The two species united under this genus agree in having only four compartments, and in these having a strong tendency to become confluent; but they resemble each other hardly in any other respect, more than do all the species of the present sub-family. [Chamæsipho columna] differs from all the other [Chthamalinæ] in the structure of its second pair of cirri, and [C. scutelliformis] differs from all in its shell,—namely, in the small size of the rostrum, with its alæ but little developed, and in the very peculiar apertures in the three other compartments. Hence this genus can hardly be considered a very natural one, though I could not introduce the two present species into [Chthamalus], or into any other genus, without doing still more violence to the principles of classification followed throughout this work. [Chamæsipho] bears nearly the same relation to [Chthamalus], as [Tetraclita] and [Elminius] do to [Balanus].
1. [CHAMÆSIPHO] COLUMNA. Pl. [19], fig. [3 a]-[3 c].
LEPAS COLUMNA. Spengler. Skrifter Naturhist. Selbskabet, b. 1, (1790), Tab. 6, fig. 6.
Sutures, excepting during early youth, generally obliterated both externally and internally: tergum with small pits for the attachment of the depressor muscle.
Hab.—New South Wales, Tasmania, New Zealand; extremely common; attached to littoral shells and rocks; often associated with [Chthamalus antennatus] and [Elminius modestus]; and in New Zealand, often thickly coating [Elminius plicatus].
I have identified, with some doubt, the present species with the Lepas columna of Spengler, obtained from Otaheite, as no description is given by him of the opercular valves, and more especially as Spengler’s specimens were an inch in height and seven lines in width, which is much larger than any of the many specimens seen by me: from Spengler’s clear description of the structure of his shell, it evidently belongs to the present genus.
General Appearance and Structure of Shell.—The sutures separating the four compartments are generally, excepting at an early age, quite obliterated, both internally and externally, the shell in this case consisting of a single piece, with its summit and opercular valves always much worn. Occasionally the sutures are preserved, and then the four compartments are seen to be of nearly equal sizes. The orifice is always broadly oval, with the carinal end the broadest; and it often approaches closely to circular. The upper part of the shell is frequently steeply conical, with the lower part spreading and folded; sometimes deeply folded. Very young shells are apt to be remarkably smooth. The radii appear never to be developed: the inside of the shell is smooth. The colour is either blackish-green (this being the tint of the corium lining the sack), with the upper part gray from disintegration; or the lower part is brown, from the investing membrane, the shell itself being pale coloured. This species seems particularly liable to grow crowded together; often covering rocks and shells with a honey-combed layer. The basal diameter of some of the largest specimens was .3 of a inch. In Mr. Cuming’s collection, however, there is an Australian specimen .55 in diameter and .3 in height, which is, moreover, remarkable from the projecting, extremely rugged, overlapping, dark-coloured layers of growth, which surround the lower part of the shell: we have seen that Spengler’s specimens, said to have come from Otaheite, are even broader and considerably higher.
Scuta: from the disintegration which the valves have undergone, the scuta and terga are externally seen to be locked together by a deeply sinuous articulation. The Scuta have a wide articular furrow and a very prominent articular ridge; but the exact outline of these parts varies greatly, very much as in the genus [Chthamalus].