OCR Text |
Show 1 9 0 4 .] FROM EAST AFRICA AND ZANZIBAR. 2 9 7 spread out, and 4*5 high when they are closed and folded together. The colour is yellowish green with black spots within and without, the borders having disappeared. The shape and other external characters are exactly as in the specimen just described. The teeth are also similar but a trifle more bent: there are 16 in the radula, and about 15 of various sizes in the heap. I think these specimens must be referred to Elysia (Pterogastron) marginata Pease, although his description is somewhat deficient in details. In view of the fact that the teeth of the animal examined resemble those of E. nigrocincta, as described by Bergh, and that the coloration is clearly very variable, it is probable that both E. nigrocincta and marginata are varieties of a protean species ranging from green spotted with black, but without a coloured border, to green with or without black spots, and a more or less continuous single, double, or triple border. E l y s ia d u b ia , sp. n. (Plate XVII. figs. 14-17.) Four specimens from Chuaka, found on Zoster a at low springtides. The animals were dark green with a few spots of dull, light blue. They were about 6 mm. long and 3 broad when at rest, but when crawling become narrower and more elongated. They can also swim on the surface of the water foot uppermost, As preserved, the specimens are of a uniform dark green, and have somewhat the appearance of a minute Aplysia, as the wings do not reach to the end of the body but terminate separately, leaving a distinct tail. The tentacles have become mere knobs, but were apparently of a fair size in life. The foot is very distinctly divided from the body by a ridge. The pericardium is continued into a long median ridge down the centre of the body. At about the point where the wings end it bifurcates. From each side of this central ridge issue seven or eight vein-like ridges, much as in Placobranchus. The radula consists of 14 teeth and about 20 in the heap; they are elongate and slender. The basal part is nearly as long as the hook and there are no denticulations. The specimens are perhaps immature. If Elysiella is regarded as a separate genus, these specimens should probably be referred to it, but Bergh (Beitr. zur Kenntniss der Aeolidiaden, viii. 1886, p. 17) seems doubtful as to the validity of the genus and its definition. For the present I think it simpler to refer this form to Elysia. E X P L AN A T IO N OF TH E PLATES. P l a t e X V I . Fig. 1 Phyllidia nobilis, dorsal view (p. 282). 2. Hervia lineata, dorsal view (p. 286). 3. „ „ one of the cerata. 4. Facelina lineata, dorsal view (p. 288). 5. „ „ one of the cerata. 6. Stiliger varians, three teeth (p. 290). The outline of the middle tooth is coloured red for distinctness. 7. Elysia marginata, dorsal view with wings open (p. 296). 8. ,, „ dorsal view with wings closed and body elongated, |