GASTEROPODA. 185 



Type, D. membranaceum, Meek. Medit. 



Animal oblong, truncated behind, the angles produced and dilated or 

 filiform ; head ovate-oblong, retuse in front ; side-lobes expanded, wing-like ; 

 mantle investing a rudimentary, membranous shell. 



GASTROPTERON, Meckel. 



Type, G. Meckelii, Bl. (Clio amate, Chiaje) Medit. 



Animal shell-less, oval, with side-lobes developed into wing-like expan- 

 sions meeting and uniting behind ; cephalic disk triangular, obtuse in front, 

 pointed behind, eyes centrally immersed; lingual teeth 5.1.5.; mantle? 

 branchial plume exposed on the right side ; reproductive orifice in front of 

 the gill, excretory opening behind it. Lon. 1, lat. 2 inches. 



Sormetus Adansonii, Bl. is described as semi-cylindrical, with sides grooved, 

 head indistinct ; shell unguiform, thin, and transparent. 



Atlas (Peronii, Bl.) Lesueur. Head with 2 small tentacular lobes; body con- 

 tracted in the middle ; foot dilated circularly, and fringed at the margin. 



FAMILY III. APLYSIAD^. 



Shell wanting, or rudimentary and covered by the mantle, oblong, tri- 

 % gonal, or slightly convoluted. 



Animal slug-like, with distinct head, tentacles and eyes; foot long, 

 drawn out into a tail behind ; sides with extensive lobes, reflected over the 

 back and shell ; branchial plume concealed. Sexes united. 



APLYSIA, Gmelin. Sea Hare. 



Type. A. depilans, PI. XIV. fig. 14. Syn. Siphonotus (geographicus) Ad. 



Shell oblong, convex, flexible and translucent, with a posterior slightly 

 incurved apex. 



Animal oval, with a long neck and prominent back ; head with 4 ten- 

 tacles, dorsal pair ear -like with eyes at anterior lateral bases ; mouth probos- 

 cidiform, with horny jaws, lingual teeth 13.1.13, hooked and serrated, about 

 30 rows ; gizzard armed with horny spines ; sides with ample lobes folding 

 over the back, and capable of being used for swimming ; gill in the middle of 

 the back, covered by the shell, and by a lobe of the mantle which is folded 

 posteriorly to form an excretory siphon. 



Distr. 40 sp. W. Indies, Norway, Brit. Medit. Mauritius, China. 



The Sea-hares are mixed feeders, living chiefly on sea- weed, but also de- 

 vouring animal substances ; they inhabit the laminarian zone, and oviposit 

 amongst the weed in spring, at which time they are frequently gregarious 

 (Forbes}. They are perfectly harmless animals and may be handled with im- 

 punity. When molested they discharge a violet fluid from the edge of the 

 internal surface of the mantle, which does not injure the skin, has but a 

 faint smell, and changes to wine-red (Goodsir). ' In old times they were 



K 2 



