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Show 1903.] FROM EAST AFRICA AND ZANZIBAR. 369 rhinophores are bent backwards. The foot is fairly broad: it is grooved anteriorly, and the upper lamina is notched and developed into fairly ample flaps on each side of the division. The oral tentacles are digitate, and white with yellow ends. On the white labial cuticle are two small yellow patches, measuring 1 millimetre in length in the largest specimens. They are composed of an irregular collection of rods, similar to those which form the labial armature of the Discodorids, but can hardly be described as plates since the outline is ill-defined and the texture loose. The radula consists of about 45-55 rows, containing about 80 teeth, on each side of the naked rhachis, over which the innermost teeth close so as to render it invisible. The teeth (PI. XXXIII. fig. 4, a k b) are of the ordinary hamate shape and all alike, except that the innermost are distinctly smaller. At the outer end of some, but not all the rows, is found a small degraded tooth. The stomach is free from the hepatic mass, and the lower part is somewhat muscular and laminated internally. The genitalia are remarkable for the structure of the glans (PL XXXIII. figs. 6 & 7), which is long, twisted spirally, and provided with two rows of tubercles. The central nervous system (PI. X X X I I I . fig. 8) is much concentrated, as in Asteronotus, and the different ganglia cannot be distinguished. All m y specimens were found adhering to the underside of stones in a manner suggestive of sedentary habits. The animal is able, however, to swim well upon occasion with a motion somewhat resembling that of a sole. It has also some power of self-mutilation, and can cast off portions of the mantle, though it does so less readily than some allied forms. The branchiae are very sensitive, and retract if the shadow of a hand is allowed to fall on them. The dorsal papillae are kept in constant motion. It is extremely difficult to determine the true affinities of this species. It. has the general form and soft pointed papillae of Thordisa, and to that genus I think it had better on the whole be referred. But it has also a rudimentary labial armature, a concentrated nervous system, and a peculiar conformation of the genitalia. In this last point it offers some, but not complete, analogies to Phialodoris, in which, however, the back is minutely granulated and not covered with papillae. 12. TRIPPA AREOLATA (A. & H.). [A. & H., "Notes on a Collection of Nud. Moll, made in India," Tr. Z. S. iii. 1864, p. 119.] TWT O specimens, one from Mombasa, the other from Wasin. Alder and Hancock's figure gives a good idea of the living animal, but hardly emphasises sufficiently its extraordinary resemblance to a piece of old worm-eaten sponge Though conspicuous enough when placed by itself in a basin, it is invisible in its natural haunts, among sponges and seaweeds. Both my specimens were detected by touch only, not by sight, and I suspect that the creature is really common. PROC ZOOL. SOC-1903, YOL. II. No. XXIY. 24 |
