

  ALEPAS: disc small, slightly elongated, with two or more spines on the
  hinder margin; end segment, with two long spines on the upper _inner_
  corner, and four shorter ones on the exterior corner.

      |_A. cornuta_,
      |    |60
      |    |    |--
      |    |    |    |24
      |    |    |    |    |14
      |    |    |    |    |    |12
      |    |    |    |    |    |    |8
      |    |    |    |    |    |    |    |20

  IBLA (parasitic males of): disc, _hoof-like_, _pointed_, elongated, with
  a single spine on the hinder margin; end segment, with four short spines
  on the upper exterior corner.

      |_I. Cumingii_,
      |    |22
      |    |    |--
      |    |    |    |7-8
      |    |    |    |    |7
      |    |    |    |    |    |--
      |    |    |    |    |    |    |3-4
      |    |    |    |    |    |    |    |7-8

      |_I. quadrivalvis_,
      |    |32-33
      |    |    |--
      |    |    |    |10
      |    |    |    |    |8
      |    |    |    |    |    |5
      |    |    |    |    |    |    |4
      |    |    |    |    |    |    |    |8

  SCALPELLUM: disc _hoof-like_, generally _pointed_ and elongated, with a
  single spine on the hinder margin; end segment, with a notch on the
  inner[61] side, bearing two spines, longer than on the exterior corner.

      |_S. vulgare_,
      |    |39
      |    |    |19
      |    |    |    |10
      |    |    |    |    |10-11
      |    |    |    |    |    |5-6
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |7

      |_S. ornatum_,
      |    |36
      |    |    |21
      |    |    |    |10
      |    |    |    |    |12
      |    |    |    |    |    |--
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

      |_S. Peronii_,
      |    |30
      |    |    |19
      |    |    |    |--
      |    |    |    |    |9
      |    |    |    |    |    |6
      |    |    |    |    |    |    |5
      |    |    |    |    |    |    |    |10

  POLLICIPES: disc small, _hoof-like_, not pointed, with a single spine on
  the hinder margin; end segment, as in _Scalpellum_.

      |_P. cornucopia_,
      |    |20
      |    |    |--
      |    |    |    |6
      |    |    |    |    |6
      |    |    |    |    |    |6
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |8

   [61] In the diameter of the disc, the thin membranous border,
   which is present in the first three genera, is included; but I
   have some doubts, whether this border be not the first rim of
   cementing tissue, as all the specimens, of which measurements are
   here given, had been removed after attachment. In using the terms
   inner and outer sides of the end segment, it is supposed, that
   this segment is stretched straight forwards, instead of being
   bent rectangularly outwards, as in its natural position; and then
   there can be no doubt which is the inner and outer sides.

It should be observed that the evidence in this summary is of a
cumulative nature. If we think it highly, or in some degree
probable,--from the ordinary form of _Ibla Cumingii_ having been shown
on good evidence to be exclusively female,--from the absence of ova and
ovaria in the assumed males of both species of Ibla, at the period when
their vesiculæ seminales were gorged with spermatozoa,--from the close
general resemblance between the parts of the mouth in the parasites and
in the Iblas to which they are attached,--from the differences between
the two parasites being strictly analogous to the differences between
the two species of Ibla,--from the generic character of their prehensile
antennæ,--and from other such points,--if from these several
considerations, we admit that these parasites really are the males of
the two species to which they adhere, then in some degree the occurrence
of parasitic males in the allied genus Scalpellum is rendered more
probable. So the absolute similarity in the antennæ of the males and
hermaphrodites both in _S. vulgare_ and _S. Peronii_; and such relations
as that of the relative villosity of the several species in this same
genus, all in return strengthen the case in Ibla. Again, the six-valved
parasites of _S. Peronii_ and _S. villosum_ are so closely similar, that
their nature, whatever it may be, must be the same; hence we may add up
the evidence derived from the identity of the antennæ in the parasite
and hermaphrodite _S. Peronii_, with that from the antennæ in the male
_S. villosum_, approaching in character to Pollicipes, to which genus
the hermaphrodite is so closely allied; and to this evidence, again, may
be added the singular coincident absence of caudal appendages in the
male and hermaphrodite _S. villosum_. If these two six-valved parasites
be received as the complemental males of their respective species, no
one, probably, will doubt regarding the nature of the parasite of _S.
rostratum_, in which the direct evidence is the weakest; but even in
this case, the particular point of attachment, and the state of
development of the valves, form a link connecting in some degree, the
parasites of the first three species with the last two species of
Scalpellum, in accordance with the affinities of the hermaphrodites.

When first examining the parasites of _S. rostratum_, _S. Peronii_, and
_S. villosum_, before the weight of the cumulative evidence had struck
me, and noting their apparent state of immaturity, it occurred to me
that possibly they were the young of their respective species, in their
normal state of development, attached to old individuals, as may often
be seen in Lepas; this, however, would be a surprising fact, considering
that _S. rostratum_ and _S. Peronii_ are ordinarily attached, in a
certain definite position, to horny corallines, and considering that the
exact points of attachment in these three parasites, (of which I have
seen no other instance amongst common Cirripedes,) namely, between the
scuta, would inevitably cause their early destruction, either directly
or indirectly, by their living supports being destroyed. Nevertheless, I
carefully examined a young specimen of _S. rostratum_ only thrice as
large as the parasite; and not having very young specimens of _S.
Peronii_ and _villosum_, I procured the young of closely-allied forms,
namely, of _S. vulgare_, (with a capitulum only 4/100th of an inch in
length,) and of _Pollicipes polymerus_, (with a capitulum of less size
than that of one of the parasites,) and there was not the least sign of
anything abnormal in the development of the valves. In _S. vulgare_, at
a period when the calcified scuta could have been only 1/100th of an
inch in length, (and therefore considerably less than the scuta in the
parasites,) the upper latera must have been as much as 4/1000ths of an
inch in length, and the valves of the lower whorl certainly
distinguishable.

To sum up the evidence on the sex of the parasites, I was not able to
discover a vestige of ova or ovaria in the two male Iblas; and I can
venture to affirm positively, that the parasites of _S. Peronii_ and _S.
villosum_ are not female. On the other hand, in the two male Iblas, I
was enabled to demonstrate all the male organs, and I most distinctly
saw spermatozoa. In the parasitic complemental male of _S. vulgare_, I
also most plainly saw spermatozoa. In the parasites of _S. rostratum_,
_S. Peronii_, and _S. villosum_, the external male organs were present.
I may here just allude to the facts given in detail under Ibla, showing
that it was hardly possible that I could be mistaken regarding the
exclusively female sex of the ordinary form of _I. Cumingii_, seeing how
immediately I perceived all the male organs in the hermaphrodite _I.
quadrivalvis_; and as the parasite contained spermatozoa and no ova, the
only possible way to escape from the conclusion that it was the male and
_I. Cumingii_ the female of the same species, was to invent two
hypothetical creatures, of opposite sexes to the Ibla and its parasite,
and which, though Cirripedes, would have to be locomotive! I insisted
upon this alternative, because if the parasite of _I. Cumingii_ be the
male of that species, then unquestionably we have in _I. quadrivalvis_ a
male, complemental to an hermaphrodite,--a conclusion, as we have seen,
hardly to be avoided in the genus Scalpellum, even if we trust
exclusively to the facts therein exhibited.

With respect to the positions of the parasitic males, in relation to the
impregnation of the ova in the females and hermaphrodites, it may be
observed that in the two male Iblas, the elongated moveable body seems
perfectly adapted for this end; in the males of the first three species
of Scalpellum, the spermatozoa, owing to the manner in which the thorax
is bent when protruded, would be easily discharged into the sack of the
female or hermaphrodite; this would likewise probably happen with the
complemental male of _S. rostratum_, considering its position within the
orifice of the capitulum, between the mouth and the adductor scutorum
muscle. The males of _S. Peronii_ and _villosum_ being fixed a little
way beneath the orifice of the sack, below the adductor muscle, are less
favorably situated, but the spermatozoa would probably be drawn into the
sack by the ordinary action of the cirri of the hermaphrodite, and
therefore would at least have as good a chance of fertilising some of
the ova, as the pollen of many dioecious plants, trusted to the wind,
has of reaching the stigmas of the female plants. Regarding the final
cause, both of the simpler case of the separation of the sexes,
notwithstanding that the two individuals, after the metamorphosis of the
male, become indissolubly united together, and of the much more singular
fact of the existence of Complemental males, I can throw no light; I
will only repeat the observation made more than once, that in some of
the hermaphrodites, the vesiculæ seminales were small, and that in
others the probosciformed penis was unusually short and thin.

Viewing the parasitic males, in relation to the structure and appearance
of the species to which they belong, they present a singular series. In
_S. Peronii_ and _S. villosum_, the internal organs have the appearance
of immaturity; the shape of the capitulum is specially modified for its
reception between the scuta of the hermaphrodite, and several of the
valves have not been developed. This atrophy of the valves, is carried
much further in _S. rostratum_. In Ibla, many of the parts are embryonic
in character, but others mature and perfect; some parts, as the
capitulum, thorax, and cirri, are in a quite extraordinary state of
atrophy; in fact, the parasitic males of Ibla consist almost exclusively
of a mouth, mounted on the summit of the three anterior segments of the
21 normal segments of the archetype crustacean. In the males of the
first three species of Scalpellum, some of the characters are
embryonic,--as the absence of a mouth, the presence of the abdominal
lobe, and the position of the few existing internal organs; other
characters, such as the general external form, the four bead-like
valves, the narrow orifice, the peculiar thorax and limbs, are special
developments. These three latter parasites, certainly, are wonderfully
unlike the hermaphrodites or females to which they belong; if classed as
independent animals, they would assuredly be placed not in another
family, but in another Order. When mature they may be said essentially
to be mere bags of spermatozoa.

In looking for analogies to the facts here described, I have already
referred to the minute male Lerneidæ which cling to their females,--to
the worm-like males of certain Cephalopoda, parasitic on the
females,--and to certain Entozoons, in which the sexes cohere, or even
are organically blended by one extremity of their bodies. The females in
certain insects depart in structure, nearly or quite as widely from the
Order to which they belong, as do these male parasitic Cirripedes; some
of these females, like the males of the first three species of
Scalpellum, do not feed, and some, I believe, have their mouths in a
rudimentary condition; but in this latter respect, we have, amongst the
Rotifera, a closely analogous case in the male of the Asplanchna of
Gosse, which was discovered by Mr. Brightwell[62] to be entirely
destitute of mouth and stomach, exactly as I find to be the case with
the parasitic male of _S. vulgare_, and doubtless with its two close
allies. For any analogy to the existence of males, complemental to
hermaphrodites, we must look to the vegetable kingdom.

Finally, the simple fact of the diversity in the sexual relations,
displayed within the limits of the general Ibla and Scalpellum, appears
to me eminently curious; we have (1st) a female, with a male (or rarely
two) permanently attached to her, protected by her, and nourished by any
minute animals which may enter her sack; (2d) a female, with successive
pairs of short-lived males, destitute of mouth and stomach, inhabiting
two pouches formed on the under sides of her valves; (3d) an
hermaphrodite, with from one or two, up to five or six similar
short-lived males without mouth or stomach, attached to one particular
spot on each side of the orifice of the capitulum; and (4th)
hermaphrodites, with occasionally one, two, or three males, capable of
seizing and devouring their prey in the ordinary Cirripedial method,
attached to two different parts of the capitulum, in both cases being
protected by the closing of the scuta. As I am summing up the
singularity of the phenomena here presented, I will allude to the
marvellous assemblage of beings seen by me within the sack of an _Ibla
quadrivalvis_,--namely, an old and young male, both minute, worm-like,
destitute of a capitulum, with a great mouth, and rudimentary thorax and
limbs, attached to each other and to the hermaphrodite, which latter is
utterly different in appearance and structure; secondly, the four or
five, free, boat-shaped larvæ, with their curious prehensile antennæ,
two great compound eyes, no mouth, and six natatory legs; and lastly,
several hundreds of the larvæ in their first stage of development,
globular, with horn-shaped projections on their carapaces, minute single
eyes, filiformed antennæ, probosciformed mouths, and only three pair of
natatory legs; what diverse beings, with scarcely anything in common,
and yet all belonging to the same species!

   [62] 'Annals of Natural History,' vol. ii, (2d series, 1848,) p.
   153, Pl. vi. Mr. Dalrymple has published a very interesting paper
   on the same subject in the 'Philosophical Transactions,' (p.
   342,) 1849; and there is another Memoir by Mr. Gosse in the
   'Annals of Natural History,' vol. vi, (1850,) p. 18.


_Genus_--POLLICIPES. Pl. VII.

  POLLICIES. _Leach._ Journal de Physique, tom. lxxxv, Julius,
        1817.[63]

  LEPAS. _Linn._ Systema Naturæ, 1767.

  ANATIFA. _Brugière._ Encyclop. Méthod. (des Vers), 1789.

  MITELLA. _Oken._ Lehrbuch der Naturgeschichte, 1815.

  RAMPHIDIONA. _Schumacher._ Essai d'un Nouveau Syst. &c., 1817
        (ante Julium).

  POLYLEPAS. _De Blainville._ Dict. des Sc. Nat., 1824.

  CAPITULUM (secundum Klein). _J. E. Gray._ Annals of Philos., tom.
        x, new series, Aug. 1825.

   [63] This is one of the rare cases in which, after much
   deliberation, and with the advice of several distinguished
   naturalists, I have departed from the Rules of the British
   Association; for it will be seen that _Mitella_ of Oken, and
   _Ramphidiona_ of Schumacher, are both prior to _Pollicipes_ of
   Leach; yet, as the latter name has been universally adopted
   throughout Europe and North America, and has been extensively
   used in geological works, it appears to me to be as useless as
   hopeless to attempt any change. It may be observed that the genus
   _Pollicipes_ was originally proposed by Sir John Hill ('History
   of Animals,' vol. iii, p. 170), in 1752, but as this was before
   the discovery of the binomial system, by the Rules it is
   absolutely excluded as of any authority. In my opinion, under all
   these circumstances, it would be mere pedantry to go back to
   Oken's 'Lehrbuch der Naturgeschichte' for the name _Mitella_,--a
   work little known, and displaying entire ignorance regarding the
   Cirripedia.

_Valvæ ab 18 usque ad 100 et amplius: lateribus verticilli inferioris
multis; lineis incrementi deorsùm ordinatis: sub-rostrum semper adest:
pedunculus squamiferus._

Valves from 18 to above 100 in number: latera of the lower whorl
numerous, with their lines of growth directed downwards: sub-rostrum
always present: peduncle squamiferous.

Hermaphrodite; filamentary appendages either none, or numerous and
seated on the prosoma and at the bases of the first pair of cirri;
labrum bullate; trophi various; olfactory orifices generally highly
prominent; caudal appendages uni-articulate and spinose, or
multi-articulate.

    Attached to fixed, or less commonly to floating objects, in the
    warmer temperate, and tropical seas.

It has been remarked, under Scalpellum, how imperfectly that genus is
separated from Pollicipes; and we have seen under _Scalpellum villosum_
that the addition of a few small valves to the lower whorl, would
convert it into a Pollicipes, most closely allied to _P. sertus_ and
_spinosus_. It has also been shown, that the six recent species of
Pollicipes might be divided into three genera, of which _P. cornucopia_,
_P. elegans_, and _P. polymerus_, would form one thoroughly natural
genus, as natural as Lepas and the earlier genera; _P. mitella_ would
form a second; and _P. sertus_ and _P. spinosus_ a third; but I have
acted to the best of my judgment in at present retaining the six species
together. As far as the valves of the capitulum are concerned, it would
be very difficult to separate _P. mitella_ from _P. sertus_ and
_spinosus_.

_Description._ The number of valves in the capitulum has in this genus
acquired its maximum. The number varies considerably in the same
species, and even on opposite sides of the same individual, and
generally increases with age. It is more important, that the number of
the whorls in _P. cornucopia_, and in the two following closely-allied
forms, also increases with age. In _P. sertus_ and _P. spinosus_, even
the number of the whorls varies in different individuals, independently
of age. The valves are arranged alternately with those above and below;
they are generally thick and strong, making the capitulum somewhat
massive; in some species they are subject to much disintegration; but in
others, the apices of the several valves, especially of the carina and
rostrum, are well preserved, and project freely: they are covered with
membrane, which, differently from in most species of Scalpellum, either
does not bear any spines, or only exceedingly minute points. In all the
species there is a sub-rostrum and sub-carina, and often beneath these a
second sub-rostrum and sub-carina. In medium-sized specimens there are
at least 20 valves in the lowermost whorl. The carina is either straight
or curved, but never rectangularly bent, and is always of considerable
breadth. None of the valves are added to at their upper ends. The scuta
have a deep pit for the adductor muscle. The valves lie either some
little way apart, or more commonly close together. In _P. mitella_ the
scuta and terga are locked together by a fold, and the valves of the
lower whorl overlap each other in a peculiar manner, resembling that in
which the compartments in the shells of Sessile Cirripedes fold over
each other.

The _Peduncle_ is of considerable length in some of the species, and
rather short in others; it is, in every case, clothed with calcified
scales. The scales in the first four species are placed alternately and
symmetrically; they are formed and added to in the same manner as in
Scalpellum; they differ in size according to the size of the individual,
and consequently the lower scales on the peduncle, formed when the
specimen was young, are smaller than the upper scales; the lower scales
are separated from each other by wide interspaces of membrane, owing to
the continued growth of the peduncle by the formation of new layers of
membrane, and the disintegration of the old outer layers. Each scale is
invested by tough membrane (or has been, for it is often abraded off),
in the same manner as the valves; each is furnished with one or more
tubuli, in connection with the underlying corium. In _P. sertus_ and _P.
spinosus_, the scales are small, spindle-shaped, and not of equal sizes,
and the rows are distant from each other, so that their alternate
arrangement is not distinguishable; in these two species, new scales are
formed round the summit of the peduncle, and the growth of each is
completed whilst remaining in the uppermost row; but, besides these
normal scales, such as exist in the other species of Pollicipes and in
Scalpellum, new scales are formed in the lower part of the peduncle,
which are generally of very irregular shapes, are often larger than the
upper ones, are crowded together, and sometimes do not reach the outer
surface of the membrane. This formation of scales in the lower part of
the peduncle, independently of the regular rows round the uppermost
part, is perhaps a feeble representation of the calcareous cup at the
bottom of the peduncle in the genus Lithotrya. The prehensile antennæ
will be described under _P. cornucopia_.

_Size._--Most of the species are large: and _P. mitella_ is the most
massive of the Pedunculated Cirripedes.

The _Mouth_ is not placed far from the adductor muscle. The labrum is
highly bullate. The mandibles have either three or four main teeth (Pl.
X, fig. 1), with often either one or two smaller teeth inserted between
the first and second. The maxillæ (Pl. X, figs. 13, 14), have their
edges either straight and square, or notched, or more commonly with two
or three prominences bearing tufts of finer spines. The outer maxillæ
(fig. 17) generally have a deep notch on their inner edges, but this is
not invariable. The olfactory orifices in most of the species are highly
prominent.

_Cirri._--The first pair is never placed far distant from the second.
The posterior cirri have strong, somewhat protuberant segments; and
between each of the four or five pair of main spines (Pl. X, fig. 27),
there is a rather large tuft of straight, fine, short bristles. The
second and third pair have the basal segments, either of the anterior
rami, or of both rami, so thickly clothed with spines (fig. 25), as to
be brush-like: in _P. mitella_, however, the third pair is like the
three posterior pair in the arrangement of its spines, in this respect
resembling the sessile Chthamalinæ. The caudal appendages are either
uni-articulate and spinose, or multi-articulate: it is remarkable that
there should be this difference in such closely allied species as _P.
cornucopia_ and _P. polymerus_: the short, obtuse, obscurely-articulated
caudal appendage of the former species (fig. 22) makes an excellent
passage from the uni-articulate (fig. 19) to the multi-articulate form,
as in _P. mitella_.

The stomach, in those species which I opened, is destitute of cæca; the
hepatic glands are arranged in straight lines; the rectum is unusually
short. The prosoma is well developed.

In _P. cornucopia_, _P. elegans_, and _P. polymerus_, there are numerous
filamentary appendages both on the prosoma, and at the bases of the
first pair of cirri: these appendages are occupied by testes, and I
suspect stand in relation to the length of the peduncle and consequent
great development of the ovaria. In order to give space for the
filamentary appendages, the sack (generally roughened by small
inwardly-pointing papillæ) penetrates more deeply than usual into the
upper part of the peduncle. There are small ovigerous fræna in _P.
sertus_, _P. spinosus_, and _P. mitella_: in the three other species,
the frænum or fold occupies the usual position on each side, and is
large; but in one specimen carefully examined by me, I was unable to see
any glands; and in another specimen, the ovigerous lamellæ were not
attached to the fræna; hence I conclude that the fræna are functionless
in these three species.

_Affinities._--I have already remarked on the close relationship between
this genus and Scalpellum; there is also some affinity with Lithotrya.

    _Distribution._--All over the world. The _P. cornucopia_ ranges
    from Scotland to Teneriffe: the _P. polymerus_ is found in
    opposite hemispheres in the Pacific Ocean, extending from
    California to at least as far as 32° south of the Equator.

_Geological History._--Having so lately given, in the 'Memoirs of the
Palæontographical Society,' a full account of all the fossil species
known, I will not repeat here the conclusions there arrived at. I will
only state, that species of Pollicipes are found in all the formations,
extending from the Lower Oolite to the Upper Tertiary beds.


1. POLLICIPES CORNUCOPIA. Pl. VII, fig. 1.

  POLLICIPES CORNUCOPIA. _Leach._ Encyclop. Brit. Supp., vol. iii,
        1824.

  ---- SMYTHII, var. _Leach_. Ibid.

  LEPAS POLLICIPES. _Gmelin._ Systema Naturæ, 1789.

  ---- GALLORUM. _Spengler._ Skrivter Naturhist. Selskabet, Bd. i,
        Tab. vi, fig. 9, 1790.

_P. capitulo, valvarum duobus aut pluribus sub-rostro verticillis
instructo: valvis albis, aut glaucis: pedunculo, squamarum densis
verticillis symmetricè dispositis._

Capitulum with two or more whorls of valves under the rostrum; valves
white or gray; scales on the peduncle symmetrically arranged in close
whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines:
segments in the first cirrus less than half the number of those in the
sixth cirrus: caudal appendages multi-articulate: filamentary appendages
attached to the prosoma.

    Coast of Portugal; mouth of the Tagus. England,[64] Ireland, and
    the Frith of Forth in Scotland. Mediterranean (according to
    Brugière): Teneriffe: Mogador, Africa.

   [64] This species is said by Montagu ('Test. Brit. Supplement')
   to have been found attached to drift timber in the Frith of
   Forth, and to the bottom of a wrecked vessel towed into
   Dartmouth. According to Mr. W. Thompson ('Annals of Nat. Hist.'
   vol. xiii, p. 436), it has been found attached to wood-work near
   Dublin.

Capitulum, obtusely triangular, massive: valves close together, rather
thick, with their exterior surfaces convex, naked, except in the lower
parts, where united together by tough, greenish-brown membrane,
destitute of spines. The edges of the orifice are widely bordered by
membrane, coloured fine crimson red. The valves, in a specimen with a
capitulum above three quarters of an inch long, were 52 in number; in a
specimen one fifth of an inch long, only between 20 and 30. Two whorls
of valves are distinct beneath the carina and rostrum. In one specimen
in Mr. Cuming's collection, with a capitulum 1.4 of an inch long, there
were three whorls beneath the rostrum, and four beneath the carina. The
scuta, terga, and carina are much larger than the other valves.

_Scuta_, oval, the basal and tergo-lateral margins sweeping into each
other, and the apex pointed; internally (Pl. VII, fig. 1 _a_) the pit
for the adductor muscle is deep.

_Terga_, larger than the scuta, internally (fig. 1 _a_) slightly
concave; carinal margin much curved and protuberant; basal angle blunt;
scutal margin either curved with the upper part straight, or formed of
two almost distinct lines, corresponding with the tergal margin of the
scutum, and with one of the sides of the upper latus.

_Carina_, much curved, extending far up between the terga, internally
deeply concave, widening much from the top to the bottom; basal margin
highly protuberant, with a central portion either truncated and very
slightly hollowed out, or bluntly and rectangularly pointed, with the
apex itself rounded.

_Rostrum_, not one third of the length of the carina, concave,
triangular, with the basal margin slightly protuberant. Of the other
valves, including the sub-carina and sub-rostrum, the shape of their
inner surfaces is sub-triangular, with the basal margin convex;
externally the umbones are pointed, and slightly curled inwards, so as
to overlap each other like tiles: the smaller valves, however, of the
lower whorls (fig. 1 _a_) are more or less transversely elongated, so as
to become almost elliptic instead of triangular. Of the latera, the
upper pair, which corresponds to the interspace between the scuta and
terga, is the largest, but barely exceeds in size the pair answering to
the carinal latera in Scalpellum, which lie between the terga and
carina: the next largest pair is the rostral, or that between the scuta
and rostrum. Some, however, of the lower latera are of nearly equal
size.

_Peduncle_, narrower, but generally longer than the capitulum; upper
part encased with small calcareous scales, with their apices curved
inwards, and overlapping each other. The inner surface of each scale is
triangular, with the basal margin protuberant. The scales continue to
grow or be added to, only in about the ten upper whorls, which form but
a small part of the whole peduncle; in the lower part, the scales become
further and further separated from each other. The surface of
attachment, in full-grown specimens, is broad; but in two very young
specimens, which I removed with great care after the action of potash, I
found the peduncle ending in a filiform prolongation, such as often
occurs in _Scalpellum vulgare_ and in _Lepas fascicularis_. At the
extremity of the pointed peduncle, there were seated the larval
prehensile antennæ, of which the following measurements are given to
show how minute they are.

                                                            _Inch._
  Length, from apex of disc, to the further
      edge of the basal articulation                       20/6000
  Breadth of basal segment, in broadest part                6/6000
  Hoof-like disc, length of                                 6/6000
  Ultimate segment, entire length of                        6/6000
      "       "     breadth, in broadest part               6/20000

The disc resembles a broad, rounded hoof, very little longer than broad,
and narrowed in at the heel; the apex is not at all pointed, and bears
some minute and thin spines. There is one large spine on the under side
of the disc; and another on the basal segment, on the outside, in the
usual position. The ultimate segment is long and thin; it has a notch on
the inner side (the segment supposed to be stretched forward), bearing
two or three long flexuous spines; and there are three or four other
spines on the summit: altogether there is a close resemblance with the
antennæ in Scalpellum, excepting that the hoof-like disc is not here
pointed.

_Colours._--Valves internally tinted, in parts, grey; peduncle, brown;
corium of sack, purplish-brown, of peduncle, rich coppery brown; cirri,
banded dorsally, and with the front surfaces of the segments,
purplish-brown. Edge of the orifice of sack, fine crimson red. The
specimen here described had been dried for a few weeks, and was then
moistened.

_Dimensions._--The largest specimen which I have seen, in Mr. Cuming's
collection, had a capitulum 1 and 4/10ths of an inch long; a fine
specimen, from Teneriffe, was 9/10ths in length. In a specimen with a
capitulum 1/20th of an inch long, and about the same in breadth, there
were eighteen valves; so that, besides the principal valves, five pair
of latera, the sub-carina, and sub-rostrum, were already developed, and
on the upper part of the peduncle, there were many calcareous scales.

_Filamentary Appendages._--The prosoma is well-developed, with thirteen
or fourteen pair of short, blunt filaments, placed close together in two
longitudinal rows; those nearest the thorax are the longest; outside
this double row, on each side, there is a row of papillæ, indicating a
tendency to the formation of two other rows of filaments. There is a
pair of longer filaments, one on each side of the mouth, pointing
upwards, and thinly clothed with long spines; at the bases of the first
pair of cirri there is a second pair of filaments, shorter and bearing a
few minute spines. The bottom of the sack is studded with small rounded
papillæ, with roughened summits.

_Mouth_, not placed very far from the adductor muscle.

_Labrum_, highly bullate, equalling, in its longitudinal diameter, the
rest of the mouth; upper part square, not overhanging the lower part;
there are some small teeth on the crest.

_Palpi_, oval, outer and inner margins nearly alike, thickly clothed
with spines.

_Mandibles_, with three very strong, yellow teeth; inferior point broad,
coarsely pectinated. In one specimen, on one side, the third tooth was
represented by two smaller teeth.

The _Maxillæ_ bear three conspicuous tufts of fine bristles, separated
by larger spines; the first tuft is placed close to the two, upper,
large, but unequally-sized spines; the second tuft is placed in the
middle, and the third at the inferior angle. The two latter tufts stand
on prominences; between the two upper tufts there are three pair, and
between the two lower tufts four or more pair of rather strong spines:
(see the figure, 13, Pl. X, in the allied _P. polymerus_.)

_Outer Maxillæ_, with the inner edge divided in the middle by a
conspicuous notch, and with the bristles above and below short, making
two _equal_ combs. On the exterior surface, the bristles are longer and
more spread out. Olfactory orifices prominent, protected by a punctured
swelling between the bases of the first pair of cirri.

_Cirri_, short and rather thick; the first pair is not far removed from
the second. The segments of the three posterior pair are somewhat
protuberant, bearing six pair of short, strong spines, graduated in
length, between which there is a very thick, longitudinal brush of
short, fine, straight bristles, of which the lower ones are the longest;
some thick, minute spines arise from the upper lateral edges of the
segments. The spines in the dorsal tufts are short, much crowded, and of
nearly equal length; see figure, 27, Pl. X, in the allied _P.
polymerus_. In a specimen in which the sixth cirrus had seventeen
segments, the first cirrus had, in the shorter ramus, eight segments, of
which the lower four were thick and protuberant, with the spines doubly
serrated. In this same specimen, the anterior ramus of the second cirrus
had twelve segments, of which the five basal ones were highly
protuberant, and thickly clothed with non-serrated spines. In the third
cirrus the basal segments of the anterior ramus are highly protuberant.
The basal segments in the posterior rami of both these cirri, are
slightly protuberant, but otherwise resemble the segments in the three
posterior pair.

The _Caudal Appendages_ (Pl. X, fig. 22), in full-grown specimens, just
exceed in length the lower segments of the pedicels of the sixth cirrus;
they are nearly cylindrical, bluntly pointed, with five oblique
imperfect articulations; the lower or basal articulations cannot be
traced all round, being distinct only on the ventral surface. There is a
row of short spines round the upper edge of each segment, with a little,
short tuft on the point of the terminal segment. In a rather young
specimen, however, with its capitulum one fifth of an inch long, each
appendage certainly consisted of a single segment, with spines only on
the summit.

_Penis_ purple, with excessively short and fine spines in tufts, chiefly
near the extremity. In a specimen with a capitulum only one fifth of an
inch long, the penis consisted of a mere pointed papilla, not so long as
the caudal appendage, and therefore equalling in length only the lower
segment of the pedicel of the sixth cirrus.

_Ovigerous fræna._--I could see none, though there were two large
lamellæ in the sack. The ova were flesh-coloured, but they had been
dried and then placed in spirits. The ova were wonderfully numerous,
oval, much elongated, and 1/100th of an inch in length.


2. POLLICIPES ELEGANS.

  POLLICIPES ELEGANS. _Lesson._ Voyage de la Coquille, tom. ii, p.
        441, 1830, et Illust. Zool., Pl. xxxix, 1831.

  ---- RUBER. _G. B. Sowerby._ Zoolog. Proc., 1833, p. 74.

_P. capitulo, valvarum duobus aut pluribus sub-rostro verticillis
instructo: valvis et pedunculi squamis rufo-aurantiacis: squamarum
verticillis densis symmetricè dispositis._

Capitulum with two or more whorls of valves under the rostrum: valves
and scales of peduncle reddish-orange; the latter symmetrically arranged
in close whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines;
segments is in the first cirrus more than half the number of those in
the sixth cirrus; caudal appendages multi-articulate; filamentary
appendages attached to the prosoma.

    Coast of Peru, Payta, attached to wooden posts, according to
    Lesson: Lobos Island, Peru, Mus. Cuming: West Coast of Mexico,
    Tehuantepec, on an exposed rock, according to Hinds.

The resemblance of this species is so close to _P. cornucopia_, that it
is quite useless to do more than point out the few points of difference.
Valves of the capitulum and scales of the peduncle, coloured (after
having been in spirits,) reddish-orange. In a specimen in which the
capitulum was 1.3 of an inch in length, there were three whorls of
valves below the carina; in this large specimen altogether there were
about eighty valves; in medium-sized specimens, the number is about the
same as in _P. cornucopia_. The upper latus, (viewed internally,) has an
area about twice as large as that latus, which corresponds to the
interspace between the carina and terga; whereas in _P. cornucopia_ the
upper latus is only slightly larger than this same valve. The apex of
the basal internal margin of the carina is here rounded, instead of
being square, as is generally the case with _P. cornucopia_. The strong
membranous margin of the orifice of the sack, in its upper part, is
almost one third as wide as the widest part of the terga, whereas in _P.
cornucopia_ it is only one fourth of this same width. The peduncle
apparently is rather longer, compared with _P. cornucopia_, and the
calcareous scales on it perhaps a little larger in proportion.

In a very young specimen, with the capitulum barely exceeding 1/20th of
an inch in length, I could distinguish the sub-rostrum, sub-carina, the
upper, and some of the lower latera.

_Filamentary Appendages._--These, in a medium-sized specimen, are
arranged on the prosoma in four longitudinal approximate rows, there
being twelve in each row; those in the two outer rows are only half the
length of those in the two inner rows; those nearest the thorax are the
longest; there are some papillæ outside the outer rows. In a very large
specimen with its capitulum 1.3 in length, these filaments were very
much more numerous, and some were placed on the first segment of the
thorax, and at the bases of several of the posterior cirri. Some of the
filaments are bifid, trifid, and even branched. In all the specimens, at
the bases of the first pair of cirri, there are, on each side, a pair of
filaments, (one below the other,) pointing upwards, less than half as
long as those on the prosoma: also on each side of the mouth, there is a
longer and thicker filament, pointing upwards, with a few very minute
scattered spines on it; the apices of these three pair of filaments, as
well as of some of the others, are roughened with very minute pectinated
scales. All these filaments were gorged with the branching testes.

_Mouth._--The parts are closely similar to those in _P. cornucopia_; in
the mandibles, the interspace between the third tooth and the inferior
angle, is slightly pectinated: in the maxillæ, there are six or eight
pairs of spines between the two upper tufts of fine spines.

_Cirri._--These are in most respects similar, to those of _P.
cornucopia_. In a specimen in which the sixth cirrus had eighteen
segments, the shorter ramus of the first pair had ten segments, of which
the five lower segments were thick and clothed with doubly serrated
spines. In the second cirrus the anterior ramus had fifteen segments, of
which the four basal ones were highly protuberant, and thickly clothed
with spines. These spines, and some on the third cirrus, and a few on
the first cirrus, have peculiar bent teeth, presently to be described
under _P. polymerus_. These singularly toothed spines are absent in _P.
cornucopia_. From the above numbers, we see that the first and second
pairs of cirri have more segments in proportion to the sixth pair, than
in _P. cornucopia_; and in the second pair, a fewer proportional number
of the basal segments are protuberant and thickly clothed with spines.

_Caudal Appendages_, shorter than the lower segments of the pedicels of
the sixth cirrus, with only four articulations; rather constricted near
the base.

The _Ovigerous Fræna_ consist of very long and prominent folds, thinning
out to nothing towards the bases of the scuta, but not furnished, as far
as I could see, with glands, and therefore not normally functional.

_Diagnosis with P. cornucopia._--The reddish-orange colour of the valves
alone suffices. There is a very slight difference, in the larger
proportional size of the upper latera, and in the outline of the basal
margin of the carina. In the maxillæ there is, in _P. elegans_, a
greater width between the two upper tufts of fine spines. In the cirri,
the segments in the first pair, are more than half as many as those in
the sixth pair; in the anterior ramus of the second pair, only 4/15ths
of the segments are protuberant and brush-like, whereas in _P.
cornucopia_ 5/12ths are in this condition.


3. POLLICIPES POLYMERUS. Pl. VII, fig. 2.

  POLLICIPES POLYMERUS.(!) _G.B. Sowerby._ Proc. Zool. Soc., 1833,
        p. 74.

  --MORTONI. (!) _Conrad._ Journal Acad. Nat. Sci. Philadelphia,
        vol. vii, p. 261, Pl. xx, fig. 12, 1837.

_P. capitulo, valvarum duobus, tribus, aut pluribus sub-rostro
verticillis instructo: valvis sub-fuscis: lateribus à supremo ad infimum
gradatim quoad magnitudinem positis: carinæ margine basali (introrsùm
spectanti) ad medium excavato: pedunculi squamarum verticillis densis,
symmetricè dispositis._

Capitulum with two, three, or more whorls of valves under the rostrum:
valves brownish: latera regularly graduated in size from the uppermost
to the lowest: carina with the basal margin, (viewed internally,)
hollowed out in the middle: scales of the peduncle symmetrically
arranged in close whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines;
caudal appendages uniarticulate; filamentary appendages attached to the
prosoma.

    Upper California, St. Diego and Barbara, 32° to 35° N.,
    according to Conrad; Mus. Cuming: Low Archipelago, Pacific
    Ocean; Mus. Coll. of Surgeons: Southern Pacific Ocean, collected
    during the Antarctic Expedition, Mus. Brit.

_Capitulum_, but little compressed, broad, with the scuta and terga
placed in a more oblique direction, with respect to the peduncle, than
is usual, so that the line of orifice forms an unusually small angle
with the basal margin of the capitulum. The capitulum is composed of
several whorls of valves, which gradually decrease in size from above
downwards. In a medium-sized specimen there were four whorls under the
rostrum; in the lowest of these whorls, there were between eighty and
ninety valves, and in the whole capitulum from one hundred and seventy,
to one hundred and eighty. The valves in the lower whorls are not of
equal sizes. Viewed externally, the valves seem to touch and overlap
each other; viewed internally (Pl. VII, fig. 2 _a_) they are found to be
just separated from each other by transparent membrane; none of the
valves are articulated together. The outer surfaces of nearly all the
valves, except in the two last formed whorls, are much disintegrated,
and seem to be composed of alternate white and brown layers of shell.
The membrane connecting the valves, as well as that of the peduncle, (in
specimens long kept in spirits,) is brown; but in some dried specimens,
there are indications of its having been coloured crimson (as in _P.
cornucopia_), round the orifice and between the valves.

_Scuta_, irregularly oval, convex, narrow at the upper end; basal margin
may be almost said to be formed of three short, unequal margins,
corresponding with the rostrum, the rostral and the adjoining latus. The
edge corresponding with the latter, is the best marked, and is generally
slightly hollowed out, as if a piece had been broken off. The
tergo-lateral margin is curved and protuberant. The umbo projects a
little over the scutal margin of the terga.

_Terga_, projecting beyond the other valves to an unusually small
degree, broadly oval; basal angle bluntly pointed, apex rounded, blunt;
scutal margin, hollowed out to receive the upper part of the tergal
margin of the scuta; carinal margin curved and protuberant; occludent
margin consists of two short sides at right angles to each other. The
whole valve in length and area is about equal to the scuta; internally,
somewhat concave.

_Carina_, triangular, rather narrow, internally deeply concave, very
slightly curled inwards; basal margin protuberant, with a large central
portion considerably hollowed out.

_Rostrum_, triangular, of nearly the same shape as the carina, but only
one third of its length, internally very slightly concave, and with the
basal margin various, being either truncated or angularly prominent in
the middle.

_Latera._--The upper pair (corresponding to the interval between the
scuta and terga) is only a trifle larger than the latera immediately
beneath; and these only a little larger than those lower down. In the
lowest whorl, the valves are very minute, though still about twice as
large as the scales on the peduncle, and of a different shape from them.
The upper latera (viewed internally) are almost diamond-shaped, owing to
the prominence of the basal margin, but this varies considerably in
degree. The latera in the next whorl are triangular, with the basal
margins protuberant and arched, in a less and less degree in the lower
whorls, until in the lowest, the valves are elongated transversely.

_Microscopical Structure._--A valve placed in acid leaves a thick opaque
mass, formed of three different kinds of tissue, one having a finely
shaded appearance; a second with a largely hexagonal reticulated
structure, and the third thin, transparent, and marked with arborescent
lines, which I imagine to be tubes, as will be hereafter seen in
Lithotrya. Near the exterior surface, there are many tubuli. It appears
to me probable that the strong tendency which the valves in this species
have to disintegrate, is connected with the unusual quantity of
animalized tissue contained by them. Externally the valves are covered
by a strong membrane, either white or yellow, or white streaked with
yellow, and marked by lines of growth, and by longitudinal, sinuous,
little ridges.

_Peduncle_, in the upper part, of rather less diameter than the
capitulum; twice or thrice as long as it; tapering a little downwards;
surface of attachment wide and flat. Calcareous scales, minute,
symmetrically and closely packed together: each scale is much flattened,
and its shape, including the imbedded portion, is that of a spear with
its point broken off. The basal end of each scale is conically hollow,
and from the layers of growth conforming to this hollow, there is a
false _appearance_ of an open tube running through the scale.

_Attachment._--The surface of attachment is wide: the two cement-ducts,
after running down the sides of the peduncle in a sinuous course, within
the longitudinal muscles and close outside the ovarian tubes, pass
through the corium, and then separately form the most abrupt loops or
folds. These are represented in Pl. IX, fig. 2, in which a space about
1/10th of an inch square is given, as seen from the outside. At each of
the bends, an aperture has been formed through the membrane of the
peduncle, and cement poured forth. The manner in which the discs of
cement (_b_) come out of the two ducts (_a_ _a_), and reach the external
surface, is shown in the section, figure 2 _a´_. The two tubes are
firmly attached to the older layers of membrane, and are covered by the
last-formed layers. In a young specimen, the cement-ducts were a little
above 2/2000ths of an inch in diameter, which had increased, in a
medium-sized specimen, to 5/2000. The cement-glands are retort-shaped,
seated near each other, high up in the peduncle.

_Size._--The largest specimen which I have seen, was three inches in
length including the peduncle; the capitulum was 9/10ths of an inch
long, and one in width.

_Young Specimen._--I examined one with a capitulum 18/1000ths of an inch
long, measured from the lowest whorl to the tips of the terga; the width
was only 13/1000ths of an inch; in old specimens the width of the
capitulum is greater than the length. The length of one of the scuta was
14/1000ths of an inch, therefore, greater than the width of the entire
capitulum, which is not the case with mature specimens. Besides the
scuta and terga, the carina and rostrum, and three pair of large latera,
there was a lower whorl formed of ten or twelve valves, giving
altogether to the capitulum of this very small specimen, either
twenty-two or twenty-four valves.

_Shape of Body, Sack, Colours, &c._--From the position of the orifice of
the capitulum, the animal's body is suspended to the scuta in a more
transverse direction than is usual. The prosoma is well-developed, and
is distinctly separated from the three posterior thoracic segments, by
a band of thin membrane. The tunic of the basal part of the sack, where
it enters the peduncle in a blunt point, is thickened and covered with
roughened rounded papillæ. The corium of the sack under the valves, is
coloured (after spirits) so dark a brown as to be nearly black; the
cirri and trophi are similar, but with a tinge of greenish-purple.

_Filamentary Appendages._--Of these there were, on the prosoma of one
specimen, twelve pairs, and in another specimen fourteen pairs, seated
in two approximate rows; the middle filaments are the longest, equalling
about half the diameter of the thorax: each is flattened, and tapers but
little towards its summit, which is roughened with microscopical crests
serrated on both sides; on the summit, also, there are a few bristles
and some very short, thick, minute spines. These appendages are directed
rather towards each other, and towards the thorax. I do not doubt that
their numbers vary according to the size of the specimen. I believe that
they are occupied by testes. Outside these filaments, on each side of
the prosoma, there are two very irregular rows of papillæ, intermediate
in length between the filaments and the rounded swellings at the bottom
of the sack. Beneath the basal articulation of the first cirrus, there
is on each side, a short appendage, with a few bristles on its summit.
Lastly, on each side of the middle of the mouth, on the prosoma, there
is a longer appendage, dark-coloured, furnished with a few scattered
bristles on its sides and apex, and directed upwards and a little
towards the adductor scutorum muscle.

_Mouth._--Labrum highly bullate, but with the uppermost part not more
bullate than the lower part, and therefore not overhanging it; basal
margin much produced; crest with some small blunt teeth and some
bristles. The inner fold of the labrum is much thickened, yellow,
punctured, and with a tuft of fine bristles on each side.

_Palpi_, approaching each other but not touching, club-shaped, or with
broad and square extremities, thickly fringed with serrated bristles.

_Mandibles_ with three unusually strong teeth, slightly graduated in
size, with the inferior angle very coarsely pectinated; the lower edges
of the main teeth are roughened.

_Maxillæ_, (Pl. X. fig. 13). Spinose edge about half the length of the
mandibles; the two upper spines are unusually strong; close under, and
almost hidden by them, there is a tuft of fine spines; in the middle
there is a second similar tuft mounted on a prominence; and at the
inferior angle there is a third tuft, also mounted on a rather wider
prominence, not quite accurately figured. In the interspaces between
these tufts there are three or four pairs of spines of the usual
appearance and projecting just beyond the fine tufts; the upper of the
two interspaces is rather narrower, but rather deeper, than the lower
interspace. Apodeme very long, irregularly shaped, like an =S=, with a
remarkable elbow near its attachment; apex slightly enlarged, thin and
rounded.

_Outer Maxillæ._--On the inner margin there is a deep and conspicuous
notch, above and beneath which, there is a compact row of serrated
bristles; exteriorly the bristles are rather longer.

_Olfactory Orifices_ very prominent, pointing obliquely towards each
other.

_Cirri._--Posterior cirri moderately long, much curled, with the
segments (Pl. X, fig. 27) flattened and wide; the anterior surface
hemispherically protuberant, supporting six pairs of spines, of which
the lower ones approach each other; between these spines there is a
large tuft of very fine spines, of which the central ones are the
longest; there is an upper lateral group of very short strong spines;
dorsal tufts composed of short, fine numerous spines. _First pair_
seated close to the second pair, short, having in both rami eight
segments, whereas in the same individual the second pair, which is
nearly twice as long, had thirteen, and the sixth pair eighteen
segments. Rami of the first pair nearly equal in length, with their
segments, excepting the two upper ones, thickly paved with bristles, in
the midst of which a tuft of fine spines, as in the posterior cirri,
may be distinguished; the dorsal tufts encircle the whole of each
segment; the spine-bearing anterior surfaces are protuberant chiefly in
the upper part, so that they are oblique. The posterior (?) ramus has
its segments much wider than those on the other ramus; and amongst the
common spines, in the third and fourth segments, (counting from the
bottom,) there are some very strong spines with their upper ends
coarsely and doubly pectinated, each tooth being upwardly bent into a
rectangular elbow. In the fifth segment, some of the spines are doubly
pectinated with simple teeth; and most of the spines are doubly
serrated. The _Second_ (Pl. X, fig. 25) and _Third cirri_ have the five
basal segments (5/13ths of the whole number in the second cirrus, and
5/14ths in the third cirrus) of their anterior rami, extremely broad,
protuberant, and paved with serrated bristles, amongst which, (except on
the actual lowest segment,) there are some simply pectinated spines, and
others with their teeth elbowed, exactly as in the first cirrus. The
basal segments of the posterior rami of the second and third cirri,
differ from the three posterior cirri only in the spines being slightly
more numerous; but none of them are pectinated.

_Pedicels_, rather short; the upper segment resembles, in the
arrangement of its spines, the segments of the posterior cirri; the
lower segment is longer than the upper, and has _two_ tufts of fine
spines, between the two rows of long spines. In the second and third
cirri, these two intermediate tufts on the lower segment of the pedicel,
are not so distinctly separated from each other.

_Caudal Appendages_, very small, uniarticulate, blunt and rounded; tips
bearing a few, very short, thick spines.

_Alimentary Canal._--OEsophagus, somewhat curved at the lower end, where
it enters the stomach, which has no cæca; rectum, unusually short,
extending from the anus only to the base of the fifth pair of cirri.
Within the stomach, from top to bottom, there were thousands of a
bivalve entomostracous crustacean.

_Generative System._--Both ovaria and testes are largely developed; the
former fill the long peduncle; the testes enter both the pedicels of the
cirri, and the filamentary appendages on the prosoma; vesiculæ seminales
very large, reflected at their ends, extending across each side of the
stomach. Penis rather small, coloured purplish, with numerous little
tufts of bristles.

_Variation._--In some specimens in the British Museum, collected by Sir
J. Ross, in the Southern ocean, and in another older set from an unknown
source, several parts of the outer tunic of the animal's body presented
the remarkable fact of being calcified, but to a variable degree;
whereas in several specimens from California, there was no vestige of
this encasement. Considering it most improbable that the calcification
of the integuments should be a variable character, I most carefully
compared the above-mentioned sets of specimens, valve by valve, trophi
by trophi, and cirri by cirri, and found no other difference of any
kind; therefore I cannot hesitate to consider both to be the same
species. The first Southern specimen which I examined presented the
following characters: on the prosoma there was a central longitudinal
band, formed of a thin, brittle, brown-coloured calcified layer, which
became irregularly rather narrow towards the thorax; on each side it
sent out six or seven irregular rectangular plates, which surrounded and
supported the bases of the two rows of filamentary appendages; and
outside these, some of the papilliform projections also had their bases
surrounded by small, calcified, separate rings. The thoracic segments
corresponding with the second, fourth, fifth, and sixth cirri had, on
each side, an elongated calcified plate; on the ventral surface of the
thorax, between the first and second cirri, there were two minute
plates. In all the cirri, excepting the first pair, the segments of the
rami, and in the three posterior pairs, the segments of the pedicels,
had their dorsal surfaces strengthened by oblong, quadrilateral,
calcified shields, the upper margins of which are notched for the dorsal
tufts of spine, and the two lateral margins are also slightly hollowed
out; these are represented in figure 27. The lower segments of the
pedicels of some of the cirri, had an additional calcified plate on the
antero-lateral face.

These plates are of a faint-brown or yellowish colour, and are
conspicuous: the degree of calcification differs considerably; some are
quite brittle and very thin, others half horny, and effervesce only
slightly in acids. After having been placed in acid, there is no
apparent difference between the parts before occupied by the calcified
plates and the surrounding membrane; these plates, however, are not
superficial, but consist of several of the laminæ, which together
compose the ordinary integument, in a calcified condition. Like the
integuments of the body, and unlike the valves of the capitulum, these
calcified plates are thrown off at each exuviation. Neither the exact
shape nor number of the plates corresponded in different individuals,
nor even on opposite sides of the same individual. The margins of the
plates often have a sinuous corroded appearance; they are, moreover,
often penetrated by minute rounded holes, that is, by minute, rounded,
non-calcified portions. In one specimen from the Antarctic expedition,
there were only here and there a single shield on the segments of the
posterior rami, and no plate on the prosoma. Of two specimens in another
and older set in the British Museum, from an unknown locality, both had
shields on the segments of the cirri, but only one had the large plate
on the prosoma. I may here mention that in one specimen, in which the
calcified plates were most developed, and which was nearly ready to
moult, there were, within the filamentary appendages on the prosoma,
small irregular balls of calcareous matter, appearing to me as if
calcareous matter had been morbidly excreted, and not like a provision
for the future.

_Range._--This species, in the present state of our knowledge, seems to
range further than any other of the genus, extending from Upper
California, (lat. 32° to 35° N.,) across the Pacific, to at least 32°
S., perhaps much farther south, for it was collected during the
Antarctic expedition, and 32° was the highest latitude traversed by that
expedition.

_Affinities._--This species is closely related to _P. cornucopia_ and
_P. elegans_, but differs rather more from them, than these two do from
each other. In the capitulum the chief distinctive characters are--the
more perfect graduation in size, and the greater number, (taking
equal-sized specimens,) of the whorls of latera--the darker colours--the
central part of the basal margin of the carina in this species, being
considerably excised--the peculiar form of the basal margin of the
scuta--and lastly, the scutal margin of the terga being more hollowed
out. In the animal's body, the most obvious distinctive character is the
uniarticulate caudal appendage. This species agrees with _P. elegans_,
in the presence of the singular elbowed teeth, on some of the spines in
the first three pairs of cirri.


4. POLLICIPES MITELLA. Pl. VII, fig. 3.

  LEPAS MITELLA. _Linn._ Systema Naturæ, 1767.

  POLLICIPES MITELLA. _G. B. Sowerby._ Genera of Shells, fig. 2.

  POLYLEPAS MITELLA. _De Blainville._ Dict. Sc. Nat. (1824) Plate,
        fig. 5.

  CAPITULUM MITELLA. _J. E. Gray._ Annals of Philosoph., new series,
        vol. x, 1825.

_P. capitulo valvarum unico sub-rostro verticillo instructo: laterum
pari superiore (introrsum spectanti) inferiorum magnitudinem ter aut
quater superante: lateribus inferioribus utrinque obtegentibus:
pedunculi squarmarum verticillis densis, symmetricè dispositis._

Capitulum with only one whorl of valves under the rostrum: the upper
pair of latera, viewed internally, are three or four times as large as
the lower latera, which overlap each other laterally: scales of the
peduncle symmetrically arranged in close whorls.

Maxillæ, deeply notched: caudal appendages, multi-articulated:
filamentary appendages, none.

    Philippine Archipelago, Mus. Cuming: China Sea, Mus. Brit.:
    Amboyna and East Indian Archipelago, according to Rumphius and
    other authors: Madagascar, according to J. E. Gray.

_Capitulum_, compressed, consisting of the scuta, terga, carina,
rostrum, and a large pair of upper latera, with a single lower whorl of
smaller valves; these latter vary from 22 in very small specimens, to 26
in large specimens. The capitulum, therefore, is formed of at most 34
valves; but in the largest specimen seen by me, the capitulum being 2.3
of an inch in width, there were only 32 valves. In the smallest, namely,
with a capitulum .15 of an inch in width, there were 30 valves. The
valves are remarkably strong, and formed of white shelly matter; they
are closely approximate, and overlap each other: the scuta and terga are
articulated together by a fold; the apices of the valves are either worn
and disintegrated, or they project freely like horns beyond the sack, to
a much greater extent than in any other recent species of the genus:
even a considerable portion of the scuta projects obliquely upwards. The
exterior surfaces of the valves (when not worn) are covered by a strong
yellow membrane, and the upper free parts are generally attached
together for some little length by this same membrane. The valves are
plainly marked by the zones of successive growth; and most of them are
ribbed and furrowed slightly, from their umbones to their basal margins.
The yellow external membrane, examined microscopically, is marked by, or
rather formed of, numerous growth-lines, crossed by longitudinal beaded
ridges. The tubuli are not numerous, and of small diameter.

_Scuta_ (Pl. VII, fig. 3 _a´_, _a_) triangular, with the apex more or
less produced, according to the state of its preservation, and a little
curved towards the terga; basal margin, and in some degree the
tergo-lateral margin, arched, and slightly protuberant; occludent margin
thickened, slightly prominent, with the inner edge covered by the
yellow membrane, like the exterior surface of the valve. The upper part
of the tergo-lateral margin overlaps a little the edge of the tergum,
and receives it in a furrow,--the two valves being thus locked together.
This furrow lies in the freely-projecting, membrane-covered portion, and
extends up to the apex; it is of variable depth. Internally the scuta
are concave, and in some old specimens to a high degree. In these
latter, the basal margin, towards the tergo-lateral side, is strongly
sinuous; the prominences are formed by the terminations of the external
longitudinal ridges, and correspond to the interspaces between the
valves of the lower whorl. These ridges, which are interesting, from
throwing light on similar ridges in some fossil species, are present,
both on old and young specimens, and run from the apex of the valve, in
a slightly curved line, to the tergo-lateral half of the basal margin,
where, as we have just seen, they sometimes form prominences. They
consist of three or even four obscure, almost confluent, ridges, of
which the middle one is generally (but not always) the smallest:
together they cover the whole of that part of the scutum, which is not
overlapped along the basal margin by the rostrum and large upper latus;
and they seem evidently due to the growth of the shell in this
interspace having been freer. So, again, the three or four small,
confluent, component ridges have the same relation to the interspaces
between the small latera of the lower whorl.

_Terga_ large, four-sided, with the internal growing surface (fig. 3
_a´_ _b_), almost diamond-shaped; basal angle blunt, rounded;
exteriorly, from the apex to the basal angle there is a rather broad,
very slight prominence, which bears the same relation to the carina and
upper latus, as do the compound ridges on the scuta to the rostrum and
upper latus. The upper part of the scutal margin forms a
slightly-projecting, rounded shoulder, though variable in its degree of
prominence, in relation to the variable depth of the recipient furrow in
the scuta. Externally, parallel to the occludent margin, and close
below the prominent shoulder, just mentioned, there is a slight and
variable depression, extending up to the apex of the valve. This
depression is due to the prominence, variable in degree, of the tergal
edge of the recipient furrow in the scuta.

_Carina_, triangular, strong, inwardly bowed, generally with a large
upper portion freely projecting; exteriorly with a narrow, sharp,
central ridge or keel, which is solid, the interior concavity not
reaching so deep; inner growing surface (fig. 3 _b´_, _b_) deeply
concave, triangular. Basal margin square--that is, transverse to the
longer axis of the carina, or it even rises (as is best seen in the
growth-ridges) a little towards the exterior keel. On each side of the
central exterior keel, there is a narrow longitudinal ridge,
corresponding with the interspace between the sub-carina and the
next-but-one latus of the lower whorl; the latus next to the sub-carina
is very small, and overlies the ridge itself. In a very large specimen,
these lateral longitudinal ridges formed (as they likewise did on the
rostrum) slight prominences on the basal margin. In one specimen the
carina was straight.

_Rostrum_ closely similar, in almost every respect, to the carina, even
to the exterior, lateral, longitudinal ridges, and in their relation to
the interspaces in the lower whorl. The valve is generally not so long,
but rather wider, more inwardly bowed, and with the exterior solid keel
less prominent than in the carina. The inner growing surface (fig. 3
_b´_ _d_) is less acuminated at its upper end.

_Upper pair of Latera._--These are much larger than the remaining valves
of the lower whorl; they are straight, triangular, and much acuminated,
with their apices, when well preserved, extending far up, for fully
three fourths of the height of the scuta. They nearly equal in length
the carina. The growing surface (fig. 3 _b´_, _a_) is flat, triangular,
in well-preserved specimens forming only a third or a quarter of the
entire length of the valve. In the middle of the basal margin there is a
very slight prominence, corresponding with a slight external central
ridge, formed as heretofore by the overlapping of two of the valves of
the lower whorl. Basal margin nearly on a level with that of the scuta
and with the basal points of the terga. The foregoing eight larger
valves form the main cavity, in which the body of the animal is lodged.

_Valves of the Lower Whorl._--These, seen externally, seem to belong to
more than one whorl, but internally their basal margins stand on a
level. They vary in number, as already stated, from 22 to 26. I have
seen an individual with a valve more on one side than on the other. They
are of unequal sizes, but they are rather variable in this respect: the
largest are not above half the size of the upper latera: three or four
pairs, together with the sub-rostrum (_e_) and sub-carina (_c_), are
always larger than the others: these two latter valves differ from the
others only in being more concave. Seen externally, all these valves
project considerably, and curl a little inwards, with their apices
generally worn and truncated. Viewed internally (fig. 3 _b´_), whilst
the valves are in their proper places, the inner and growing surfaces of
the smallest are seen to be triangular,--of the larger, some are
rhomboidal, and others quadrilateral with the upper side much longer
than the lower. These latter valves overlap the upper parts of the
little valves on both sides of them; the rhomboidal valves overlap a
valve on one side, and are overlapped on the other; the triangular
valves are overlapped on both sides.

The corium lining the capitulum is produced into narrow purple crests,
which enter the interstices between the valves, more especially along
the line separating the upper and lower whorls. There is, also, a
distinct flattened, tapering, free projection of corium, which enters
between the carina and sub-carina; and another between the rostrum and
sub-rostrum.

_Peduncle_, much compressed, short, rarely as long as the capitulum; in
one very large specimen it was extremely short, barely one fifth of the
length of the capitulum. The attached portion, which is moderately
pointed in young specimens, becomes extremely broad in old specimens.
The calcified scales sometimes differ a little in size, in specimens of
the same age: they are always compactly and symmetrically arranged: in
old specimens they are much larger than in young ones: each scale has,
at first, a transversely elliptic growing base, which ultimately becomes
nearly circular. Exteriorly the tips of the scales are always
disintegrated; they are sometimes club-shaped, owing to the scales
having been re-added to after a period of reduced growth. The scales are
fringed with brown disintegrating membrane.

_Attachment._--At the base of the peduncle, the two cement-ducts running
together, twist about in a singular manner, and at their bends pour
forth cement. According to the age of the specimen, the ducts vary in
diameter from 1/2000th to 5/2000ths of an inch. The two cement glands
are small and difficult to find; they are retort-shaped, with two
ovarian tubes entering each. They lie close together, in nearly the
centre of the peduncle, and less than half-way down it. This proximity
of the two cement-glands, and their position low down the peduncle, are
of interest in relation to the position of these same glands in the
sessile Cirripedes.

_Size and Colours._--This is the largest and most massive species in the
family. I have seen one specimen in the British Museum, from the Coast
of China, 2.3 inches across the capitulum, and 1.5 in length, with the
valves surprisingly thick. The relative width and length of the
capitulum varies. The sack (in specimens long kept in spirits) is dirty
purple, and exteriorly between the scuta, dark purple. The cirri,
trophi, penis, caudal appendages, three posterior segments of the
thorax, and the abdominal surface are dark-brownish purple.

_Body._--Thorax remarkably compressed and carinated; prosoma pretty well
developed. Extending from the base of the second cirrus, to nearly a
central line on the thorax, there is on each side a rounded ridge: there
is a second transverse ridge, running from the base of the first cirrus
to near the adductor scutorum muscle: these ridges seem formed merely to
allow of the larger development of the testes.

_Mouth._--Labrum highly bullate; crest without any teeth, but with a few
minute hairs. The inner fold of the labrum forming the supra-oesophageal
cavity, is thickened, and shows a trace of a central line of junction,
as in Sessile Cirripedes.

_Palpi_ (Pl. X, fig. 7), small; of a singular club-like shape, owing to
the convexity of the outer margin; exterior spines long, all doubly
serrated.

_Mandibles_ (Pl. X. fig. 1), with five teeth, of which the second is
very small; inferior angle coarsely pectinated.

_Maxillæ_ (fig. 14), with a deep narrow notch (bearing some fine spines)
beneath the two upper great spines, which stand on a prominence; edge
straight, bearing fourteen or fifteen pairs of spines: on the inferior
angle there is an obscure tuft of shorter and finer spines: apodeme
long, sinuous, and slender.

_Outer Maxillæ_ (fig. 17), with the inner margin divided by a deep notch
into two lobes, of which the upper one is rather short; both are clothed
with a compact row of short bristles; exterior margin with longer
bristles.

_Olfactory Orifices_, large and prominent to an unusual degree.

_Cirri_, moderately long and curled; the four posterior pair are alike;
each segment has its anterior face somewhat protuberant, and bears six
pairs of long spines, with a rather large, narrow tuft of intermediate
spines, some of which are finely and doubly serrated. The dorsal tufts
consist of short, thick spines, with some fine longer ones. The first
cirrus is seated near the second; its rami are slightly unequal in
length; lower segments paved with bristles; one ramus is thicker than
the other, and some of its segments have coarsely pectinated spines.
Second cirrus has the five basal segments of its anterior ramus highly
protuberant, and paved with bristles, of which some are coarsely
pectinated; the basal segments of the posterior ramus are rather more
thickly clothed with bristles than are the posterior cirri, but
otherwise resemble them. The third cirrus, as already stated, is exactly
like the three posterior pairs; and this is a very unusual circumstance.
On the dorsal surfaces and sides of the pedicels of the posterior cirri,
there are some scattered, short, thick, minute spines.

_Caudal Appendages_, multi-articulate: in a medium-sized specimen, each
contained eight segments, which reached half-way up the upper segment of
the pedicel of the sixth cirrus. Lower segments flattened; the upper,
tapering, and cylindrical; all have their upper margins furnished with
stiff, little spines. In a young specimen (only .3 of an inch in length,
including the peduncle), the caudal appendage contained only four
segments, and the tip did not reach to the upper edge of the lower
segment of the pedicel of the sixth cirrus.

_Stomach_, without cæca.

_Generative System._--Vesiculæ seminales not reflexed at their broad
ends; white, spotted with black. Testes, pear-shaped, borne on long
footstalks: penis covered with minute bristles, in little tufts arranged
in straight lines. The ovarian tubes fill up the peduncle to its base,
but do not surround the sack; they are of small diameter, and simply
branched. There is a very narrow ovigerous frænum, with a straight edge,
lying on each side under the line of junction between the scutum and
upper latus.

_Affinities._--This species differs from all the others of the genus, in
the third cirrus resembling exactly the three posterior pairs. In most
of its characters--namely, in the symmetrical arrangement of the scales
on the peduncle, in the considerable size of the valves of the lower
whorl, in the general approximation of the valves, in the
multi-articulated caudal appendages, in the form of the outer maxillæ,
in the prominent olfactory orifices, in the basal segments of the
anterior ramus alone of the second cirrus being paved with bristles,
there is more affinity to _P. cornucopia_, _P. elegans_, and _P.
polymerus_ than to _P. sertus_ and _P. spinosus_.

In the scuta and terga being articulated together, in the union of all
the valves by stiff membrane, in the peculiar manner in which the valves
of the lower whorl overlap each other, in the corium entering between
some of the valves in filiformed appendages, in the near equality of
size of the rostrum and carina, in the shortness of the peduncle in old
specimens, in the position of the cement-glands, and lastly in the
characters of the third pair of cirri, this species presents a closer
affinity to the sessile Cirripedes, more especially to the Chthamalinæ,
than does any other species of any other genus amongst the Lepadidæ. The
movements, however, of the four opercular valves are not at all more
independent of the other valves, than in the other Pedunculated
Cirripedes; and the peduncle is furnished with all its characteristic
muscles.


5. POLLICIPES SPINOSUS. Pl. VII, fig. 4.

  ANATIFA SPINOSA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe. Pl.
        xciii, fig. 17.

_P. capitulo valvarum uno aut pluribus sub-rostro verticillis instructo:
laterum pari superiore vix inferioribus longiore: membranâ valvas
tegente (post desiccationem) subfuscâ flavescente: pedunculi squamis
inæqualibus, non symmetricis: verticillis longiusculè distantibus._

Capitulum with one or more whorls of valves under the rostrum: upper
pair of latera only slightly larger than the lower latera: membrane
covering the valves (when dried) light yellowish-brown: scales of the
peduncle of unequal sizes, unsymmetrical, arranged in rather distant
whorls.

Maxillæ, with the edge square and straight: caudal appendages
uniarticulate: filamentary appendages, none.

    New Zealand. Mus. Jardin des Plantes, Paris: Mus. Cuming.

_Capitulum_, flattened, triangular, broad, with the valves varying in
number, in full-grown specimens of the same size, from 30 to above 60;
the scuta, terga, and carina are very much larger than the other valves;
the rostrum, however, is nearly half the size of the carina; the
remaining valves are exceedingly small. In some specimens there is only
one whorl under the carina; in other specimens there are distinctly two
whorls. The scuta, terga, and carina stand pretty close together; they
are moderately thick, and are covered, in chief part, by yellowish-brown
membrane, which is destitute of spines.

_Scuta_, triangular, broad, basal margin slightly protuberant.

_Terga_, as large as the scuta, flat, regularly oval, basal point blunt
and rounded.

_Carina_ very slightly curved, triangular, internally rather deeply
concave, basal margin straight. The inner and growing surface is four
fifths of the entire length of the valve. In half-grown specimens the
apex projects a little outwards.

_Rostrum_, small, much curled inwards; the basal margin is much hollowed
out; the inner surface is broadly triangular, more than twice as wide as
high, and about one fourth of the entire length of the valve. The
remaining valves, about 26 in number, do not correspond on the opposite
sides of the same individual, they are exceedingly small, with the
sub-carina, sub-rostrum, and three pairs of latera a trifle larger than
the lower latera, which are generally arranged in two whorls. In shape
all the latera are nearly alike; they consist of flattened styles, with
their inner surfaces transversely oval, and more or less elongated, the
larger ones being most elongated.

_Peduncle_, broad, barely as long as the capitulum. The calcareous
scales are irregularly shaped, minute, elongated and pointed, placed in
separate transverse rows, and crowded together in each row. Only the
scales in the uppermost row grow regularly; but some of the lower scales
continue to be added to irregularly, and hence are the largest. On the
other hand, the lower part of the peduncle, from the first formed scales
having been worn away, is often quite naked. From this cause, and from
the continued and irregular growth of some of the lower scales, the rows
in this part of the peduncle, generally become irregular. The surface of
attachment is broad.

In a half-grown specimen, with a capitulum only 3/10ths of an inch long,
all the lower valves were considerably larger in proportion to the
scuta, terga, and carina, than in full-grown individuals.

_Size and Colours._--Length of capitulum in the largest specimen,
7/10ths of an inch; breadth, slightly exceeding the length. Colours
after having been long in spirits--upper part of sack, thorax, pedicels
of cirri, and penis, clouded with fine purple; cirri banded with the
same; exterior convex surface of the outer and inner maxillæ and palpi
dark purple; prosoma yellow. The membrane of the peduncle and of the
capitulum is dirty yellow, with bands of purple between some of the
valves.

_Filamentary Appendages_, none. Ovigerous fræna placed near the middle
of the basal margin of the scuta; small, semi-oval, with an elliptical
ring of bead-like glands; glands seated on long footstalks.

_Mouth._--Labrum far produced towards the adductor muscle; upper part
highly bullate, nearly equalling the longitudinal diameter of the rest
of the mouth, and very slightly overhanging the lower part; crest with
very minute bead-like teeth.

_Palpi_, with their inner margins considerably excised, most thickly
clothed with spines.

_Mandibles_, with three strong teeth, two unequal-sized small teeth
being placed between the first and second, thus making five altogether;
inferior angle broad, pectinated.

_Maxillæ_, with its edge broad, straight, bearing about twenty pairs of
spines, shorter than the large upper spines.

_Outer Maxillæ_, with the bristles in front, continuous, and without any
notch; exterior surface with a prominence clothed with long spines.
Olfactory orifices slightly prominent.

_Cirri._--First cirrus placed near to the second; posterior cirri not
much elongated, with their segments slightly protuberant, bearing four
pairs of spines, of which the lower pair is small; spines slightly
serrated. In the lower segments, these spines are exceedingly unequal in
length, the inner spines on both rami, not being above one fourth of the
length of the outer corresponding spine in each pair. The tufts
intermediate between these pairs, are not very large: on the lateral
upper rims there are some strong, short spines: dorsal tufts with short,
thick spines. First cirrus about three fourths as long as the second
cirrus, with numerous tapering segments, three or four of the lower ones
being thick and protuberant: in the first cirrus there are eleven
segments, and in the sixth cirrus, seventeen. Second cirrus, with the
anterior ramus slightly thicker than the posterior ramus: a few of the
basal segments of both rami are protuberant, and thickly clothed with
spines. In the third cirrus, the two rami are nearly equally thick, with
some of the basal segments in both clothed, like a brush, with spines.
In these brushes on the first, second, and third cirri, most of the
spines are doubly toothed, each tooth being simply conical.

_Caudal Appendages_, small, much flattened, straight on the exterior
side, and curved on the inner side, with a row of short, rather thick
spines on the crest, and a few on the exterior margin.

The _Affinities_ of this species will be given under the head of the
following, _P. sertus_.


6. POLLICIPES SERTUS. Pl. VII, fig. 5.

_P. capitulo valvarum uno aut pluribus sub-rostro verticillis instructo:
laterum pari superiore vix inferioribus longiore: membranâ valvas
tegente (post desiccationem) fusco rufescente obscuro: rostro dimidiam
carinæ longitudinem æquante, superficiei internæ altitudine latitudinem
plus duplo superante: pedunculi squamis inæqualibus, non symmetricis:
verticillis longiusculè distantibus._

Capitulum with one or more whorls of valves under the rostrum: upper
pair of latera only slightly larger than the lower latera: membrane
covering the valves (when dried) dark reddish-brown: rostrum half as
long as the carina, with its inner surface more than twice as high as
broad: scales of peduncle of unequal sizes, unsymmetrically arranged in
rather distant whorls.

Maxillæ with two tufts of fine bristles, separated by larger spines:
caudal appendages uniarticulate: filamentary appendages none.

    New Zealand; Mus. Cuming.

_Capitulum_, much flattened, broad, sub-triangular. Valves exceedingly
various in number; in the largest specimen with a capitulum 8/10ths of
an inch high, and 9/10ths of an inch wide, there were only thirty-one
valves, and these formed only a single whorl under the carina and
rostrum; whereas, in another specimen, which was barely 6/10ths of an
inch in length, there were fifty-two valves, and these formed two or
three distinct whorls under the carina. Scuta, terga, carina, and
rostrum, much larger than the other valves. All are moderately thick,
placed rather distant from each other, covered with thick membrane which
abounds with tubuli, arranged in rows; surface apparently smooth, but
with a very high power, extremely minute spines can be seen at the
extremities of almost all the tubuli. Little bunches of reddish fibrous
matter are imbedded in the membrane, like tufts of sea-weed floating in
water.

_Scuta_, triangular, basal margin curved, protuberant; the upper part of
the tergo-lateral margin is, also, slightly protuberant.

_Terga_, large, oval, basal angle broad, square; lower part of carinal
margin straight, upper part narrowed in; the apex is covered with
membrane and projects freely.

_Carina_, triangular, internally deeply concave, either straight, and
with the apex free, or inwardly and considerably curved; basal margin
nearly straight.

_Rostrum_, about half the length of the carina; either straight or
inwardly curved; it projects freely for full half its length; inner
growing surface triangular, more than twice as high as wide; basal
margin very slightly hollowed out. The _sub-carina_ and _sub-rostrum_
are larger than the largest of the latera; their inner surfaces are
transversely elongated, rounded at both ends, and slightly concave;
externally they are pointed, and project outwards; sometimes the
sub-carina, and sometimes the sub-rostrum is the largest.

_Latera_, small, with their inner surfaces transversely elongated, the
larger being the most elongated. Externally they are acuminated, and
directed upwards; they project but very little beyond the thick membrane
in which they are imbedded. Neither the number, size, nor shape of the
latera agree on opposite sides of the same individual; and it would
appear that, occasionally, some of them cease to grow, and disappear. In
the large specimen with only thirty-one valves, the three pairs of
latera, corresponding to the upper, rostral, and carinal latera in
Scalpellum, were larger in a marked manner than the others; but in the
specimen with fifty-four valves, this could hardly be said to be the
case. In this latter specimen, some of the valves in the lowermost whorl
were exceedingly minute.

_Peduncle_, broad, about as long as the capitulum; surface of attachment
wide; calcareous scales minute, placed in transverse rows, which become
less and less regular in the lower part. The scales do not stand very
close together; they are of unequal sizes and irregular outline;
generally spindle-shaped; calcareous matter is added regularly only to
the scales in the uppermost row, and irregularly to some of the lower
scales. The latter, consequently, are the largest, and often much
elongated; they are sometimes of singular and irregular shapes.

_Colour._--The membrane covering the valves and forming the peduncle,
(after having been long kept dry, and not having been in spirits,) is
dark reddish chocolate-brown; corium of sack dark purple; cirri banded
with dark purplish-brown, with the lower parts of the trophi similarly
coloured.

_Filamentary Appendages_, none, but on the prosoma there are scattered
some small papillæ, which are roughened by finely spinose scales, like
combs; these papillæ certainly seem to represent the filaments in
_Pollicipes cornucopia_ and its two allies.

_Ovigerous Fræna_, seated in the same position as in _P. spinosus_, but
rather longer, with an elliptical _tuft_ of glands on the crest.

_Mouth_, not placed far from the adductor muscle.

_Labrum_, moderately bullate, with the upper part not overhanging; no
teeth on the crest. _Palpi_, short, broad, blunt.

_Mandibles_, with three main teeth, with either one or two smaller teeth
inserted between the first and second, making four or five altogether;
inferior angle rather narrow, pectinated with long and fine spines.

_Maxillæ_, rather broad, with two long upper spines; beneath which there
is a very small prominence bearing a minute tuft of fine bristles;
beneath this, there are eleven pairs of rather long and strong spines;
and the inferior angle is formed by a rather broad, upraised, and
obliquely rounded prominence, bearing a broad tuft of fine spines.

_Outer Maxillæ_, with the inner surface continuously clothed with short
spines; exteriorly there is a slight prominence with long hirsute
spines.

_Olfactory Orifices_ barely prominent.

_Cirri._--First pair placed near the second; the segments of the three
posterior pairs are slightly protuberant, and bear three or four pairs
of finely serrated spines; intermediate tufts long, the middle spines
being the longest; spines on the upper lateral edges long and strong;
dorsal tufts rather short. _First cirrus_, long, multiarticulate, having
fourteen or fifteen segments, whilst the sixth cirrus had nineteen
segments; rami unequal in length by about two segments; basal segments
protuberant brush-like. _Second_ and _third cirri_ with five basal
segments of both rami protuberant and brush-like; but the anterior rami
in both cirri are broader than the posterior rami. Spines on the
protuberant segments of both rami of both cirri, coarsely and doubly
pectinated.

_Caudal Appendages_ (Pl. X, fig. 19), minute, uniarticulate,
club-shaped, with the enlarged ends directed inwards, or towards each
other; summits sparingly clothed with very short spines.

_Penis_, small.

_Affinities._--This species makes a very close approach in the general
form and relative sizes of all the valves, and in the variability of the
number of the whorls, to _P. spinosus_; there is a still closer and more
important resemblance, in the inequality and manner of growth of the
calcareous scales on the peduncle. These species differ, in the colour
of the membrane covering the valves, and in the greater development of
both rostrum and sub-rostrum in _P. sertus_. The rostrum of the latter
is longer than half the length of the carina, and its inner surface is
more than twice as high as wide; and the sub-rostrum is twice as large
as any of the latera,--all points of difference from P. _spinosus_.

In the characters of the mandibles, and more especially of the outer
maxillæ; in the length of the first pair of cirri; in both rami of the
second and third cirri having their basal segments brush-like, with
pectinated spines; and in the shape of the caudal appendages, there is a
close relationship to _P. spinosus_, and through this species to
_Scalpellum villosum_. In the little prominence of the olfactory
orifices, P. _sertus_ differs from most of the allied forms, excepting
_P. spinosus_. In the maxillæ having two prominences bearing fine tufts
of bristles, in the roughened knobs on the prosoma, and in the presence,
in some individuals, of two or three whorls of valves under the carina
and rostrum, there is a marked tendency in _P. sertus_ to approach _P.
cornucopia_, _P. elegans_, and _P. polymerus_.


_Genus_--LITHOTRYA. Pl. VIII, IX.

  LITHOTRYA. _G. B. Sowerby._ Genera of Shells, April 1822.

  LITHOLEPAS. _De Blainville._ Dict. des Scienc. Nat., 1824.

  ABSIA.[65] _Leach._ Zoological Journal, vol. ii, July 1825.

  BRISNÆUS et CONCHOTRYA. _J. E. Gray._ Annals of Philosophy, vol.
        x, (new series,) August 1825.

  LEPAS. _Gmelin._ Systema Naturæ, 1789.

  ANATIPA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, 1832.

   [65] The description of Absia is so inaccurate, that I should not
   have recognised it, had not the _Lithotrya Nicobarica_, in a
   bottle in the British Museum, borne this name.

_Valvæ 8, si inter eas parvum (sæpe rudimentale) rostrum et duo parva
latera numerentur; incrementi lineis concinnè crenatis: pedunculus
squamis calcareis parvis vestitus, in verticillis superioribus crenatis;
aut calyci basali calcareo aut discorum ordini affixus._

Valves 8, including a small, often rudimentary rostrum and a pair of
small latera: lines of growth finely crenated. Peduncle covered with
small calcareous scales, those of the upper whorls crenated; attached
either to a basal calcareous cup, or to a row of discs.

Body lodged within the peduncle: mandibles with three teeth, the
interspaces being pectinated; maxillæ various: olfactory orifices
slightly prominent: caudal appendages multiarticulate.

    Lodged in cavities, bored in calcareous rocks, or shells, or
    corals; generally within the Tropics.

_Description._--The capitulum is not much compressed, a horizontal
section giving an oval figure; it is placed obliquely on the peduncle,
the scuta descending lower than the terga and carina. There are eight
valves, of which the scuta, terga, and carina are large; the rostrum and
a pair of latera are very small and often rudimentary. These three
latter valves are essentially distinguished from the scales of the
peduncle, the upper ones of which they sometimes hardly exceed in size,
by not being moulted at each period of exuviation. The latera overlie
the carinal half of the terga; I presume that they are homologous with
the carinal latera in Scalpellum. Each successive layer of shell forming
the valves is thick, and extends over nearly the whole inner surface;
hence the carina and terga, and to a certain extent the scuta, either
actually do project freely much beyond the sack, or would have done so,
had not their upper ends been removed; for the upper and old layers of
shell, in most of the species, either scale off or disintegrate and wear
away. A rectangularly projecting rim, serrated by small teeth, is formed
at the bottom of each fresh layer of growth, along the external surfaces
of each valve (see upper part of fig. 1 _b´_ Pl. VIII.) This structure,
as well as that of the crenated scales on the peduncle, is important,
for by this means the animal, as we shall presently see, forms and
enlarges the cavity in the rock or shell in which it is imbedded.

The scutum overlaps either about one third or even one half of the
entire width of the tergum, and abuts against a prominent longitudinal
ridge on its exterior surface. In _L. truncata_ and _L. Valentiana_,
this ridge on the tergum being folded over towards the scutum, forms a
conspicuous furrow, receiving the tergal margin of the latter. In _L.
Valentiana_, there is a second furrow on the carinal side of the tergum,
receiving the upper end of the corium-covered or growing surface of the
carina. Besides these provisions for holding together the valves, there
are, apparently, others for a similar purpose; thus in each scutum,
under the rostral angle, there is a roughened knob-like tooth, which
touches the under side of the little rostrum, and no doubt serves to
give attachment to the membrane uniting the three valves together. In
some species, the adjoining basal margins of the scuta and terga, where
touching each other, are inflected and roughened; again in _L.
Rhodiopus_, the carinal angles of the terga are produced into points,
and in _L. truncata_ and _L. Valentiana_ into prominent roughened knobs,
which touch two corresponding small knobs, on the upper part of the
growing surface of the carina. Moreover, considerable portions of the
inner surfaces of the scuta and terga, are roughened with minute sharp,
imbricated points, apparently for the firmer attachment of the corium.
The roughened knobs at the rostral angles of the scuta, no doubt are
homologous with the teeth in a similar position on one or both scuta in
Lepas, and in some fossil species of Pollicipes, as in _P. validus_. The
other projections and roughened surfaces are peculiar to Lithotrya. The
growth of all the valves is, as in Pollicipes, simply downwards.

The _Scuta_ are triangular, with their umbones or centres of growth at
the apex; the tergal margin, as seen from within, is either nearly
straight or much hollowed out, accordingly as the scuta simply overlap
the terga, or are received in a furrow. In some of the species there is
a distinct pit for the adductor muscle, and in others this cannot be
distinguished.

_Terga._--These present great differences in shape; but all appear to be
modifications, (as seen internally,) of a rhomboidal figure, which seems
to be the normal form of the terga in the Lepadidæ. Of the lower part of
the valve, the whole exterior surface, with the exception of a narrow
ridge running from the apex down to the basal angle, is hidden by the
overlapping of the scuta, latera, and carina.

The _Carina_, in outline is triangular, with the basal margin in some
species extremely protuberant. In the first four species, the internal
surface is concave, in _L. truncata_ and _L. Valentiana_ it is convex,
with a central raised ridge, and consequently the upper
freely-projecting portion of the valve, has a prominent central crest or
ridge; in _L. Nicobarica_ and _L. Rhodiopus_ there is only a trace of
this ridge. The rostrum, as before stated, is always very small; it, as
well as the latera, are most developed in _L. Nicobarica_, and least in
_L. truncata_ and _L. Valentiana_; generally only a few zones of growth
are preserved, and from their being enlarged at their basal serrated
rims, the rostrum sometimes appears like a few beads of a necklace
strung together.

The _Latera_ are remarkable from being placed over the carinal half of
the terga, in an oblique position, parallel to the lower carinal margin
of the terga. A section, parallel to the growth layers, varies in the
different species from elliptic to broadly oval, and in _L. Nicobarica_
it is triangular. Only a few layers of growth are ever preserved. In _L.
truncata_, where the latera are represented by mere stiles, (like
strings of beads), and are even less in width than the rostrum, they are
imperfectly calcified.

_Microscopical Structure of the Valves._--The shelly layers are white,
and generally separate easily, so that in _L. dorsalis_ it is rare to
find a specimen with the upper part of the valves perfect. The valves
are so translucent, that in the thin margins, even the tubuli could be
sometimes distinguished. The valves are coated by strong yellow
membrane, which, after the shelly matter in _L. dorsalis_ had been
dissolved in acid, separated into broad slips, answering to each zone of
growth. On the lower margin of each slip, there is a row of closely
approximate spines, generally slightly hooked, pointed, 1/650th of an
inch in length, and 1/10000th of an inch in diameter; they arise out of
a little fold; all are furnished with tubuli of the same diameter with
themselves, running through the whole thickness of the shelly layers,
and attached, apparently, by their apices, to the underlying corium. As
the spines are very numerous, so are the parallel rows of tubuli. After
the shelly layers had been dissolved, there was left in _L. dorsalis_
(well seen in the latera), an extraordinary, conferva-like mass of
branching, jointed, excessively thin tubes, sometimes slightly enlarged
at the articulations, and appearing to contain brown granular matter:
other portions of the valves, instead of this appearance, exhibited
membranes or films with similar, branching, articulated tubes or vessels
attached to them: I have not seen this appearance in any other
cirripede. The yellow exterior enveloping membrane, with its spines, is
present in all the species of the genus; in _L. Rhodiopus_ these spines
are much larger than in _L. dorsalis_, and on the inner sides of the
carina they are trifid and quadrifid, and large enough to be conspicuous
with a lens of weak power.

_Peduncle._--The most remarkable fact concerning this part, is that the
outer tunic, together with the calcareous scales with which it is
covered, is moulted at each successive period of exuviation and growth.
I demonstrated this fact in _L. dorsalis_ and _L. truncata_, by removing
the old tunic and finding a new membrane with perfect calcified scales
beneath; and as these two species, (I obtained, also, pretty good
evidence in _L. Nicobarica_,) are at the opposite extremes of the genus,
no doubt this fact is common to the whole genus. I know of no other
instance, amongst Cirripedia, in which _calcified_ valves or scales are
moulted. I am not certain that the whole skin of the peduncle is thrown
off in a single piece; though this almost certainly is the case with the
uppermost and lowest portions. The animal's body is partly lodged within
the peduncle, which is generally from one to three times as long as the
capitulum, and in the upper part is fully as broad as it. The scales
with which it is clothed, extend up in the triangular interspaces
between the basal margins of the valves. The scales of the upper whorl,
or of the two or three upper whorls (Pl. VIII, figs. 1 _b´_ and 3 _d_)
are larger than those below; and these latter rapidly decrease in size,
so as to become low down on the peduncle, almost or quite invisible to
the naked eye. The scales in each whorl, are placed alternately with
those in the whorls, above and below. All the upper scales are packed
rather closely together; those in the uppermost row are generally nearly
quadrilateral; those in the few next succeeding whorls, are triangular,
with their basal margins protuberant and arched; the scales, low down on
the peduncle, stand some way apart from each other, and generally
consist of simple rounded calcareous beads, of which some of the
smallest in _L. dorsalis_ were only 1/400th of an inch in diameter. In
the lowest part of the peduncle these scales, after each fresh
exuviation, are apparently soon worn entirely away by the friction
against the sides of the cavity; hence in most specimens this part of
the peduncle is quite naked. This same part, however, is furnished with
nail- or rather star-headed little projections of hard, yellow, horny
chitine (fig. 3 _e_). The star on the summit seems generally to have
about five irregular points; one star which I measured was 7/6000th of
an inch in total width, the footstalk being only 2/6000th of an inch in
diameter; the whole projected 10/6000ths of an inch above the surface of
the peduncle; from the footstalk a fine tubulus runs through the
membrane to the underlying corium. These star-headed little points are
often much worn down; in one specimen which was on the point of
exuviation, there remained, in the lower part, close above the basal
calcareous cup, only some hard, smooth, yellow, little discs, on a level
with the general surface of the membrane,--these being the intersected
or worn down footstalks, with every trace of the calcareous beads gone.
But in this same specimen, under the old peduncular membrane, there was
a new one, studded with the usual circular calcareous beads, slightly
unequal in size, generally about 1/400th of an inch in diameter, and
each furnished with a tubulus; but as yet none of the star-headed points
of chitine had been formed. I believe that these latter are developed
from the tubuli leading to the calcified beads, and, therefore, are
formed directly under them. In _L. cauta_ the lowest scales on the
peduncle are a little larger than in _L. dorsalis_, giving a frosted
appearance to it, and all of them are serrated (fig. 3 _d_) round their
entire margins. Generally only the scales in the uppermost, or in the
three or four upper rows are serrated, and this only on their arched and
protuberant lower margins. The state of the serrated edge varies
extremely in the same species, from elongated conical teeth to mere
notches, according to the amount of wear and tear the individual has
suffered since the last period of exuviation; so also do the teeth or
serrated margins on the valves of the capitulum. Each scale has a fine
tubulus passing from the corium through the membrane of the peduncle to
its bluntly-pointed imbedded fang or base. The membrane is transparent,
thin, and tender, to a degree I have not seen equalled in the other
Lepadidæ, except, perhaps, in Ibla. It is much wrinkled transversely.

_Muscles of the Peduncle._--These consist of the usual interior and
longitudinal,--exterior and transverse--and oblique fasciæ; the former
are unusually strong; downwards they are attached to the basal
calcareous cup or disc, and upwards they extend all round to the lower
curved margins of the valves. They are, as usual, without transverse
striæ. Besides these, there are, (at least in _L. dorsalis_ and _L.
Nicobarica_,) two little fans of striæ-less muscles, which occur in no
other pedunculated cirripede; they are attached on each side of the
central line of the carina, near its base; they extend transversely and
a little upwards, and each fan converges to a point where the lower
margins of the carina and terga touch; of these muscles, the upper
fasciæ are the longest. Their action, I conceive, must be either to draw
slightly together the basal points of the terga, and so serve to open
their occludent margins, or to draw inwards the base of the carina:
these muscles apparently first shadow forth the posterior or carinal,
transversely-striated, opercular muscles of sessile cirripedes.

_Basal Calcareous Cup or Discs._--I have seen this part in all the
species, except _L. Valentiana_, and in this it probably occurs,
considering its very close alliance with _L. truncata_. The size, form,
and conditions of the cup or disc varies infinitely according to the
age, size, and position of the individual specimen. We will commence
with a full-sized animal, which has ceased to burrow downwards into the
rock, in which case the discs usually grow into a cup, and become
largely developed. In _L. dorsalis_ alone, I have seen many specimens,
so that the following description and remarks, though applicable I
believe to all the species, are drawn up from that alone. The cup (Pl.
VIII, fig. 1 _a´_, 1 _c´_) is hardly ever regular in outline, and is
either slightly or very deeply concave; I have seen one, half an inch in
diameter; it is formed of several thick layers of dirty white,
translucent, calcareous matter, with sinuous margins; externally the
surface is very irregular, and is coated by yellow membrane presently to
be described. The innermost and last-formed layer sometimes covers the
whole inside of the cup, and extends a little beyond its margin all
round; but more generally it projects beyond only one side, leaving the
other sides deserted. I have seen a _single_ new layer extending beyond
the underlying old layers, as much as one sixth of an inch; and again I
have seen a part of the cup, as much as a quarter of an inch in width,
deserted and covered with serpulæ. So irregular, however, is the growth,
that after a period an old deserted portion will occasionally be again
covered by a new layer, though of course without organic adhesion. Again
it sometimes happens that the last-formed layer, remaining central, is
very much less than the older layers; in one such instance the innermost
and last-formed layer (fig. 1 _a´_) had a diameter of only a quarter of
that of the whole cup, in the middle of which it was placed; the cup
thus tends to become filled up in the middle. The cup, in its fully
developed condition, is seated at the very bottom of the cavity in the
rock. From the aggregate thickness of the several component layers
forming the cup, the old and mature animal rises a little in its burrow;
for instance, the bottom of the cup in one specimen which I measured,
was 4/10ths of an inch in thickness.

In a younger condition, before the animal has bored down to the full
depth, and whilst the cavity is only of moderate diameter, the lower
part of the peduncle, instead of being attached to the inside of a cup,
adheres to small, irregular, nearly flat, calcareous discs, overlapping
each other like tiles (figs. 1, 2 _a´_). They are placed one below the
other, generally in a straight line, and are attached firmly to one side
of the burrow. The discs are oval, or rounded, or irregular, and are
commonly from 1/20th to 1/10th of an inch across: they usually form a
quite straight ribbon, widening a little downwards: each little disc
overlaps and extends beyond the one last formed, fully half its own
diameter. I have seen one row of discs an inch in length, but the upper
discs are always worn away by the friction of the calcified serrated
scales on the peduncle. It is very important to observe that the lowest
disc is not fixed, (as was the case with the cup,) at the very bottom of
the burrow, but on one side, just above the bottom, which latter part is
occupied by the blunt basal end of the peduncle.

In a valuable paper on _L. Nicobarica_, by Reinhardt, presently to be
referred to, the disc is said to be attached on the carinal side (see
fig. 2) of the peduncle; and this, I believe, is general. I have seen
one instance in which, during the excavation of a new burrow, an old
burrow was met with, and the row of discs turned down it, making, with
their previous course, nearly a right-angle. In another similar
instance, the discs, instead of turning down, became very large and
broad, and so fairly formed a bridge across the old burrow (fig.
1),--becoming narrow again as soon as the animal recommenced burrowing
into the solid rock. Sometimes, as it appears, the animal, whilst still
small, from some unknown cause, stops burrowing downwards, and then a
cup is formed at the bottom of the hole. As soon as the animal has got
to its full depth, the burrow increases only in diameter, and during
this process the linear row of discs is ground away and lost; a cup is
then formed. The little discs can be deposited or formed only at each
fresh exuviation; and as some of the burrows are above two inches in
depth, and as on an average each disc does not extend beyond the
underlying disc more than 1/15th of an inch, an animal which has bored
two inches in depth, must have moulted at least thirty times. I may here
remark that I have reason to believe, from some interesting
observations made by Mr. W. Thompson, of Belfast, that some sessile
cirripedes moult about every fortnight.

_Internal Structure of the Cup._--When the cup is dissolved in acid,
each shelly layer is represented by a rather tough, pale-brown membrane,
itself composed of numerous fine laminæ, which, under a one-eighth of an
inch object glass, exhibit generally only the appearance of a mezzotinto
drawing; but there often were layers of branching vessels, (like
moss-agate,) less than the 1/10,000th of an inch in diameter, and of a
darkish colour; these vessels are not articulated, but otherwise
resemble the same peculiar structure in the valves of the capitulum. The
exterior yellow membrane is marked, or rather composed of successive
narrow rims, which, in fact, are the lines of termination of the laminæ
of membrane, which in a calcified state form the cup itself. In most
parts, both on the borders and under the centre of the cup, but not
everywhere, there are imbedded in the yellow membrane, elongated,
irregular, top-shaped masses of bright yellow chitine, each furnished
with a tubulus, which penetrating the calcareous laminæ leads to the
corium; the little apertures thus formed, are clearly visible in the
layers of membrane, left after exposure to acid. In _L. Nicobarica_, the
innermost shelly layer of the cup was punctured, like the surface of the
shell in Chthamalus and many other sessile Cirripedes, by the internal
orifices of these tubuli. The top-shaped masses often have star-shaped
summits; and they differ in no essential respects from those on the
lower part of the peduncle, excepting that they are quite imbedded in
the membrane covering the under surface of the cup, whereas those on the
peduncle project freely. I found these top-shaped bodies in the outer
membrane of the cups in _L. dorsalis_, _L. cauta_, and _L. Rhodiopus_,
which alone I was enabled to dissolve in acid; and I mention this fact,
as indicating the probable presence of the more important star-headed
projections on the lower parts of the peduncle in these same species.
The basal calcareous cup resembles, in essential structure, the valves
of the capitulum; the chief difference being that in the former there is
a larger proportion of animal matter or membranous layers.

After the dissolution of the cups, in _L. dorsalis_ and _L. Rhodiopus_,
I most distinctly traced the two cement-ducts; they included the usual
darker chord of cellular matter; they were of rather small diameter,
namely, 2/3000th of an inch. The two (in _L. dorsalis_) ran in a very
irregular course, not parallel to each other, making the most abrupt
bends. They passed through the membranous layers, (as seen after
dissolution,) and running for short spaces parallel to the component
laminæ, were attached to them. In their irregular course, these
cement-ducts resemble those of _Pollicipes mitella_, but I could not
perceive that any cement had been poured out at the abrupt bends. In one
specimen of a basal cup, which I was enabled to examine whilst still
attached to the rock, I found under the very centre, (and of course
outside the yellow membrane,) a very small area of dark brown cement of
the usual appearance. In several specimens of full-sized cups, I was not
able to perceive any cement on the external surfaces of the upper and
later-formed layers; hence I believe that the cup is cemented to the
bottom of the hole only during the early stages of its formation; and
this, considering its protected situation, would no doubt be sufficient
to affix the animal. This probably accounts for the small size of the
cement-ducts, and for the facility with which, as it appears, the cups
can be removed in an unbroken condition from the rock. In the case,
however, of the small, flat, calcareous discs, which are formed whilst
the animal is burrowing into the rock, these are attached firmly to the
sides of the holes, in the usual manner, by cement. In this cirripede it
would be useless to look for the prehensile antennæ of the larva under
the cup, for the animal, during the formation of the successive discs,
must have travelled some distance from the spot on which the larva first
attached itself.

The membrane of the peduncle is continuous with the yellow membrane
coating the external surface of the cup; and this latter membrane is
continuous with those delicate laminæ which, in a calcified condition,
form the layers of the cup itself. In an exactly similar manner, in this
and other cirripedes, the membrane of the peduncle, at the top, is
continuous with that coating the valves, and is attached to the lower
exterior edge of the last-formed layer of shell. When a new shelly layer
is formed, both under the valves of the capitulum and inside the basal
calcareous cup, it projects beyond the old layer, and is included within
the old, as yet not moulted, membrane of the peduncle. Within the cup of
_L. Nicobarica_ I found a lately-formed layer of shell, projecting
1/10th of an inch on one side of the cup, and by its protuberance
distinguishable even through the old coat of the peduncle, which was
nearly ready to be moulted. In an analogous manner, in the capitulum of
_L. dorsalis_ and _L. truncata_, I have found a new peduncular membrane
bearing the usual, but then sharp, calcified scales, attached to the
lower projecting edge of the last-formed shelly layer, lying under the
old peduncular membrane, which was attached to the penultimate layer of
shell, and with its worn scales was just ready to be moulted.

The final cause of the moulting of the calcified scales, together with
the membrane of the peduncle to which they are attached,--a case
confined to Lithotrya,--I have scarcely any doubt is the reproduction of
a succession of scales, sharply serrated for the purpose of enlarging
the cavity in which the animal is lodged. The extreme thinness of the
membrane of the peduncle has been noticed; this may be partly related to
its protected condition, but partly, I think, to the necessity of its
being formed in a very extensible condition; for the new coat, owing to
the projection of the new shelly layers under the valves, and within the
basal cup, is by so much shorter than the old peduncle, yet after
exuviation it has to stretch to a greater length than the old membrane,
to allow of the growth of the Cirripede. Owing to the thinness and
fragility of this membrane, the basal attachment of the Cirripede is, no
doubt, chiefly effected by the unusually strong longitudinal muscles;
and the necessity of a surface of attachment for these muscles, stronger
than the external membrane of the peduncle, probably is one of the final
causes of the basal calcareous disc and cup, and likewise for the
unusual manner in which the valves of the capitulum are locked together
by folds and small roughened projections. The basal discs and cup,
however, apparently serve for several other purposes, namely, for
raising the animal a little in its burrow, (which is narrow and pointed
at the bottom,) at that period of growth when it has ceased to burrow
downwards, but still increases in diameter; also for carrying the
animal, as over a bridge, across any pre-existing cavity in the rock;
and lastly, perhaps, for removing lower down, in the intervals of
exuviation, the point of attachment for the longitudinal peduncular
muscles.

_Position of the animal in the rock, and its power of excavation._--A
specimen of rock, two or three inches square, in Mr. Cuming's
possession, is full of Lithotryas; the cavities extend in every possible
direction, and several were parallel, but with the animals in reversed
positions; the same thing is apparent in some specimens of Mr.
Stutchbury's, and it was evident that the positions occupied by the
animals were entirely due to chance. In Mr. Cuming's specimen of rock, a
considerable portion of the external surface is preserved, and here it
can be seen that many of the specimens have their capitulums directed
from the external surface directly inwards. These individuals, which
were of full size, must have preyed on infusoria inhabiting the cavities
of the porous, calcareous rock. On the other hand, I have seen some
young specimens of _L. dorsalis_ with their valves not at all rubbed,
and others of full size with uninjured Balani and corallines on the tips
of the valves, and again a specimen of _L. truncata_ with minute
pale-green sea-weed on the summit of the capitulum,--all which
appearances induce me to believe that in these cases, the valves had
projected freely beyond the cavity in which their peduncles were lodged.
I may here also mention that in Mr. Cuming's specimen, above alluded to,
the basal cups of five specimens touched and adhered to each other; I
was not able to make out whether there had originally existed separate
burrows, as I think is most probable, and that the walls had been wholly
worn away, or whether the five specimens had fixed themselves on one
side of a large pre-existing, common cavity. Young specimens seem to
burrow to the full depth, before nearly acquiring the diameter which
they ultimately attain. I measured one burrow, 1.2 of an inch in depth,
which, at its mouth or widest part, was only .17 in diameter.

The several species occur imbedded in soft calcareous rocks, in massive
corals, and in the shells of mollusca and of cirripedes. It has been
doubted by several naturalists, whether the basal calcareous cup at all
belongs to the Lithotrya, but after the foregoing microscopical
observations on its structure, it is useless to discuss this point. So
again it has been doubted whether the cavity is formed by the cirripede
itself; but there is so obvious a relation between the diameters of
specimens of various sizes, and the holes occupied by them, that I can
entertain no doubt on this head. The holes, moreover, are not quite
cylindrical, but broadly oval, like the section of the animal. The
simple fact, that in this genus alone each fresh shelly layer round the
bases of the valves, and therefore at the widest part of the capitulum,
are sharply toothed; and secondly, that in this genus alone a succession
of sharply serrated scales, on the upper and widest part of the
peduncle, are periodically formed at each exuviation; and that
consequently the teeth on the valves and scales are sharp, and fit for
wearing soft stone, at that very period when the animal has to increase
in size, would alone render the view probable that the Lithotrya makes
or at least enlarges the cavities in which it is imbedded.

Although it may be admitted that Lithotrya has the power of enlarging
its cavity, how does it first bore down into the rock? It is quite
certain that the basal cup is absolutely fixed, and that neither in form
nor state of surface it is at all fitted for boring.[66] I was quite
unable to answer the foregoing question, until seeing the admirable
figures by Reinhardt[67], (Pl. VIII, figs. 2 and 2 _a´_) of _L.
Nicobarica_, still attached in its cavity. Subsequently I obtained from
Mr. Stutchbury several pieces of rock completely drilled with holes,
many of small diameter, by _L. dorsalis_, and in these I found numerous
instances of the linear rows of little discs, like those of _L.
Nicobarica_, showing in the plainest manner, that each time a new disc
is formed, that is, at each exuviation, the animal moves a short step
downwards; and as the lowest of these little discs _in none of the
burrows_ was placed at the very bottom, we see that the lowest point of
the peduncle must be the wearing agent. In the peduncle of an
individual of _L. dorsalis_, nearly ready to moult, I found, it may be
remembered, beneath and round the basal disc, under the old membrane of
the peduncle, a new membrane studded with calcified beads, but with the
horny star-headed spines not yet developed, whilst on the old outer coat
these latter had been worn down quite smooth, and the calcified beads
worn entirely away. Here, then, we have an excellent rasping surface.
With respect to the power of movement necessary for the boring action,
the peduncle is amply furnished with transverse, oblique, and
longitudinal striæ-less muscles,--the latter attached to the basal disc.
In all the pedunculata, I have reason to believe that these muscles are
in constant slight involuntary action. This being the case, I conceive
that the small, blunt, spur-like portion of the peduncle, descending
beneath the basal rim of the lowest disc, would inevitably partake
slightly of the movements of the whole distended animal. As soon as the
Lithotrya has reached that depth, which its instinct points out as most
suitable to its habits, the discs are converted into an irregularly
growing cup, and the animal then only increases in diameter, enlarging
its cavity by the action of the serrated scales on the peduncle, and of
the serrated lower edges of the valves of the capitulum. With respect to
those reversed individuals attached with their capitulums downwards, I
suppose that the larvæ had crept into some deep cavity, perhaps made
originally by a Lithotrya, of which the rock in the specimen in question
was quite full, and had there attached themselves. Finally, it appears
that in Lithotrya the burrowing is simply a mechanical action; it is
effected by each layer of shell in the basal attached discs overlapping,
in a straight line, the last-formed layer,--by the membrane of the
peduncle and the valves of the capitulum having excellent and often
renewed rasping surfaces,--and, lastly, by the end of the peduncle (that
is homologically the front of the head) thus roughened, extending
beyond the surface of attachment, and possessing the power of slight
movement.

   [66] Mr. Hancock, in his admirable account of his burrowing
   Cirripede, _Alcippe lampas_, ('Annals of Nat. Hist.,' Nov. 1849,
   p. 313,) came to this conclusion regarding the cup of Lithotrya,
   and hence was led to think that this genus did not form its own
   burrows, but inhabited pre-existing cavities. I am much indebted
   to this gentleman, who has been so eminently successful in his
   researches on the boring powers of marine animals, for giving me
   his opinion on several points connected with the present
   discussion.

   [67] I owe to the great kindness of Prof. Steenstrup the sight of
   this Plate, published in the 'Scientific Communications from the
   Union of Natural History,' Copenhagen, January 30, 1850, No. I.
   Since this sheet has been set up in type, I have received from
   Prof. Steenstrup the memoir, in Danish, belonging to the figures
   in question; and the greater part of this has been translated to
   me by the kindness of a friend. My account of the means of
   burrowing is essentially the same as that published by Reinhardt;
   but the moulting of the scales on the peduncle, the presence of
   scales and of points of a different nature, the method of
   attachment by cement, the conversion of the discs into a cup,
   &c., seem not to have been known to this naturalist. Reinhardt
   states that the points on the peduncle will scratch Iceland spar,
   and that, apparently, they are formed of phosphate of lime: in
   the case of the closely-allied _L. dorsalis_, I must believe that
   the scales or beads on the peduncle are formed of carbonate of
   lime, for they were quickly dissolved with effervescence in
   acetic acid; and the star-headed points, which are subsequently
   developed under the calcareous scales, appeared to me, under the
   compound microscope, to be formed of a horn or chitine substance.
   Reinhardt states that the basal point of the peduncle is arched a
   little under the lowest disc, and there forms for itself a slight
   furrow (as represented in the lateral view, Pl. VIII, fig. 2);
   but in the burrows examined by me, this furrow or depression did
   not really exist, the appearance resulting from the basal margin
   of the lowest disc, projecting beyond the wall of the cavity by
   the amount of its own slight thickness.

       *       *       *       *       *

We will now proceed with our generic description.--

_Animal's Body._--This, as already stated, is partially lodged within
the peduncle. The prosoma is rather largely developed.

The _Mouth_ is placed at a moderate distance from the adductor muscle.

The _Labrum_ is moderately bullate, with a row of blunt bead-like teeth,
mingled with fine bristles, on the crest, which in the middle part is
generally somewhat flattened.

The _Palpi_ are blunt, and even squarely truncated at their ends; they
are of large size, so that, if they had been half as large again, or
even less, their tips would have met.

_Mandibles_ (Pl. X, fig. 2), with three nearly equal large teeth, and
the inferior angle produced, broad, and strongly pectinated: in the
interspaces between these teeth there are, in all the species, some very
fine teeth or pectinations, which are seated a little on one side of the
medial line. The mandibles are somewhat singular from the size of the
transparent flexible apodemes (_a_ _a_) to which the muscles are
attached; these are oval and constricted at their origins: in _L.
dorsalis_ they are roughened with little points; in _L. cauta_ and _L.
truncata_ they are large, of the same shape, but smooth.

_Maxillæ._--These are larger, compared to the mandibles, than is usual
with pedunculated Cirripedes; they differ in shape in the different
species, being either nearly straight on their edge, and notched or not
(fig. 10), or notched with the inferior part forming a double prominence
(fig. 12); the spines on the inferior angle, which is sometimes slightly
produced, are always crowded together into a brush, and are finer than
those on the upper parts. The apodemes are less straight than is usual,
and at their origin take, in all the species, a rather abrupt bend;
their extremity is enlarged into a little disc, which in _L. dorsalis_
is covered with strong points, but in the other species is, as usual,
smooth.

_Outer Maxillæ._--The inner margin is slightly concave, and in _L.
truncata_ alone, the bristles are hardly continuous, being interrupted
in the middle part. The olfactory orifices are only very slightly
prominent. The spines on all the trophi are more or less doubly
serrated.

_Cirri._--The three posterior pair are elongated, with their anterior
surfaces not at all protuberant. The segments bear from three to five
pair of spines, with a row of three or four small intermediate spines;
there are, as usual, some little lateral upper rim spines; the dorsal
tufts contain some thick and thin spines mingled. _First_ cirrus is
short, and placed not quite close to the second pair; the basal segments
are broad and thickly paved with bristles. The _second_ pair is rather
short compared with the _third_ pair; a varying number of the basal
segments in both rami of both these cirri are protuberant, and are
thickly paved with bristles; such segments are more numerous and are
broader on the anterior rami than on the posterior rami. In _L. cauta_
alone, none of the basal segments in the posterior rami of the second
and third cirri are thickly paved with bristles. The pedicels of the
first three pair are irregularly covered with spines; those of the three
posterior pair have the spines arranged in a regular double line. Most
of the spines are doubly serrated.

_Caudal Appendages_ (Pl. X, fig. 23 and 24), multiarticulate, with thin
elongated segments fringed with short spines; in length generally
exceeding the pedicel of the sixth cirrus, and in _L. Nicobarica_
equalling half the entire length of this cirrus.

_Stomach_, destitute of cæca; oesophagus somewhat curled.

_Filamentary Appendages_, none.

_Ovaria_ filling up the peduncle and surrounding the sack, but not
extending up to the bases of the scuta and terga; I saw the ova only in
_L. truncata_; they were here oval and large, being nearly 9/400ths of
an inch in length.

_Penis_, elongated; vesiculæ seminales extending into the prosoma. I
noticed the ovigerous fræna only in _L. truncata_; here they were large,
with an almost bilobed outline; the margin and whole lateral surface
being covered with elongated cylinders, finely pointed, but not enlarged
at their extremities, as are the glands observed in most of the other
genera.

_Colours._--The posterior thoracic segments, the pedicels, the anterior
and dorsal surfaces of the segments of the cirri, the caudal appendages,
and the outer sides of the trophi are, in most of the species, more or
less mottled with dark purple; parts of the interior surfaces of the
valves in some of the species are coloured fine purple.

_Geographical Distribution._--The species are found all round the world
in the tropical seas; this fact may have some connection with the
presence of soft coral-reef limestone and of massive corals in these
seas. The presence, however, of _L. cauta_ on the shores of New South
Wales, shows that the genus is not strictly tropical.

_Affinities._--Lithotrya is a well-pronounced distinct genus; although
there is a considerable difference in the shape of the valves between
_L. dorsalis_ and _L. Valentiana_, at the opposite extremes of the
genus, the strict uniformity of the internal characters shows that there
are no grounds whatever for any generic separation; moreover, _L.
Rhodiopus_ neatly blends together these extreme forms. Indeed it is not
easy to imagine a better marked series of transitional forms, than those
presented by the terga, in passing from _L. dorsalis_ through _L.
Nicobarica_, _L. Rhodiopus_, and _L. truncata_, to _L. Valentiana_.
Lithotrya has most affinity to _Scalpellum villosum_ or to _Pollicipes
spinosus_ and _P. sertus_; though the affinity is far from close. In
these two species of Pollicipes, we have seen that large irregular
calcified spines are formed at the base of the peduncle, whereas in the
other Pedunculata the scales or spines are formed exclusively round the
upper margin of the peduncle. Lithotrya, as has been remarked by Sowerby
and other authors, exhibits some affinity to the sessile Cirripedes, as
shown by the calcareous basis,--by the manner in which the scuta and
terga are locked together,--by the two little fans of muscle attached to
near the basal points of the terga,--and perhaps by some of the
characters of the trophi; nevertheless, this affinity is far from being
well-marked, and I think is hardly so plain as in _Pollicipes mitella_.


1. LITHOTRYA DORSALIS. Pl. VIII, fig. 1 _a´_.

  LITHOTRYA DORSALIS. _G.B. Sowerby._ Genera of Shells, April,
        1822.

  LEPAS DORSALIS. _Ellis._ Nat. Hist. Zoophytes, Tab. xv, fig. 5,
        1786.

  LITHOLEPAS DE MONT SERRAT. _De Blainville._ Dict. des Sc. Nat.,
        Plate, fig. 5, 1824.

_L. scutis terga angustè obtegentibus: carinâ intùs concavâ: rostro,
duorum aut trium squamarum subjacentium latitudinem æquante: lateribus,
squamarum quinque subjacentium longitudinem æquantibus, superficie
internâ angustè ellipticâ: pedunculi squamis superioribus verticillum
secundum minus duplo superantibus._

Scuta, narrowly overlapping the terga: carina internally concave:
rostrum as wide as two or three of the subjacent scales: latera with
their internal surfaces narrowly elliptical, as long as five of the
subjacent scales: upper scales of the peduncle less than twice as large
as those in the second whorl.

Mandibles, with twice as many pectinations between the first and second
main teeth, as between the second and third teeth. Maxillæ without a
notch, edge nearly straight, and spines very numerous: caudal appendages
exceeding, by half, the length of the pedicel of the sixth cirrus.

    Barbadoes, West Indies; Venezuela; Honduras; imbedded in
    limestone; Mus. Brit. Cuming and Stutchbury.

The state of preservation of the valves in different specimens varies
greatly; generally only two or three, or even only the last-formed
shelly layer, is preserved, the upper ones having scaled off; in a few
young specimens, however, all the layers were perfect. The carina is
generally better preserved than the other valves, and hence the upper
part usually projects freely; in one specimen no less than ten zones of
growth were preserved in the carina, whilst the other valves consisted
of only three: the terga generally project rather more than the scuta.
As each growth-layer is thick, if the scaling process had not taken
place, all the valves would have projected greatly. The little teeth lie
close together on the prominent serrated rims, on each zone of growth.
The internal surfaces of the valves are roughened with small imbricated
points. Exteriorly the valves are covered with yellow membrane, with
rows, corresponding with each zone of growth, of very minute, yellow,
horny spines, generally having their tips bent over, and so made
hook-shaped. These spines are less than 1/600th of an inch in length.

_Scuta_, triangular; internally concave, with a large depression for the
adductor muscle; there is the usual small roughened internal knob, or
tooth, at the rostral angle of both the right and left hand valves.
Tergal margin straight, overlapping about one third of the entire width
of the terga.

_Terga_, irregularly oval, with the scutal margin straight; basal point
blunt, with the two sides placed at about an angle of 45° to each other;
the lower part of the carinal margin, immediately over the latera, (as
seen internally,) is slightly hollowed out. Exteriorly, towards the
bottom of the valve, from the overlapping of the scuta, of the latera,
and of the carina, only a narrow rounded ridge is exposed, which runs
down to the basal angle at about one third of the entire width of the
valve, from the scutal margin. Internally the valve is slightly concave.

The _Carina_ slightly overlaps the terga; internally concave; generally
with a large upper portion freely projecting; inwardly curved, without
any central crest or ridge; valve nearly as wide as the middle part of
the terga; inner growing or corium-covered surface, with its basal
margin, protuberant and arched.

_Rostrum_ (Pl. VIII, fig. 1 _a´_, _a_, and greatly magnified 1 _b´_)
very narrow; rarely more than two or three layers of growth are
preserved; the sides are deeply sinuous, owing to each zone widening
downwards; basal margin rounded; in width equalling about two and a half
of the uppermost scales of the peduncle, and about half as wide as the
latera.

_Latera_, small, placed obliquely, and parallel to the lower carinal
margin of the terga; longer axis equal to five of the uppermost scales
of the peduncle, and to nearly half the width of the base of the carina;
growing surface (or a section made parallel to the growth-layers,) is
narrow, elliptic, pointed at both ends, but the carinal half rather
thicker than the scutal half.

The _Peduncle_ varies in length, generally about twice as long as the
capitulum, in one specimen above thrice as long. The upper part as wide
as the capitulum, the lower part sometimes much attenuated. The
calcified scales in the uppermost whorl (Pl. VIII, fig. 1 _b´_) are only
slightly larger than those in the second whorl; the scales in the
succeeding three or four whorls, are considerably larger than those
below, which latter very gradually decrease in size, till, low down on
the peduncle, they are barely visible to the naked eye. In this lower
part, they may be called calcareous beads; they stand some way apart
from each other; they are nearly hemispherical, smooth, translucent, and
furnished with a conical fang; some of the smallest were 1/325th and
1/400th of an inch in diameter. The upper scales vary somewhat in the
outline, the most usual shape being sub-triangular, with the lower
margin arched and protuberant; and this margin, in the two or three
upper whorls, is crenated with teeth, which are conical and sharp, after
exuviation, but soon become reduced to mere notches. The scales in the
uppermost whorl are usually nearly quadrilateral; the imbedded portion,
or fang of each scale, is, in all, produced into a blunt rounded point.
The basal calcareous cup (fig. 1 _a´_ and 1 _c´_) is well developed, and
is sometimes even half an inch in diameter. Before the cup is formed,
there is a row of small, flat discs (fig. 1, and like those in fig. 2
_a´_) attached to the sides of the burrow: but a full account of these
parts of the peduncle, and of the burrowing habits of this species, has
been given under the generic description.

_Size and Colour._--Full average-sized specimens have a capitulum half
an inch in width and height; the entire length, with the contracted
peduncle, being about an inch and a half. Valves coloured dirty white,
with the enveloping membrane, when preserved, yellow. The outer maxillæ,
palpi, pedicels of the cirri, anterior faces of the segments, dorsal
tufts, caudal appendages, and penis, dark purple. Thoracic segments
brown. There is a purple spot between the bases of the first pair of
cirri.

_Mouth._--Labrum considerably bullate, equalling about half the
longitudinal diameter of the mouth; inferior part produced so as to
separate the mouth some way from the adductor muscle; crest with a row
of blunt teeth and hairs; central part depressed and flattened.

_Palpi_, rather large, separated from each other by only half their own
length; bluntly pointed, thickly clothed with spines.

_Mandibles_ (Pl. X, fig. 2), with twice as many pectinations, namely 15,
between the first and second main teeth, as between the second and third
teeth, namely about 7; inferior angle strongly and coarsely pectinated;
distance between the tips of the first and second main teeth,
considerably less than between the tips of the second tooth and of the
inferior angle; sides hirsute.

_Maxillæ_ (fig. 10), with the edge not quite straight, with the whole
inferior part slightly projecting; spines very numerous, thirty or forty
pairs; those close beneath the two upper great unequal spines, form a
tuft and are rather thinner than the others, as are also those near the
inferior angle; sides hirsute.

_Outer Maxillæ_, rather pointed, with the inner edge slightly concave,
continuously and thickly clothed with short spines; spines on the outer
edge long; there are also some minute, short, thinly scattered spines or
points on the sides. Bristles on all the trophi doubly serrated.

_Cirri._--The first pair is placed at a small distance from the second.
The segments in the three posterior pairs, support five pairs of very
long spines, with a row of (I believe) four small intermediate spines;
on the lateral upper edges, there are some short blunt spines; anterior
faces of the segments not protuberant; the dorsal tufts consist of thick
serrated, and of thin spines. The whole integument is hirsute with
minute pectinated scales. Two or three of the basal segments in the
sixth cirrus are confluent. _First cirrus_, anterior ramus rather
shorter and thicker than the posterior ramus; basal segments thickly
paved with serrated spines; in the posterior ramus, the six terminal
segments are not paved with bristles. _Second cirrus_ has the seven
basal segments of the anterior ramus very broad, and paved with
bristles; the eight terminal segments having the usual structure; in the
posterior ramus the three or four basal segments are similarly paved,
but to a very much less degree, and the remaining thirteen have the
usual structure. _Third cirrus_ has the six basal segments of the
anterior ramus very broad and paved, and the fourteen terminal ones of
the usual structure; in the posterior ramus, the three or four basal
segments are similarly paved, but to a very much less degree, and the
seventeen terminal ones have the usual structure. The pedicel of the
first cirrus has very few spines; those of the second and third cirrus
are thickly and irregularly clothed with spines; and those of the three
posterior pair have a double row with intermediate small spines. On the
antero-lateral faces of the pedicels of the second, third, and fourth
pairs of cirri, there is an elongated white swelling or shield.
Moreover, on the posterior thoracic segments, there are similar
white-coloured swellings, with the membrane more plainly marked with
scales than in other parts. The spines on the first three pairs of
cirri are coarsely serrated.

_Caudal Appendages_ (Pl. X, fig. 23), with numerous tapering segments,
almost equalling one and a half times the length of the pedicel of the
sixth cirrus. Each segment is elongated and somewhat constricted in the
middle, with its upper edge (fig. 24) crowned with short spines; in a
full-sized specimen there were seventeen segments.


2. LITHOTRYA CAUTA. Pl. VIII, fig. 3.

_L. scutis terga amplè obtegentibus: carinâ intus concavâ: rostro
squamarum subjacentium latitudinem vix æquante: lateribus, squamas
subjacentes sesquitertio superantibus; superficie internâ latè
ellipticâ: pedunculi squamis superioribus verticillum secundum pæne
quadruplo superantibus._

Scuta largely overlapping the terga: carina internally concave: rostrum
hardly as wide as one of the subjacent scales: latera with their
internal surfaces broadly elliptical, as long as two and a half of the
subjacent scales: upper scales of the peduncle nearly four times as
large as those in the second whorl.

Mandibles with an equal number of pectinations between the first,
second, and third main teeth: maxillæ notched, edge nearly straight:
posterior rami of the second and third cirri, with their basal segments
not paved with bristles: caudal appendages slightly exceeding in length
the pedicels of the sixth cirrus.

    New South Wales, Australia, imbedded in a Conia, (unique
    specimen,) Mus. Stutchbury.

Valves thin, white, translucent; upper layers of growth well preserved,
excepting on the terga. A large portion of the carina projected freely.
The teeth on the projecting margins of the growth-layers are broad,
blunt, and often stand rather distant from each other.

_Scuta_ (Pl. VIII, fig. 3 _a_), triangular, internally concave with no
distinct pit for the adductor muscle. The scuta largely overlap the
terga.

_Terga_ (fig. 3 _b_) approaching to rhomboidal; basal angle rectangular,
almost central, and consequently the exterior longitudinal ridge, which
is rounded, is likewise nearly central.

_Carina_, internally concave, with no trace of a central internal ridge
in the upper free portion; the growing or corium-covered surface is
transversely oval, and is as wide as the widest part of the terga.

_Rostrum_, exceedingly minute, enlarged at each zone of growth, not so
wide as the immediately subjacent scale on the peduncle.

_Latera_ (fig. 3 _c_), in width equalling two and a half of the upper
peduncular scales, or about one fourth or one fifth of the width of the
carina; growing surface, (or a section parallel to the layers of
growth,) broadly elliptic, pointed at both ends.

_Peduncle_, about twice as long as the capitulum; the scales of the
uppermost whorl are quadrilateral (fig. 3 _d_), and nearly four times as
large as those in the second whorl; these latter are about twice as
large as those in the third whorl, which are very little larger than the
small, almost equal-sized, equally distant, round beads scattered over
the rest of the peduncle, down to the basal cup. All these scales are
dentated, the upper rows most plainly and only on their basal margins;
the lower little beads are very slightly crenated round their entire
margins; they are mingled with star-headed spines (fig. 3 _e_) of yellow
chitine. Basal calcareous discs thin, plainly marked exteriorly by
concentric lines of growth, and covered by the usual yellow membrane,
including the horny, spindle-shaped bodies.

_Size and Colours._--The whole specimen, including the peduncle, was
only one fifth of an inch in length; the capitulum being 3/40ths of an
inch in width. I do not know whether the specimen had attained its full
size, but think this is probable, as a large-sized species would not
have made its habitation in one of the valves of so small a shell as a
Conia. Shell white, exterior membrane, where preserved, yellow, and
bearing small spines. Thoracic segments, the lower segments of the
second, third, and fourth cirri, all the segments of the first cirrus
and the trophi, slightly mottled with darkish purple.

_Mouth._--The teeth or beads on the crest of the labrum are blunt, few,
not very small, and equidistant.

_Palpi_, bluntly pointed.

_Mandibles_, with the three main teeth nearly equal in size; the
pectinations are equal in number, namely, only three between the first
and second, and the second and third main teeth; the inferior angle is
coarsely pectinated, with one central spine much longer than the others;
the distance between the tips of the first and second main teeth, equals
that between the second tooth and the inferior angle.

_Maxillæ_, with the two upper spines very large; beneath them there are
two small spines, and a considerable notch; the inferior part of the
edge is nearly straight, bearing about thirteen pairs of spines,
obscurely divided into two groups, the lower spines being smaller than
the upper ones. The upper convex margin is hirsute with long hairs.

_Outer Maxillæ_, blunt, with the inner margin slightly concave;
continuously, but thinly clothed with spines.

_Cirri._--The segments of the three posterior pairs bear four pairs of
spines, with the usual intermediate fine spines; dorsal spines thin and
thick mingled together. _First cirrus_, short, with the anterior ramus
rather the thickest and shortest; all the segments thickly paved with
bristles, except the two terminal segments, of which the ultimate one
bears some serrated spines of most unusual length, namely, equalling
within one segment the entire length of the ramus. I presume that these
spines serve as feelers. _Second cirrus_; anterior ramus much thicker
and considerably shorter than the posterior ramus; six basal segments
paved with bristles, the two terminal segments having the usual
structure; posterior ramus with all its nine segments on the usual
structure. _Third cirrus_, longer, to a remarkable degree, than the
second cirrus, with its anterior ramus having the four basal segments
paved, and the seven terminal ones on the usual structure; posterior
ramus with twelve segments, of which none are paved. The pedicels of the
second and third cirri thickly and irregularly clothed with spines. The
upper segments of the pedicels of all the cirri are unusually long.

_Caudal Appendages_, longer than the pedicels of the sixth cirrus, by
barely one third of their own length. Segments much elongated, seven in
number; I may add for comparison that each ramus of the sixth cirrus
contained, in this specimen, sixteen or seventeen segments.

_General Remarks._--It is difficult to give obvious characters,
(excepting the smallness of the rostrum compared with the scales on the
peduncle,) by which this species can be externally discriminated from
_L. dorsalis_, _L. Nicobarica_, and _L. Rhodiopus_; yet almost all the
valves differ slightly in shape. In this species alone, (the peduncle of
_L. Rhodiopus_ is not known,) the lower, microscopically minute,
bead-like scales of the peduncle are crenated, though obscurely, all
round. In the animal's body, the diagnostic characters are strongly
marked;--the long spines on the terminal segment of the first
cirrus,--none of the segments in the posterior rami of the second and
third cirri being thickened and paved with bristles,--the pectinations
being equal in number between the main teeth of the mandibles,--are all
characters exclusively confined to this species.


3. LITHOTRYA NICOBARICA. Pl. VIII, fig. 2.

  L. NICOBARICA. _Reinhardt_, Naturhist; Selskabet, Copenhagen. No.
        I. 1850. Tab. I, fig. 1-3.[68]

   [68] I am not at all sure that the proper title of the periodical
   in which this species has been described, is here given. I am
   greatly indebted to Prof. Steenstrup for sending me a separate
   copy of the paper in question, written in Danish. I believe I am
   right in identifying the specimen here described, from Timor,
   with the species from the Nicobar Islands, named by Reinhardt,
   _L. Nicobarica_.

_L. scutis terga angustè obtegentibus: carinæ cristâ internâ tenui in
parte superiore positâ: rostro conspicuo, squamarum sex subjacentium
latitudinem æquante: lateribus, superficie internâ triangulâ, squamarum
septem subjacentium latitudinem æquantibus._

Scuta narrowly overlapping the terga: carina with a slight central
internal ridge in the upper part: rostrum conspicuous, as wide as six of
the subjacent scales: latera, with their internal surfaces triangular,
as wide as seven of the subjacent scales.

Palpi square at their ends: mandibles with twice as many pectinations
between the first and second main teeth, as between the second and
third: maxillæ slightly notched, with the inferior angle slightly
prominent: caudal appendages more than twice as long as the pedicels of
the sixth cirrus.

    Timor; Brit. Mus., (given by Cuvier to Leach); Nicobar Islands,
    according to Reinhardt.

Capitulum as in _L. dorsalis_. The teeth on the prominent rims of the
valves are small and approximate; but the specimen was much worn.

_Scuta_, triangular, slightly overlapping the terga; the line of
junction between these valves slightly sinuous, the upper part of the
tergal margin of the scuta being slightly hollowed out, and the
corresponding upper portion of the margin of the terga being slightly
protuberant. Internally, there is a considerable depression for the
adductor muscle; and besides the usual knob at the rostral angle, there
is a trace of a knob at the baso-tergal angle.

_Terga_, as seen internally, irregularly rhomboidal, ending downwards in
a blunt point, of which the two sides, (neither being sensibly hollowed
out,) stand at about an angle of 45° to each other. Scutal margin, with
the upper part, (as above remarked,) slightly protuberant: near the
bottom of this margin, there is a very slight projection, answering to
the small knob at the baso-tergal angle of the scutum. Externally,
towards the basal angle, the narrow strip not concealed by the
overlapping of the latera and carina is square-edged, with the zones of
growth on it straight.

_Carina_, internally concave in the upper free part, with a slight,
central, internal crest, caused by the projection of each successive
zone of growth. The inner growing surface is almost pentagonal in
outline; with the basal margin square and truncated in the middle.

_Rostrum_ (fig. 2 _a_), rather conspicuous, many zones of growth being
preserved. It equals in width six of the subjacent scales of the
peduncle, but as these are rather smaller than elsewhere, the width
equals about five of the ordinary uppermost scales; compared with the
latera, it is nearly 5/7ths of their width.

_Latera_, unusually large; as seen on their interior surfaces, (or in a
section parallel to the zones of growth,) they are triangular, elongated
transversely, with the carinal angle a rectangle. In width they equal
the seven subjacent scales of the peduncle, and are more than half as
long as the basal margin of the carina.

_Peduncle_, with the upper scales varying from circular to
quadrilateral, thrice as large as those in the second whorl; beneath
which, in the next three or four whorls, the scales rapidly decrease in
size; and beneath these the whole peduncle is studded with equal-sized,
rounded, calcareous beads, so minute as to be quite invisible to the
naked eye. This specimen was nearly ready to moult, and perhaps in
consequence of this, even the upper scales were most obscurely serrated
on their lower margins, and all the others quite smooth: there were some
much worn horny spines close to the bottom of the peduncle. Basal
calcareous cup slightly concave, of moderate size; its diameter, in the
one specimen examined, was 9/10ths of an inch; it was composed of
several layers. In the specimen figured (2 _a´_) by Reinhardt, instead
of a cup, there is a straight row of small discs, which are attached to
the walls of the cavity, as explained in the generic description.

_Mouth._--Palpi with their ends square and truncated; thickly clothed
with long spines.

_Mandibles_, with fully twice as many pectinations, (viz. from 16 to
20,) between the first and second main teeth, as between (viz. 8 to 10)
the second and third main teeth. Inferior angle, coarsely pectinated.
The distance between the tips of the first and second teeth, is
considerably less than between the tip of the second tooth and the
inferior angle.

_Maxillæ_, with the edge very slightly irregular; beneath the two great
upper spines there is a slight notch, with some small spines: inferior
angle slightly prominent, with a brush of moderately fine spines;
besides these, there are about seventeen pairs of large spines; sides
very hairy.

_Outer Maxillæ_, with the inner margin slightly concave, and with the
spines continuous.

_Cirri._--The segments in the three posterior pairs support three or
four pairs of long spines, with a single row of moderately long
intermediate spines; the dorsal tufts consist of a few rather thick, and
some long and thin spines. The front of the segments is not protuberant;
the whole surface is hirsute with minute comb-like scales. _Second
cirrus_, with the anterior ramus having its eight basal segments highly
protuberant and thickly clothed with spines, the upper nine having the
usual structure; the posterior ramus has four or five basal segments
thickly clothed with spines, and the twelve upper ones with the usual
structure. _Third cirrus_, with the anterior ramus having six segments
highly protuberant and thickly clothed with bristles, and the fifteen
upper ones on the usual structure; in the posterior ramus, only three or
four of the basal segments are paved with bristles. The spines on the
first three pairs of cirri, are coarsely and doubly serrated.

The _Caudal Appendages_ are more than twice as long as the pedicels of
the sixth cirrus, and equal half the length of the whole cirrus. In a
specimen in which the sixth cirrus contained twenty-two segments, the
caudal appendages actually contained twenty. The segments are thin, with
their upper edges clothed with serrated spines. The slip of membrane on
each side, whence this organ springs is united, for a little space, to
the lower segment of the pedicel of the sixth cirrus.

_Size and Colour._--Width of the capitulum rather above 4/10ths of an
inch; length, including the peduncle, (contracted by spirits,) nearly
one inch. Valves, as usual, dirty white, partly invested by yellow
membrane, furnished with a few minute yellow horny spines. Pedicels of
the first four cirri, caudal appendages, penis, the two posterior
thoracic segments, the segments of the cirri, and the trophi, clouded,
banded, or spotted, with blackish purple.

_Affinities._--This species, in the characters derived from the valves,
comes perhaps nearest to _L. Rhodiopus_; in the characters derived from
the animal's body, it is nearest to _L. dorsalis_.


4. LITHOTRYA RHODIOPUS. Pl. VIII, fig. 4.

  BRISNÆUS RHODIOPUS. _J. E. Gray._ Annals of Philosoph., vol. x,
        (new series,) 1825.

  ---- ---- _J. E. Gray._ Spicilegia Zoolog., Tab. xvi, fig. 17,
        1830.

_L. scutis terga ample obtegentibus: carinæ cristâ internâ tenui, in
parte superiore positâ: lateribus, superficie internâ symmetricè et latè
ovatâ, carinæ latitudinis plus quam tertiam partem æquantibus: tergorum
basali apice tenui, et angulo carinali producto: rostro et pedunculo
ignotis._

Scuta largely overlapping the terga. Carina with a slight central
internal ridge in the upper part. Latera with their internal surfaces
symmetrically and broadly oval, more than one third of the width of the
carina. Terga with the basal points narrow, and the carinal angle
produced. Rostrum and peduncle unknown.

Mandibles, with four times as many pectinations between the first and
second main teeth, as between the second and third; distance greater
between the tips of the first and second teeth, than between the tip of
the second tooth and the inferior angle. Maxillæ widely notched, with
the inferior part forming two obscure prominences.

    Hab. unknown. Imbedded in a massive coral. Brit. Mus.

The specimens are in a rather bad condition, and have been
disarticulated. They are of rather small size; the rostrum and peduncle
are lost, and animal's body much injured.

Valves white, thin, translucent; teeth on the projecting rims small,
narrow, standing further apart than their own width. The upper layers
have undergone but little disintegration or scaling off, and
consequently the carina and terga project freely. The valves, where not
rubbed, are covered by bright yellow membrane, which is thickly clothed
with rows of spines; these are small on the exterior surfaces, but are
very large and hooked in certain parts, as near the tergal margins of
the scuta, and on the carinal margins of the terga, and especially on
the inner face of the upper free part of the carina. Here the hooked
spines (fig. 4 _d_) are trifid or quadrifid, and are very conspicuous.

_Scuta_, as seen externally, triangular; they overlap half the width of
the terga; on their internal faces (fig. 4 _a_), in the upper projecting
part, there is a strong ridge, against which the scutal margin of the
terga abuts. There is a deep and conspicuous pit for the adductor
muscle.

_Terga_, as seen externally, nearly triangular. The ridge which leads
from the apex to the basal angle, is rounded, central, and extremely
prominent; but does not form a furrow, or include the overlapping margin
of the scuta. The basal angle is narrow, spur-like, and slightly
hollowed out on both margins. The growing corium-covered surface (fig.
4 _b_) is transversely elongated, with the occludent margin rounded, and
the carinal angle much produced, but not forming a roughened knob.

_Carina_ (fig. 4 _d_), concave within, with a slight central ridge in
the upper free portion. The inner growing surface is concave, almost
pentagonal, with a just perceptibly raised central rim in the upper
part, and with two minute prominences on each side, against which the
produced carinal angles of the terga abut.

_Rostrum_, lost.

_Latera_ (fig. 4 _c_), growing surface (or a section parallel to the
growth-layers,) symmetrically oval, more than one third as wide as the
basal margin of the carina. Several zones of growth preserved.

_Peduncle_, lost, but a few scales accidentally adhering to one of the
valves, show that they are crenated in the three or four upper whorls.
No basal calcareous cup was preserved, but by clearing out the base of
one of the holes in the coral, in which a specimen had been imbedded, I
found a little flat disc about the size of a pin's head; it was composed
of two or three layers, and was externally coated by yellow membrane,
including the usual spindle-shaped bodies and tubuli. The cement-ducts
were also discovered after dissolution in acid. So that there could be
no doubt regarding the nature of the little disc.

_Mouth._--Labrum with a row of little blunt teeth.

_Palpi_, blunt, rather expanded at their ends, with the extreme margin
much arched and furnished with two rows of long spines; there is a
fringe of short spines on the straight inner side.

_Mandibles._--There are nine pectinations between the first and second
main teeth, and only two between the second and third teeth; the
inferior angle is coarsely pectinated, with one central spine twice as
long as the others. The distance between the tips of the first and
second main teeth, is greater than between the tip of the second tooth
and the inferior angle.

_Maxillæ_ (Pl. X, fig. 12).--These may be described as having their edge
formed into three prominences; or, as having a very wide notch under the
two upper great spines, and with the whole inferior part forming two
prominences. There are, altogether, about twelve pairs of spines, of
which two stand singly on the inferior side of the wide notch under the
two upper great spines. The spines on the inferior angle are rather
smaller than those above; sides hirsute.

_Outer Maxillæ_, with the inner margin slightly concave, and sparingly
covered with bristles.

_Cirri_, imperfectly preserved; the three posterior pairs have segments
of the usual character, bearing five pairs of very long spines, with the
usual little intermediate, the minute lateral, and the dorsal spines.
First cirrus lost; second and third with only their few basal segments
preserved, sufficient, however, to show that at least two or three
segments, in both the anterior and posterior rami of both cirri, were
paved with bristles.

_Pedicels_, as in the other species.

_Caudal Appendages_, lost.

This species comes very close, as far as the characters derived from the
trophi serve, to the _L. truncata_, though readily distinguished from
that species by the shape of the valves. On the other hand, the
capitulum of this species is distinguished with difficulty from that of
_L. Nicobarica_ and _L. cauta_; no doubt this difficulty is much
enhanced by the rostrum and peduncle having been lost.


5. LITHOTRYA TRUNCATA. Pl. IX, fig. 1.

  ANATIFA TRUNCATA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.
        xciii, figs. 12 to 15, 1834.

_L. scutis in profundam tergorum plicam insertis: carinæ cristâ centrali
prominente et rotundatâ in parte superiore: rostro et lateribus
rudimentalibus, carinæ latitudinis quindecimam fere partem æquantibus._

Scuta locked into a deep fold in the terga: carina with a prominent
central rounded ridge in the upper part: rostrum and latera rudimentary,
about 1/15th of the width of the carina.

Mandibles, with nearly three times as many pectinations between the
first and second teeth, as between the second and third teeth; distance
between the tips of the first and second teeth equal to that between the
tip of the second tooth and inferior angle. Maxillæ widely notched, with
the inferior part forming two prominences. Caudal appendages shorter
than, or barely exceeding in length, the pedicels of the sixth cirrus.

    Friendly Archipelago, Mus. Paris; Philippine Archipelago, Mus.
    Cuming; imbedded in coral rock.

Capitulum rather thick, with the five main valves having their free
apices, diverging and truncated. The upper and old layers of shell do
not here scale off so readily as in many of the foregoing species; and
hence an unusually large proportional length of each valve projects
freely above the sack; and the valves are of unusual thickness. The
capitulum is very nearly as wide at its summit as at its base, owing to
the divergence of the apices of the valves. The scuta and terga are
articulated together by a conspicuous fold, which, when seen from
vertically above, (Pl. IX, fig. 1 _a´_,) appears like a deep
wedge-formed notch in the terga. On the exterior surfaces of the valves,
the teeth on the successive rims are approximate; on the inner surfaces,
the rims are covered by strong yellow membrane, which is generally
fringed with small horny spines.

_Scuta_, exterior surface convex, sub-triangular, with the apex
truncated: seen vertically from above, there is a small rectangular
indentation or fold which receives the projecting scutal margin of the
terga. The inner growing or corium-covered surface (fig. 1 _b_, _b´_) is
triangular, with its tergal margin _largely_ hollowed out. Along the
occludent margin there is a slight ridge, which terminates at the
rostral angle, in both the right and left-hand valves, in a rounded,
knob-like, roughened tooth. The lower part of the tergal margin is
slightly inflected and roughened, where it meets the corresponding lower
part of the scutal margin of the terga. There is a deep pit for the
adductor muscle. The interior surface of the valve above this pit is
faintly-coloured purple. The inner surfaces of both scuta and terga, are
roughened with little points.

_Terga_, seen externally, are almost quadrilateral (owing to the apex
being truncated), with the free margin facing the scutum, arched. Seen
vertically from above, each shows a deep fold, which receives the lower
part of the tergal margin of the scutum. In the foregoing species, a
prominent ridge runs down the exterior surface of the terga from the
apex to the basal angle, against which ridge, the margin of the
overlapping scuta abuts: here this ridge, instead of projecting straight
out, is oblique or folded over, and thus forms a furrow, receiving the
margin of the scuta. The interior growing surface of the tergum (fig. 1
_b´_, _c_), presents so irregular a figure, that it can hardly be
described; in area it quite equals the scuta; it is slightly concave; at
the upper point of the carinal margin, there is a large, rounded,
protuberant, roughened knob, which corresponds with a small knob on each
side of the inner face of the carina; these knobs seem firmly united
together by membrane. The scutal margin of the terga, in the upper part,
forms a shoulder, largely projecting over the scuta; on its lower part,
there is a small roughened projection. The occludent margin is arched
and protuberant, with a slight fold above the knob on the carinal
margin, just mentioned: this fold is caused by the protuberance of the
central internal ridge of the carina, but is so small, that when the
capitulum is seen from vertically above, it can hardly be distinguished.
Finally, the basal half of the carinal margin, runs in the same line
with the basal margin of the scuta.

_Carina_, moderately large; seen externally, the surface presents an
elongated triangle, with the apex truncated; on the internal face (fig.
1 _b´_, _d_) of the free part, there is (instead of being concave as is
usual) a great central ridge, which projects between the diverging
apices of the terga, as may be seen from vertically above; hence the
thickness of the upper part of the carina, in a longitudinal plane,
almost equals its breadth. The edge of this ridge is rounded. The inner
or growing surface of the carina is tinted purple, and lies in a plane,
oblique to the longer axis of the valve; it is triangular, with the apex
cut off, and the basal margin rounded and protuberant; it is not
concave. There is a central raised line or slight ridge on this inner
surface, and on each side in the upper part there is a small, white,
roughened knob, corresponding with the similar knobs on the carinal
margins of the terga.

_Rostrum_ (fig. 1 _b´_, _a_), rudimentary; in one specimen it was about
1/50th of an inch in width; it is either as wide, or only half as wide,
as the subjacent scale on the peduncle.

_Latera_, rudimentary, placed between the edges of the carina and the
terga; rather smaller than the rostrum; almost cylindrical, slightly
flattened, enlarged at each zone of growth, with one or two sharp teeth
or spines on both faces; imperfectly calcified; in width barely 1/15th
part of the carina.

_Peduncle_, short; the scales alone in the uppermost whorl are plainly
toothed; they are transversely elongated, and almost quadrangular, and
are nearly twice as large as those in the second whorl. Beneath this
second whorl, there are two or three whorls, with scales, graduated in
size; and the rest of the peduncle is covered by rather distantly
scattered, minute, rounded or acutely pointed scales: the pointed scales
are directed upwards, and are best developed under the carina. The basal
calcareous cup, judging from two specimens, is thin, and not much
developed.

_Size and Colour._--The largest specimen was nearly 6/10ths of an inch
across its capitulum. The calcareous valves are dirty white. The sack
is (after having been long kept in spirits) pale coloured, excepting a
small purple space, between the scuta and another over the carina. The
three posterior segments of the thorax and portions under the second and
third cirri, the trophi, the pedicels and the anterior faces of the
segments (especially of the basal segments in the second and third
cirri), and a spot on their dorsal surfaces, and the penis are all
coloured dark purplish-black. The prosoma is pale coloured.

_Mouth._--Crest of labrum with a row of bead-like teeth and hairs.
_Palpi_ bluntly pointed, with neither margin hollowed out.

_Mandibles_, with eight pectinations between the first and second main
teeth, and three between the second and third teeth; inferior angle
coarsely pectinated, with a central spine much longer than the others;
the distance between the tips of the first and second main teeth, is
about equal to that between the tip of the second tooth and of the
inferior angle.

_Maxillæ._--Under the two upper long spines (associated with some
smaller ones), there is a slight and wide hollow; and the whole inferior
edge obscurely forms two blunt points, with the spines on the lower
projection smaller than the upper spines.

_Outer Maxillæ_, considerably concave in front, with the spines almost
discontinuous in the middle part.

_Cirri._--First pair rather far separated from the second pair. The
segments of the three posterior cirri bear three or four pairs of main
spines, and are otherwise characterised like the foregoing species.
_First cirrus_, with its anterior ramus much thicker than the posterior
ramus, and of nearly equal length; all the segments, except the two
terminal ones, thickly clothed with serrated spines. _Second cirrus_
considerably shorter than the third cirrus: anterior ramus with the
seven basal segments very protuberant, and paved with bristles, and the
four terminal ones on the usual structure; posterior ramus, with the
five basal segments paved (but much less thickly than in the anterior
ramus), and the nine terminal ones on the usual structure. _Third
cirrus_, the anterior ramus, with the five basal segments, thick and
paved, and eleven terminal segments on the usual structure: posterior
ramus, with one basal segment paved, and sixteen other segments on the
usual structure. In the posterior rami, however, of both the second and
third cirri, it is difficult to draw any distinct line between the paved
segments and the others.

_Caudal Appendages_, short, either just exceeding in length the pedicels
of the sixth cirrus, or equalling only the lower segment: segments
flattened, cylindrical, six in number, there being, in the same
individual, twenty-one segments in both rami of the sixth cirrus.


6. LITHOTRYA VALENTIANA. Pl. VIII, fig. 5.

  CONCHOTRYA VALENTIANA. _J. E. Gray._ Annals of Philosoph., vol. x
        (new series), 1825.

_L. scutis in profundam tergorum plicam invertis: tergorum opposito
superiore margine, plicâ alterâ æquè profundâ instructo: carinæ cristâ
prominente centrali, marginibus quadratis, in parte superiore: rostro
rudimentali: lateribus et pedunculo ignotis._

Scuta locked into a deep fold in the terga; the latter having a second
equally deep fold on the opposite upper margin. Carina with a prominent,
central, square-edged ridge in the upper part: rostrum rudimentary.
Latera and peduncle unknown.

Animal unknown.

    Red Sea, imbedded in an oyster-shell. British Museum.

_General Remarks._--The two specimens in the British Museum are small,
and in an imperfect condition, without the peduncle or the latera, and
without the body of the animal. The capitulum so closely resembles that
of _L. truncata_, that it is quite superfluous to do more than point
out the few differences. It is just possible, though not probable, that
this form may prove to be merely a variety or younger state of _L.
truncata_, in which case this latter name would have to be sunk. The
difference, though one only of degree, in the form of the terga of the
two species is conspicuous, and there is a slight difference in the
carina, and again some dissimilarity in habits.

_Description._--The valves, as just stated, generally resemble those of
_L. truncata_; scarcely any appreciable difference can be detected in
the scuta; the apex, however, of the inner surface seems coloured a
darker purple. The terga, as seen from vertically above (Pl. VIII, fig.
5 _b_), have a fold or indentation on the upper or occludent margin, as
large and as conspicuous as that receiving the margin of the scuta: this
fold, as seen on the inner corium-covered surface (fig. 5 _a_), descends
below the roughened knob at the upper angle of the carinal margin, which
is not the case with the slight fold in the same place in _L. truncata_;
its presence seems caused by the edge of the central internal crest, in
the upper part of the carina, being square (instead of round, as in _L.
truncata_), and thus more deeply affecting the outline of the terga,
between which it is inserted. The upper part of the scutal margin of the
terga, as seen internally (fig. 5 _a_), overlaps the scuta in a large
_rectangular_ projection. From the depth of the two opposite folds,
namely, that caused by the tergal edge of the scuta and that by the
crest of the carina, the inner face of the tergum is divided into two
almost equal areas. The carina has its central crest square (fig. 5 _c_,
_d_,) instead of being rounded as in _L. truncata_. The inner growing or
corium-covered face is nearly at right angles to the longitudinal axis
of the whole valve, instead of being oblique to it; it is convex or
protuberant, with a central raised line, and two little knobs on each
side of the upper part; the two lateral margins are slightly hollowed
out, and the basal margin is not highly protuberant. The rostrum is
excessively minute, barely above 1/200th of an inch in width; it is a
little enlarged at each zone of growth. Latera lost; no doubt they were
rudimentary.

A fragment of a posterior cirrus, which adhered to one of the valves,
shows that each segment supported four pairs of spines.

Width of the capitulum before disarticulation, probably was about 1/10th
of an inch.

       *       *       *       *       *

_Species mihi non satis notæ, aut dubiæ._

  ANATIFA VILLOSA. _Brugière._ Encyclop. Meth. Des. Vers., tom. i,
        1789, p. 62, Pl. clxvi.

    On ships: Mediterranean.

  ANATIFA HIRSUTA[69] _Conrad._ Journal of the Acad. of Nat. Sc.,
        Philadelphia, vol. vii, 1837, p. 262.

    On fuci, Fayal, Azores.

The specimens, to which these names have been given by the above two
authors, are described as small, and the _A. villosa_ was suspected by
Brugière to be young. The _A. hirsuta_ is said by Conrad to have the
valves minutely striated, granulated, and covered by a strong hirsute
epidermis; the scuta, compared with the other valves, are very large;
the entire length of this specimen was a quarter of an inch. The _A.
villosa_ is described as having smooth valves, and apparently the
peduncle alone is hirsute. Now, in young individuals of _Lepas
australis_, the peduncle is hairy, whilst in full-grown specimens it is
quite smooth. Again, in some varieties of _L. fascicularis_, the thorax,
prosoma, and cirri are hirsute, whereas they are generally quite smooth;
hence I am inclined to suspect that _A. villosa_ is the young, in a
state of variation, of _L. anatifera_; and that _A. hirsuta_ bears a
similar relation to _L. anserifera_. In Lamarck's 'Animaux sans
Vertèbres,' _Pollicipes villosus_ of Sowerby is quite incorrectly given
as a synonym to the above _A. villosa_.

   [69] The _Anatifa hirsuta_ of Quoy and Gaimard is the _Ibla
   quadrivalvis_ of this work.


  ANATIFA ELONGATA. _Quoy_ et _Gaimard_. Voyage de l'Astrolabe, Pl.
        xciii, fig. 6.

This, I think, is certainly a distinct and new species, but I am unable
to decide whether to place it in Lepas or Pæcilasma. It is briefly
described and pretty well figured in the above work. It was procured at
New Zealand, but it is not stated to what object it was attached. The
capitulum is much elongated, and one inch in length; the peduncle is
from six to eight lines long. The carina is said to be very narrow; it
is not stated whether it terminates downwards in a fork or disc; judging
from the figure, it extends some way up between the terga, the basal
ends of which are bluntly pointed. The scuta are almost quadrilateral.
The peduncle is short, yellow, and tuberculated. The general appearance
of the drawing makes me suspect that it is a Pæcilasma.


  CLYPTRA. _Leach._ Zoological Journal, vol. ii, p. 208, July,
        1825.

Leach has most briefly characterised a specimen in Savigny's Museum,
from the Red Sea, under the above name of _Clyptra_. It has only four
valves, and its peduncle is smooth; by the latter character it is
distinguished from Ibla. Apparently this is a distinct and new genus.

       *       *       *       *       *

Mr. J. E. Gray, in 'Proc. Zoolog. Soc.,' 1848, p. 44, quotes a
description by Stroem ('Nym. Saml. Danske,' 1788, 295, n. iii, f. 20),
namely, "_Lepas testâ compressâ 7-valvis, stipite lamellosâ_." It is
found attached to _Gorgonia placomus_, in the North Sea. I suspect that
this is the common _Scalpellum vulgare_, and that Stroem counted the
valves only on one side, overlooking the rudimentary and concealed
rostrum; and this would give seven for the number of the valves. Had it
not been for the expression "stipite lamellosâ," I should have thought
this might have been an unknown species of Dichelaspis.


  SCALPELLUM LÆVIS. _Risso._ Hist. Nat. des Product. de l'Europe
        Mérid., 1826, Tom. iv, p. 385.

The chief characteristic of this species appears to be indicated by its
specific name. It is found in the Mediterranean, attached to Cidarites.
I am inclined to believe that it is distinct from _S. vulgare_.


  SCALPELLUM PAPILLOSUM. _King._ Zoolog. Journal, vol. v, p. 334.

Captain King has described this species, taken from the depth of 48
fathoms, on the coast of Patagonia, in Lat. 44° 30´ S. It is probably
distinct, but is so imperfectly described, that not even the number of
the valves is given.


  POLYLEPAS (POLLICIPES), Sinensis. _Chenu._ Illust. Conchyliolog.,
        Pl. II, fig. 7.

This species is said to come from China; it is nearest to _P. spinosus_,
but is, I think, distinct.




EXPLANATION OF THE PLATES.


TAB. I.

Fig.

  1. _Lepas anatifera_, (nat. size.) _Var._, with a row of square,
        dark-coloured marks on the scuta and terga.

  1_a._ _Lepas anatifera_, external view of carina, magnified
        thrice.

  1_b._ _Lepas anatifera_, lateral view of carina, magnified thrice;
        var. _dentata_.

  1_c._ _Lepas anatifera_, internal view of right-hand scutum, to
        show the tooth at the umbo.

  2. _Lepas Hillii_, (nat. size.)

  3. _Lepas pectinata_, (magnified thrice.)

  3_a._ _Lepas pectinata_, var. (_spirulæ_), tergum, magnified
        thrice.

  4. _Lepas anserifera_, (nat. size.)

  5. _Lepas australis_, (nat. size.)

  5_a._ _Lepas australis_, carina, external view of, magnified
        twice.

  6. _Lepas fascicularis_, (nat. size,) with its peduncle, together
        with those of three other specimens, imbedded in a vesicular
        ball of their own formation, of which a slice has been cut
        off to show the internal structure. The specimen is in the
        College of Surgeons.

  6_a._ _Lepas fascicularis_, carina of, nat. size.

  6_b._ _Lepas fascicularis_, var. _villosa_.

  6_c._ _Lepas fascicularis_, var. _villosa_, carina of.

  6_d._ Part of the membrane from one side of the peduncle of _Lepas
        fascicularis_, with the ball removed, showing one of the
        cement-ducts, and the orifices through which the vesicular
        membrane forming the ball has been secreted; greatly
        magnified; viewed from the outside.


TAB. II.

Fig.

  1. _Poecilisma Kæmpferi_, (magnified two and a half times.)

  1_a._ _Poecilisma Kæmpferi_, carina of.

  2. _Poecilisma aurantia_, (magnified two and a half times.)

  3. _Poecilisma crassa_, (magnified twice.)

  3_a._ _Poecilisma crassa_, carina of.

  4. _Poecilasma fissa_, (magnified five times.)

  5. _Poecilasma eburnea_, (magnified five times.)

  5_a._ _Poecilasma eburnea_, carina of, external view of.

  5_c._ _Poecilasma eburnea_, carina of, lateral view of.

  5_b._ _Poecilasma eburnea_, scutum, internal view of.

  6. _Dichelaspis Warwickii_, (magnified five times.)

  6_a._ _Dichelaspis Warwickii_, transverse section of the top of
        the peduncle, showing the deeply-notched end of the inwardly
        bent carina; magnified five times.

  6_b._ _Dichelaspis Warwickii_, _var._, scutum and tergum.

  7. _Dichelaspis pellucida_, (magnified five times.)

  7_a._ _Dichelaspis pellucida_, basal end of carina of, much
        magnified.

  8. _Dichelaspis Lowei_, (magnified nearly ten times.)

  8_a._ _Dichelaspis Lowei_, fork of carina of, viewed internally.

  9. _Dichelaspis Grayii_, (magnified eight or nine times.)

  10. _Dichelaspis orthogonia_, (magnified six times.)

  10_a._ _Dichelaspis orthogonia_, carina, lateral view of.

  10_b._ _Dichelaspis orthogonia_, basal end of carina, viewed
        internally, much magnified.


TAB. III.

Fig.

  1. _Oxynaspis celata_, (magnified three times.)

  1_a´._ _Oxynaspis celata_, with the skin of the encrusting horny
        zoophyte removed. (_a_), scutum; (_b_), tergum; and (_c_),
        carina.

  2. _Conchoderma virgata_ (magnified twice.)

  2_a._ _Conchoderma virgata_ carina, viewed externally.

  2_b._ _Conchoderma virgata_ summit of capitulum, showing the terga
        from vertically above.

  2_c._ _Conchoderma virgata_ var. _chelonophila_, (magnified four
        times).

  2_d._ _Conchoderma virgata_ var. _Olfersii_, (scutum.)

  3. _Conchoderma Hunteri_, (magnified five times.)

  4. _Conchoderma aurita_, (nat. size,) with the rudimentary carina
        exhibited on the right hand.

  4_a._ _Conchoderma aurita_, summit of capitulum, viewed from
        vertically above, showing the ear-like appendages and the
        rudimentary terga.

  4_b._ _Conchoderma aurita_, section near the bases of the ear-like
        appendages, showing their folds.

  4_c._ _Conchoderma aurita_, (var.), scutum.

  5. _Alepas minuta_, (magnified five times.)

  6. _Alepas cornuta_, (magnified five times.)


TAB. IV.

Fig.

  1. _Anelasma squalicola_, (copied from Lovèn.) The ovigerous
        lamellæ are seen within the edges of the aperture of the
        capitulum. Enlarged about one and a half times.

  2. _Anelasma squalicola_, (from Lovèn), with the membranes removed
        from one side of the capitulum and of the peduncle,
        exhibiting the body.

        (_a._) External membrane of the capitulum.

        (_a, a._) Inner membrane of ditto, lining the sack, and
          separated from the external membrane by a double fold of
          corium.

        (_b._) The ovigerous lamellæ, the edge projecting beyond the
          orifice of the capitulum.

        (_c._) Penis, succeeded by six pairs of rudimentary cirri.

        (_d._) Probosciformed mouth.

        (_e._) Orifice of the acoustic (?) sack.

        (_f._) Ovigerous frænum.

        (_g._) Ovarian branching tubes filling up the peduncle.

        (_h._) Outer integument of peduncle, lined by corium and
          muscles, continuous with the outer membrane (_a_) of the
          capitulum.

  3. _Anelasma squalicola_, Small portion of the outer integument
        of the peduncle, greatly magnified, exhibiting the natural
        lines of splitting, and showing that it is composed of
        several distinct portions or layers, which are displayed by
        the corners having been turned over. Three of the branching
        filaments, filled with pulpy corium, are given; the others
        have been cut off. The membrane (_a_) extends under (_b_),
        but not under the circular patches of membrane, (_c, c_.)

  4. _Anelasma squalicola._ Mandibles, seen from the side towards
        the maxillæ.

  5. _Anelasma squalicola._ Mandibles, seen from the side towards
        the labrum.

  6. _Anelasma squalicola._ The right-hand, rudimentary cirrus, the
        third from the mouth.

  7. _Anelasma squalicola._ Maxillæ. The thin horny apodeme, (_a_).

  8. _Ibla Cumingii_, female, (magnified four times.)

  8_a´._ _Ibla Cumingii_, female, (magnified about five times), with
        the right hand valves and right side of the peduncle
        removed. The Male (_h_) is seen attached in the sack. The
        peculiar form of the body, caused by the small development
        of the prosoma, by the distance of the first and second
        pairs of cirri, and by the distance of the mouth from the
        adductor muscle, (a dark dotted circle opposite _i_,) and
        lastly, the remarkable course of the oesophagus over the
        adductor muscle, together with the outline of the stomach,
        are here all exhibited.

        (_a._) Scutum; the end of the large rounded adductor
          muscle, which was attached to the valve now removed,
          near its apex, is plainly seen.

        (_b._) Tergum.

        (_c._) On a line with this letter, is seen the largely
          bullate labrum, forming a blunt overhanging projection.

        (_d._) Palpus, close to the upper segment of the pedicel of
          first cirrus.

        (_e._) Orifice of the acoustic (?) sack, between the bases
          of the first and second cirrus.

        (_f._) Caudal appendages.

        (_g._) Branching ovarian tubes within the peduncle.

        (_h._) Male, on the same scale, lying in its natural
          position within the sack, with the lower part of its
          peduncle bent upwards, and imbedded in the corium and
          muscles of the female.

        (_i._) Adductor scutorum muscle.

  8_b´._ _Ibla Cumingii_, Internal view of the scutum and tergum,
        and of the upper part of the outer integument of the
        peduncle, with its horny spines magnified about three
        times.

  8_c´._ _Ibla Cumingii_, A small portion of the outer integument of
        the peduncle, greatly magnified, showing the horny
        persistent spines; two of the spines have been torn out.

  9. _Ibla quadrivalvis_; internal view of scutum and tergum, and of
        the upper part of the outer integument of the peduncle;
        magnified four times.

  9_a´._ _Ibla quadrivalvis_, Penis supported on a long
        unarticulated projection; greatly magnified.


TAB. V.

Fig.

  1. Male of _Ibla Cumingii_, magnified thirty-two times.

        (_a._) Mouth.

        (_b._) A slight double fold, formed by the basal edge of the
          labrum, and by a lower fold, which at (_h_) becomes well
          developed; the latter is a rudimentary representation of
          the double membrane and valves forming the capitulum.

        (_c._) Eye.

        (_d, d._) Torn membrane from the sack of the female,
          constricted round the body of the male.

        (_e._) Terminal or basal point, with the prehensile larval
          antennæ, represented on rather too large a scale.

        (_f._) The imbedded portion of the male.

        (_g._) Two pairs of cirri.

        (_h._) The fold above alluded to, concealing a small portion
          of the slightly retracted thorax.

  2. The male of _Ibla Cumingii_, viewed from vertically above;
        magnified about sixty times. The dotted lower portion,
        represents the outline of the thorax and the positions of
        the cirri, which, from standing below the mouth, could not
        be well seen, when the summit of the mouth was in the
        proper focus.

        (_a._) Labrum, largely bullate.

        (_b._) Palpi.

        (_c._) Mandibles.

        (_d._) Maxillæ.

        (_e._) Outer maxillæ; between which and the crest of the
          labrum, the orifice of the oesophagus can be obscurely
          seen.

        (_f._) Anus.

        (_g._) Rudimentary caudal appendages, under which is the
          pore leading from the vesiculæ seminales.

        (_h._) Posterior cirrus. (_i._) Anterior cirrus.

  3. Male of _Ibla Cumingii_; labrum and palpi, as seen with the
        eye on a level with the summit of the mouth.

  4. Male of _Ibla Cumingii_, Posterior cirrus (_h_ in fig. 2) much
        magnified.

  5. Male of _Ibla Cumingii_, Larval antennæ; from the terminal
        point of the body (_e_ in fig. 1), as seen with a 1/8th of
        an inch object glass.

  6. Male of _Ibla Cumingii_, Outer maxillæ.

  7. Male of _Ibla Cumingii_, Mandibles, with the underlying
        articulated membrane, forming the side of the mouth.

  8. Male of _Ibla Cumingii_, Maxillæ, with the apodeme.

  9. Complemental Male of _Scalpellum vulgare_, attached over the
        fold in the occludent margin of the scutum of the
        hermaphrodite.

        (_a._) Orifice of the sack of the male.

        (_b._) Spinose projections above the rudimental valves; at
          the bottom of the figure are represented, as seen through
          the whole thickness of the animal, the prehensile larval
          antennæ.

        (_d._) The depression for the attachment of the adductor
          scutorum muscle of the hermaphrodite; see fig. 15 _a´_.

        (_e_, _e._) A transparent layer of chitine, which forms a
          border to the occludent margin of the scutum of the
          hermaphrodite. This border supports long spines, which are
          connected with the underlying corium by sinuous tubuli.

  10. The basal (normally anterior) portion of the above
        complemental Male, greatly magnified, viewed dorsally from
        above, exhibiting the larval prehensile antennæ, attached
        to the antero-sternal surface of the animal.

  11. One of the antennæ of ditto, viewed laterally and on the
        outside.

  12. Ditto, ultimate segment of.

  13. Body of the above complemental male, consisting of the thorax
        supporting the four pairs of limbs, and of the terminal
        abdominal lobe.

  14. Small portion of the outer integument of the complemental
        male, as seen with a 1/8th of an inch object glass.

  15. _Scalpellum vulgare_ (hermaphrodite), magnified three times.

        (_a, a._) Complemental males.

        (_b._) Rostrum, of which a separate enlarged figure (_b´_)
          is given.

  15_a´._ Scutum of the hermaphrodite _Scalpellum vulgare_,
        internal view of.

        (_a._) Fold on the occludent margin.

        (_d._) Pit for the adductor muscle.


TAB. VI.

Fig.

  1. _Scalpellum ornatum_, (female, magnified seven times.)

  1_a´._ _Scalpellum ornatum_, Upper latus, viewed internally.

  1_b´._ _Scalpellum ornatum_, Scutum of full-grown specimen, viewed
        internally, much magnified.

        (_a._) Depression for the adductor muscle.

        (_b._) Depression for the reception of the male.

  1_c´._ _Scalpellum ornatum_, cutum of half-grown specimen, viewed
        internally, much magnified, on same scale with fig. 1 _b´_.
        The depression (_b_) for the reception of the male is here
        seen, in almost the first stage of formation.

  1_d´._ _Scalpellum ornatum._ An imaginary section through the
        cavity (_x_) in which the male is lodged.

        (_a._) Section of the shell of the scutum of the female.

        (_b._) A layer of chitine homologous with the shell, and
          _partially_ lining the scutum.

        (_c._) The inner lining (of chitine) of the sack of the
          female.

        (_d._) A double fold of corium.

  2. _Scalpellum rutilum_, (magnified two and a half times).

  2_a´._ _Scalpellum rutilum_, Internal view of scutum, enlarged.

        (_a._) Depression for the adductor muscle.

        (_b._) Cavity for the reception of the male.

  2_b´._ _Scalpellum rutilum_, External view of carina.

  2_c´._ _Scalpellum rutilum_, Section across middle of carina.

  3. Complemental Male of _Scalpellum Peronii_, greatly magnified.

  4. Complemental Male of _Scalpellum villosum_, greatly magnified.

        (_a´._) Natural size.

  4, _a, b, c._ Ditto, valves separated.

        (_a._) Scutum.

        (_b._) Tergum.

        (_c._) Carina.

  5. Complemental Male of _Scalpellum rostratum_, a restored
        figure, greatly magnified. Scutum and rudimentary carina
        correct.

  6. _Scalpellum Peronii_, one and a half the natural size.

        (_a._) Rostrum a little more enlarged, front view of.

  7. _Scalpellum rostratum_, magnified six times.

        (_a._) Rostrum, front view of.

  8. _Scalpellum villosum_, magnified one and a half the natural
        size.

  8_a_, _b._ _Scalpellum villosum_

        (_a._) Internal view of rostrum.

        (_b._) Internal view of sub-rostrum.


TAB. VII.

Fig.

  1. _Pollicipes cornucopia_, (one and a half nat. size.)

  1_a._ _Pollicipes cornucopia_, internal view of valves.

  2. _Pollicipes polymerus_, (one and a half nat. size.)

  2_a._ _Pollicipes polymerus_, internal view of valves.

  3. _Pollicipes mitella_, nat. size.

  3_a´._ _Pollicipes mitella_, nat. size, internal views of

        (_a._) Scutum, and of

        (_b._) Tergum, showing articular fold.

  3_b´._ _Pollicipes mitella_, Internal view of other valves, in a
        small specimen, showing the manner in which the valves of
        the lower whorl overlap each other.

        (_a._) Upper latera.

        (_b._) Carina,

        (_c._) Sub-carina, both viewed a little obliquely.

        (_d._) Rostrum,

        (_e._) Sub-rostrum, both viewed a little obliquely.

  4. _Pollicipes spinosus_, one and a half nat. size.

  5. _Pollicipes sertus_, one and a half nat. size.


TAB. VIII.

Fig.

  1. A piece of rock bored in two directions by _Lithotrya
        dorsalis_, with the calcareous basal discs in the upper
        cavity, serving as a bridge for crossing an old cavity.
        About twice natural size.

  1_a´._ _Lithotrya dorsalis_, (nearly twice nat. size), with the
        basal calcareous cup adherent; (_a_), rostrum on same scale,
        seen externally.

  1_b´._ _Lithotrya dorsalis_, rostrum and the rostral corners of
        the two scuta, together with a small portion of the
        subjacent membrane of the peduncle, with its calcareous
        scales; viewed externally, greatly magnified, showing the
        inferior crenated edges of the scales.

  1_c´._ _Lithotrya dorsalis_, basal calcareous cup, one and a half
        the natural size; this is the largest specimen which I have
        seen.

  2. _Lithotrya Nicobarica_, (magnified nearly twice;) attached to
        the rock, copied from Reinhardt; (_a_), rostrum on the same
        scale, with the other valves, seen externally; (_b_),
        section of the row of discs; (_c_), extreme point of the
        peduncle, extending beneath the row of discs.

  2_a´._ Rock bored by _Lithotrya Nicobarica_, showing the row of
        calcareous discs, copied from Reinhardt.

  3. _Lithotrya cauta_, magnified between seven and eight times;
        (_a_), scutum; (_b_), tergum.

  3_c._ _Lithotrya cauta_, latus, greatly magnified.

  3_d._ _Lithotrya cauta_, uppermost scales of the peduncle, greatly
        magnified.

  3_e._ _Lithotrya cauta_, star-shaped discs of hard chitine,
        supported on a peduncle of the same substance, taken from
        the lower exterior surface of the peduncle, very greatly
        magnified.

  4. _Lithotrya Rhodiopus_, (magnified five times,) internal views
        of; (_a_), scutum; (_b_), tergum; (_c_), latus; (_d_),
        carina.

  5. _Lithotrya Valentiana_, (magnified between three and four
        times;) (_a_), internal view of scutum and tergum, locked
        together; (_b_), capitulum seen from vertically above;
        (_c_), internal view of carina; (_d_), section across the
        middle of the carina.


TAB. IX.

Fig.

  1. _Lithotrya truncata_, (magnified four times.)

  1_a´._ _Lithotrya truncata_, capitulum seen from vertically above,
        not so distinctly represented as in fig. 5 _b_, Pl. VIII.

  1_b´._ _Lithotrya truncata_, internal views of valves; (_a_),
        rostrum, with a few subjacent scales of the peduncle; (_b_),
        scutum; (_c_), tergum; (_d_), carina.

  2. A portion (about 1/10th of an inch square) of the surface of
        attachment of the peduncle of _Pollicipes polymerus_, seen
        from the outside, greatly magnified, showing the small
        circular (_bb_) patches of cement, poured out from the
        cement-ducts (_aa_) which lie within the peduncle.

  2_a´._ A portion of a section, still more magnified, through the
        basal membrane of the peduncle, through one of the loops of
        the cement-ducts (_aa_), and through one of the circular
        patches (_b_) of cement.

  3. Cement gland, duct, and ovarian tubes of _Conchoderma aurita_;
        (_aa_), ovarian tubes, with ova in process of formation;
        (_b_), cement-gland; (_c_), cement-duct.

  4. _Conchoderma virgata_, enlarged, with one side of the capitulum
        and of the peduncle removed, to show the form and position
        of the body.

        (_a._) tergum, edge of.

        (_b._) mouth, with one of the palpi seen on the inner, upper
          corner.

        (_c._) adductor scutorum muscle.

        (_d._) orifice of acoustic (?) sack.

        (_e._) scutum, occludent margin of.

        (_f._) branching ovarian tubes within the peduncle.

        (_g._) filamentary appendage on the prosoma.

        (_h._) ditto, close to basal articulation of the first
          cirrus.

        (_i._) ditto, on the pedicel of the first cirrus.

        (_j._) ditto, on the pedicel of the third cirrus.

        (_k._) ditto, on the pedicel of the fourth cirrus.

        (_l._) ditto, on the pedicel of the fifth cirrus.

        (_m._) edge of the carina.

        (_n._) prosoma.

  5. Apex of one of the filamentary appendages of _Conchoderma
        aurita_, greatly magnified, exhibiting the included
        branching testes.

  6. Acoustic (?) sack of _Conchoderma virgata_, taken out of the
        acoustic meatus, with the diaphragm from the summit removed;
        greatly magnified.

  7. Terminal part (magnified seven times), of the peduncle of an
        elongated specimen of _Scalpellum vulgare_, slit open, with
        the corium removed, showing the two cement-ducts (_aa_), and
        a row of circular patches (_bb_) of cement, by which the
        peduncle, along its rostral edge, is attached to the thin
        horny branches of the coralline. The larval antennæ are seen
        at the terminal point, and the two cement-ducts can be
        traced into them.


TAB. X.

_Figures all greatly magnified._

Fig.

  1. Mandibles of _Pollicipes mitella_: exhibiting the upper (_a_)
        and lower (_b_) articulations, and the three principal
        muscles; the short upper cut off muscle runs to its
        attachment at the base of the palpus.

  2. Mandibles of _Lithotrya dorsalis_, exhibiting four (_aa_)
        roughened, thin, ligamentous apodemes for the attachment of
        the muscles.

  3. Mandibles of _Scalpellum Peronii_.

  4. Mandibles of _Ibla Cumingii_.

  5. Mandibles of _Lepas anatifera_.

  6. Palpus of _Lepas anatifera_.

  7. Palpus of _Pollicipes mitella_.

  8. Palpus of _Alepas cornuta_.

  9. Maxilla of _Lepas anatifera_.

  10. Maxilla of _Lithotrya dorsalis_, exhibiting the horny, rigid
        apodeme (_a_) buried in muscles, together with the two other
        principal bundles of muscles.

  11. Maxilla of _Ibla Cumingii_.

  12. Maxilla of _Lithotrya Rhodiopus_.

  13. Maxilla of _Pollicipes polymerus_.

  14. Maxilla of _Pollicipes mitella_.

  15. Maxilla of _Poecilasma eburnea_.

  16. Outer maxilla of _Conchoderma virgata_; (_a_), orifice of the
        olfactory cavity, the inner delicate chitine membrane of
        which is seen within, the specimen having been treated with
        caustic potash.

  17. Outer maxilla of _Pollicipes mitella,_ showing the two
        principal muscles, and the prominent, tubular, (_b_)
        olfactory orifices.

  18. Caudal appendages, and basal segments of the sixth pair of
        cirri, of _Lepas anatifera_; (_a_), anus; (_b_), caudal
        appendages; (_c_), lower segment of pedicel of sixth cirrus;
        (_d_), upper segment of ditto; (_e_), basal segments of the
        two rami.

  19. Caudal appendage (right-hand side) of _Pollicipes sertus_.

  20. Caudal appendage (right-hand side) of _Scalpellum Peronii_.

  21. Caudal appendage (right-hand side) of _Scalpellum vulgare_.

  22. Caudal appendage (right-hand side) of _Pollicipes cornucopia_.

  23. Caudal appendage (left-hand) _Lithotrya dorsalis_; (_a_),
        caudal appendage; (_c_), lower segment of pedicel of sixth
        cirrus; (_d_), upper segment of ditto; (_e_), segments of
        one of the rami.

  24. Portion of caudal appendage of _Lithotrya dorsalis_, highly
        magnified.

  25. _Pollicipes polymerus_; anterior ramus of the second cirrus.

  26. _Lepas anatifera_; a segment of the sixth cirrus, showing the
        arrangement of the spines; (_a_), main anterior spines, of
        which there is a corresponding row on the opposite side;
        (_c_), dorsal tuft.

  27. _Pollicipes polymerus_; a segment of the sixth cirrus, showing
        the arrangement of the spines; (_a_), main anterior spines,
        of which there is a corresponding row on the opposite side;
        (_b b_), calcareous shields on the dorsal surfaces, with
        tufts of fine spines near their upper edges.

  28. _Alepas cornuta_; sixth cirrus of; (_a_) basal portion of one
        ramus, consisting of numerous segments; (_k_), the other and
        almost rudimentary ramus.

  29. _Poecilasma fissa_; segments of the sixth cirrus, showing the
        arrangement of the spines; (_a_), anterior spines; (_c_),
        dorsal tufts.




INDEX.

Synonyms and doubtful species are printed in italics.


  Abortion, extreme, in the male of Ibla, 202.

  _Absia_, 332.

  Acari, development of, 18.

  Acoustic (?) organs, general description of, 53.

  Adductor scutorum muscle, 39.

  Affinities of the Lepadidæ, 64.

  Alepas, Genus, 156.
    cornuta, 165.
    minuta, 160.
    parasita, 163.
    _squalicola_, 170.
    tubulosa, 169.

  Allman, Professor, on Cyclops, 38.

  _Anatifa_ vel _Anatifera_, Genus, 67, 99, 215.
    _crassa_, 107.
    _dentata_, 73.
    _elongata_, 374.
    _engonata_, 73.
    _hirsuta_, 203.
    _lævis_, 73, 77.
    _oceanica_, 92.
    _obliqua_, 264.
    _parasita_, 163.
    _quadrivalvis_, 203.
    _sessilis_, 81.
    _spinosa_, 324.
    _striata_, 81, 86.
    _substriata_, 77.
    _sulcata_, 86.
    _tricolor_, 77.
    _truncata_, 361.
    _univalvis_, 163.
    _villosa_, 367.
    _vitrea_, 92.

  Anelasma, Genus, 169.

  Antennæ, larval, 33.
    in the Lepadidæ, table of measurements, 286.
    of Ibla Cumingii, 191.
    of Lepas australis, 15.
    of Scalpellum vulgare, 237.

  Appendages, caudal, 43.
    in larva, 19.
    filamentary, 38.

  Asplanchna, male of, 292.

  Attachment of Cirripedes, 33.
    of Scalpellum vulgare, 226.
    of Pollicipes polymerus, 310.


  Balanidæ, affinities of, 64.

  Bate, Mr. C. S., on the metamorphoses of Cirripedes, 9-16.

  Bopyrus, parasite allied to, 55.

  _Branta_, 137.
    _aurita_, 141.
    _virgatum_, 146.

  Brightwell, Mr., on the Asplanchna, 292.

  _Brisnæus_, 332.
    _Rhodiopus_, 363.

  Brugière, date of work of, 67.

  Buoyancy, means of, in Lepas fascicularis, 95.

  Burmeister, Professor, on the metamorphoses of Cirripedes, 9, 13.

  Burrowing powers of, in Lithotrya, 337.


  _Calentica_, 215.
    _Homii_, 274.

  Capitulum, general description of, 28.

  _Capitulum_, Genus, 293.
    _mitella_, 316.

  Carapace of the larva, 15.

  Caudal appendages, 43.
    in larva, 19.

  Cement-discs,
    in a straight row, in Scalpellum vulgare, 226.
    in Pollicipes polymerus, 310.

  Cement-ducts, 34.
    in the larva, 20.

  Cement-glands, incipient in larva, 24, 34.

  Cement, nature of, 36.

  Cement-tissue, modified as a float in Lepas fascicularis, 95.

  Chitine, chemical nature of, 30.

  Chthamalinæ, 2, 65.

  _Cineras_, Genus, 137, 156.
    _bicolor_, 146.
    _Cranchii_, 146.
    _chelonophilus_, 146, 151.
    _megalepas_, 146.
    _membranacea_, 146.
    _Montagui_, 146.
    _Olfersii_, 146, 152.
    _Rissoanus_, 146.
    _vittatus_, 146.

  Circulation, 46.

  Cirri, general description of, 42.
    of young Cirripede, 22.

  Cirripede, immature whilst within the larva, 20.

  Cirripedes, sessile, affinities of, 64.
    sub-families of, 2.
    useful as food, 66.

  _Clyptra_, 374.

  Coates, Dr., on Lepas fascicularis, 96.

  Conchoderma, Genus, 136.
    aurita, 141.
    Hunteri, 153.
    _leporinum_, 141.
    _virgata_, 146.

  _Conchotrya_, 332.
    _Valentiana_, 371.

  Cuming, Mr., obligations to, 181, 189.
    on the Cirripedes of the Philippine Archipelago, 65.
    on Balanus psittacus, 66.

  Cup, basal calcareous, in Lithotrya, 338.


  Dana, Mr. J. D., on the ovaria in certain Crustacea, 26.
    on the antennæ of larval Cirripedes, 15, 26.

  Dichelaspis, Genus, 115.
    Grayii, 123.
    Lowei, 128.
    orthogonia, 130.
    pellucida, 125.
    Warwickii, 120.

  Distribution, geographical, 65.

  _Dosima_, 67.
    _fascicularis_, 92.

  Dujardin, on the larvæ of Acari, 18.


  Encyclopédie Method., date of, 67

  Entozoons, sexes of, 201.

  Epidermis of valves, 31.

  Exuviation, 61, 63.
    of the larval eyes, 24.
    of the larval integuments, 20.
    of the membrane of peduncle in Lithotrya, 336.

  Eyes, in the Lepadidæ, 49.
    of the larva, first stage, 10.
    last stage, 16, 24.


  Families of Cirripedes, 2.

  Farre, Dr., on the acoustic organs in Crustacea, 54.

  Female organs of generation in the Lepadidæ, 56.

  Filaments, 38.

  Forbes, Prof. E., on the homology of the peduncle, 26.

  Fræna, ovigerous, 59.


  Ganglia, ophthalmic, 49.

  Generation, organs of, in the Lepadidæ, 55.

  Glands, supposed salivary, 57.
    on the ovigerous lamellæ, 60.

  Goodsir, Mr., on the metamorphosis of Cirripedes, 9, 16.
    on the supposed male of Balanus, 55.

  Gray, Mr. J. E., on the genus Dosima, 99.
    on the metamorphosis of Cirripedes, 9.
    on the inequality of the valves in Pæcilasma, 101, 103.
    on an unknown 7-valved Lepas, 374.
    on the genus Scalpellum, 216.

  Growth, rate of, 63.

  _Gymnolepas_, 137.
    _Cranchii_, 146.
    _Cuvierii_, 141.


  Habitats, 65.

  Hancock, Mr., on the burrowing of Cirripedes, 346.
    on the larva of Lepas, 11.

  Hectocotyle, 200.

  _Heptalasmis_, 115.

  Hermaphroditism, peculiar kind of, 201.

  Heteroura androphora, 201.

  Homologies of the Cirripedia, 25-28.


  Ibla, Genus, 180.
    Cumingii (female), 183.
      (male), 189.
    _Cuvieriana_, 203.
    quadrivalvis (hermaphrodite), 203.
      (complemental male), 207.
    general summary on its sexual relations, 281.

  Impregnation of the females and hermaphrodites in Ibla and Scalpellum,
      290.


  King, Captain, on a new Scalpellum, 375.

  Kölliker, on the males of Cephalopoda, 200.


  Labrum, general description of, 40.

  Lamellæ, ovigerous, 58.

  Larvæ, general description of, 8.

  Larva of Ibla quadrivalvis, 210.

  Leidy, Professor, on the eyes of Cirripedes, 2, 49.

  Lepas, Genus, 67.
    anatifera, 73.
    anserifera, 81, 86.
    australis, 89.
    australis, metamorphosis of, 14.
    _coriacea_, 146.
    _cornuta_, 141.
    _cygnea_, 92.
    _dilata_, 92.
    _dorsalis_, 351.
    fascicularis, 92.
    fascicularis, peduncle, remarkable structure of, 95.
    _Gallorum_, 298.
    Hillii, 77.
    _leporina_, 141.
    _membranacea_, 146.
    _mitella_, 316.
    _muricata_, 85.
    _nauta_, 81.
    pectinata, 85.
    _pollicipes_, 298.
    _scalpellum_, 222.
    _sulcata_, 86.
    _virgata_, 146.

  Lerneidæ, males of, 200.

  Leucifer, 28.

  _Litholepas_, 332.
    _de Mont Serrat_, 351.

  Lithotrya, Genus, 332.
    cauta, 356.
    dorsalis, 351.
    Nicobarica, 354.
    Rhodiopus, 363.
    truncata, 366.
    Valentiana, 371.
    powers of burrowing, 337.

  Lovèn, Dr., on the habits of the _Alepas squalicola_, 178.
    on the homologies of Cirripedes, 26.

  Lowe, Rev. R. T., on the fishes of Madeira and Japan, 106.
    on the Cirripedes of Madeira, 65.


  Macgillivray, Prof., on Conchoderma, 140.
    on Lepas anserifera, 81.

  _Malacotta_, 137.
    _bivalvis_, 141.

  Male Cirripedes, discussion on, 281.
    of Ibla Cumingii, 189.
      " quadrivalvis, 207.
    of Scalpellum ornatum, 248.
      Peronii, 270.
      rostratum, 262.
      villosum, 278.
      vulgare, 231.
    organs of generation in the Lepadidæ, 55.

  Mandibles, general description of, 41.

  Martin St. Ange, on the affinities of Cirripedes, 1.
    on a closed tube within the stomach, 45.
    on the generative organs, 55.

  Maxillæ, general description of, 41.

  Membrane covering valves, 30.

  Metamorphoses, first stage, 9.
    second stage, 13.
    last stage, 14.

  _Mitella_, Genus, 293.

  Mouth, general description of, 39.
    of young Cirripede, 22.
    of the larva, first stage, 11.
      last stage, 17.

  Muscles, 39.
    without striæ in Anelasma, and in embryonic Cirripedes, 172.


  Nerves, general system of, 46.
    of Ibla Cumingii, 188.

  Nomenclature of the parts of Cirripedes, 3.
    Rules of, 293.


  _Octolasmis_, 115.
    _Warwickii_, 120.

  OEsophagus, general description of, 44.

  Orders of Cirripedes, 2.

  Organs acoustic (?) general description of, 53.
    of the larva of Lepas, 15.
    female, of generation, in the Lepadidæ, 56.
    male, of generation, in the Lepadidæ, 55.
    olfactory, general description of, 52.

  _Otion_, 137.
    _auritus_, 141.
    _Bellianus_, 141.
    _Blainvillianus_, 141.
    _Cuvieranus_, 141.
    _depressa_, 141.
    _Dumerillianus_, 141.
    _Rissoanus_, 141.
    _saccutifera_, 141.

  Ova, 58.

  Ovaria, incipient in the larva, 20, 24.
    in the Lepadidæ, 57.

  Oviducts (supposed), 59.

  Owen, Professor, on certain Entozoic Worms, 201.
    on the Conchoderma Hunteri, 154.

  Oxynaspis, Genus, 133.
    celata, 134.


  _Pamina_, 137.
    _trilineata_, 146.

  Peach, Mr., obligations to, 240.
    on the movements of pedunculated Cirripedes, 33.

  Peduncle, general description of, 31.
    origin and homologies of, 21.

  Penis, general description of, 56.
    of Ibla quadrivalvis, 206.

  _Pentalasmis_, vel _Pentalepas_, 67.
    _anseriferus_, 81.
    _dentatus_, 73.
    _dilatata_, 81.
    _Donovani_, 92.
    _fascicularis_, 92.
    _Hillii_, 77.
    _inversus_, 86.
    _lævis_, 73, 77.
    _radula_, 86.
    _spirulæ_, 86.
    _spirulicola_, 92.
    _sulcata_, 86.

  _Pentalepas vitrea_, 92.

  Poecilasma, Genus, 99.
    aurantia, 105.
    crassa, 107.
    eburnea, 112.
    fissa, 109.
    Kæmpferi, 102.

  Pollicipes, 293.
    cornucopia, 298.
    elegans, 304.
    mitella, 316.
    _Mortoni_, 307.
    _obliqua_, 264.
    polymerus, 307.
    _ruber_, 304.
    _scalpellum_, 222.
    sertus, 327.
    _sinensis_, 375.
    _Smythii_, 298.
    spinosus, 324.
    _tomentosus_, 274.
    _villosus_, 274.

  _Polylepas_, 215, 293.
    _mitella_, 316.
    _sinensis_, 375.
    _vulgare_, 222.

  Primordial valves, 22.

  Prosoma, shape of, 39.

  Proteolepas, 3, 26.

  Pupa, locomotive or last larval state, in Cirripedes, 18.


  _Ramphidiona_, 293.

  Range, geographical, 65.

  Rate of growth, 63.

  Reinhardt on the burrowing of Lithotrya, 346.

  Reproduction, organs of, in the Lepadidæ, 55.

  Rotifera, sexes of, 292.

  Rules of nomenclature, 293.


  Sack, description of, 31.
    origin of, 15, 23.

  Scalpellum, genus, 215.
    _lævis_, 376.
    _læve_, 222.
    _Sicilice_, 222.
    ornatum, (female,) 244.
      (male,) 248.
    _papillosum_, 375.
    Peronii, 264.
      (male,) 270.
    rostratum, 259.
      (male,) 262.
    rutilum, 253.
      (male,) 258.
    villosum, 274.
      (male,) 278.
    vulgare, 222.
      larva of, 9.
      (complemental male,) 231.
    general summary on sexual relations, 281.

  Schmidt, Dr., on chitine, 30.
    on the muscles in young crustacea, 172.

  _Senoclita_, 137.
    _fasciata_, 146.

  Sexes, discussion on, in Ibla and Scalpellum, 281.

  Siebold, Dr. C. Von, 201.

  _Smilium_, 215.
    _Peronii_, 264.

  Spermatozoa in Scalpellum vulgare, 236.

  Sprengel, Ch. K., on compositous flowers, 203.

  Steenstrup, Prof., on the homology of the peduncle, 26.
    on the non-hermaphroditism of Cirripedes, 55.

  Stomach of larva, 19.
    general description of, 44.

  Stroem on a seven-valved Lepas, 374.

  Syngamus trachealis, 201.


  Testes in the Lepadidæ, 55.

  _Tetralasmis_, 180.
    _hirsutus_, 203.

  _Thaliella_, 215.
    _ornata_, 244.

  Thompson, Mr. W., on Lepas anatifera, (var.) 74.
    on the exuviations of sessile Cirripedes, 63.
    obligations to, 240.
    Mr. Vaughan, on the metamorphoses of Cirripedes, 9, 10.

  _Trilasmis_, genus, 99.
    _eburnea_, 112.

  _Triton_, genus, 156.
    _fasciculatus_, 163.


  Upopi, or young acari, 18.


  Vesiculæ seminales, 56.

  Valves, general description of, 28.

  Valves, chemical nature of, 30.
    horny, colour changed by pressure, 184.
    primordial, 22.


  Wagner, R., on the male organs of generation, 55.


  _Xiphidium_, 215.


[Illustration: _Pl. I._

LEPAS.

_George Sowerby._]


[Illustration: _Pl. II._

POECILASMA: DICHELASPIS.

_George Sowerby_]


[Illustration: _Pl. III._

OXYNASPIS: CONCHODERMA: ALEFAS

_George Sowerby_]


[Illustration: _Pl. IV._

ANELASMA: IBLA.

_George Sowerby_]


[Illustration: _Pl. V._

IBLA: SCALPELLUM.

_George Sowerby_]


[Illustration: _Pl. VI._

SCALPELLUM.

_George Sowerby_]


[Illustration: _Pl. VII._

POLLICIPES

_George Sowerby_]


[Illustration: _Pl. VIII._

LITHOTRYA.

_George Sowerby_]


[Illustration: _Pl. IX._

LITHOTRYA. &c.

_George Sowerby_]


[Illustration: _Pl. X._

MANDIBLES, PALPI, MAXILLÆ, OUTER MAXILLÆ, CIRRI, & CAUDAL APPENDAGES.

_George Sowerby_]




Transcriber's Notes:


Throughout

Ditto is often represented by ---- or . . . . or ".


Page ix

Enclycopædia of Anatomy and Physiology

'Enclycopædia' changed to 'Encyclopædia'.


Page xii

CORRIGENDA AND ADDENDA.

These changes were not added, due to the general nature of most of the
comments.


Page xii

Pæcilasma is used throughout (et passim) most of the text.

It should read Poecilasma.

No change from the original.


Page 27

pedunculum mutatæ et invoucrum

'invoucrum' changed to 'involucrum'.


Page 57

touch the cæca were such exist

'were' changed to 'where'.


Page 75

References to Mouth parts read Pl. IX, where I believe that Pl. X was
meant. No change except for inserted links that refer to plate X.


Page 136

Magaz. der Gesellsch. Natuforsch.

'Natuforsch' may be 'Naturforsch'.


Page 222

Bold T used to represent a dagger here.


Page 238

  Length of whole organ, to the inner margin of
  the oblique basal articulation                } 1/6000

The number here was not legible, as printed. I think it may be 19/6000
from the table of comparative measurements later in this book.


Page 259

Bold TT used to represent double daggers.


Page 299

Frith of Forth

'Frith' may be 'Firth'.


Page 397

Lepas

  membrancea, 146

'membrancea' changed to 'membranacea'.


Inconsistent accents were verified and follow the original.


Hyphen variability

  multiarticulate     multi-articulate
  uniarticulate       uni-articulate