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.