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.