Chapter XXVI: Introduction (22)

_Generative System._--The probosciformed penis is short and thick,
and covered with very minute tufts of bristles: there is no
knife-edged projection at its dorsal base. The vesiculæ seminales are
much convoluted and of great length. The ovarian tubes form a small
sheet within the rudimentary shell, in the normal position, over
the basal membrane; and likewise higher up between the two folds of
corium surrounding the pseudo-peduncle; they do not, however, appear
to occur round the lower part of the peduncle: they extend highest
on the rostral and carinal sides, and lowest on the two lateral
faces. The ova are wonderfully numerous; they are 15/2000ths of an
inch in length: they form, instead of two thin lamellæ, two almost
cylindrical packets, which are held together by most feeble membrane.
Each packet, in the upper part lies between the two folds of the
branchiæ; and in the lower part, is embraced only by the larger outer
fold. The two packets of eggs sometimes cohere together at their
lower ends.

_Imbedment._--The shell is imbedded up to its summit, but the shell
is very shallow. The imbedment seems due either to the compression
of the epidermis of the porpoise, or to its formation beneath the
shell having been checked; the outline of the true skin under the
dark-coloured epidermis is not in the least affected. The epidermis
fills up the bay-like spaces formed by the inwardly folded walls, and
firmly adheres to them.

_Affinities._--This genus presents very varied affinities to
Tubicinella, Coronula, and Platylepas. To the latter it is more
especially allied in the compartments, being singly folded inwards,
though the sides of the folds are not here closely pressed together,
as in Platylepas: in both these genera the fold is less deep in the
rostrum, of which fact, in Platylepas, the final cause is evident,
but here there seems no cause, excepting the simple one of affinity.
Xenobalanus is further allied to Platylepas, in the lesser size of
the inner fold of each branchia, compared with the outer, and in
the structure of the cement-glands, and to a certain extent in that
of the sheath. To Coronula the special alliance is shown by the
remarkable character of the pseudo-radii lying between the parallel
and adjoining walls, and in the general character of the cirri: in
Coronula we have the terga sometimes quite aborted, and the scuta
of small size, thus exhibiting a tendency to the entire absence of
opercular valves, so remarkable in Xenobalanus. To Tubicinella, the
alliance is still more plainly shown in the external shape of the
whole animal, wider at top than at bottom,--in the opercular membrane
descending almost to the very base--in the relative positions of the
different parts and organs--in the upper end of the shell continually
scaling off--in the prominence of the transverse external ridges--in
the sheath being divided into successive zones of growth, and being
prolonged nearly to the basal membrane--and in the edges of the alæ
being smooth. Internally, the resemblance is also plainly shown,
in the strength of the internal tunic of the sack--in the branchiæ
springing from two approximate fleshy crests--in the freely depending
acoustic orifices--in the form of the thorax and prosoma--and
consequently of the alimentary canal.

Seeing the state of the almost rudimentary shell, it is not difficult to imagine its total disappearance. Thinking of this, it occurred to me to doubt for a few minutes, whether Anelasma, described in my volume on the Lepadidæ, which presents many points of resemblance with Xenobalanus,--viz., in colour, in the strength of the internal membrane of the sack, in the size of the orifice with its thin membranous margin, in the entire absence of opercular valves, and in epizoic habits,--might not in truth be a sessile cirripede, in an extremely altered condition; for the cirri of Anelasma are in so rudimentary a state, and the mouth in so modified a condition, that the internal characters by which pedunculated cirripedes can be distinguished from the Balaninæ, though not from the Chthamalinæ, are almost lost. But if Anelasma had belonged to either of the two sub-families of the Balanidæ, the sack would have penetrated almost to the bottom of the peduncle; there would have been only a single layer of longitudinal muscles round the peduncle; and there would not have existed ovigerous fræna. I believe that Anelasma and Xenobalanus are only analogically connected, being no more related together by true affinity, than any other two genera in the Lepadidæ and Balanidæ.

_Sub-Family_--CHTHAMALINÆ.

_Shell with the rostrum having alæ, but without radii: rostro-lateral compartments without alæ on either side: parietes not porose._

_Mouth with the labrum bullate; palpi hardly touching each other: third pair of cirri with the segments resembling those of the fourth pair._

The shell in this sub-family consists of four, six, or eight compartments, with the addition, in Catophragmus, of several whorls of supplemental compartments or scales, like those forming the lower part of the capitulum in Pollicipes. The rostrum has alæ and no radii; in shape and size it resembles the carina. The rostro-lateral compartments are destitute of alæ; in all cases they overlap the adjoining compartments, and have radii (when such are developed) on both sides. In the genus, Pachylasma, however, the shell must be looked to very young, in order to detect this normal structure, for soon the true rostrum and rostro-lateral compartments become blended together, making a compound rostrum, destitute, as in the Balaninæ, of alæ, but furnished with radii. The parietes are never porose, nor furnished with regular symmetrical ribs (representing the longitudinal parietal septa) on their inner surfaces: sometimes, however, on the basal internal edges, there are some irregular depending points. In conformity with the simplicity of the parietes, the Radii (which are seldom much developed) have likewise a simple structure; and often are merely formed by the simple lateral growth of the parietes. The scuta and terga are articulated together more deeply than is usual in the Balaninæ; and the terga never have a long spur.

Looking to the animal's body. The Labrum is always swollen and bullate, and though hollowed out, is never notched in the middle. The Palpi are rather small, and have not their tips nearly touching each other. The mandibles generally have their lower main teeth laterally single, though sometimes they are double: the inferior angle is always pectinated. The maxillæ are always notched under the upper pair of great spines. Of the _Cirri_, the third pair much more closely resembles, in external structure and powers of movement, the fourth than the second pair, though sometimes a few of the basal segments, especially on the anterior ramus, are thickly covered with bristles, as on the segments of the second pair. In three species belonging to two genera, there are caudal appendages, resembling those generally present amongst the Lepadidæ, but never found in the Balaninæ. The Branchiæ are generally smaller than in the Balaninæ; and are sometimes quite rudimentary.

In the introductory description (p. 152 and 176) of the Family Balanidæ, I have already discussed the relations of the Chthamalinæ to the Balaninæ, and of the several genera to each other, so that I need not here re-enter on the subject.

12. _Genus_--CHTHAMALUS. Pl. 18, 19.

CHTHAMALUS. _Ranzani._ Memoire di Storia Naturale, 1820.

EURAPHIA. _Conrad._ Journal Acad. Nat. Sc. Philadelphia, vol. 7, 1834.

_Compartments six: basis membranous, but sometimes in appearance calcareous, owing to the inflected parietes._

Distribution mundane; attached generally to littoral rocks and shells.

This, the typical genus, is the largest and widest distributed group of the sub-family Chthamalinæ. The founder of the genus apparently did not perceive its essential character; Savigny, however, as is evident from the excellent figure in the great work on Ægypt, perfectly understood the difference between Chthamalus and Balanus. I was first indebted to Dr. J. E. Gray for explaining to me this difference; but the only published account which I have met with is in a paper by the Rev. R. T. Lowe,[130] in which he states, on the authority of Mr. Clark of Bath, that in Chthamalus the anterior compartment or rostrum has alæ like the posterior compartment or carina, the anterior or rostro-lateral compartments being destitute of alæ. These characters being exactly reversed in Balanus, as I have already explained (p. 176) under the sub-family of Balaninæ.

[130] 'Zoological Journal,' vol. 3, p. 76, 1828.

The shell, owing apparently to its containing much animal matter, is particularly subject to disintegration; and when thus much affected it is quite impossible to distinguish the species by external characters. It is, in fact, best to cast on one side external appearance, though when the shells happen to be well preserved, each species has its own peculiar aspect. We have in this genus smooth and plicated, cylindrical and depressed varieties of most of the species. The development of the radii is very apt to vary, and even the compartments often become so completely united and calcified together that the sutures are almost or quite obliterated. A more serious difficulty in discriminating the species, arises from the fact of the opercular valves, not only varying extremely in external appearance in consequence of the greater or less disintegration of their apices, and consequent exposure of their articular ridges and furrows (compare fig. 1 _a_, 1 _b_, 1 _c_, in Pl. 18), but from their truly varying in outline with the varying shape of the shell: this latter circumstance is probably due to the opercular membrane which unites the valves to the shell being very narrow, and in consequence, differences in the shape of the shell affect the opercular valves, in a manner and to a degree to which the Balaninæ are not subject (compare fig. 1 _e_, 1 _f_, 1 _h_, in Pl. 18). The scuta, on the other hand, differ to an unusually slight degree in the different species. In the common _Chthamalus stellatus_, which abounds on the southern British shores, the whole external aspect of the shell is often so completely masked, owing to its varying shape, its obliterated sutures, its deeply disintegrated and punctured surface, and by the corroded condition of its opercular valves, that I have found this species, in the collections of naturalists who have attended to cirripedes, arranged actually on the same tablet, mingled with specimens of _Balanus balanoides_. I have myself several times found it less troublesome to discriminate these two genera by the included animal's body than by the shell,[131] though the latter, when well preserved and developed, possesses such obviously well-marked characters: the same thing has occurred to me with some of the other species.

[131] It will be found ultimately to save time and trouble, to soak
for half an hour in hot caustic potash, a specimen out of each
group of shells to be examined, and then well wash and brush the
separated valves and compartments; this process has been followed
by me with all the species here to be described.

_General Appearance._--The shell is generally depressed, but sometimes, when growing in groups, cylindrical. The surface is either smooth or longitudinally folded; and, as already stated, very apt to be deeply disintegrated. The radii, when developed, are narrow, with their summits oblique and rounded; but they are often quite absent, and sometimes even the sutures are almost obliterated. The rostrum and carina are of the same shape and size, and the two lateral compartments on each side are of nearly equal breadths. The orifice is generally sub-rhomboidal, being widest towards the carinal, instead of towards the rostral end, as is usual in Balanus: but in _Chthamalus fissus_ the orifice is narrow and elongated. The opercular valves have their apices generally disintegrated and worn away, and are then seen to be deeply locked together. The colour of the shell is dirty white or dull purplish-red or brown; but in _C. intertextus_ rich violet-purple. The species are small, not often exceeding half an inch in basal diameter, with the exception of _C. Hembeli_, of which I have seen a specimen two and three quarters of an inch in diameter.

_Scuta._--These present no particular character, excepting in most cases the large development of the articular ridge, and sometimes the presence of a furrow above the articular ridge, of which only traces can rarely be detected in Balanus; hence in these cases, as in _C. Hembeli_ (Pl. 18, fig. 5 _a_, 5 _c_) and _scabrosus_ (Pl. 19, fig. 2 _a_, 2 _c_), the line of articulation between the scutum and tergum is more complicated than is usual. There is generally a slight pit, sometimes even furnished with small crests, for the lateral scutal depressor muscle: in _C. scabrosus_ (fig. 2 _d_, _q_) a part of this muscle is attached to a small pit at the basi-scutal corner of the tergum,--a fact of which I have observed no instance in any other genus. In _C. intertextus_ the terga and scuta are calcified together, without even a suture being visible on their internal faces. In _C. Hembeli_ the valve is externally marked by a few longitudinal furrows.

The _Terga_, like the scuta, have a prominent articular ridge and deep furrow. In many specimens of _C. stellatus_ and in _C. scabrosus_ the valve is narrow: in _C. fissus_ it is triangular and nearly equilateral. The crests for the depressores muscles are well developed: in _C. scabrosus_ (Pl. 19, fig. 2 _d_, _p_) these crests are united into a plate, which, together with the outer lamina of the valve, forms a deep narrow pit: in _C. Hembeli_ the crests are furnished with small sub-crests. The opercular membrane is narrow; it is sometimes furnished with a few minute spines.

_Structure of Parietes._--The parietes are solid, and composed of successive layers of shell; the inner surface varies in condition in the same species, being either smooth or marked with branching impressed lines, or mamillated, or often irregularly punctured for the entrance of tubuli. Owing to these tubuli, the walls, when externally disintegrated, often become punctured. In certain depressed varieties of both _C. stellatus_ and _scabrosus_ the walls are supported by irregular depending columns, placed along either one side or both sides of the sutures. In _C. intertextus_ we have the remarkable character of the wall of the shell growing (I presume after a certain age) almost rectangularly inwards, thus forming a rather wide, flat, calcareous rim round the central basal membrane. In _C. Hembeli_ the internal basal edges of the parietes, in one moderately young specimen, were rugged with irregular points, but presented no other remarkable appearance; but in five old and very large specimens, the whole basis was calcareous, being absolutely continuous with the inner lamina of the parietes, showing that the latter had grown flatly inwards all round, and had then become confluent in the middle, so that there was no longer any basal membrane; excepting, no doubt, that which had existed in the younger stage, and which would be preserved in a functionless condition between the surface of attachment and the inflected parietes.

When an opercular valve or compartment is dissolved in acid, layers of tissue are left, and these are seen to be penetrated by tubuli, which enter at the punctures before mentioned on the inside of the shell: these tubuli often stand in groups of three or four together; they are about 1/10000th of an inch in diameter. Besides these irregularly scattered tubuli, there are in the opercular valves of _C. antennatus_, innumerable smaller parallel tubuli, running to the external investing membrane.

_Structure of the Radii and Alæ._--The radii, when developed, are always rather narrow. Their recipient furrows are generally nearly as broad as the radii themselves. Their edges are either quite smooth, as in _C. antennatus_; or very finely crenated; or, as in _C. dentatus_ and _Hembeli_ (Pl. 18, fig. 3 _a_, 5 _a_), so strongly crenated as to make the suture, both externally and internally, toothed: in these two species, the radii are ribbed in transverse lines parallel to the basis, each rib corresponding with one of the projecting and interlocking teeth on the sutures. In _C. intertextus_, and much less plainly in most specimens of _C. scabrosus_ (Pl. 19, fig. 1 _a_, 2 _a_), we have a structure in appearance very different, for the radii here consist of several very oblique plates, (_i. e._ nearly parallel to the parietes) on both sides of the sutures, which are interfolded or locked together: I believe that this structure is a mere modification of that in _C. dentatus_ and _Hembeli_, the transverse ridges on the radii of those species being here developed into oblique plates. We shall hereafter meet with a similar structure in the genus Verruca; to which genus, until meeting with these two species of Chthamalus, I had thought that the interfolding sutures had been confined. The alæ have their edges generally finely crenated: during diametric growth (when such takes place), they are rarely added to above the level of the opercular membrane, and hence their summits are oblique: in _C. intertextus_, however, the alæ are laterally added to above the opercular membrane, and their recipient furrows are likewise added to, of which fact I have seen no other distinct instance in any genus; hence on both sides of the sutures, in the sheath of this species, the lines of growth are upturned. In some much disintegrated specimens, both of _C. stellatus_ (var. _depressus_) and of _C. antennatus_, the radii have been corroded away, and the diametric growth is effected exclusively by the growth of the alæ, which are moreover much exposed, and rendered conspicuous. The sheath descends a moderate distance down the shell. When a shell is boiled in potash, the sutures (excepting when abnormally calcified together, as very often happens with some species) always fall apart, showing that the union is simply by animalised matter.

_Basis._--The basis is always membranous; but we have seen, in _C. intertextus_, that the walls form a flat ledge all round the base, and that in _old_ specimens of _C. Hembeli_, they grow so far inwards and become so completely confluent, that they might most easily be mistaken for a true calcareous basis. I may add, that in one elongated specimen of _C. stellatus_ from La Plata, the walls had likewise grown rectangularly inwards, forming a flat base, and had then turned upwards in the middle, forming a medial crest, with the edges not quite calcified together. The true basal membrane is very obscurely divided into concentric slips. I observed in several species, attached to the lower surface, an excessively fine network, quadrangular or hexagonal, of yellow vessels, which seemed insensibly to pass into the sheets, discs, and globules of cement, by which the membranous basis adheres to the supporting surface. I saw, in _C. antennatus_, numerous irregular, bifurcating, and inosculating cement-ducts, of unequal diameter, often crossing each other, and sending off branches ending in points: the older ducts, instead of being solidly filled up with cement, were only divided by septa. I did not succeed, in any species, in discovering the cement-glands.

_Mouth._--The _labrum_ is slightly bullate, with the middle portion depressed, but not forming a notch; in some species it is hairy, and in some pectinated with short spines. The _palpi_ are of moderate size. The mandibles have from three to five main teeth, the number sometimes varying even in the same species: the lower teeth are either plainly double laterally, or very obscurely double, or to all appearance quite single: a rather large lower portion of the mandible is finely pectinated. The maxillæ are always notched under the two or three large upper spines: the notch bears some fine spines: beneath the notch there are some large spines, and at the inferior angle some smaller ones.

_Cirri._--The first and second pairs are always very short compared with the four posterior pairs. The rami of the first pair are slightly unequal. The third pair, in length and arrangement of the spines, very closely resembles the three posterior pairs; in _C. intertextus_, however, the few basal segments, chiefly on the anterior ramus, are thickly clothed with bristles, like the segments of the second cirrus. In _C. antennatus_ (Pl. 29, fig. 2), the anterior ramus of this same third pair is usually (one single specimen being excepted) much elongated, having at least twice as many segments as the posterior ramus, but the number is variable; and these segments, either all, or only the upper ones, instead of having their spines regularly arranged in pairs, in a double row, are surmounted each by a circle of spines: I suspect that these elongated rami of the third cirrus act as antennæ. It can hardly be an accidental coincidence, that certain genera, as Lysmata and Pandalus, amongst the Macrourous Crustaceans, have the same leg (homologically the second thoracic limb) elongated and antenniformed. Certain varieties of _C. stellatus_ and _cirratus_, also, have the anterior ramus of this same third cirrus considerably elongated. We are thus reminded of the remarkable variability in the numbers of the segments, and in the arrangement of their spines, in the cirri of _Tetraclita porosa_; in that species, however, it was chiefly the terminal segments of the _posterior_ ramus of the third cirrus which were so highly variable. The three posterior pairs of cirri in Chthamalus support from three to five pairs of main spines on each segment, the number often varying in the same species, with some minute intermediate bristles. The dorsal surfaces of these segments, in some of the species, are serrated in an upward direction.

_Body, &c._--The body does not present any particular character: in _C. scabrosus_ there is a slight ridge running from the base of the first cirrus towards the adductor scutorum muscle: this ridge is clothed with a few hairs; there are also some hairs at the carinal end of the sack. In _C. dentatus_, also, there are hairs on the outer tunic of the prosoma. In two species which I opened, there were no cæca to the stomach. The ova vary in length from 13 to 14/2000th of an inch in length; they are packed in two lamellæ lying on each side of the animal's body. The larva just escaped out of the egg, in _C. stellatus_, _scabrosus_ and _dentatus_, had a large probosciformed mouth.

_Branchiæ._--These present a very singular amount of difference within the limits of the same genus. In _C. stellatus_ and _antennatus_ we have a simple fillet, tapering a little, barely plicated, and about half, or more than half, as long as the sack; in _C. scabrosus_ the branchiæ are entirely aborted, or are perhaps represented by the slight hairy ridge at the carinal end of the sack: in _C. dentatus_, on the other hand, each branchia consists of two large folds, barely plicated, almost covering the whole side of the sack, so that here the branchiæ are developed to an unusual degree, more than in Balanus, and as in Coronula and its allies: in the same manner as in these latter genera, the outer fold is considerably larger than the inner fold.

_Affinities._--_C. intertextus_ is the most distinct species of the genus, as shown by the peculiar radii and alæ, by the scuta and terga being calcified together, by the character of the third pair of cirri, and by the inflected parietes forming a ledge round the membranous basis; but in this latter respect _C. intertextus_ resembles _C. Hembeli_. _C. Hembeli_, in its serrated radii, is closely related to _C. dentatus_; and this latter species differs in the structure of its radii only in degree from certain varieties of _C. stellatus_. Lastly, _C. intertextus_, in its peculiar radii, closely resembles _C. scabrosus_, and this latter species does not differ much from the other species. Hence the genus Chthamalus has no claims to be subdivided into smaller genera.

_Range._--The species are found all round the world, from (as far as I have seen) 54°-55° north, to Cape Horn, in 55°-56° south. All the species, of the habits of which I know anything, are littoral; and in many parts of the world are excessively numerous, quite covering large spaces of the coast-rocks, and often coating the coast-shells. _Chthamalus dentatus_ is littoral, like the other species; but it often lives attached on _Balanus tintinnabulum_ and _amphitrite_, on the bottoms of ships arriving in British ports from the west coast of Africa. I do not know of any instance of more than two species occurring in the same region. Some of the species have large ranges: _C. scabrosus_ extends from the Falkland Islands and Tierra del Fuego to Peru; and _C. stellatus_ has an enormous extension over almost the whole world, excepting the west coast of South America and Australia. I do not believe any species of the genus, owing probably to their littoral habits, have hitherto been found fossil.

1. CHTHAMALUS STELLATUS. Pl. 18, fig. 1 _a_-1 _h_.

LEPAS STELLATA. _Poli._ Testacea Utriusque Siciliæ (1795), Tab. 5,
fig. 18-20.

---- DEPRESSA (_var._) Ib., Tab. 5, fig. 12-16.

CHTHAMALUS STELLATUS. _Ranzani._ Memoire di Storia Naturale (1820),
Tab. 3, fig. 21-24.

---- GLABER (_var._) _Ranzani._ Ib.

---- STELLATUS. _Philippi_ (!). Enumeratio Mollusc. Siciliæ.

LEPAS PUNCTATUS. _Montagu_ (!). Testacea Britannica (1803).

_Shell white or gray, generally much corroded and punctured: radii (when present) narrow, with their sutural edges most finely crenated; tergum with the crests for the depressor muscle depending barely beneath the basal margin._

_Var._ (_a_, communis) fig. 1 _a_, 1 _f_: _Shell conical depressed,
upper part corroded, walls folded, sutures moderately plain or
obliterated; radii not developed; orifice broadly oval_.

_Var. (b): Shell elongated, sub-cylindrical; sutures obliterated;
surface much corroded; orifice almost circular._

_Var._ (_c_, communis) fig. 1 _c_, 1 _e_, 1 _h_: _Shell conical,
folded, sometimes covered by membrane; radii developed, narrow;
orifice sub-hexagonal, toothed._

_Var._ (_d_, fragilis) fig. 1 _d_: _Shell conical, smooth, thin;
compartments easily separable, pale-coloured; radii developed,
narrow; orifice large, toothed, sub-hexagonal._

_Var._ (_e_, depressus) fig. 1 _b_, 1 _g_, 1 _h_: _Shell much
depressed, surface much corroded, smooth: alæ largely exposed, marked
by lines of growth: radii not present; parietes on the under side
often supported by pillars; orifice sub-hexagonal._

_Hab._--Southern shores of England, Ireland, Isle of Man,
Mediterranean, Madeira, Cape de Verde Islands, Southern United States
(Charlestown), West Indies, Brazil (Bahia), Rio Plata (Guritti
Island), Red Sea, Philippine Archipelago, Coast of China, Gulf of
Corea, Oregon or Northern California.

This species is very widely distributed and extremely common. On the coast-rocks of the southern shores of England it is, in parts, even more numerous than the _Balanus balanoides_, with which it often grows mingled. As already stated, it is often confounded in British collections with this species of Balanus, under the name of _Balanus punctatus_; that Montagu had this Chthamalus in view, when describing his _Lepas punctatus_, is certain, from his original specimen in the British Museum, but whether this was the case with his predecessor, Pulteney, in the Dorset Catalogue, I do not feel so sure. _Chthamalus stellatus_ varies, as we shall immediately see, extremely in appearance. Some of the varieties, as _var. depressus_, which in external aspect are especially distinct, I have no doubt are really varieties, but whether this is the case with some of the forms from the more distant localities, is a little more doubtful; but I beg that it may be observed, that I have, in the case of every one of the varieties, and of all the specimens from distant localities, cleaned with potash and most carefully examined the disarticulated valves, and likewise dissected the included animal's body.

_General Appearance._--British specimens are usually conical, and
have their walls folded, corroded in their upper parts, with the
radii not developed, and the sutures more or less obliterated; in
this state the orifice of the shell is entire, and very broadly oval:
I have seen specimens in this condition from Madeira, Brazil, and the
Gulf of Corea. The shells when crowded, are rendered cylindrical,
and more or less elongated, with the sutures as viewed externally
quite obliterated; the surface rugged and much disintegrated; and
the orifice nearly circular: in this extreme condition I have seen
specimens from England, from near Genoa, and from the mouth of
the Plata: the specimens from these last two localities were of
remarkable size, being half an inch in diameter, and rather more than
half an inch in height. Again, other British specimens (fig. 1 _c_),
though not nearly so common, are rather steeply conical, and have not
only their sutures distinct, but narrow radii are plainly developed
on apparently both sides of the sutures; in this case the orifice
is slightly toothed, and is rather elongated: I have seen specimens
in this condition, but with their walls rather more deeply folded,
from the Cape de Verde and Philippine Archipelago. Other specimens,
from some unknown tropical sea, differed only in the walls being but
slightly folded, and being so perfectly preserved as to be externally
covered with membrane: this latter circumstance gave the specimens
a peculiar appearance. In this condition were some specimens (fig.
1 _d_) attached to oysters sent to me by Professor Agassiz, from
Charlestown; and which differed from all the others that I have seen,
in the thinness and smoothness of their compartments, and in the
facility with which the compartments separated from each other and
from the surface of attachment: hence I have called this form, which,
until finding more important differences, I must rank as a variety,
_fragilis_: it has stronger claims than the other varieties to be
specifically separated; but I suspect that it has been exposed to
some peculiar modifying conditions.

Lastly, we have the variety (fig. 1 _b_) excellently figured and
described by Poli, under the name of _L. depressa_: this is much
depressed, with the walls thin, not folded, with the surface much
corroded, with the sutures very distinct, with the radii not at all
or barely developed, but with the alæ largely developed, and marked
with lines of growth, resulting from the diametric growth of the
shell: the orifice is hexagonal, but broadest towards the carinal
end: most of the specimens, _but not all_, have on the under sides
of their compartments rugged pillars depending from beneath the alæ,
for the purpose, apparently, of supporting the much depressed shell.
This much depressed variety attains a larger basal diameter (but not
a greater bulk or internal capacity) than any other variety, namely,
sometimes three quarters of an inch. The great peculiarities of this
variety result, apparently, from its much depressed form, deeply
corroded not folded walls, and considerable diametric growth; from
the latter cause the alæ are largely developed; as I can find neither
internally nor externally any fixed diagnostic character I have not
hesitated to rank this form as a variety. Poli found his specimens
mingled with the ordinary _C. stellatus_, on the shores of Sicily;
and I collected at St. Jago, in the Cape de Verde Archipelago, some
specimens nearly as well characterised, also associated with the
common variety.

The shell itself is dirty-white or gray, or brown: in some varieties,
however, the white is nearly pure: internally the parietes are
generally tinted dull purple. The corium of the sack is dark
greenish-black, with a white edge to the lips lining the aperture
between the opercular valves.

_Structure of Shell and Radii, &c._--The under side of the parietes
is either quite smooth, or marked with slight, branching, depressed
lines; or mamillated; or irregularly studded with large pores. I have
already alluded to the pillars, depending from the under sides of the
alæ in most specimens of _var. depressus_: these pillars tend to form
ridges, parallel to the sides of the compartment, like those we shall
presently see in certain specimens of _C. scabrosus_. The radii are
very narrow, when best developed; their edges, when disarticulated,
can be seen, when examined by a strong lens, to be finely crenated.
The edges of the alæ are likewise very finely crenated.

_Scuta._--The outline of these valves varies considerably in
specimens taken out of the same group: we have either a nearly
equilateral triangle (fig. 1 _f_) or the tergal margin (1 _e_)
is much shorter than the other margins. There is always a deep
depression for the adductor muscle, and a small pit of very variable
depth for the lateral depressor. But the tergal margin offers
the greatest variability; here we see a very prominent articular
ridge or fold, having either a straight edge or a single or double
prominence (fig. 1 _e_-1 _h_). In specimens in the same group we
find considerable variation in these points; but the amount of
difference is sometimes so great, that I long hesitated whether
to rank some of the varieties as species. The _Terga_, likewise,
vary greatly in shape and width: in some of the commonest varieties
(and in _var. depressus_) the valve is very narrow, with the under
surface channelled or concave: in other varieties the valve is much
broader and flatter. The spur is but slightly developed. The crests
for the depressor muscles barely descend beneath the basal margin of
the valve. The articular ridge, in some varieties (as in specimens
from Madeira and the Cape de Verde Islands), is extremely prominent
and straight (1 _f_); in others, it is little prominent and deeply
sinuous (1 _h_). This great variability in the articular margins
of the scutum and tergum seems to be mainly due to the corrosion
to which these valves have been subjected, and their consequently
modified growth: in some specimens the articular ridge of the scutum,
and in others that of the tergum, has been largely developed, in
either case their mutual outlines being greatly affected.

_Branchiæ._--These are narrow, hardly at all plicated, elongated,
being about half as long as the sack. In a specimen from La Plata,
this organ ended rather more abruptly in a point than it did in other
specimens.

_Mouth._--The crest of the labrum is usually hairy, but in a specimen
from Bahia (Brazil) there were some very fine teeth. The palpi vary
somewhat in shape, and sometimes have a row of bristles along their
basal exterior margins. The mandibles usually have four main teeth,
the lowest one being confluent with the inferior pectinated angle: in
_var. depressus_, in the same individual, there were only three teeth
on one side of the mouth and five on the other; the lower main teeth
are laterally double, but generally one tooth of each pair is so
small and obscure as to be perceived with difficulty. In the maxillæ,
there are some large spines above the notch, and in the notch some
fine ones: in _var. depressus_, and in a cylindrical _var._ from La
Plata, there was quite a tuft of small spines above the notch.

_Cirri._--The outer surface of the pedicel of the second cirrus
bears a tuft of long, fine, plumose hairs: the terminal segments of
the rami of this cirrus sometimes (as in the La Plata specimens)
support a clump of coarsely pectinated spines. In specimens having
six segments in the shorter ramus of the second cirrus, the shorter
ramus of the third cirrus had fifteen segments. The two rami of the
third cirrus are usually equal in length and in the number of their
segments; but in the Brazilian specimen there were fifteen segments
in the posterior, and twenty-six in the anterior ramus; in another
specimen, fixed on a tropical Perna, there were in the two rami of
this third cirrus eighteen and twenty-four segments. In the three
posterior pairs of cirri each segment carries either four or five
pairs of main spines: the segments vary a little in the degree to
which they are elongated, being most elongated in the var. from La
Plata, with an elongated shell.

_Varieties._--It will have been observed, that the shell, in the
specimens from several distant quarters of the world over which this
species, as I believe, ranges, differs considerably in external
aspect: so do the opercular valves; and so do the parts of the
mouth and cirri: but I cannot make out that these differences are
coordinated. Thus, _var. depressus_, which is so entirely different
from the others in appearance, differs only internally in the
presence of a tuft of fine spines above the notch of the maxillæ;
and this character is found in the La Plata variety, which, as far
as the shell and opercular valves are concerned, is at the other end
of the scale of variation. Again, _var. fragilis_, from Charlestown,
presents, in the animal's body, hardly any difference. The Brazilian
specimens, which in the shell and operculum offer only quite common
characters, have the remarkable peculiarity of a considerable
difference in the length and number of the segments in the rami of
the third cirrus; they, also, have the segments of the sixth cirrus
considerably elongated, and the labrum finely toothed. Of these
peculiarities one alone, namely, the inequality in the rami of the
third cirrus, but in a lesser degree, is common to the specimens
adhering to the tropical Perna, which had a shell very unlike the
Brazilian variety, but which, on the other hand, differed scarcely in
a single character from some other specimens from an unknown tropical
sea, in which the rami of the third cirrus were quite equal. The La
Plata specimens differ most in internal characters, viz., in the
tuft of fine spines above the notch of the maxillæ, in the coarsely
pectinated spines on the tips of the second pair of cirri, in having
the segments of the sixth cirrus much elongated, and in the apex of
the branchiæ being abruptly pointed; yet in the shell and operculum
they were identical with certain Mediterranean varieties. From these
several facts, I must believe that all the widely distributed forms
here grouped together, do really belong to the same species.

2. CHTHAMALUS ANTENNATUS. Pl. 18, fig. 2.

_Shell conical, generally smooth: when not deeply corroded of a pale dirty flesh-colour: sutures always distinct: radii, when present, with their sutural edges quite smooth._

_Hab._--New South Wales, (Moreton Bay, 27° S.; Sydney; Twofold Bay),
Van Diemen's Land (Hobart Town). Attached to littoral rocks and
shells; Mus. Brit., Cuming, Darwin.

_General Appearance and Structure of Shell._--Shell conical, rather
smooth; when not much corroded, of a pale dirty flesh-colour; often
covered by membrane; sometimes deeply corroded, extremely rugged,
and then of a brown colour; in this condition not much punctured,
as generally is the case with _C. stellatus_. Sutures almost always
quite distinct; rarely the shell becomes cylindrical with the sutures
obliterated. Orifice moderately elongated, sub-hexagonal. Radii
rather narrow, but not so narrow as in _C. stellatus_, smooth, with
their upper margins very oblique: when disarticulated their edges
are quite smooth. The edges of the alæ are sometimes crenated, and
sometimes not so, being only marked by lines of growth; they are
often rather thick. The parietes are usually rather thick, with their
internal surfaces smooth, and not mamillated, as is so often the case
with _C. stellatus_. The largest specimens which I have seen, were .6
of an inch in basal diameter.

_Opercular Valves._--These are hardly distinguishable from those of
_C. stellatus_. The only very slight difference which I can point out
is, that the crests for the tergal depressores are less spread out,
and depend rather more beneath the basal margin of the valve; and
lastly, that the surface of the tergum, just above these crests, is
rather prominent.

_Branchiæ_: these are oblong; taper but little, and have a broad
rounded end: they are scarcely plicated.

_Mouth._--The crest of labrum is hairy: the palpi are square, and
have no bristles along their basal exterior margins, but long ones
at their truncated ends. The mandibles have three or four main teeth
apparently single: the inferior coarsely pectinated portion is short.
The maxillæ are deeply notched.

_Cirri._--The first and second pairs, and portions of the third, are
darker coloured than the three posterior pairs. The rami in both of
the first two pairs are slightly unequal in length. The third cirrus
is much longer than the second: in a specimen in which there were
six segments in the shorter ramus of the first and second pairs,
there were twenty segments in the posterior and shorter ramus of
the third cirrus; and in this same individual there were no less
than forty-nine segments in the anterior ramus. In another specimen
(Pl. 29, fig. 2) the number of segments in the two rami of the
third cirrus, was 20 and 41; in another, the numbers were 18 and
53; in several other specimens the numbers varied in about these
proportions; but in one single specimen the numbers were equal.
Not only did the number of segments thus vary in the two rami,
but likewise the arrangement of the spines on the segments in the
anterior and longer ramus; in some specimens the spines on all the
segments were arranged in a single circle, and then the organ had a
specially antenniformed appearance: in other specimens, some of the
lower segments (in one case thirteen in number) had the spines placed
in regular pairs precisely as on the posterior ramus, and as on the
three posterior pairs of cirri. Under the genus I have pointed out
the resemblance between this structure and that occurring in certain
Macrourous Crustaceans. The pedicel of the third cirrus had its
spines more crowded and irregular than on the three posterior pairs
of cirri. The segments in the latter vary in bearing either three or
four pairs of main spines. The whole dorsal surfaces of the lower
segments of the several posterior cirri are serrated in an upward
direction by short spines, but to a variable degree.

3. CHTHAMALUS CIRRATUS. Pl. 18, fig. 4 _a_, 4 _b_.

_Shell white or gray: sheath and opercular valves generally clothed by fimbriated membrane: tergum, with its basi-carinal angle depending and pointed._

_Hab._--Peru, Chile, Chiloe, Northern Chonos Islands. Attached to
littoral rocks, and sometimes to littoral shells, often mingled with
_Chthamalus scabrosus_; Mus. Brit., Cuming, Darwin.

_General Appearance and Structure of Shell._--Shell dirty white or
gray: sometimes tinted pale purple within; irregularly conical, or
much depressed, or cylindrical and much elongated. Generally much
corroded, sometimes well preserved and covered by membrane. Orifice
rather large, of variable shape. Sutures often quite obliterated.
Radii when developed narrow, with their sutural edges, as well as
those of the alæ, generally very finely crenated, but to a variable
degree. The membrane lining the sheath and covering the opercular
valves, is remarkable from each zone being fimbriated; for this
expression is more correct than to say that the membrane bears a row
of spines, though the fimbriæ do approach in character to spines;
sometimes, though rarely, the fimbriæ are branched. The largest
specimens which I have seen (from Coquimbo and Valparaiso) were half
an inch in basal diameter, and some of these were so much elongated
as to be one inch in height.

_Scuta._--The scuta are rather narrow: they have a somewhat peculiar
appearance, from the articular furrow being wide, and from the
articular ridge projecting with a uniform curvature: the pit for the
lateral depressor muscle has some minute crests, of which I have seen
traces in the foregoing species. The _Terga_ vary somewhat in shape:
they have the basi-carinal angle of the valve, where the narrow
crests for the depressores are placed, pointed and dependent, and
the surface of the valve above these crests is prominent. Altogether
the opercular valves have a sufficiently distinct character to be
recognised without much difficulty.

_Mouth._--The crest of the labrum is not toothed; the palpi have long
hairs along the exterior basal margin. The lower main teeth of the
mandibles are plainly laterally double. _Cirri._--The pedicel of the
second cirrus is extremely broad, and on the exterior margin supports
a tuft of very long, finely plumose spines: in some specimens each of
the lower segments of the anterior ramus of this cirrus bore one or
two very large spines, doubly and extremely coarsely pectinated. In
two specimens the rami of the third cirrus were of equal length: but
in one specimen (from Iquique, Peru), having seven segments in the
shorter ramus of the first and second pairs of cirri, the posterior
ramus of the third pair had fourteen segments, and the anterior ramus
twenty-two segments. The posterior cirri have segments carrying five
pairs of main spines: the dorsal surfaces of the lower segments are
serrated.

4. CHTHAMALUS FISSUS. Pl. 18, fig. 6 _a_, 6 _b_.

_Shell brownish, plicated; orifice twice as long as broad: tergum triangular, equilateral, with the basal and carinal margins slightly protuberant._

_Hab._--California, attached to _Lottia grandis_. Peru(?); Mus. Brit.

_General Appearance and Structure of Shell._--Shell globulo-conical,
irregular, with the walls much folded. Colour brownish. Sutures
generally distinct in young specimens, and nearly obliterated in
full-grown individuals. Radii, when present, very narrow. The orifice
of the shell, in full-grown specimens which have their summits a
little worn, is narrow, much elongated, about twice as long as wide,
oval or ovate, with the rostral end the narrowest: the elongation of
the orifice offers almost the only character by which this species
can be externally recognised. The lateral compartments are rather
wider than usual in proportion to the rostro-lateral compartments.
Basal diameter of largest specimen .2 of an inch.

_Scuta_, elongated transversely, with the pit for the adductor muscle
bordered on the under side by an adductor ridge rather more prominent
than usual in this genus. _Terga_, triangular, equilateral, with
the margins slightly curved and protuberant: the basal margin is
regularly and equably curved from one end to the other.

Neither the _Mouth_ nor _Cirri_ offer any peculiar characters
distinct from the genus. I may mention, however, that the crest of
the labrum is toothed, and that the segments of the posterior pairs
of cirri support five pairs of main spines.

The characters by which this species differs from _C. stellatus_ and from the other species, consist almost exclusively in the triangular and equilateral terga, and in the much elongated orifice of the shell; and these differences I believe to be of specific value. I must, however, confess that I have examined one young specimen attached to a _Pollicipes elegans_, in which the orifice was not nearly so much elongated, and in which the terga were not so equilateral, with the basal margin not quite equably curved, but more protuberant on the scutal than on the carinal side: from an examination, however, of only one specimen, and that a young one, I cannot decide on its specific nature.

5. CHTHAMALUS DENTATUS. Pl. 18, fig. 3 _a_-3 _c_.

CHTHAMALUS DENTATUS. _Krauss_ (!). Die Südafrikanischen Mollusken,
1848, tab. 6, fig. 27.

_Shell dirty white or brownish: sutures formed by interlocking teeth: tergum with the carinal margin protuberant._

_Hab._--South Africa, Natal; West Africa, Loanda and the Gold Coast;
West Indies (?). Attached to ships' bottoms and to littoral shells,
and to _Tetraclita serrata_, _Balanus perforatus_, and _amphitrite_;
often attached to _Balanus tintinnabulum_ and _amphitrite_ on ships'
bottoms.

_General Appearance and Structure of Shell._--Shell dirty white,
pale brown, or gray: conical, moderately depressed: walls either
broadly and irregularly folded (fig. 3 _a_), with the surface
corroded, or (when attached to ships' bottoms and sometimes to other
Cirripedes) narrowly and regularly folded (3 _b_), with the surface
well preserved, smooth, and generally covered by thin brown membrane.
These latter specimens generally have the shell more steeply conical,
with the orifice rather smaller, and the radii broader, than in
the first-mentioned specimens, which are attached to coast-rocks
and shells, and have had their summits worn down. The sutures in
all cases are tolerably distinct, and have their edges toothed and
interlocked: the crenations are visible before the compartments are
disarticulated, when viewed either internally or externally, but
occasionally they are obscure. The radii, when best developed, are
rather narrow, and of equal width on both sides of the sutures, with
their summits rounded: their surfaces are finely ribbed transversely,
each rib corresponding with, or rather forming a point of, the
toothed edge. On the under side these teeth usually are a little
hollow or are pitted: the radii, in fact, may be said to be folded,
like the parietes, only more symmetrically and narrowly, so that the
points in the opposed edges interlock. The edges of alæ are serrated,
but more finely than the radii. The parietes are rather thin, with
their under surfaces generally smooth. The sheath does not descend
far down the shell. The colour of the corium lining the sack and the
animal's body varies considerably, being either almost black or pale
purple; and the specimens adhering to ships' bottoms are internally
almost white. Of these latter specimens, I have seen some .6 of an
inch in basal diameter: of corroded specimens attached to littoral
shells, I have not seen one quite .4 of an inch in basal diameter.

_Scuta_, with the articular ridge very prominent: the pit for the
adductor is deep, and there are generally some distinct, though
minute, pits for the lateral depressores. The _Terga_ (fig. 3 _c_)
have the articular ridge very prominent; and the carinal margin is
rather more arched and protuberant than in the other species.

_Mouth._--The crest of the _labrum_ is toothed: the palpi are short,
truncated, with long spines arising from their ends, and along the
basal exterior margin. In the mandibles the first tooth is seated
rather far from the succeeding teeth: the inferior part is coarsely
pectinated: the maxillæ are deeply notched. The tips of second pair
of _Cirri_ have many coarsely pectinated spines: the shorter ramus
had six segments, whilst the shorter ramus of the third pair had
eighteen segments: the segments on the posterior cirri carry five
pairs of main spines.

_Branchiæ, &c._--These consist of a double fold, the outer one being
the largest, and the inner semi-circular, as has been described under
the genus. In a young specimen, only one tenth of an inch in basal
diameter, the branchiæ consisted of a single fold; in a specimen a
little larger, there were two folds, but these were of equal size:
ultimately the outer fold increases in size so as to become nearly
double the inner fold. The _Ovarian tubes_ are remarkable from their
large diameter. I was surprised to observe in the specimen only one
tenth of an inch in basal diameter, that the larvæ were ready to
escape. On the prosoma, there are some longish _hairs_ arranged in
short rows, and some few on the membrane lining the sack, and some on
the opercular membrane and valves.

It may be seen in Pl. 18, fig. 3 _a_, and 3 _b_, that I have here united two varieties considerably different in external aspect: I have done this without hesitation, inasmuch as there are intermediate forms, and as the differences are analogous with those so commonly occurring in sessile cirripedes; dependent on whether or not the specimens have been exposed to corrosion. I have seen both varieties from Natal, and both from the west coast of Africa; although the smooth, well-preserved, narrowly plicated varieties seem more common in western than in southern Africa. With respect to the range of the species, I have seen a specimen from the West Indies, but it was the variety which so commonly adheres to ships' bottoms. This variety often arrives alive in British ports; and I have seen a specimen picked up dead on the beach near Dublin.

6. CHTHAMALUS HEMBELI. Pl. 18, fig. 5 _a_-5 _d_, _e_.

EURAPHIA HEMBELI. _Conrad._ Journal Acad. Nat. Sc. Philadelphia, vol.
7, 1831, Pl. 20, fig. 6.

_Shell dull reddish purple: sutures, when not obliterated, formed by interlocking teeth: basis sometimes rendered calcareous by the inflexion of the parietes: scutum with two or three furrows extending down the middle of the valve._

_Hab._--California, near S. Diego, according to Conrad. Mus. Brit.,
Cuming.

I have seen five, old, large specimens, from an unknown locality, with their whole surfaces deeply corroded, and with most of the sutures obliterated; and three separated valves of a young specimen. From these materials, imperfect as they are, I feel no hesitation in identifying this species with the _Euraphia Hembeli_ of Conrad, which is remarkable in several respects, and especially from being gigantic in size, compared to other members of its sub-family.

_General Appearance and Structure of Shell._--The young specimen
(fig. 5 _b_, about .7 of an inch in basal diameter) consists only of
the carina, and the two lateral compartments; but these, as far as
I can judge, resemble the specimen figured and described by Conrad,
which was two inches in diameter. Shell depressed, spreading, surface
moderately smooth, covered by brownish membrane: shell itself pale
dull reddish-purple. The radii are not very narrow, with their
summits rounded and very oblique: their edges are toothed, and their
external surfaces are transversely ribbed, in correspondence with
the interlocking points of the sutures. On the internal surface, the
toothed suture is not visible, except near the base of the shell,
owing to the overlapping of the alæ. The alæ have oblique summits,
which are slightly notched owing to the upturned prominent lines of
growth. The parietes are thick; their basal internal surfaces are
rugged, with slightly branching ridges.