68 MOLLUSCA. GASTEROPODA. 



Gen. 24. DORIS, Lam. Lin. 



Body oblong, plane, convex, or subprismatic, bordered all around 

 by a membrane, which extends to the head ; mouth anterior, 

 and below ; four tentacula ; two placed anteriorly on the 

 body in a hollow, and the two others near the mouth ; anus 

 towards the base of the back, surrounded by projecting, laci- 

 niated and fringed branchiae ; aperture for generation on the 

 right side. 



D. verrucosa, Cuv. Body ovate, oblong, convex, verrucose ; supe- 

 rior tentacula between two projecting lamellae. Inhabits Indian 

 seas An. Mus. iv. pi. 1, fig. 4, 5, 6. 



D. Argus, Lam. Body oblong, nearly smooth ; branchial plumes 

 about twelve in number ; colour lemon-yellow, slightly freckled 

 with brown. 3 inches long. Inhabits European seas. B. Pen. 

 Brit. Zool. iv. pi. 24. 



Gen. 25. TETHYS, Lam. Gmel. 



Body fleshy, semitransparent, oblong, narrowed into a point 

 posteriorly, and terminated anteriorly by a broad semicircu- 

 lar mantle, covering the head ; mouth under the mantle ; 

 two tentacula ; branchiae dorsal, projecting, naked, in branch- 

 ing tufts, disposed in two longitudinal rows ; orifice of ge- 

 neration and the anus on the right side. 



T. leporina, Gmel. Margin of the mantle in longish fimbriated fila- 

 ments. An. Mus. xii. pi. 24. 



Gen. 26. SCYLLJEA, Lam. Lin. 



Body gelatinous, oblong, much compressed on the sides, canalicu- 

 late below ; back raised into an elevated crest, with four wings 

 disposed in pairs ; head scarcely projecting ; two tentacula, 

 dilated above, and narrowed toward their base ; branchiae 

 spread in brushes over the internal face of the wings ; orifices 

 for generation and the anus on the right side. 



S. pelagica, Gmel. Head indistinct ; foot hollowed longitudinally. 

 Cuv. An. Mus. vi. pi. 61, fig. 1, 3, 4. 



Gen. 27. TRITONIA, Cuv. 



Body oval oblong, convex above, with the head short, broad, 

 sessile, and two retractile tentacula, simple or divided; 

 branchiae dorsal, in branched tufts, in two longitudinal rows ; 

 orifices of generation and of the anus on the right side. 



T. Hombergii, Cuv. Body oblong, subtetragonous, verrucose above ; 

 sides compressed and smooth j branchiae forming a continuous 

 plumose crest. 2^ inches long. Inhabits European seas. B. 

 An. Mus. i. pi. 31, fig. 1, 2. 



T. arbor escens, Cuv. Body oblong, tumid ; branchiae ramose, dis- 

 tinct, five on each side, the posterior smaller. 1 inch long. In- 

 habits European seas An. Mus. vi, pi. 61, fig. 8, 9, 10. 



