_Hab._--Attached to Gorgoniæ, West Coast of Africa. Tubicoreen, near Madras, (Dr. Johnston), associated with _B. navicula_. Mediterranean (?). Mus. Brit., Cuming, Stutchbury. _Fossil._ Coralline Crag; Mus. S. Wood. I must premise, with respect to the nomenclature of this and the three following quite distinct species, that in the published descriptions no allusion is made to any one of the characters by which alone they can be distinguished: hence I have been guided by geographical probabilities in assigning the specific name of _calceolus_ to the present species, as Ellis's specimens came from the Mediterranean; and that of _galeatus_ to the North American and West Indian specimens, as Linnæus' original specimens (according to a statement by Spengler) came from the West Indies. I have assigned new names to the two remaining East Indian species. I may here add that Spengler ('Skrifter af Naturhist.' 1 B, tab. 6, fig. 3, 1790) has described, under the name of _B. cassis_, an allied form attached to the _Gorgonia placomus_ from the seas of Norway; but I do not believe that it is the same with our present species. _General Appearance._--The degree of elongation of the shell in its rostro-carinal axis varies considerably (3 _a_, 3 _b_): the elongation is due to the production of the rostrum and of the corresponding end of the basal cup. These two portions of the shell always form together an angle, and sometimes an acute angle, whereas in all the many specimens which I have seen, the carina and the carinal end (or heel) of the basis together form a straight line; yet I should not be surprised if this end of the shell was sometimes produced. The surface of the shell is smooth, or sometimes marked with very minute projecting points: it is almost always covered by the horny bark of the Gorgonia. The colour is either dull purplish-red or dull purple, with obscure longitudinal stripes, and often more or less transversely banded with white. The rostrum is either white or very feebly tinted, being always paler than the rest of the shell: the radii are usually paler than the parietes, and are sometimes white: the carinal end of the basal cup is tinted of the same colour with, but rather paler than, the compartments. The orifice is rather small compared to the shell, and nearly heart-shaped. The carino-lateral compartments are about one-third of the width of the lateral compartments. The shell is very strong, and the sutures resist the action of boiling caustic potash. The largest specimen which I have seen was .7 of an inch in extreme length, and under .25 in extreme breadth.