Chapter XXIII: Introduction (19)

This is a distinct and well-defined genus. Several authors have confounded it with Coronula, but this has been owing to an entire misapprehension of the structure of the shell in the two genera. In Coronula, the parietes are very thin, and are so deeply folded as to appear like rays or septa connecting the outside of the shell (the expanded ends of the folds) and the internal surface of the shell, but the open spaces between the folds are occupied by the epidermis of the Whale, and are external to the cirripede. In Chelonobia, the parietes are remarkably thick; hence the plates or septa, connecting the outer and inner lamina, are of unusual length; and the spaces between them, though of course internal with regard to the cirripede and occupied by the ovaria, have been compared to the spaces external to and between the folded walls of Coronula. There is but little special affinity between these genera; and I regret that they have come to be placed one after the other in this work: but the elongated opercular valves,--the thick and double opercular membrane,--the weak depressor muscles,--and the peculiar manner in which the scutum is articulated by the aid of a horny projection to the tergum, may indicate some real but slight affinity to Coronula; the many points of difference, however, in the structure of the shell and of the opercular valves, and especially in the cementing apparatus of the basal membrane, and in the branchiæ, all prove that the genera are very distinct. The singular structure of the rostrum, which, in fact, consists of three compartments externally blended together, and which three correspond in all essential respects to the rostrum and two rostro-lateral compartments in the Chthamalinæ, offers a very striking point of identity with that sub-family; but neither in the mouth, cirri, or other part, can I detect any other evidence of this relationship. Having so far discussed the affinities of the genus, I may add, that the three species, though decidedly distinct, are closely and nearly equally related to each other.

_General Appearance._--The shell is generally depressed, and broadly oval or almost circular; in _C. testudinaria_ and _caretta_, it has a massive appearance: the surface is generally smooth, or, when disintegrated, finely striated: the colour is white. The six compartments do not differ much in size: the rostrum is rather larger than the carina, and the lateral compartments, than the carino-lateral compartments. It is remarkable that in _C. caretta_ (Pl. 14, fig. 2), even in specimens which have not grown crowded together, the compartments are almost invariably placed rather unsymmetrically, the rostrum and carina not exactly facing each other.[121] The shell, though so thick and massive, yields easily along the lines of suture. The radii are moderately wide, or narrow, or not at all developed, being represented by mere sutures: in this latter case, in _C. caretta_, the orifice of the shell is enlarged, in the same manner as we have seen in some species of Balanus and Tetraclita, by the gradual wearing away of the upper part of the shell. In _C. testudinaria_, the radii have a singular notched structure (fig. 1 _a_), and the whole shell a star-like appearance. The orifice is not filled up by the elongated opercular valves,--a considerable extent of opercular membrane being visible on the two sides. The largest specimen which I have seen, namely, of _C. testudinaria_, was nearly two and a half inches in its longer diameter.

[121] In Mr. Stutchbury's collection there is a specimen of _C.
testudinaria_ in which there are only five compartments, one of the
lateral compartments having been aborted; of this I have seen no
other instance in any genus.

_Structure of the Parietes._--The parietes are of unequalled thickness, especially in the first two species of the genus. From the outer lamina (see Pl. 14, fig. 4, and the section in Pl. 15, fig. 1), numerous vertical plates extend inwards, alternately to a less or greater distance, some of them reaching to the inner lamina: these answer to the longitudinal parietal septa in other genera, and the elongated cavities between them (which occur in _C. testudinaria_ and _patula_) answer to the parietal tubes or pores. The radiating plates or septa have their sides finely channelled, and their basal edges generally slightly sinuous and always finely toothed. The interspaces between the plates in the uppermost part of the shell are filled up solidly, and, in _C. caretta_, even down to near the basis: in this latter species, the plates are irregular and much broken up, so as in parts to consist of little, separate, flattened points. In _C. patula_, the inner lamina of the parietes (_b_, in fig. 4. Pl. 14) can be best made out to be distinct from the sheath (_e c e_ in fig. 4, and _c′_ in the section of _C. testudinaria_, fig. 1, Pl. 15). The sheath in this genus descends in a very remarkable manner to the basal membrane, and has its basal edge toothed like the basal edges of the radiating septa. The inner lamina itself does not descend to the basal membrane. In _C. testudinaria_, the inner lamina is of great thickness; but in the section, (fig. 1) owing to its having been taken high up, the inner lamina, (_b_), is not distinct from the shelly matter deposited between the septa. In _C. caretta_, the line of separation between the inner and outer laminæ can in no part be distinguished, owing to the interspaces between the septa having been solidly filled up, close down to the basis.

_Sheath._--The layer of shell surrounding the internal cavity (_e c e_, fig. 4, Pl. 14), and extending down to the basal membrane, I have called the sheath, owing to its being distinctly continuous with the innermost layer in the upper part of the shell, to which the opercular membrane is attached: this can be best seen by examining the alæ in the separated compartments of _C. patula_. The sheath is not only remarkable from thus descending to the basal membrane, but in _C. testudinaria_ and _patula_ from its lower edge being perforated by arched channels (under _c_, in fig. 4), allowing thick ribbons of corium to reach the interspaces between the radiating septa. There is one central arch or channel in the middle of the lower part of the sheath of each compartment, and one on each line of suture, the sheath being a little hollowed out on both sides of the sutures. As the rostrum, as far as its internal structure is concerned, consists of three compartments, we have altogether in the shell eight compartments and eight sutures, and consequently altogether sixteen arches through the lower part of the sheath, allowing sixteen thick ribbons of corium to penetrate the parietes, and thus likewise reach the radii. There is, however, sometimes a little variation in the number of these arched channels. The upper part of the sheath is transversely marked by zones of growth, to the lower one of which the opercular membrane is attached. The line of attachment is not low down the sheath.

_Radii and Alæ._--The radii, when the compartments are disarticulated, present a remarkable structure, from appearing to consist of a distinct inner and outer portion. The radius normally consists of an inner and outer lamina, united by septa parallel to the basis; but here the inner portion is formed by a central ridge (_a a_, fig. 5, Pl. 14), sending off on both sides little septa, often sub-branched; it is of nearly uniform width; and there is no distinct inner lamina. The outer portion (_b_), which often equals or exceeds in thickness the inner portion, is, in fact, the normal outer lamina, developed to an unparalleled degree. In most Cirripedes the edge of the radius is received in a slight furrow in the opposed compartment, the lid of which furrow is narrow, and matches the outer lamina of the radius; here the lid of the recipient furrow is very broad, and resembles the outer lamina of the radius in all its characters. In order to allow of growth between the _thick_ opposed edges of the outer lamina of the radius and the lid of the recipient furrow, the two surfaces are finely dentated (look in fig. 5, under the pits, marked _b_), almost like the crown of a molar tooth; thus allowing films of corium to enter. The structure here described is common, in a greater or less degree, to all three species, but is best seen in _C. testudinaria_. In this species, moreover, (fig. 5, _b_), the outer lamina, instead of being smooth and of either equal or gradually increasing thickness from top to bottom, is generally, but not always, (fig. 1 _a_), deeply pitted or notched in transverse lines, the outer lamina being thus rendered alternately thicker and thinner, and so formed into transverse ridges and valleys. Hence the lines of suture become toothed, the points of the teeth facing each other, and not interlocking. In the transverse section, fig. 1, Pl. 15, of the same species, taken high up across the shell, (_f_) is the pitted outer lamina, and (_e_) the inner portion of the radius. Although the radii are thus specially added to in thickness, they are not so thick as the very thick walls, and hence the lines of suture form furrows more or less deep. The _alæ_ are of moderate thickness, and have their sutural edges crenated by fine transverse septa.

_Rostrum._--I have already alluded to the peculiar compounded structure of this compartment, unlike anything we have as yet seen.[122] The thin outer lamina is quite continuous, and shows no trace of the triple nature of the compartment; as may be seen by comparing the drawing (Pl. 14, fig. 1 _a_) of the shell of _C. testudinaria_, with the transverse section (Pl. 15, fig. 1) of the same species: in this latter figure, _a_ is the outer lamina, and B A B the three compartments of the rostrum. But when the outer lamina is worn away, as is always the case with the upper part of the walls in _C. caretta_ (Pl. 14, fig. 2), the two fissures separating the three compartments of the compounded rostrum, are plainly exhibited on the outside of the upper part of the shell. On the internal surface, the sutures separating the three compartments are always open, except in the upper part of the sheath, above the attachment of the opercular membrane, where they are partially obliterated by a thin continuous layer of shell. That these three portions of the rostrum are in their essential nature compartments, is well shown in _C. patula_ and _testudinaria_, by the sheath or inner lamina having loopholes or channels (such as before described) in the middle of each, and on each line of suture. From the number of these channels, seven altogether, (the two between the compound rostrum and lateral compartments being counted,) the sheath of the compound rostrum is reduced to mere flattened pillars between the several channels. By slight violence, the rostrum breaks into the three portions; and the sutures between them are found to be marked on both sides by sinuous, slight, calcareous ridges, those on opposite sides locking into each; these represent the septa on the edges of the radii and alæ and their recipient furrows, in the ordinary compartments. The outline of the middle compartment of the three (best seen in section Pl. 15, fig. 1, A), much resembles that of the carina; in fact, if we suppose the growth of the two alæ of the carina to have been arrested, no essential difference can be pointed out: in this rudimentary compartment, therefore, we have a rostrum, characterised as in the sub-family of the Chthamalinæ. In the two little rostro-lateral compartments, moreover, (B B), a slight swelling on the side opposite to the large existing radius, shows that if the development of these compartments had not been prevented, each, probably, would have had, exactly as in the Chthamalinæ, a radius on both sides. In the introduction to the Balanidæ, I have argued, from the structure here described and from some other facts, that in the Balaninæ the rostrum is composed of the three anterior compartments, which we see in the Chthamalinæ, indissolubly united together; hence in Chelonobia the middle one of the three partially-blended compartments is properly the rostrum, and those on the sides the rostro-lateral compartments.

[122] My attention was first called to this peculiar structure of
the rostrum by Mr. Stutchbury.

_Basis._--The basal membrane extends under the thick walls to the outside. I was not able to make out the whole cementing apparatus. The main trunk is remarkable from its small diameter, (_f f_ in fig. 2, Pl. 28), and from the distance at which the cement-glands stand apart. Each gland gives rise to a pair of cement-ducts, which tend to run in parallel groups; these ducts repeatedly bifurcate, occasionally inosculate, and decrease in diameter; they debouch and allow the cement to escape at numerous points, placed at irregular distances, on the edges of each new slip of the basal membrane.

_Opercular Valves._--These are elongated; they do not fill the orifice of the shell; they are attached by a strong opercular membrane a little way down the sheath. The opercular membrane is generally double, for the last-formed membrane is not immediately moulted as soon as a new one is formed, as generally happens in Balanus. Externally, the valves are marked by rather rugged, broad zones of growth. The _Scuta_ are elongated in the line of the orifice of the sack; the occludent margin (Pl. 14, fig. 1 _b_) is much inflected, and generally sinuous; along this inflected portion a distinct square-edged ridge runs, which widens from the apex downwards. The depression for the adductor muscle is very deep: there are no pits or crests for the other muscles. When the scutum is thoroughly cleaned and all the membrane removed by caustic potash, the tergal margin is marked by a slight articular ridge and furrow. This articular ridge is very remarkable from supporting a prominent, flattened crest (fig. 1 _b_), composed of hard, yellow, horny membrane, which overlaps the inner surface of the tergum, and exactly corresponds, in shape and purpose, with the calcareous articular ridge, when best developed in other genera. Beneath the basal and generally slightly sinuous exterior margin of the valve, that is, the margin to which the opercular membrane is attached, a slight ledge depends (fig. 1 _d_), which narrows off towards the rostral end of the valve. I should have thought that this had been a depending adductor ridge, as in several species of Pyrgoma, had there not been a nearly similar ledge beneath the middle part of the basal margin of the tergum. The _Tergum_ is mitre-formed, with the summit more or less truncated, and with the carinal margin generally more sloping than the scutal margin: near the carinal margin there is a slight furrow (fig. 1 _d_), sometimes difficult to be distinguished, with the lines of growth curving down to it on each side, and consequently with a very slight, but variable, corresponding projection on the basal margin. This furrow and slight projection, there can be hardly any doubt, represent the spur, though here placed close to the carinal instead of to the scutal margin, as in other genera. The tergum has a small articular ridge, against which the overlapping horny articular ridge of the scutum abuts. There are no crests for the tergal depressor muscles. Altogether the scuta and terga are very peculiar. A portion dissolved in acid exhibits no tubuli. On the opercular membrane there are no hairs. The rostral depressor muscles of the scuta are singularly feeble, each consisting of only one or two, or sometimes three or four, very thin ribbon-like fasciæ; the lateral depressores of the scutum are twice as strong as the rostral depressores; and the tergal depressores a little stronger than the lateral depressores. All these muscles are plainly marked with transverse striæ.

_Mouth._--The labrum is not in the least bullate, which character, as well as some others that follow, I specify on account of the apparent affinity of Chelonobia to the Chthamalinæ, as indicated by its rostrum. The crest of the labrum is notched, and on each side of the notch there is a long row of teeth, which, however, are sometimes worn away. The mandibles have five main teeth; all excepting the first being laterally double. The maxillæ are not notched. The outer maxillæ are bilobed on their inner sides.

_Cirri._--The four posterior pairs, in proportion to the size of the animal, are much elongated, and are remarkable from the number of their short segments. The rami of the first cirrus are a little unequal in length. The second cirrus is moderately short, with its segments rather broad and protuberant, and thickly clothed with spines. The third cirrus is of unusual length, being but little shorter than the fourth pair; its segments, however, are broad, and are thickly clothed with spines, as are the two segments of its pedicel: hence there is no real approach to that important character of the Chthamalinæ, namely, the similarity of the third with the three posterior pairs of cirri. The numerous segments of the fourth, fifth, and sixth pairs of cirri each support only two pairs of main spines; between each of these pairs there is a little tuft of fine intermediate spines; the upper of the two tufts on each segment is the longest. In a specimen of _C. patula_, in which there were fifteen segments in one ramus of the second cirrus, there were fifty segments in either ramus of the sixth cirrus. At the exterior bases of the pedicels of some of the anterior cirri, there are large tufts of finely plumose, delicate hairs.

_Branchiæ._--These are of large size: they consist of a single fold, much plicated and sub-plicated.

_Ovaria._--The ovarian tubes run into the parietes, and fill up the interspaces between the radiating septa.

_Range, &c._--The three species seem to range together, over the tropical and warmer temperate seas of the whole world. _C. patula_ and _testudinaria_ are found in the Mediterranean, and the former at Charleston, in the United States; I have not heard of specimens from any point further north. _C. testudinaria_ and _caretta_ live attached to turtles; whilst _C. patula_ always adheres to crustacea, to large and smooth gasteropod mollusca, and, I believe, sometimes to ships' bottoms. I have not heard of the discovery of any fossil species.

_Attachment._--_Chelonobia patula_ leaves no impression on the crabs and shells to which it is attached. I have seen only a few specimens of _C. testudinaria_ attached, and the carapaces of the turtle were not at all, or scarcely at all, indented by them. The case is very different with _C. caretta_, in which the shell, even of young specimens, is always, as far as I have seen, imbedded to some depth, and occasionally to a very great depth in the tortoise-shell. From the extreme hardness of the tortoise-shell, when dry, the imbedment appears more wonderful even than it really is. The younger shells have the appearance of having grown from within the carapace, and then of having burst through it, almost like little volcanos. I have seen only one very young shell (1/10th of an inch in external diameter) attached, and here there was nothing to countenance an idea which at one time occurred to me, namely, that the larva perhaps fixed itself in some little crack or cavity in the carapace, and there underwent its metamorphosis. I believe that the imbedment is effected simply by the sharp, growing, basal edges of the walls of the shell indenting the surface, and finally rupturing the outer laminæ of the tortoise-shell, through that same force by which the tender radicle of a plant penetrates very hard ground. As soon as the surface was once ruptured, the shell of the Chelonobia, growing outwards and downwards, would easily, like a wedge, turn up the laminæ of the tortoise-shell; and their ragged ends would surround the Chelonobia, as is seen actually to be the case. In the genus Coronula and its allies, which are attached to Cetaceans, we shall presently see, that the epidermis immediately under the downward growing shell, and apparently in consequence of the pressure thus exerted, is thinner than in the surrounding parts. In two specimens of _Chelonobia caretta_, imbedded much more deeply than usual--in one of which half the basal edge of the shell had fairly cut through the carapace, and in the other was on the point of effecting this--the tortoise-shell manifestly thinned out towards the line of yielding; now this, I suppose, must be attributed either to absorption, or to the living tortoise-shell being actually stretched till rendered transparent and ready to burst or until bursted. On the latter view of the tortoise-shell having been stretched, we must further suppose that the pressure has prevented fresh layers of tortoise-shell being deposited under the old and yielding laminæ. In one of the above two specimens, the walls of the Chelonobia were deeply folded, nevertheless the laminæ of the tortoise-shell followed every curvature, showing that, though now so rigid, during the slow imbedment of the Cirripede it must have been sufficiently pliant. A shell attached, as these two specimens were, could never be removed, and, whether dead or alive, would remain for ever imbedded in the tortoise-shell. Dr. R. Ball, of Dublin, informs me, that he has seen specimens in which the shell of the cirripede not only had penetrated the carapace, but likewise the underlying bone, and had even entered some way into the body of the turtle: it is well known that the tusk of a boar or the horn of a ruminant, when curving in abnormally, will sometimes penetrate deeply into the bones of the face or head; and this, I believe, is effected, not by the fracture of the bone, but by the absorption of the point pressed on: I conceive a similar process must have taken place in the curious specimens examined by Dr. Ball.

1. CHELONOBIA TESTUDINARIA. Pl. 14, fig. 1 _a_-1 _d_, fig. 5; Pl. 15, fig. 1.

LEPAS TESTUDINARIA. _Linn._ Syst. Naturæ, 1767.

VERRUCA TESTUDINARIA. _Ellis._ Phil. Transact., vol. 50, 1758, Pl.
34, fig. 12.

BALANUS POLYTHALAMIUS. _Bock._ Naturforscher, Stuch. 12, 1778, fig. 9.

LEPAS TESTUDINARIA. _Poli._ Testacea Utriusque Siciliæ (1795) Tab.
5, fig. 9-11.

CORONULA TESTUDINARIA. _Ranzani._ Memoire di Storia Naturale, Decade
1, (1820).

---- ---- _De Blainville._ Dict. des Sciences Nat., (1824), Tab.
117, fig. 2.

CHELONOBIA SAVIGNII (?) _Leach._ Encyclop. Brit. Suppl., vol. 3, 1824.

ASTROLEPAS ROTUNDARIUS. _J. E. Gray._ Annals of Philosoph. (new
series), vol. 10, 1825.

_Shell conical, depressed, heavy: radii rather narrow, depressed, generally notched on both sides._

_Hab._--Mediterranean; west coast of Africa; north-east coast of
Australia; Low Archipelago, Pacific Ocean; west coast of Mexico, 23°
N. Attached to turtles.

It is impossible to feel sure which of the three species of the genus Linnæus had in view, when describing his _Lepas testudinaria_; but as Spengler has well discriminated the following species under the specific name of _caretta_,[123] and Ranzani the third species under _patula_, the present name may, without question, be retained for the following species. In several respects this species is intermediate between _C. caretta_ and _patula_, but it can most conveniently be described first.

[123] I am indebted to Dr. J. E. Gray for having guided me to this
identification.

_General Appearance._--Shell strong, globulo-conical, depressed;
outline broadly oval; surface smooth, generally well preserved, but
when disintegrated, upper part finely striated; colour dead white;
orifice oval elongated, rather exceeding in length one third of the
longer basal diameter of the shell. The radii are rather narrow, and
deeply depressed; they have their summits square: their outer lamina,
as explained under the genus, on both sides of each suture is in most
specimens divided into teeth, the points of which face and touch
each other. These teeth or notches give quite a peculiar appearance
to the shell, and alone suffice to discriminate this species; they
are sometimes blunt and partially obliterated, but it is rare to
find a specimen in which some few teeth do not occur in some one of
the six radii. I have, however, seen two or three specimens with all
six radii perfectly smooth; in one of these the general shape of the
shell, without the aid of any internal characters, almost sufficed
to show that it belonged to the present species; but in another
specimen, which had unusually narrow radii, and the whole surface of
which had undergone considerable disintegration, and was consequently
striated, could only be distinguished from _C. caretta_ by internal
characters. I have seen several specimens having very irregularly
shaped compartments, but generally the appearance of the whole shell
is highly symmetrical, like a star; and the genus was appropriately
named by old Klein, _Astrolepas_. In some specimens, in Mr. Cuming's
collection, from the Low Archipelago, in the Pacific, taken off the
toe-nail of a turtle, the shape was almost cylindrical; the shell
almost resembling that of _Coronula diadema_. The largest specimen
which I have seen was 2.3 of an inch in basal diameter, but only .55
in height.

_Structure of Shell and Radii._--After the full generic description,
the only point to which I need allude is, that the radiating,
parietal septa, as well as the descending sheath, are much thicker
than in _C. patula_, and that their basal edges can be plainly seen
by the naked eye to be dentated with numerous points. The thickness
of these plates and of the sheath varies considerably. In _C.
caretta_, I may add, the plates are broken up into many separate
points, and in this species the descending sheath is not generally
perforated, excepting at the sutures, by loop-holes for the entrance
of ribbons of corium. The sheath and inner lamina of the parietes
in _C. testudinaria_, taken together, fully equal one third of the
entire thickness of the walls. Flattened cavities or tubes run up
between the parietal septa for about two thirds of the height of the
inside of the shell. With respect to the radii, I have only to add,
that the thickness of the inner portion relatively to the generally
notched outer lamina, varies considerably.

_Opercular Valves_ (fig. 1 _b_-1 _d_).--These closely resemble
each other in all three species, and have been almost sufficiently
described under the genus. The scutum has its occludent margin always
sinuous, but to a variable degree. In one specimen there was a deep
little pit at the rostral end for the rostral depressor muscle. The
terga vary considerably in shape, according as the basi-carinal
corner is more or less truncated. The external furrow, marking the
position of the rudimentary spur, varies much in distinctness,
chiefly depending upon its nearness to the carinal margin of the
valve.

_Mouth and Cirri._--The labrum sometimes has its teeth worn away.
The second pair of cirri, relatively to the others, is shorter and
thicker than in the two following species.

2. CHELONOBIA CARETTA. Pl. 14, fig. 2.

LEPAS CARETTA. _Spengler._ Skrifter, Naturhist. Selbskabet, Bd. 1,
1790, Tab. 6, fig. 4.

BALANUS CHELYTRYPETES. _Hincks_ (!) sine descript., Annals of Nat.
Hist., vol. 5, p. 333.

CORONULA SULCATA. _Chenu._ Illust. Conch., Tab. 1, fig. 1.

_Shell globulo-convex, extremely massive and heavy; upper part worn, sub-striated: radii either not developed or very narrow: parietes without cavities extending up between the interrupted, radiating septa._

_Hab._--West coast of Africa; northern Australia; common. Attached
to, and generally imbedded in, the carapaces of turtles.

_General Appearance._--Shell extremely strong, massive, heavy,
broadly oval, globulo-convex, though sometimes depressed; dirty
white: surface in the upper part always worn and disintegrated,
hence finely striated; in the lower part a little rugged, slightly
folded, and occasionally, in deeply imbedded specimens, much folded
or ribbed. Orifice oval, not at all angular, rather exceeding in
length one third of the basal diameter of the shell. Radii either not
at all developed, or very narrow; but even in the former case the six
lines of suture are plain; and in the latter case the radii lie at
some depth beneath the surface of the shell. It is remarkable that
the compartments are hardly ever arranged symmetrically, the rostrum
and carina not facing each other exactly; and this holds good in
specimens attached separately, without any apparent cause for this
want of symmetry. The largest specimen which I have seen was 2.1 in
basal diameter; and this, which was a steeply conical individual,
was 1.1 in height; and therefore nearly twice as high as an ordinary
large specimen of _C. testudinaria_.

_Structure of Shell and Radii._--The descending sheath and radiating
septa are of very variable thickness, and have their basal edges
finely dentated. The septa are not continuous, from the circumference
to the sheath, in unbroken plates, but are irregularly divided into
separate, often short portions, and even occasionally into mere
points. The sheath differs from that of the other two species in
having loopholes for the entrance of ribbons of corium only on the
eight lines of suture, and not (with rare exceptions) in the middle
of each compartment: this is evidently due to fewer filaments of
corium being here sufficient to supply the less deep interspaces
between the radiating septa; for in this species there are no
flattened cavities or tubes running far up the shell. The inner
lamina of the walls cannot be here distinguished, for a solid, flat,
calcareous surface extends from the circumference, between the
radiating septa, to the sheath. The sheath, had it not been from the
light thrown on this part by the other species, would have certainly
been mistaken for the inner lamina of the walls. The absence of the
flattened cavities or tubes extending up the parietes, seems to be
the least varying character; and serves to distinguish this species
from those worn and massive specimens of _C. testudinaria_, which
have narrow and not-notched radii.

In specimens in which the radii are not developed, no vestige of the
outer lamina can be detected, the lateral faces of the adjoining
compartments being closely pressed together; but in specimens in
which the radii have been developed and have grown, the outer lamina
of course is present, and is extremely thick, with the growing edge
having a branched and mammilated surface, as in _C. testudinaria_,
but with the external surface not pitted or notched as in that
species. The inner portion of the radius, whether or not developed,
has nearly the same appearance, consisting of rather thick transverse
septa, branching from a central ridge, which is sometimes obscure.

The _Alæ_ are remarkably little prominent, as least in those
specimens in which the radii are not developed, so that Spengler
seems to have thought that the structure of the shell was essentially
different from that of Balanus, which certainly is by no means the
case. The edges of the alæ are very thick, nearly as thick as the
inner portion of the radius.

The _Opercular Valves_ hardly present any essential difference,
compared with those of the other species; but the occludent margin
of the scutum is apt to be more sinuous, and its rostral end blunter
and squarer. The carinal end of the tergum is also squarer than in
any common variety of _C. testudinaria_; the external furrow or spur,
near the carinal margin, is very indistinct, and even sometimes is
quite absent.

Neither the mouth nor cirri present any deviations from the generic
character.

3. CHELONOBIA PATULA. Pl. 14, fig. 3 _a_, 3 _b_, 4.

CORONULA PATULA. _Ranzani._ Memoire di Storia Naturale (1820), Tab.
3, fig. 25-28.

ASTROLEPAS LÆVIS. _J. E. Gray_ (!). Annals of Philosophy (new
series), vol. 10, 1825.

VERRUCA CANCRI AMERICANI. _Ellis._ Phil. Trans., vol. 50, 1758, Pl.
34, fig. 13.

_Shell steeply conical, very smooth and light; orifice large, generally exceeding half the basal diameter of the shell: radii broad, smooth, only slightly depressed._

_Hab._--Mediterranean; Gambia, West Africa; Charlestown; Jamaica;
Honduras; Brazil; Australia. Attached to Crustacea, smooth univalve
shells, and apparently to ships' bottoms.

_General Appearance._--Shell white, very smooth, of little specific
gravity, steeply conical, but not high; orifice broadly oval,
polygonal, very large, namely, generally exceeding half the basal
diameter of the shell. The summits of the compartments are usually
perfectly preserved, pointed, and often a little recurved. The radii
are rather broad, very smooth, with their summits slightly oblique
and arched: they are seated only a little below the general level
of the parietes. I have seen one specimen rather more than one and
a half inch in basal diameter, but this is an unusual size; this
species not growing to so large a size as the two foregoing forms.

_Structure of Shell and Radii._--The walls are here thinner than in
the two foregoing species; and the basal surface of a compartment
rarely equals half the basal diameter of the internal cavity of the
shell, measured transversely to its longer axis. The radiating septa
are also much thinner, generally sinuous, and so finely dentated
along their basal edges, that the teeth can be clearly perceived
only by the aid of a lens. The interspaces between the septa run up
to nearly the summits of the compartments, and hence the lightness
of the whole shell. The inner lamina of the parietes is here not so
thick (fig. 4), and is more distinct from the descending sheath than
in the foregoing species. The sheath is thin, like the radiating
septa; the medial loophole in each compartment, for the entrance of
a filament of corium, is much wider than in _C. testudinaria_, for
it is generally as wide as the bordering plate on either hand; and
in not a few specimens, the medial loophole is so wide as hardly
any longer to deserve being so called, for the descending sheath
is reduced to mere flattened pillars or legs on the sides of the
sutures. Although the parietes are here not nearly so thick as in
the two foregoing species, yet as the radii stand but little beneath
the level of the parietes, the outer lamina of the radius has a
considerable thickness, and is sometimes separated from the inner
portion of the radius by an interval, in the same manner as in _C.
testudinaria_; and the growing edges of the outer lamina exhibit
traces of the same mamillated structure as figured in that species.

The _Opercular Valves_ are apt to be rather narrower and more
elongated than in the foregoing species, with the occludent margin
of the scutum generally, but not always, only slightly sinuous:
externally the scutum is sometimes feebly striated longitudinally. In
the tergum (Pl. 14, fig. 3 _b_) the longitudinal furrow is generally
plainer, from being more distant from the carinal margin, and the
rudimentary spur itself is more prominent.

The mandibles usually have five narrow teeth; but I have seen
one specimen having only four teeth, and with the inferior angle
truncated. The cirri present no particular character.

SECOND SECTION OF THE SUB-FAMILY OF BALANINÆ.

[_Scutum and tergum (when both are present) not overlapping each other, or articulated together; basis membranous; parietes often deeply folded, with the outer lamina, towards the basis, generally imperfect; each branchia composed of two plicated folds; shell attached to living vertebrata._]

8. _Genus_--CORONULA. Pl. 15, 16.

CORONULA. _Lamarck._ Annales du Museum, tom. 1 (1802).

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

CETOPIRUS (SED NON CORONULA). _Ranzani._ Memoire di Storia Naturale
(1820).

POLYLEPAS. _J. E. Gray, (Klein)._ Annals of Philosophy, (new series),
vol. 10, 1825.

_Compartments six, of equal sizes: walls thin, deeply folded, with the folds forming cavities, open only on the under side of the shell: opercular valves much smaller than the orifice of the shell._

_Distribution_, mundane, imbedded in Cetacea.

This genus and the three following, namely, Platylepas, Tubicinella, and Xenobalanus, have very considerable claims to be separated as a sub-family, as has been proposed by Drs. Leach and Gray. Although in structure and habits they are certainly closely related together; yet only few characters can be predicated of all four in common,--some characters failing in one genus and some in another. All four, however, differ from the foregoing genera in the opercular valves not being articulated together, being simply united by tough horny membrane; but Chelonobia makes some approach in this respect. All four have the branchiæ composed of a double fold; but this can hardly be considered a character of much weight, as may be inferred from the remarks made on this subject at p. 153 of the Introduction, where the differences of these four genera from the other genera of the family are discussed at some length. Altogether I have been led to conclude, though with much hesitation, that these genera had better not be separated as the sub-family of Coronulinæ.

Our present genus, Coronula, is closely related to Platylepas, and likewise to Xenobalanus, though this latter genus is so very different in external aspect that it might easily be mistaken for a pedunculated Cirripede. Lamarck and some other authors have placed the species of Chelonobia under Coronula, but this has arisen, as explained under that genus, from a misapprehension of their structure; the folded very thin walls in Coronula having been compared with the radiating septa of the very thick walls in Chelonobia. I may further add, that Coronula has been divided into two genera by Ranzani, on palpably insufficient grounds.

_General Appearance._--The three recent species of this genus have a very handsome and striking appearance. The shell is highly symmetrical, owing to the six compartments being of the same size and having exactly the same outline. The general shape is either depressed or, as expressed by the name, like a crown. The walls are longitudinally and slightly ribbed, owing, as we shall presently see, to their wonderfully folded structure; and the surface is marked by very fine longitudinal striæ, crossed by finely beaded lines of growth. Hence the walls offer a strong contrast in appearance with the six, smooth radii, of equal breadth. The symmetrically hexagonal, or rounded-hexagonal orifice of the shell is closed by a thick, nearly horizontal membrane, supporting, towards the rostral end, the small opercular valves, with a slit, having protuberant lips, in the middle, for the protrusion of the cirri. The opercular membrane is attached all round, but a short distance beneath the summit of the shell. In regard to size, I have seen a specimen of _C. diadema_ two inches in height and two and a half in diameter.

_Structure of the Shell._--The structure at first appears singularly complicated, and quite unlike that of any other Cirripede; but the whole results simply from the folding of the very thin walls, which in all essential respects are constructed like those in Balanus. In a young specimen of _C. balænaris_, having the orifice of the shell 2/10ths of an inch in diameter, I found the upper part of each compartment only slightly sinuous, not more so than is common in many varieties of Balanus, but more symmetrical, for each compartment had three slight furrows, making, for the whole shell, eighteen furrows. The ensuing changes during the growth of the shell will be best understood by looking at the diagrams _a_, _b_, _c_, in fig. 10, Pl. 15, which are supposed to represent the basal margins of the walls of a single compartment: (_a_) shows the simply sinuous wall of the young shell. As the shell grows, the furrows rapidly grow deeper and deeper (_b_), and wider and wider; at the same time, the folds or ridges between the furrows gradually become drawn out at their ends into transverse loops (_c_), the extremities of which ultimately become closely pressed together--the furrows being thus converted into cavities, extending from the top to the base of the compartments. This structure in the mature shell will be best understood by looking at the transverse or horizontal section (Pl. 16, fig. 7) of the rostral end of the shell of _C. diadema_, in which species the folding of the walls is simpler than in _C. balænaris_ or _C. reginæ_: the walls (_e_) are represented by a double line connected by little cross lines,--(_h_) being one of the transverse loops at the outer end of one of the folds, and (_f′_) one of the cavities between the folded walls, open at the bottom of the shell, and occupied by the epidermis of the Whale. The walls of the compartments, as here represented, (A being the rostrum, C C the lateral compartments, D D the alæ of the carino-lateral compartments,) are separated from each other by the broad radii; but if the section had been taken low down near the basis, the end of the folded wall of one compartment would have been separated from that of the adjoining compartment only by the close suture: this will be understood by a glance at the entire shell, given in fig. 3, Pl. 15. The rostrum of the same species, viewed from the inside, is shown at fig. 1, Pl. 16; here it may be observed, that the basal margin (_e e′ e′′_) of the folded wall is extremely oblique, the outer portion having extended downwards much more than the inner portion: this obliquity is more clearly shown in the lateral view (fig. 2) of a lateral compartment, for this figure will equally well serve for a lateral view of the rostrum (fig. 1), if the ala (_a′_) be supposed to be removed. The section of the rostrum in fig. 7, (A), will now be intelligible in relation to the view of the rostrum given in fig. 1, if it be borne in mind that the section has been taken high up, near the letters _a_, _b_, _c′′_ in fig. 1.

As above stated, the folds or ridges in the young shell become more and more transversely drawn out at their ends into the transverse loops, till the latter join and touch each other. In _C. balænaris_ the lines of junction are simple, though very close; in the other species, the ends of the transverse loops, where touching, are finely and elegantly toothed, and thus locked together. These teeth appear single when the shell is viewed either externally or internally, but when the walls along the lines of junction are forced apart, they are seen really to consist of transverse rows of minute teeth. These teeth are less distinct, forming only sinuous ridges in _C. barbara_ (fig. 6, Pl. 15); in all cases the teeth are formed by the modification of the very minute beads, which ornament the lines of growth on the external surface of the shell. In the rostrum of _C. diadema_, as seen internally (fig. 1, Pl. 16), the serrated and closely-fitting lines of junction (_f_) between the ends of the transverse loops of the folded walls are plainly shown. It is the more or less rounded surfaces of the transverse loops which give to the external surface of the parietes its longitudinally ribbed structure: the ribs are plainest in _C. diadema_, fig. 3, Pl. 15. The shell, in fact, as seen externally, consists of but an extremely small portion of the external surface of the whole length of wall, being exclusively formed of the transversely looped ends of the radiating folds, together with the radii. Owing to the ends of the transverse loops being so closely pressed together, the furrows are practically converted (as already remarked) into cavities, open only on the under side of the shell, and extending from the oblique bases of the compartments up to their apices; and these are invariably filled by the black epidermis of the Whale. Owing to this circumstance, the skin of the Whale has been mistaken by some authors for parts of the Cirripede! In _C. diadema_, in which the summit of the shell is often a little disintegrated, the whale's skin is often there exposed, forming three black spots at the top of each compartment. It should always be remembered that these flattened and deep cavities are furrows, which homologically ought to be open in longitudinal lines along the external surface of the shell, from the top to the bottom.

As the shell increases in diameter, each of the original eighteen transverse loops, forming the exterior surface of the shell, increases in breadth; and they would have had to increase extremely, had not some of the transverse loops become, during growth, divided into two or three new transverse loops, in a manner strictly analogous with the first formation of the eighteen folds in the young shell. In Pl. 15, fig. 7, 8, 9, we see how one of the circumferential transverse loops, by the formation of a medial furrow, or rather bay, becomes developed into two transverse loops; and it is rather important to observe that three new loops might equally well have been contemporaneously formed. By the repeated formation of new circumferential loops and the consequent formation of new folds, the wall of the shell, when old, especially in _C. balænaris_, becomes folded in a wonderfully complicated manner, as may be seen in Pl. 15, fig. 5, which is an exact tracing of the extreme basal edge of the wall of a shell of _C. balænaris_; to perceive the full amount of complication, it is advisable to trace the wall of any one of the compartments, from one suture (_s_) to another. In this figure the sutures are purposely drawn a little open. It may be seen that the new transverse loops, and consequently the new folds of the walls, have been, in this species, mostly formed in symmetrical order, on both sides of the six sutures; this results from the transverse loops on the sutures almost always giving rise contemporaneously to three new transverse loops. In _C. diadema_ the transverse loops on the sutures usually divide into only two new loops, one on the rostral side and one still remaining at the suture; hence the folding of the walls in this species is much less symmetrical. The number, however, of the transverse loops and the exact pattern of the folding is variable in all four species of the genus. I may further add, to show the complication of the folds, that in a shell of _C. balænaris_, having a basal diameter of two inches, and which had the walls as little folded as ever they are, yet I found, by careful measurement, that the entire basal edge of the wall, if stretched straight, would have extended for a length of fifty-two inches! Therefore, if the wall had not been folded, but had been simply circular, as in ordinary cirripedes, the basal diameter of the specimen would have been between sixteen and seventeen inches!

The central membranous basis is flat, but the bottom of the folded walls of the shell is concave, which is caused by the outer ends of the folded walls having grown at a greater rate than the inner ends. The concavity is deep in _C. diadema_; in _C. balænaris_ it is much less so, and here the inner hood-like ends of the folded walls are rather abruptly, but in a variable degree, produced downwards, generally even slightly beneath the level of the circumference of the shell; this fact is of interest in relation to the peculiar, depending, spur-like processes in the genus Platylepas. A lateral view of a compartment in both these species, is given in Pl. 16, figs. 2 and 3; and by supposing in each case a compartment to stand opposite, at a distance which may be judged of from fig. 5, the vertical sectional outline of the whole shell will be understood: in fig. 3 of _C. balænaris_, however, the inner hood-like ends of the folded walls are not produced so much downwards as is usual.

In the same manner, as the outside of the shell consists of the transversely expanded ends of the folded walls, pressed closely together, so the cavity in which the animal's body is lodged, is formed by the inner and less closely joined ends of the folds, lined by the thick sheath (_a_, fig. 1 and 7, Pl. 16), which latter extends down very near to the basal membrane. The cavity for the body, is small compared to the whole shell; in _C. diadema_ it is deeply cup-formed, with a small, flat, membranous bottom or basis; in _C. balænaris_ it is wider and shallower, with a broader bottom, and with the upper edges of the walls more inflected. In both species, the thick membrane connecting the opercular valves to the shell, is attached all round near the summit of the sheath. The uppermost portion of the sheath is not marked by concentric lines, as in most of the Balanidæ, owing to the opercular membrane not being, as we shall presently see, regularly moulted. A portion of a single wall, when closely examined, is found to be formed of an outer and inner lamina, united by longitudinal septa, and is thus permeated by minute, square, longitudinal pores,--exactly as in the normal structure of Balanus. The walls are extremely thin, and are striated longitudinally, owing to the slight projection, on both the inner and outer surfaces, of the longitudinal septa; they are thicker in the part forming the external transverse loops, being here, in _C. balænaris_, as much as 15/1000ths of an inch in thickness; but when forming one side of the spoke-like folds, the thickness is only 6/1000ths of an inch. The inner lamina is thicker, contrary to what is usual, than the outer lamina; the sharp tips of the longitudinal septa project a little beyond either lamina, giving to the basal edge of the wall a serrated outline. It is singular that the thin outer lamina is first formed as a rim or ledge on each side of the longitudinal septa; these ledges being not closely united for some little space up the wall, as is represented in the enlarged drawing of a bit of the basal wall of _C. diadema_, Pl. 16, fig. 6. The open clefts thus left are, of course, covered by the so-called epidermis, for otherwise the included threads of corium would have been exposed. Each fresh period of growth, in the case of _C. diadema_ (fig. 6) and _reginæ_, and to a certain extent in _C. balænaris_, is marked by little knobs on the longitudinal, slightly prominent, septa, and this prefigures an analogous strongly marked structure in Tubicinella. A fine thread of corium runs up each pore to the summit of the compartment; for these pores are not, as in Balanus, cut off by transverse calcareous septa, or have their upper ends solidly filled up with shelly matter. As, however, the summit of the shell in Coronula is sometimes disintegrated, the threads of corium within the pores would have been exposed, had not each thread formed for itself, as I suppose, a transverse membranous septum near the summit of the shell; at least this is the case with the larger pores of the radii. The walls, where closely pressed together in the spoke-like folds, are disunited at the extreme base, but above this they are firmly calcified together. A ribbon of corium runs along the basal edge of each spoke, and sends threads of corium up the parietal pores on each side, and its upper edge serves to deposit calcareous matter (homologous with the layers of the sheath) and thus to unite the two walls firmly together. In _C. diadema_, the walls of the terminal transverse loops are simply calcified together like the spoke-like portions; but in _C. balænaris_ the opposite sides of the loops are united by septa (see the transverse section in Pl. 15, fig. 2 _a_), making from five to eleven longitudinal tubes within each transverse loop; these tubes being larger than the parietal pores. When a piece of the shell is dissolved in acid, no tubuli can be discovered, which may be accounted for by the thinness of the walls; nor are there any spines on any of the external membranes. The number of the pores, in the parietes of a moderately-sized specimen of _C. balænaris_, I calculated was at 3400, each occupied by a thread of corium springing from the eighteen branched ribbons, diverging from the corium, surrounding the base of the sack. To this number must be added between 300 and 400 larger threads of corium running up the tubes in the transverse loops; and no less than about 2300 fringes and threads occupying the pores in the six radii: thus we see that the dermal system in Coronula is wonderfully complicated.