1903.] PROM EAST AFRICA AND ZANZIBAR. 369 



rhinopliores are bent backwaixls. 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, contain- 

 ing 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 & V) 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 fi-om the hepatic mass, and 

 the lower part is somewhat muscular and laminated intei-nally. 

 The genitalia are remarkable for the structure of the glans 

 (PI. XXXIII. figs. 6 & 7), which is long, twisted spirally, and 

 provided with two rows of tubercles. The central nervous system 

 (PI. XXXIII. fig. 8) is much concentrated, as in Asteronotus, 

 and the difierent ganglia cannot be distinguished. 



All my 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 branchiaj are very 

 sensitive, and retract if the shadow of a hand is allowed to fall on 

 them. The dorsal papillfe are kept in constant motion. 



It is extremely difiicult 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 ofiers some, but not complete, 

 analogies to Phicdodoris, 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.] 



Two 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 con- 

 spicuous 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, Vol. II. No. XXIY. 24 



