Part 48

_Mouth._--The palpi are furnished with a row, extending along the whole basal exterior margin, of very long upwardly pointing spines; on their upper edges there is a brush of small spines. The edge of the labrum is clothed with extremely fine spines, and is furnished with a few minute teeth. The mandibles have four teeth, and the lower end is broadly rounded and coarsely spinose: the second and third teeth are double at their points, and between the second and third, and again between the third and fourth, there is a small intermediate tooth.

Regarding the _Cirri_, I have nothing especial to remark.

_Geographical Distribution._--I have examined nine sets of specimens, having localities attached to them: three from off New South Wales; two off the Cape of Good Hope; two from the west coast of South America; and two marked only "South Sea." Hence I am led to conclude that this species is confined to the southern hemisphere, or if it extends into the northern hemisphere, it is probably only in the Pacific Ocean. I do not believe (though so stated in some works) that this species occurs on the shores of Europe. It seems often to be associated with Tubicinella. Some specimens thus associated, sent by Mr. Bennett to Professor Owen, were said to have been attached to the _Balæna australis_.

2. CORONULA DIADEMA. Pl. 15, fig. 3, 3 _a_, 3 _b_; Pl. 16, fig. 1, 2, 7.

LEPAS DIADEMA. _Linn._ Systema Naturæ, 1767.

---- ---- _Chemnitz._ Conch., vol. 8, Tab. 99, figs. 843, 844.

BALANUS DIADEMA. _Bruguière._ Encyclop. Method., n. 164, fig. 13, 14 (1789).

CORONULA ---- _De Blainville._ Dict. des Sc. Nat. (1824), Tab. 117, fig. 4.

---- ---- _Leach._ Encyclop. Brit. Suppl., vol. iii, 1824.

---- ---- _Chenu._ Illust. Conch., Plate, fig. 3.

---- ---- _Burmeister._ Beiträge zur Naturgeschichte der Rankenfüsser, 1834, Tab. 2, fig. 1-14, 18.

_Shell crown-shaped, with longitudinal convex ribs, having their edges crenated; orifice hexagonal: radii moderately thick, very broad: terga absent or rudimentary._

_Hab._--Attached to whales, in the Arctic Seas; United States and Great Britain; Gulf-Stream, Atlantic Ocean; New Zealand(?).

_General Appearance._--As previously remarked, owing to the fulness of the generic description, minute details on structure, excepting those characteristic of the present species, need not here be given. The crown-like shape of the shell is well expressed by its name of _Diadema_, but the crown tends to pass into a cylinder. The radii are extremely broad. The orifice is large, and neatly hexagonal: when the operculum is removed the whole inside of the cup-formed shell can be seen at once, for the flat membranous basis is much smaller than the orifice. The under side of the shell is deeply concave. The outside of each compartment is formed by broad, rounded, and somewhat prominent, rarely divided, ribs (_i. e._ the transverse ends of the folded walls); these ribs are closely united together by finely serrated lines of junction (Pl. 16, fig. 1, _f_). Their surfaces outside are delicately striated longitudinally, and plainly crossed (more plainly than in the foregoing and the next species) by irregular, transverse ridges, especially in the lower part of the shell. The largest specimen which I have seen was two and a half inches in diameter and two in height.

_Scuta._--These are placed close together at the rostral end of the orifice, and are imbedded in the brownish, tough, longitudinally plicated, horny substance, which extends far beyond both ends of the valves. In outline (fig. 3 _b_) they are mitre-shaped, or rounded and sub-triangular, a little curved, and more or less elongated, being most so in young specimens; they are, however, less elongated and rather more massive than in _C. balænaris_. _Terga_,--these seem entirely absent in most specimens; but in one (fig. 3 _a_) I found a rudiment, namely, a short thin plate of shell, barely visible to the naked eye, extending parallel and near to the tergal margin of the scutum. The lips of the aperture of the sack are prominent, and highly so towards the carinal end.

_Structure of Shell and Radii._--Owing to the shell not spreading much at the base, new folds in the walls are much seldomer formed, and therefore the external longitudinal ribs (_i. e._ the terminal transversely elongated loops), are much seldomer divided, than in _C. balænaris_ or _reginæ_; even rather large specimens sometimes having only the original eighteen folds.[125] When new folds are formed, only one is formed on one, viz., the rostral, side of each suture, instead of on both sides, as in _C. balænaris_. The inner ends of the folded walls, surrounding the basal membrane, are narrow, instead of being almost square, as in _C. balænaris_. The lower edge of the sheath, which projects freely, descends almost to the level of the basal edges of the walls. The outer ends of the folded walls, forming the transverse loops, are internally filled up solidly by calcareous matter, instead of by septa forming tubes, as in _C. balænaris_. The radii (Pl. 16, fig. 2) are a little thicker in the lower and outer than in the upper and inner part of each compartment; in the middle, they do not reach the sheath by about half the thickness of the compartment, and consequently they are separated from the plates (_c′′_ in fig. 1 and 7) on which the alæ rest, by large chambers (_v_ in fig. 7), which extend up to nearly the apices of the compartments: the extent, however, to which the upper ends of these chambers have been solidly filled up, varies a little. The sinuous plates forming the main portion of the compound radii are rather thinner and closer together than in _C. balænaris_. The alæ are thick, being thickest in the middle part, and there equal the radii in thickness; their lower margins are very short compared with their upper margins, hence they are almost wedge-formed.

[125] These should be counted on the under side of the shell, for if counted from the outside, the number would be thought to be twenty-four, as on the side of each compartment bordering the radius, a half-fold has the appearance of being a whole fold, so that in appearance six folds are added to the real number of the folds. This caution is necessary whatever the number of real folds may be, that is, whether or not the original eighteen folds have been increased by subsequent plications. These remarks, also, are applicable to the other species.

_Mouth._--The teeth and fine hairs on the labrum are sometimes obscure, and sometimes plain: close outside the bottom of the medial notch, there is a small hard prominence. The palpi are broad; on their basal exterior margins there is a short row of spines, which do not equal in length the width of the palpi, and therefore are not so long as in _C. balænaris_. The mandibles have five main teeth, of which the second and third show only an obscure rudiment of being double; between these two teeth, and between the third and fourth tooth, there is a small intermediate tooth: the inferior angle is narrow, rounded, and spinose. The extremity of the apodeme of the maxillæ is expanded.

_Cirri._--I have only to remark, that the pedicel of the first cirrus is extremely broad, and that the rami are set on in an unusually crooked manner: the basal segment of the shorter and broader ramus of this cirrus has its dorsal surface produced into a plate fringed with very fine hairs.

_Geographical Distribution._--I have received only four specimens with certain localities attached to them: namely, the Arctic Seas of Scandinavia; the coast of the United States, and of Britain; and the Gulf-Stream. There is also a specimen in the British Museum, sent by Mr. Stephenson, mingled with shells of Mollusca from New Zealand; but a Coronula, procured from a floating whale in the early part of the outward voyage, might so easily be sent home with specimens subsequently collected in another county, that I do not as yet fully admit that this species is an inhabitant of the Southern Pacific Ocean: I am less willing to admit this, from suspecting that _C. reginæ_ in the Pacific, replaces the _C. diadema_ of our Northern Seas.

3. CORONULA REGINÆ. Pl. 15, fig. 5; Pl. 16, fig. 4.

_Shell globulo-conical or depressed, with longitudinal, much flattened ribs, having their edges crenated, and their surfaces striated and granulated; orifice hexagonal: radii thin, not exceeding one fifth of the thickness of a compartment: terga absent._

_Hab._--Attached to whales, Pacific Ocean; Mus. Cuming, Stutchbury, and Darwin.

I have seen eight specimens of this form--two in Mr. Cuming's collection, one of which was procured at Iquique in Peru, the other from an unknown locality; one was given me in Chile, and was stated to have come from the Pacific; two others are in Mr. Stutchbury's collection, from unknown but distinct localities, and three in a group in the British Museum. These eight specimens, of which six were collected separately, all strikingly agree in general aspect and in details of structure, so that I can easily recognise the shell, and can at once pick out a single compartment, when mingled with those of the two foregoing species; nevertheless, the differences are so small, that I at first hesitated whether to name the species; but, upon reflection, I am convinced that it is distinct. _Coronula reginæ_ is much more closely related to _C. diadema_ than to _C. balænaris_, and I suspect that it replaces in the Pacific the former of these two species.

_General Appearance_; shell conical, straight-sided; some specimens being nearly as much depressed as _C. balænaris_, and considerably more depressed than any variety of _C. diadema_; other specimens being globulo-conical, but rather less globular than the ordinary form of _C. diadema_. I may here remark, that shape is of more value in this genus, in which the shell is attached to the yielding skin of whales, than in those genera in which it adheres to rocks. The orifice is neatly hexagonal, and the whole internal cavity, when the opercular membrane is removed, can be seen from one point of view, owing to the contraction of the lower part of the cavity and small size of the basal membrane. The surface of the shell is smooth, but has, even up to the summit, a peculiar frosted appearance, different from that of the foregoing species, caused by the longitudinal striæ being rather more distinct, and being crossed by beaded, very delicate transverse lines of growth. The ends of the transverse loops, forming the exterior surfaces of the compartments, are much flattened, even more so than in _C. balænaris_. The lines of junction between the loops, are finely serrated, as in _C. diadema_; and internally they are solidly filled up, instead of being formed into a set of tubes by longitudinal septa, as in _C. balænaris_. The under side of the shell, with its folded walls, presents an appearance intermediate between the variable appearance of this part in the above two species.

The sutural edges of the radii (Pl. 16, fig. 4) offer by far the most remarkable character, in their thinness from top to bottom; for they hardly exceed one fifth of the thickness of the compartment, measured from the external surface to the base of the sheath; hence a very large cavity is left between the radii and alæ: in the thickness of the radii the three species already described form a series, _C. reginæ_ at one end and _C. balænaris_ at the other. The sinuous plates, forming the lower part of the radius, are coarser and stand rather further apart than in _C. diadema_. The alæ are thick, and have the same outline, being narrow at their basal margins and broad at top, as in _C. diadema_, with their sutural edges similarly constructed: the basal edge of the sheath likewise projects freely.

_Operculum._--This resembles most closely that of _C. diadema_. There are no rudiments of terga. The scuta cannot be distinguished from those of _C. diadema_.

_Mouth._--The labrum has a row of inwardly curved little teeth along the whole crest, and these I did not notice in _C. diadema_: there is only a trace of the prominence on the outside at the bottom of the central notch. The hairs on the basal exterior margin of the palpi are moderately long. The mandibles have five teeth. In the _Cirri_, the first pair resembles in its peculiar structure those of _C. diadema_. In the sixth pair, however, the segments support only three pairs of main spines: but the specimen was not very large, and probably in old specimens there would have been four pairs.

_Summary._--The present species differs from both the foregoing only in its rather more conical and straight-sided outline, smooth, frosted surface, and in the narrowness of the sutural edges of the radii, and consequent large size of the chambers between the radii and alæ. It resembles _C. diadema_, as far as the shell is concerned, in the external ribs or transverse loops having their lines of junction serrated and in being solidly filled up--in the shape of the orifice and of the internal cavity of the shell--in the shape and structure of the alæ--and in the basal edge of the sheath being free. It comes nearer to _C. diadema_ than to _C. balænaris_ in the structure of the radii. It differs from _C. diadema_, and comes nearer to _C. balænaris_, in the external ribs being flattened, instead of being convex, and in the lines of growth being very delicate. But as it resembles _C. diadema_ in the several foregoing characters of its shell, in the opercular valves, in all parts of the mouth (excepting the labrum), and in the cirri, it is very much more nearly related to that species than to _C. balænaris_.

4. CORONULA BARBARA. Pl. 15, fig. 6.

CORONULITES DIADEMA (?) _Parkinson_, Organic Remains (1811), vol. 3, p. 240, Pl. 16, fig. 19.

_Shell (probably) crown-shaped, with longitudinal convex ribs, having their edges crenated, and their surfaces rugged, both externally and internally, with transverse ridges: radii moderately thick; the spaces between the radii and the alæ solidly filled up._

_Fossil_ in Red Crag, (Bawdsey and Sutton); Mus. S. Wood and Geological Society.

The species here described, though near to _C. diadema_ and easily confounded with it, I have no doubt is distinct. I owe to the kindness of the Rev. Mr. Image an examination of the original specimen figured by Parkinson; and in Mr. Stutchbury's collection there is a similar and more perfect specimen; both of these resemble _C. diadema_ in general form, but have been too much worn to be positively identified. The following description is drawn up from some compartments collected by Mr. Searles Wood, belonging certainly to three, and probably to four individuals, one of which was young; as these specimens agree in all essential respects, I feel pretty confident that the characters, by which the present species differs from _C. diadema_, are of specific value.

_Structure of Shell._--The longitudinal ribs on each compartment (_i. e._ the terminal transverse loops), are convex and prominent, as in _C. diadema_, but they are crossed by more prominent ridges of growth than even in the roughest varieties of that species, so that the surface of the shell is more rugged. In the three previous species, the surface of the wall entirely round the cavities occupied by the whale's skin, is striated only by longitudinal very fine lines; but here, the outer portion, or that (fig. 6) formed by each transverse loop, is crossed by transverse ridges of growth, like, but less prominent than, those on the external surface of the shell. The minute teeth, along the lines of junction between the transverse loops, are here less regular, and can hardly be said to exist; for the two edges are locked together by what may be more strictly called minute zig-zag ridges than teeth. The exact number of the circumferential plications in the walls is variable in the same manner as in the three foregoing species. The sutural edges of the radii are about as thick as, or rather thicker than, in _C. diadema_. As in this latter species, and in _C. reginæ_, each ala rests, not on the internal surface (as in _C. balænaris_, and in all other Balanidæ) of the radius, but on a special plate; but in _C. barbara_, instead of a deep chamber, running up to the apex of the compartment, being left between the radius and ala, this part is filled up almost entirely by solid shell. Although the extent to which this chamber is filled up varies a little, and although its depth varies a little in _C. diadema_, yet there is a marked difference between the specimens of this latter species, in which the chamber is most filled up, and those of _C. barbara_, in which it is least filled up. The alæ are thick, as in _C. diadema_, and their sutural edges have a central ridge, sending off on both sides sinuous ridges. The basal margins of the alæ are not short compared with their upper margins, and therefore the whole ala is not wedge-formed; and in this rather important respect _C. barbara_ resembles _C. balænaris_ (Pl. 16, fig. 3), and differs from _C. diadema_ (fig. 2). The lower edge of the sheath does not seem to have projected freely,--in this respect, also, resembling _C. balænaris_. From the basal margin of the alæ not being narrow, and from the inner ends of the folded walls being, as it would appear, also broad, I have little doubt that the cavity in which the animal's body was lodged, resembled in shape that in _C. balænaris_, the membranous basis being larger than the orifice of the shell.

Opercular valves unknown.

_Summary._--This species is more nearly related to _C. diadema_ than to the others; but in some points, just specified, it resembles _C. balænaris_. The characters by which it differs from all the species are, firstly, the more prominent transverse ridges on the external surface of the shell, and more especially on the surfaces bounding the outer sides of the cavities occupied by the epidermis of the whale. Secondly, the character of the teeth, or rather ridges, along the lines of junction between the transverse loops. And, thirdly, the spaces between the radii and the plates on which the alæ rest, being solidly filled up.

_Species Dubiæ._

The _Coronula bifida_ is an Italian tertiary species, so named by Bronn, in his "Italiens Tertiär-Gebilde" (1831), p. 126. It is very possible that this may be identical with _C. barbara_, but Bronn does not seem to have been aware of the absolute necessity of giving minute details in his descriptions of fossil cirripedes. The chief character of _C. bifida_ is thus given:--"Eine tiefe Furche oder Spalte theilt die Längenrippe von oben herab bis zur Hälfte, welche bei der sonst ähnlichen _C. diadema_ entweder ganz fehlt, oder nur zuweilen kurz angedeutet ist." Had it been stated that the longitudinal ribs were divided from the middle down to the base, instead of from the top to the middle, the description would have been intelligible to me, though the character thus afforded would not have been of specific value, as this dividing of the ribs occasionally occurs in all four species, and is produced by the formation of new folds to the walls.

9. _Genus_--PLATYLEPAS. Pl. 17, fig. 1 _a_-2 _b_.

PLATYLEPAS. _J. E. Gray._ Annals of Philosophy, (new series), vol. x (1825).

CORONULA. _De Blainville._ Dict. des Sciences Nat. (1824).

COLUMELLINA. _Bivona_ (fide _Philippi_). Nuovi generi, &c. di Molluschi, Palermo (1832).

_Compartments six, each bilobed and inwardly produced, so as to form six midribs, which support the outwardly convex, membranous basis._

_Distribution_, throughout the tropical and warmer temperate seas. Imbedded in turtles, sea-snakes and manatee.

This small genus, consisting of three species (though I have named only two), is a very natural one, yet closely allied to Coronula. Most authors have united these genera, but in doing so they destroy two very natural little groups. Platylepas, moreover, when all its characters are considered, has as good a claim to be generically separated from Coronula, as has Tubicinella,--a genus universally admitted. I shall presently recur to this subject.

_General Appearance._--The most remarkable character, and which gives a peculiar aspect to the whole shell, is that each of the six compartments has a medial fissure or fold; the shell thus consisting of twelve lobes. Each fold extends from the summit to the base of the shell, and is produced inwards in the shape of a midrib (Pl. 17, fig. 1 _a_). The membranous basis is supported by the basal edges of the six midribs, and is thus rendered convex. As the midrib on the rostrum would have interfered, if fully developed, with that part of the animal's thorax which I have called the prosoma, it is of less size than the other midribs; and from this same cause the whole rostrum is pushed a little on one side, generally to the left, so that the shell is not perfectly symmetrical. The midrib of the carina is less than the lateral midribs. The orifice is oval, and is more or less plainly indented by six angular points,--the worn-down summits of the six midribs. The narrow elongated opercular valves stretch from one end of the orifice to the other. The rostrum is much broader than the carina: the lateral compartments are but little broader than the carino-lateral compartments. The radii are narrow, though variable in width. The general shape of the shell varies much in the same species, being either much depressed, or rather steeply conical; either circular, or more commonly oval. The (so called) epidermis is usually persistent in the lower part of the shell. The shell itself is white. The basal diameter of the largest specimen of _P. bissexlobata_ was nearly three-quarters of an inch.

_Structure of the Parietes, Radii, &c._--The walls of the shell in _P. bissexlobata_ are permeated by minute pores, and have exactly the same structure as in Coronula; the pores being completed by the union of ledges on the outer sides of the longitudinal septa, and the latter have little knobs formed on them at each period of growth. In _P. decorata_ the walls are solid. Each compartment, as already stated, has a deep nearly medial furrow, the sides of which are closely pressed together, thus forming the midribs, and thus differing from the furrows in Coronula, which not being pressed together, form cavities on the under side of the shell. The inner longitudinal margin of each midrib is thickly coated by a layer of shell, and is thus rendered much more prominent than it would have been if formed exclusively by the inward folding of the wall. The upper part of each midrib forms a slight, longitudinal ridge (fig. 1 _d_) on the sheath, having become encased by the sheath during its downward growth. Owing to the small size of the midrib of the rostrum, there is scarcely any ridge on the sheath of this compartment. The sheath does not descend half-way down the walls in _P. bissexlobata_, but further down in _P. decorata_; but perhaps the thickened inner margins of the midribs may be considered as the downward prolongations of the sheath, and on this view the sheath descends actually to the basal membrane. The radii are narrow: their edges have simple septa, with the interspaces filled up solidly. The alæ have their sutural edges smooth.