Art. XXV.—On a new Genus of Opisthobranchiate Mollusca.
[Read before the Auckland Institute, 16th August, 1880.]
In some tide-pools near the Tamaki heads, in Auckland harbour, I have repeatedly obtained specimens of a curious little Opisthobranch, that appears to me to be not only undescribed, but also to form the type of a new genus. The following is a description.
Melanochlamys cylindrica, nov. gen.
Body elongated, almost cylindrical, 1–1¼ in. long; colour a deep rich velvetty black. Cephalic disc narrow oblong-quadrate, slightly expanded in front, so as to project over the foot and mouth, truncate behind. Mantle small, entirely concealing the shell, at its posterior end 2-lobed and with a large gaping orifice. Foot large, with ample side-lobes, which are folded up to the sides of the head-disc and mantle, leaving, however, the back exposed. Shell quite internal, triangular, spire minute, inner lip with a small spoon-shaped projection. Branchiæ minute, situated far back on the right side under the mantle. Gizzard very large and muscular, without calcareous plates. Odontophore apparently wanting.
I assume that the proper position of this animal is with the Philinidæ, with which it agrees in most of its characters. It differs, however, in having no odontophore, and in the gizzard not being strengthened with calcareous plates. Aglaia (of Renier), appears to be its nearest ally; but I am unable to place it in that genus, as it differs from the species figured in Adams' “Genera” in being much more elongated, in the cephalic disc being larger and projecting beyond the foot, in the branchiæ being smaller and always concealed by the mantle, and in the side-lobes of the foot being closely appressed to the sides of the animal, and not spreading.
In addition to the specimens collected by myself I have examined some obtained by Mr. G. M. Thomson near Dunedin, and kindly forwarded to me by Prof. Hutton. Very probably it will be found to be common in suitable localities all round our shores.