Chapter XXVII: Introduction (23)

The old specimens (fig. 5 _a_) are so much corroded that not a
particle of the external surface is left: one of them which was
2-3/4 of an inch in basal diameter. Shell much depressed, spreading;
colour pale purple; orifice large, rhomboidal, with a slight hollow
on each side for the corners of the scuta: sutures generally in
part or wholly obliterated; where still preserved, the interlocking
toothed structure is distinct; the sheath is strongly marked by lines
of growth, and is of a dark brown colour. The carina and rostrum
are of unusually large size compared with the lateral compartments;
and this, as far as I can judge, must have been the case with the
younger specimens. That portion of the rostro-lateral compartment
which forms part of the sheath, is reduced to a mere ridge. The most
remarkable character is, that all these old specimens (of which the
smallest measured nearly one inch and a half in diameter) had a flat,
wide, calcareous basis, which is absolutely continuous with the inner
lamina of the parietes, whereas in the younger specimen there was no
appearance of any tendency in the parietes thus to grow inflected.
There can be hardly any doubt that in a series of specimens some
would be found with the parietes first forming a flat narrow ledge
round the true basal membrane (as in the following species); and that
in others, this ledge would be wider and wider, till its edges met in
the middle, and coalesced into a continuous plate.

_Opercular Valves._--I have seen these only in the old corroded
specimens (fig. 5 _c_, 5 _d_): they are locked together by remarkably
strong articular ridges and furrows.

The _Scuta_ have externally two or three impressed lines or narrow
furrows, proceeding from the apex to the middle of the basal margin;
these can be seen only in one of my specimens, owing to the degree
to which the valves have suffered disintegration; but they are
mentioned by Conrad. The basal margin is rather short compared with
the other two margins. The tergal margin is remarkable from the depth
of the upper furrow above the articular ridge, and from the size of
the prominence (appearing like the true apex of the valve) above
this upper furrow. There is a hollow for the adductor muscle, and
traces of crests for both the rostral and lateral depressores. The
_Terga_ are generally but little corroded, and hence the dark brown
membrane with which they are covered is well preserved; the shelly
matter itself is also brown: there is only a trace of this colour in
the more corroded scuta: the external surface of the terga is very
smooth. The spur is pretty well developed, and is half as wide as
the whole valve. The lines of growth are upturned along the carinal
margin. The articular ridges and furrows are much developed. The
crests for the depressor muscles are extremely strong; they depend
beneath the basal margin, and are remarkable (fig. 5 _c_) from being
furnished each with fine sub-crests.

_Animal's body_, unknown.

7. CHTHAMALUS INTERTEXTUS. Pl. 19, fig. 1 _a_, 1 _b_.

_Shell, when well preserved, violet-purple: sutures, when not obliterated, formed by oblique interfolding laminæ: basis membranous, but surrounded by a ledge formed by the inflected basal edges of the parietes: scutum and tergum completely calcified together._

_Hab._--Philippine Archipelago; Mus. Cuming.

_General Appearance and Structure._--Shell depressed, with a
large diamond-shaped orifice. Colour beautiful violet-purple, but
externally much obscured by disintegration, causing the shell to
be ashy gray. Walls smooth or slightly folded. Sutures generally
quite, or almost quite obliterated; but when well preserved, they
differ remarkably in appearance from those in the foregoing species;
for the radii externally here consist of oblique plates or laminæ
arising on both sides of the sutures, standing nearly parallel to the
parietes, and interfolding with each other. These laminæ are rather
plainly marked by lines of growth. Essentially the radii do not
differ much from those in _C. dentatus_ and _Hembeli_; we have but
to produce obliquely upwards the transverse and interlocking ribs on
their radii, and so convert them into laminæ. During the diametric
growth of the shell, the sutural edges of the alæ are added to, in
the usual manner, by upturned lines of growth; and, in addition, the
recipient furrows of the alæ are similarly added to, so that the
lines of growth are upturned, and alæ appear to have been developed
on both sides of the sutures in the same way as the radii appear to
have been developed on both sides in many Chthamalinæ, though rarely
in the Balaninæ. The inside of the shell is beautifully coloured rich
violet; it is punctured with small holes as so often is the case with
_C. stellatus_. In every specimen (all full-grown) which I opened,
the inner basal edges of the parietes were inflected rectangularly
inwards, forming a smooth-edged ledge all round the basal membrane,
which, in proportion to the width of this ledge, was by so much
reduced in diameter. The largest specimen which I have seen was .35
of an inch in basal diameter.

_Opercular valves._--The scuta and terga, in all the specimens which
I have seen, were firmly calcified together; in some, a trace of a
suture could be seen externally, but hardly a trace internally. In
one specimen, there were vestiges of some impressed lines on the
scutum, in exactly the same position in which such occur in _C.
Hembeli_. The scutum is rather narrow. The basal margin of the tergum
is either straight, or depends a little on the scutal side, thus
producing a small spur: the crests for the depressor muscles are
strongly marked, and depend beneath the basal margin.

_Mouth._--The labrum is strongly toothed: the palpi have long hairs
along the exterior basal margin: the mandibles have only three main
teeth, and the inferior coarsely pectinated portion is short; the
maxillæ deeply notched. _Cirri_: the first and second pairs have
their rami slightly unequal in length; the third pair differs from
the same pair in the other species of the genus, in having some few
of the basal segments on the anterior ramus thickly clothed with
spines, so as to be brush-like: there is even a trace of a similar
structure in the lowest segments of the posterior ramus. In the three
posterior pairs of cirri the segments are much elongated, and support
four pairs of spines.

_Branchiæ._--Unknown.

8. CHTHAMALUS SCABROSUS. Pl. 19, fig. 2 _a_-2 _d_.

_Shell (when well preserved) dull purplish-brown: sutures formed by oblique interfolding though rarely well developed: tergum with a deep narrow pit, at the basi-carinal angle, for the depressor muscle._

_Hab._--Peru, Chile, Tierra del Fuego, Falkland Islands. Very common;
attached to littoral rocks and shells, and often associated with
_Balanus flosculus_, and sometimes with _Chthamalus cirratus_; Mus.
Brit., Cuming, W. Dunker, Darwin.

_General Appearance and Structure._--Shell generally depressed; when
growing crowded, sometimes cylindrical: colour dingy purplish-brown,
but when much corroded, dirty gray; very young shells are very dark
green, owing to the corium, which is of this colour, being seen
through the valves. Surface generally rugged, from irregular slight
longitudinal folds, and from the transverse overlapping tile-like
lines of growth; but sometimes the surface is nearly smooth, with
very slight longitudinal folds, these being gray coloured, the
intermediate parts being pale dingy purple, the shell thus becoming
striped. Orifice rhomboidal, passing into trigonal, owing to the
great width of the carinal end. Sutures generally very distinct,
rarely obliterated in the cylindrical varieties. Radii narrow,
generally exposing much of the alæ, which are plainly marked by
lines of growth: the radii themselves, when well developed, which
is not often the case, consist of small laminæ or ridges, placed
on both sides of the sutures, and interfolded or interlocked
together: usually only a trace of this structure is exhibited,
but occasionally, along some or along all the sutures (as in the
specimen figured), the laminæ of the radii interfold, as plainly as
in _C. intertextus_. The alæ differ slightly from the alæ of the
other species, in not forming so much of a rectangular projection,
the lower margin running with a gentle curve into the parietes. The
internal surface of the parietes is either smooth, or near the basal
margin is roughened with depending points: in some specimens from the
Falkland Islands, both edges of each suture were inflected, forming
a double ridge, with roughened edges, resting on the basal membrane,
and supporting the shell. I must mention that in my notes made at
these Islands, I remark that the basal membrane seemed sometimes to
be surrounded by a calcareous rim; none of the specimens brought home
are thus characterised; but bearing in mind the affinity of this
species to _C. intertextus_, no doubt we have here an indication
of the shelly ledge surrounding the basis, as described under that
species. The largest specimens which I have seen are a quarter of an
inch in basal diameter.

The _Opercular Valves_ generally have their summits much worn down.
The _scuta_ are elongated in the line of the longer axis of the
orifice; the articular ridge is very prominent, and is placed in
the middle of the tergal margin. The _terga_ are very narrow, as
in some varieties of _C. stellatus_: they are remarkable in two
respects, namely, in the depressor muscle being attached to a plate,
formed apparently by the union of the usual crests, parallel to the
outer lamina of the valve itself, a deep narrow cavity (fig. 2 _d_,
_p_) being thus formed; and secondly, in the far more extraordinary
circumstance of the existence of a small pit (_q_) at the extreme
basi-scutal corner of the valve, in which about half of the scutal
lateral depressor muscle is attached: I have observed no other
instance in any cirripede of the partial attachment of a muscle
properly belonging to one valve to another valve. The figures of
the valves 2 _b_, 2 _c_, 2 _d_, are from specimens most unusually
perfect, with the upper portion not worn away; the ordinary
appearance of the valves as seen from above, is given in fig. 2 _a_;
at fig. 2 _d_, a view is given of the tergum seen from vertically
beneath, showing the cavity for its own depressor muscle, and for
part of the lateral depressor muscle of the scutum.

_Mouth._--The crest of the labrum is hairy, without teeth: the palpi
have long spines at the end, but none along the inferior margin: the
mandibles have either four or five graduated teeth, the lower ones of
which are plainly double laterally: the maxillæ have a very sinuous
edge. _Cirri_: the first and second pairs are very short: on the four
posterior pairs the segments support either four or five pairs of
main spines, with the small intermediate spines rather larger than
usual.

_Branchiæ._--None; but where they ought to occur, there are two very
slight ridges clothed with hairs, about the 1/100th of an inch in
length. On the prosoma, there is a slight ridge, extending from the
base of the first cirrus towards the adductor scutorum muscle, also
clothed with hairs; this unusual character of the prosoma being hairy
is common to _C. dentatus_.

This species is the commonest cirripede on the shores of the Falkland Islands: many of the specimens are there crowded together, and rendered elongated and cylindrical, with the walls very thin, and the sutures often obliterated; as the opercular membrane is very narrow, the opercular valves are much influenced both in their outline and in their crests and articulations, by the varying form of the shell: I have even seen specimens with the scutum and tergum on one side twice as large as on the other side.

13. CHAMÆSIPHO--_Nov. Genus_.[132] Pl. 19.

[132] Χαμαι [Greek: Chamai], on the ground, and σιφων [Greek:
siphôn], a tube.

_Compartments four, with the sutures often much obliterated: basis membranous._

_Distribution_, Australia, China (?). Attached to littoral shells and
rocks.

The two species united under this genus agree in having only four compartments, and in these having a strong tendency to become confluent; but they resemble each other hardly in any other respect, more than do all the species of the present sub-family. _Chamæsipho columna_ differs from all the other Chthamalinæ in the structure of its second pair of cirri, and _C. scutelliformis_ differs from all in its shell,--namely, in the small size of the rostrum, with its alæ but little developed, and in the very peculiar apertures in the three other compartments. Hence this genus can hardly be considered a very natural one, though I could not introduce the two present species into Chthamalus, or into any other genus, without doing still more violence to the principles of classification followed throughout this work. Chamæsipho bears nearly the same relation to Chthamalus, as Tetraclita and Elminius do to Balanus.

1. CHAMÆSIPHO COLUMNA. Pl. 19, fig. 3 _a_-3 _c_.

LEPAS COLUMNA. _Spengler._ Skrifter Naturhist. Selbskabet, b. 1,
(1790), Tab. 6, fig. 6.

_Sutures, excepting during early youth, generally obliterated both externally and internally: tergum with small pits for the attachment of the depressor muscle._

_Hab._--New South Wales, Tasmania, New Zealand; extremely common;
attached to littoral shells and rocks; often associated with
_Chthamalus antennatus_ and _Elminius modestus_; and in New Zealand,
often thickly coating _Elminius plicatus_.

I have identified, with some doubt, the present species with the _Lepas columna_ of Spengler, obtained from Otaheite, as no description is given by him of the opercular valves, and more especially as Spengler's specimens were an inch in height and seven lines in width, which is much larger than any of the many specimens seen by me: from Spengler's clear description of the structure of his shell, it evidently belongs to the present genus.

_General Appearance and Structure of Shell._--The sutures separating
the four compartments are generally, excepting at an early age, quite
obliterated, both internally and externally, the shell in this case
consisting of a single piece, with its summit and opercular valves
always much worn. Occasionally the sutures are preserved, and then
the four compartments are seen to be of nearly equal sizes. The
orifice is always broadly oval, with the carinal end the broadest;
and it often approaches closely to circular. The upper part of the
shell is frequently steeply conical, with the lower part spreading
and folded; sometimes deeply folded. Very young shells are apt to
be remarkably smooth. The radii appear never to be developed: the
inside of the shell is smooth. The colour is either blackish-green
(this being the tint of the corium lining the sack), with the upper
part gray from disintegration; or the lower part is brown, from
the investing membrane, the shell itself being pale coloured. This
species seems particularly liable to grow crowded together; often
covering rocks and shells with a honey-combed layer. The basal
diameter of some of the largest specimens was .3 of a inch. In Mr.
Cuming's collection, however, there is an Australian specimen .55
in diameter and .3 in height, which is, moreover, remarkable from
the projecting, extremely rugged, overlapping, dark-coloured layers
of growth, which surround the lower part of the shell: we have seen
that Spengler's specimens, said to have come from Otaheite, are even
broader and considerably higher.

_Scuta_: from the disintegration which the valves have undergone, the
scuta and terga are externally seen to be locked together by a deeply
sinuous articulation. The _Scuta_ have a wide articular furrow and a
very prominent articular ridge; but the exact outline of these parts
varies greatly, very much as in the genus Chthamalus.

The _Terga_ are very narrow, with the under surface channelled: the
attachment of the depressor muscle offers the only peculiarity,--the
muscle being attached to four or five little pits, placed
transversely to the longer axis of the valve; the septa between these
little pits evidently answering to the crests as usually developed.

_Mouth._--The crest of the labrum is hairy, and slightly bullate.
The palpi are rather small, with long spines at their ends. The
mandibles have four (sometimes five) teeth, with the inferior portion
pectinated. The maxillæ are notched.

_Cirri._--The first pair presents no remarkable character. The second
and third pairs are subject to extreme variation, as in _Chthamalus
antennatus_ and _Tetraclita porosa_. In all the specimens, the
anterior ramus of the second cirrus is short, with all the segments
thickly covered with bristles; it is the posterior ramus which varies
so much in relative length and in the arrangement of the bristles;
but in no case are all the segments clothed with bristles as on
the anterior ramus, and as is normally the case with all sessile
cirripedes. In some specimens from New Zealand, the anterior ramus
having only five segments, the posterior ramus was twice as long,
having sixteen segments, with the bristles arranged in circles,
but standing rather thicker together on the basal segments. In a
Tasmanian specimen, the posterior ramus was only a little longer than
the anterior ramus, and the spines were arranged in regular pairs (as
on the three posterior pairs of cirri) on all the segments, excepting
the few basal ones, on which they were more crowded: a nearly similar
arrangement occurred in some other specimens from unknown localities,
excepting that the rami were of nearly equal length. In the third
cirrus, in all the specimens, the anterior ramus has three or four of
its basal segments much broader than the upper segments, and thickly
clothed with spines (as is the case with one species of Chthamalus,
viz. _C. intertextus_) all the other segments having regular pairs
of spines. The posterior ramus of the third cirrus varies in being
either much longer than, or only equal in length to, the anterior
ramus; in the former case (in the New Zealand specimen) the spines
were arranged in circles, giving an antenniformed structure to the
ramus; and in the latter case they were arranged in regular pairs.
In Mr. Cuming's great Australian specimen, there was a further
peculiarity, in the presence on the posterior cirri of a tuft of
intermediate spines between the main pairs; and, in there being on
those segments, which are thickly covered with spines, certain very
large spines, doubly pectinated, with the pectinations elbowed,
closely like the spines met with on the cirri in certain species of
Pollicipes. Finally, the segments in the three posterior pairs of
cirri support five or six pairs of main spines; the dorsal surfaces
of the segment are rough and hairy.

_Branchiæ_, rudimentary; consisting of a small, simple, tongue-formed
fold, projecting about 1/100th of an inch. Ova, 16/2000ths of an inch
in length.

2. CHAMÆSIPHO SCUTELLIFORMIS. Pl. 19, fig. 4 _a_-4 _d_.

_Rostrum very small, elongated, triangular: lateral compartments, each with an aperture, and carina with two similar apertures, all four leading into shelly tubular columns._

_Hab._--Attached to _Pollicipes mitella_, probably from the seas of
China; Mus. Brit.

_General Appearance._--This very singular shell would not, without
some examination, be thought to be a cirripede. From the symmetrical
position of the four apertures, with the diamond-shaped orifice in
the middle, with the sutures on each side of the rostrum, and from
its depressed and circular form, this shell bears some resemblance to
the perforated species of Scutella. Shell much depressed, generally
nearly circular, with the basal margin highly sinuous and even
sometimes almost branched. Surface slightly irregular, marked by
fine lines of growth, and covered by brown membrane. Of the four
compartments, the _Rostrum_ is very narrow, triangular, and comes up
to the orifice almost in a point: it is rather depressed, that is, it
lies rather below the level of the other compartments: the straight
sutures separating it from the lateral compartments are distinct in
the upper part, though always obliterated in old shells in the lower
part: these sutures are generally far plainer than those separating
the lateral compartment from the carina, which in most cases are
obliterated and calcified together, excepting close to the orifice.
The alæ of the rostrum are not externally visible, and there are no
radii to any of the compartments. The _Carina_ is twice as broad as
the rostrum, and is furnished with alæ of the usual shape, which are,
to a certain extent, externally visible. The _Lateral Compartments_
are broad, being broader than the carina; they are both penetrated,
down to the surface of attachment, by a hole or rather tube,--the
two holes standing opposite the rostral end of the operculum: the
carina is penetrated by two rather smaller but similar holes. It
is these four holes which give to this cirripede its very singular
aspect: they are rather smaller than the orifice of the shell; they
are oval, with their longer axes placed in the direction of the ray
of the circular shell: their manner of formation will be immediately
explained. The orifice is neatly diamond-shaped and broad: it is
rather small compared with the whole shell, and is closed by the
operculum, which is seated near the summit of the shell. Basal
diameter of largest specimen 2/10 of an inch; few, however, attained
this size, and perfect larvæ were included in much smaller specimens.

_Structure of Shell._--The rostrum (fig. 4 _c_) is remarkable from
its small size, and from the plainness of its sutures, in comparison
with those separating the other compartments, and this is exactly
the reverse of what I should have expected in a compartment tending
to become rudimentary. Not only is the rostrum small, but the alæ
project to an unusually small degree, and gradually slope away into
the lower part of the parietes. These peculiarities are even more
strongly marked in very young shells: thus in one of the size of a
pin's head, the rostrum consisted of a minute parallelogram, without,
as far as I could see, any alæ, and was only one fourth of the size
of the carina,--this latter compartment being only half as wide as
the lateral compartments. The carina, at this early period, had quite
distinct alæ.

The tubular prolongations from the four external holes are of course
very conspicuous on the under side of the shell (4 _b_); and their
structure is there plainly seen. In extremely young shells the holes
are not present; but very soon, at four points of the circumference,
namely, two in the carina and one in each lateral compartment, the
basal edge becomes indented, and during growth more and more deeply
indented; at last the horns or points of the bays, thus formed in
the circumference of the shell, grow inwards and meet, the four
indentations being thus converted into four rings or holes; as
the shell is added to, at its circumference, these come to stand
further and further from the exterior margin; and as the shell at
the same time rises above the surface of attachment, the holes are
added to at their basal edges, and are thus converted into shelly
tubes, generally freely open at the bottom as well as at the top.
Sometimes these tubes are closed at the bottom, and this is usually
caused by their sides having been added to in a spiral direction. A
somewhat sinuous double ridge or fissure, leading from the tubes or
holes to the exterior border, can always be perceived on the under
side of the shell. Occasionally, though rarely, in very old shells,
a second series of holes is formed outside the first four holes,
and often a tendency to this may be perceived in the just-mentioned
fissures expanding a little at their outer ends, thus forming four
new circumferential indentations. The purpose of this peculiar
structure, apparently, is to give support to the much depressed and
thin shell. In _Chthamalus stellatus_ and _scabrosus_, we have seen
a slight indication of a similar structure, in the formation on the
under side of the shell, but confined to the lines of sutures, of
obscurely tubular pillars: we have also something analogous in the
singular midribs, in Platylepas, causing the membranous basis to be
convex. I need only further add, that the parietes, in Chamæsipho,
are rather thin, and are composed of translucent shell, punctured for
the entrance of tubuli, with the punctures often arranged in straight
lines.

_Opercular Valves_ (fig. 4 _d_).--These are attached by a narrow
opercular membrane to the sheath, but little beneath the summit
of the shell. The _Scuta_ are considerably arched or convex: the
articular ridge is very prominent, and there is a thick strong
adductor ridge. The _Terga_ have a short, rather broad, rounded spur,
placed very nearly in the middle of the valve: the crests for the
tergal depressores are moderately developed, and are simple.

_Mouth._--The crest of the labrum is hairy, and is much hollowed
out. The palpi are small and narrow, with long bristles at their
apices. The mandibles have four or five teeth, with the lower part
pectinated. The maxillæ are notched. Of the _Cirri_, the second pair
is short, and all the segments are thickly clothed with bristles.
The third pair in the arrangement of the bristles resembles the four
posterior pairs. The segments in these pairs are elongated, and
support four pairs of main spines.

I was not able to observe any _Branchiæ_.

14. PACHYLASMA--_Nov. Genus._[133] Pl. 19, 20.

[133] Παχυς [Greek: Pachus] thick, and ελασμα [Greek: elasma], a
valve.

CHTHAMALUS. _Philippi._ Enumeratio Mollusc. Siciliæ.

_Compartments, when the shell is very young, eight; when mature, either six, or in appearance only four owing to the close union of the lateral compartments: basis calcareous._

_Distribution_, Mediterranean, and New South Wales; deep water.

The two species here included form a very natural genus, though, as far as the shell alone is concerned, at first sight there is an unusual amount of difference between them. This genus offers an instance of a case, far from uncommon in nature, though so unfortunate for the systematist, in which the most obvious and useful characters of a group are completely masked. When I first examined _Pachylasma giganteum_,[134] I did not doubt that it was a _Balanus_; and when I first looked at _P. aurantiacum_, I thought, from there being in appearance only four compartments, that it was an Elminius; in neither case, from the absence of alæ to the rostrum, did I even suspect that the species belonged to the sub-family of the Chthamalinæ. But when I examined the included animal's body, I found, in both species, the labrum bullate, not notched, with the palpi small, and the mandibles with their lower teeth not laterally double. Again I found in the third pair of cirri only the basal segments thickly clothed with spines; and lastly, there were caudal appendages. Now these characters are pre-eminently those of the Chthamalinæ; in fact, they are those met with in the typical genus Octomeris, with the exception of the presence of caudal appendages, and these occur in Catophragmus,--a genus standing next to Octomeris, and in no other genus of sessile cirripedes. Moreover, if we look to the shell of Pachylasma, the absence of pores in the parietes, or at least of symmetrical longitudinal ribs on their inner surfaces, and the peculiar character of the narrow radii, hardly differing in structure from the parietes, are characters which are rare in the Balaninæ, but universal in the Chthamalinæ. Hence, taking the whole organisation of the two species of Pachylasma, it is certain that they must be ranked amongst the Chthamalinæ, though the leading character of the group, namely, the rostrum being furnished, like the carina, with alæ, here fails. Owing to this conviction, I examined very young individuals of _P. giganteum_, and in specimens only the 1/100th of an inch in height, I was interested by finding eight separate compartments, with the rostrum having distinct alæ; hence, at this early age, as far as the shell is concerned, this species may be said to be an Octomeris; and we have seen that this likewise holds good with the included animal's body; as the young shell increases in size the minute rostrum and rostro-lateral compartments blend together (Pl. 19, fig. 5 _b_), without even traces of sutures being left.

[134] Dr. Philippi called this species a Chthamalus; giving this
generic name from an examination only of the separated valves in a
fossil condition.

With respect to _Pachylasma aurantiacum_, I have no doubt that at an early age it would possess a perfectly distinct rostrum with alæ; for in the one specimen which I have seen, the compound rostrum is divided by sutures, faintly visible, both externally and internally (Pl. 20, fig. 1 _a_, 1 _b_), into three compartments (B, A, B), of which the middle one, or true rostrum, still shows, in the manner in which it underlaps the little rostro-lateral compartments, vestiges of alæ. I may remark, that we have here the same structure as in Chelonobia, formerly described, with the following differences, that here the sutures pass through the outer lamina of the parietes, so that, as seen externally, the separation of the three compartments is much more perfect than in Chelonobia; on the other hand, internally, the separation is less distinct, as the two rudimentary rostro-lateral compartments do not form part of the sheath. _Pachylasma aurantiacum_ is further remarkable, from the two lateral compartments (C, D) on each side, tending to blend together, being only separated by sutures not more distinct, externally, than those separating the compound rostrum, but more distinct internally, for they run up the sheath. From these facts it follows, that this species, viewed outside, without particular care, would be said to consist, like an Elminius or Chamæsipho, of only four compartments; if the sheath alone were looked at, there would be said to be six compartments; but when the walls, especially their basal edges, are carefully examined, either internally or externally, the eight compartments can be plainly distinguished.

With respect to the affinities of this genus, we have seen that both in the included animal's body, and, at an early age, in the shell, it is extremely close to Octomeris: in the presence of caudal appendages, and in the basis being calcareous, we have a clear affinity with Catophragmus; in the two lateral compartments of _P. aurantiacum_, tending to become blended together, we have some relationship exhibited to Chamæsipho, as is likewise shown in the structure of the second and third pairs of cirri. If the genera of the Chthamalinæ were ranged in a circle, Pachylasma would be the point of contact with the Balaninæ. I must repeat, that it is extremely unfortunate that when the shell alone of _P. giganteum_ is examined, it is hardly possible to separate this genus from Balanus.

1. PACHYLASMA GIGANTEUM. Pl. 19, fig. 5 _a_-5 _d_.

CHTHAMALUS GIGANTEUS. _Philippi_ (!). Enum. Mollusc. Siciliæ, 1836.

_Shell and operculum dirty white: carino-lateral and lateral compartments furnished with similar alæ._

_Hab._--Mediterranean; Sicily; deep water; often attached to the
_Millepora aspera_, and sometimes associated with _B. tulipiformis_.
_Fossil_ in the tertiary beds, near Messina. Mus. Brit., Cuming,
Stutchbury, Lyell, Philippi.

I owe to the kindness of Dr. Philippi, authentic specimens of his _Chthamalus giganteus_, from the tertiary beds of Messina: had this distinguished naturalist seen recent specimens, or a fossil one with all the valves united, he would no doubt have perceived that this species cannot be classed with Chthamalus. I am also indebted to Sir Charles Lyell for some magnificent specimens, which he himself collected near Messina.

_General Appearance._--Shell conical, rugged, irregular, with the
lines of growth plain; colour dead dirty white. Orifice large,
diamond-shaped, narrow towards the carinal end; notched. Radii
narrow, barely distinct from the parietes; in the same individual
sometimes absent, and sometimes forming a mere ribbon, confined to
the lower edge of a compartment. The diametric growth is effected
by the alæ, which seen externally are broad, and strongly marked by
lines of growth. Basal diameter of largest recent specimen 1.15;
height of highest compartment (a carina) 1.4; and width at base of
widest rostrum .85 of an inch. Amongst the fossil specimens, height
of highest compartment (a carina) 1.8, width of the same one inch;
width of widest rostrum 1.1 of a inch. One of these carinæ, a little
below the middle point, was actually .3 of an inch in thickness, from
which circumstance I have given the generic name of Pachylasma.

_Scuta_, triangular, but the width varies a little: growth-ridges
prominent, sinuous, with a few slight furrows radiating from the apex
of the valve. Internally, the articular ridge is not very prominent;
nor is there a deep depression for the adductor muscle, and none for
the lateral depressor muscles. The upper part of the valve projects
freely.

_Terga_, broad, broader than the scuta: the growth-ridges are
prominent, and angularly upturned close along the scutal margin; the
carinal half of the valve is smooth, with the faintest traces of
longitudinal striæ. A portion of the valve, nearly half of its entire
width on the scutal side, is slightly depressed below the general
level, and depends slightly beneath the basal margin on the carinal
side: this evidently forms the spur. The carinal margin is nearly
straight, with the lines of growth upturned along it. Internally, the
articular ridge in the upper part is extremely prominent: the crests
for the depressor muscles are very prominent, and depend beneath the
basal margin like a comb: they extend over nearly half the basal
margin, and the muscle, in a corresponding manner, is unusually
spread out.

_Structure of Shell and Radii_: the compartments are attached to
each other less strongly than in any other cirripede which I have
examined, so that when dried specimens are soaked in spirits of wine
they generally fall to pieces with a touch. In full and half-grown
specimens the carino-lateral compartments are nearly as broad as the
lateral compartments; in very young specimens, about 1/20th of an
inch in basal diameter, they are proportionally much narrower. The
_walls_ are strong even in young specimens; in old ones they attain a
thickness I have scarcely seen equalled except in Chelonobia. Their
internal surfaces are smooth, as is the basal internal margin in
young specimens, but in old specimens it is roughened with short,
blunt ridges and little points. The _Radii_ are often absent; when
present they are very narrow, and consist merely of a ribbon-like
portion, formed by obliquely upturned layers of growth, more
prominent than on the parietes. The _Alæ_ are very largely developed;
they are added to, during the diametric growth of the shell, in a
regular sweep all the way down to the basal margin, and consequently
they do not form a rectangular shoulder as is usual; externally they
are plainly marked by lines of growth: they are added to a little
above the line of attachment of the opercular membrane; their summits
are very oblique. The sheath has its basal edge slightly hollowed out.

_Basis_, solid, calcareous, very irregular, and of variable thickness.

I have, under the Genus, alluded to the structure of the rostrum:
in one shell, the basal diameter of which barely exceeded 1/20th
of an inch; the compound rostrum (being 5/200ths of an inch in
height), had its basal margin (being 9/200ths of an inch in width)
rendered deeply sinuous (see Pl. 19, fig. 5 _b_) by two indentations,
corresponding with and caused by two notches at the top of the valve.
These two notches extended down barely 1/100th of an inch (strictly
4/1000ths) from the summit and then disappeared; so that when the
shell was under 1/100th of an inch in height, (only one distinct zone
of growth having been formed), the now compound rostrum consisted
of three separate compartments; and there were eight compartments
altogether. Of the above three little compartments, the middle one,
or true rostrum, had large alæ, which could be most distinctly seen,
extending on both sides, under the little rudimentary rostro-lateral
compartments. These latter overlapped the compartments on both sides
of them, as in all the Chthamalinæ.

_Mouth_: labrum bullate, with no central notch; nor is the inner fold
of the labrum, forming the supra-œsophageal cavity, thickened, as in
Balanus: minute muscles run from this inner fold straight back to the
cavity formed by the outer bullate fold: the crest of the labrum is
hairy, with a row of the minutest bead-like points or teeth. _Palpi_,
small, broad, placed almost parallel to the sides of the mouth, with
their apices not nearly touching each other. _Mandibles_, with three
large nearly equal-sized _single_ teeth; the whole inferior angle
strongly pectinated. _Maxillæ_, small, with a broad, square notch
beneath the two or three great upper spines.

_Cirri_: first pair short, with the rami equal in length. Second
pair, with the anterior ramus having broader segments than those
of the posterior ramus, and with all the segments, except the few
uppermost, thickly covered with spines; the posterior ramus has
rather less than half the segments thickly covered. Third pair, very
slightly shorter than the sixth pair; anterior ramus with the lower
segments, less than half of the whole in number, thickly covered
with spines; posterior ramus with only the lowest segments, about
one fifth of the entire number, thickly covered; the other segments
of these two rami, and the upper segments of the posterior ramus of
the second pair, closely resemble in the regular arrangement of their
spines in pairs, the three posterior pairs of cirri. The pedicel of
the third pair supports numerous, irregularly scattered bristles. The
segments of the sixth pair bear four or five pairs of main spines,
with a few intermediate spines.

_Caudal Appendages._--Multiarticulate, narrow, tapering, situated on
each side of the anus: each segment has two little tufts of spines
on each side of its upper edge. These appendages are about one third
longer than the pedicel of the sixth pair of cirri: in a specimen,
in which the rami of the sixth pair had twenty-three segments, the
caudal appendages had nineteen segments.

_Penis_ short, hairy, finely-ringed, with no projecting point at its
dorsal basis. _Branchiæ_ moderately large, nearly circular, not much
plicated.

_Fossil Specimens._--With respect to the Sicilian specimens sent me
by Dr. Philippi and Sir C. Lyell, I can see no difference whatever
from the recent specimens, excepting in their greater size and
thickness; it must, however, be borne in mind that I have seen only
half-a-dozen recent shells. The one fossil scutum which I have seen
is rather broader than is usual with the recent, but I have seen one
nearly as broad. This species seems to have been extremely common
when the beds at Messina were deposited, and probably it attained
a larger size than it does at present. The compartments are always
found separated, which is easily understood, by the facility with
which, as above stated, recent specimens fall to pieces.

2. PACHYLASMA AURANTIACUM. Pl. 20, fig. 1 _a_-1 _d_.

_Shell tinged with orange; viewed externally seems formed of only four compartments, owing to the carino-lateral and lateral compartments on each side being separated only by an obscure fissure._

_Hab._--New South Wales; apparently from deep water, attached to
sandstone.[135]

[135] I am indebted to Mr. Bowerbank for this unique and
interesting species, which I have deposited in the British Museum.

_General Appearance._--Shell conical, smooth, with a tinge of orange
colour; orifice large, deeply notched, sub-triangular. Viewed
externally, the compartments in appearance are only four; but on
close examination, the lateral compartments are seen to be divided
by a very fine fissure into two nearly equal compartments. The
rostrum is broad and flat, and when carefully examined, it also is
seen to be divided by two fine fissures into three compartments;
of these the middle one, or true rostrum, is a very little broader
than the rostro-lateral compartment on each side; hence, on careful
examination, the shell is found to consist of eight compartments. The
carina is much compressed. The radii (in my one specimen) are not
developed. The carina, and the two lateral compartments alone, have
alæ; for the carino-lateral compartments are too closely joined to
the lateral compartments, and the true rostrum is too closely joined
to the rostro-lateral compartments, to have their alæ developed. The
four alæ which are developed, are very broad, widely exposed, and
marked externally by lines of growth. The basal diameter of my one,
apparently old specimen, is one inch.

_Structure of Shell, &c._--The inner surface (fig. 1 _b_) of the
rather thick parietes is smooth, except close to the base, where
it is roughened by a few irregular points. The sheath descends
low down, and has its lower edge slightly free. The sutures are
much plainer on the internal than on the external surface, and
can be here plainly seen to be eight in number. That portion of
the carino-lateral compartment, which helps to form the sheath,
is narrow, though the whole compartment is of very nearly equal
width with the lateral compartment. It is a singular fact, that no
portion of the rostro-lateral compartment helps to form the sheath;
for the alæ of the lateral compartments, overlap the whole upper
part of the rostro-lateral compartments, and abut against the true
rostrum. Hence, when the sheath alone is examined, the number of
the compartments appears only six. In a section the true rostrum
can be seen to underlie the rostro-lateral compartments, and thus
exhibits vestiges of alæ. The fact of the rudimentary rostro-lateral
compartments not forming a part of the sheath offers a marked
difference from Chelonobia, which otherwise has this part of the
shell very similarly constructed. The diametric growth of the shell,
which seems to be considerable, is effected by the four large alæ of
the carina and of the lateral compartment on each side. The sutural
edges of the alæ are added to in a regularly inclined line down to
the basis. The _basis_ is calcareous, and not very thin.

Both opercular valves (fig. 1 _c_, 1 _d_) closely resemble those of
the last species.

The _Scuta_ are remarkably narrow and elongated: the external
surface is slightly furrowed longitudinally, the prominent lines
of growth are much wrinkled. The articular ridge is blunt, and not
very prominent. The upper part of the valve is reflexed, and a
considerable portion must have projected freely. The _Terga_ are
nearly twice as broad as the scuta: the carinal half of the valve is
very smooth, and is coloured beautiful reddish-orange. The spur is
tolerably distinct. The articular ridge is not very prominent.

The _Mouth_ resembles that of the last species. The mandibles have
three sharp teeth, with the inferior part narrow and pectinated
with long spines: the edge, also, between the upper main teeth, is
pectinated with short spines, which latter often have their summits
crenated. The _maxillæ_ are notched; the inferior corner is produced
into a small step-formed projection. The outer maxillæ are more
pointed than is usual.

The _Cirri_ most closely resemble in every detail those of _P.
giganteum_; I can point out only one slight difference, namely, that
the lower segments, in the posterior ramus of the third cirrus, which
are thickly clothed with spines, are more numerous in proportion to
the upper segments with the spines arranged in regular pairs (being
as 4 to 14), than in _P. giganteum_, in which only one fifth (or 4 to
20) are so clothed.

_Caudal Appendages._--These are very small, not being more than
one fifth of the length of the pedicel of the sixth cirrus: their
segments are indistinct, and they support a very few coarse spines.
The rami of the sixth cirrus, in the one specimen, had twenty-five
segments, whilst each caudal appendage had only five. Hence the
caudal appendages are far less developed than in _P. giganteum_.

15. _Genus_--OCTOMERIS. Pl. 20.

OCTOMERIS. _G. B. Sowerby._ Zoological Journal, vol. 2, p. 244, July,
1825.

_Compartments eight: radii with their edges crenated: basis membranous._

_Distribution_, Cape of Good Hope; Philippine Archipelago.

The two species of this genus differ considerably in external appearance, though not in essential character. Both, as the name expresses, have eight compartments: the carino-lateral pair are rather narrower than the lateral. The basis is membranous. The radii are narrow, and are distinctly crenated on both sides of the sutures with the teeth neatly interlocking; but these teeth can hardly be distinguished in the large, corroded specimens of _O. angulosa_. The crenated structure of the radii is identical with that described under _Chthamalus dentatus_ and _Hembeli_; if, indeed, we were to add carino-lateral compartments to the shells of these two species, they would belong to Octomeris. I have seen only a few specimens of either species of Octomeris, and none preserved in spirits; and therefore I know nothing of the anatomy of the softer parts: I was not able to make out distinctly any branchiæ. The cirri differ considerably in the two species, in nearly the same way as in the two species of Chamæsipho. In the structure of the second pair of cirri, and in the tendency of the basal margin of the parietes to form bay-like indentations, _Octomeris angulosa_ shows some special affinity to _Chamæsipho scutelliformis_. Under Pachylasma, I stated that that genus was closely related to Octomeris; and I have just alluded to the close affinity of the latter to the division of the genus Chthamalus, which has crenated radii.

1. OCTOMERIS ANGULOSA. Pl. 20, fig. 2 _a_-2 _b_.

OCTOMERIS ANGULOSA. _G. B. Sowerby._ Zoological Journal, vol. 2,
July, 1825. And Genera of Recent and Fossil Shells, Plate.

---- STUTCHBURII. _J. E. Gray._ Annals of Philosophy, new series,
vol. 10, August, 1825.

---- AUGUBRA (?) _Chenu._ Illust. Conch., Tab. 4, fig. 2.

_Shell dirty white, rugged and massive: alæ thick, with their sutural edges coarsely crenated._

_Hab._--Algoa Bay, Cape of Good Hope. Attached to littoral rocks;
often associated with _Balanus Capensis_ and _Chthamalus dentatus_;
Mus. Brit., Cuming, Stutchbury, Bowerbank.

_General Appearance and Structure of Shell._--Shell extremely rugged,
irregular, massive, generally much corroded, steeply conical or even
sub-cylindrical: orifice large, broad, rhomboidal, of nearly equal
breadth at both ends. Colour dirty white, often slightly tinted
yellow from the investing membrane, and from thin layers of punctured
membrane alternating with the laminæ of shell. The parietes, in old
specimens, have very irregular longitudinal ridges, or rather plates
projecting out, sometimes much branched, and generally curved inwards
so as to meet each other, thus forming round the basal margin a
circle of cylindrical apertures. In old large specimens the radii are
not developed, and till the compartments are disarticulated there
is no trace of the toothed structure of their sutural edges: in
this condition the sutures exist as deep, rugged, narrow fissures.
In younger shells, the radii, though narrow, are distinct, and have
their surfaces transversely ribbed, and their edges toothed and
interlocked with the teeth of the recipient furrow. Some of the
specimens present a curiously deceptive resemblance to _Elminius
plicatus_. Basal diameter of largest specimen, one inch and a
quarter; height one inch.

The parietes are remarkably thick, but the compartments separate
easily: I have, however, seen one instance in which they were
partially calcified together. Their internal surfaces are
very smooth. The sheath does not descend low. The alæ project
rectangularly; they have thick edges, and these are coarsely crenated
in transverse lines. Of the radii sufficient has been said.

_Scuta_ (fig. 2 _b_): these, in all the specimens seen by me but
one, have been deeply corroded, and their outline, as in Chthamalus,
considerably modified: in the one specimen well preserved, the
exterior growth-ridges were extremely prominent. The articular ridge
does not project much, nor is the articular furrow very deep. There
are more or less distinct crests for the lateral depressor muscles.
The _Terga_ are rather narrow, with a small rounded spur, moderately
distinct. The tips of the crests for the depressor muscle barely
depend beneath the basal margin.

_Mouth_: labrum considerably bullate, with the crest hairy and
furnished with a few most minute teeth. Palpi small, with their
tips not nearly touching each other. Mandibles with four teeth,
of which the lower ones are laterally double: inferior pectinated
portion small. The maxillæ are notched, but their outline differed on
opposite sides of the individual examined. Outer maxillæ bilobed on
their inner face.

_Cirri._--The first pair has the rami unequal in length by about
three segments, having six segments on one and nine on the other
ramus. In the second pair the anterior ramus is remarkably short and
extremely broad; the five segments of which it is composed being
thickly covered with bristles, some of which are very coarsely and
doubly pectinated: the posterior ramus is nearly twice as long as
the anterior ramus, and has eleven segments; of these, excepting the
two basal segments which are rather thickly covered with spines, the
others resemble in the arrangement of their spines the four posterior
pairs of cirri, with the exception that there is a single transverse
row of rather long spines along the upper and inner lateral edge
of each segment. The segments in all the four posterior pairs of
cirri resemble each other in bearing each four pairs of main spines
(of which the two lower pairs are short), with a tuft of small
intermediate spines.

The penis is remarkable from its very small size and shortness, not
being more than once and a half as long as the pedicel of the sixth
cirrus.

2. OCTOMERIS BRUNNEA. Pl. 20, fig. 3 _a_, 3 _b_.

_Shell reddish-brown, depressed, thin, finely furrowed longitudinally: tergum with the basal margin having a slight angular bend._

_Hab._--Philippine Archipelago; rare; Mus. Cuming.

_General Appearance and Structure._--Shell circular, much depressed;
coloured brown, with an orange-red tint; surface regularly and
narrowly furrowed in longitudinal lines, the intermediate rounded
ridges projecting at the basal margin in finger-like points. The
eight compartments, when disarticulated, are of nearly equal sizes;
the carino-lateral and rostro-lateral compartments being rather
smaller than the others. The radii are neatly toothed; but with the
exception of these teeth, which are equally developed on both sides
of the sutures, and which closely interlock in the lower part of the
shell, but stand a little apart in the upper part, the radii can
hardly be said to be developed. The alæ do not form a rectangular
shoulder, the lower margin being regularly curved into the parietes;
the upper margin is only slightly oblique; the external surface
is furrowed by lines of growth. The shell increases a little in
diameter, chiefly by the growth of the alæ. The parietes are not very
thick, with the inner surface smooth, but with punctures placed in
rows for the entrance of the tubuli: the laminæ of shell alternate
with layers of yellow finely punctured membrane. Basis formed of thin
membrane, in concentric slips. Basal diameter of largest specimen, .6
of an inch.

_Scuta_ broad, with the lines of growth few in number, but extremely
prominent, so as to form folds: basal margin with a very slight
angular bend: articular ridge not very prominent. _Terga_, with a
narrow slip along the scutal margin, having the lines or folds of
growth so prominent as almost to form a series of small transverse
pits: the basal margin of this portion forms an angle with the rest
of the basal margin: no spur can be said to exist: the crests for the
depressor muscle depend a little beneath the basal margin: articular
ridge very prominent.

_Mouth_: labrum and palpi as in the last species. Mandibles with
three main teeth, apparently single, of which the lower tooth has
its upper edge pectinated: the inferior part of the mandible is
pectinated as usual. The maxillæ have two notches, one beneath the
two upper large spines, and the other in the middle, separating some
thicker and thinner spines.

_Cirri_: first and second pairs short, with the anterior rami in
each longer by about two segments than the posterior rami; all the
segments thickly covered with bristles. The third cirrus is much
longer than the second cirrus, with the posterior ramus longer than
the anterior ramus; on the latter the three basal segments, and on
the posterior ramus the two basal segments are thickly covered with
bristles; the other segments have bristles arranged as on the three
posterior pairs of cirri, namely, each segment has four pairs of main
spines, of which the two lower pairs are short.

The unarticulated support, whence the articulated portion of the
penis arises, is unusually long, equalling the pedicel of the sixth
cirrus.

16. _Genus_--CATOPHRAGMUS. Pl. 20.

CATOPHRAGMUS. _G. B. Sowerby._ Genera of Recent and Fossil Shells.
Plate.

_Interior compartments eight, with several exterior whorls of small supplemental compartments: basis either membranous or calcareous._

_Distribution_, West Indies and Australia. Attached to littoral
shells and rocks.