GASTEROPODA PECTI.VIBRANCHIATA. Gl 



they arc circulated and have lut two tcntacula, would resemble tli 

 Auriculae, that we think may come here, vi/. 



ACTION, Montf.* TORN LTBLLA, Lam. 



Whore the shell is elliptical, the spire hut slightly silient, the aper- 

 ture lengthened into a crescent and widened below, and the base of 

 the columella marked bygone or two large plicie or oblique callosi- 



: and the 



PVK AMIDELLA, Lam. 



\\'here the spin- is turn-tod, the aperture crescent-like and wide, 

 and the base of the columella obliqcly contorted and marked with 

 sharp spiral plicae}. 



JANTHINA, Lam. 



The form of the animal separates the Janthinac from all the preced- 

 ing genera. Their shell, however, is similar to that of the terres- 

 trial Limaces, the columellar margin being also indented, but slightly 

 angular at the external edge, and the columella somewhat extended 

 beyond the luilf-oval, which, without this prolongation, would he 

 formed by that edge. 



The animal has no operculum, but the under surface of its foot is 

 furnished with a vesicular organ resembling a bubble of foam, but 

 composed of a solid substance, which prevents it from crawling, but 

 allows it to float on the surface of the water. The head, a cylindri- 

 eal proboscis, terminated by a vertically cleft mouth, and armed with 

 little hooks, has a bifurcated tentaculum on each side. 



The common species, Helix Janthina, L,: List., 572, 24, has 

 a pretty violet shell, and is very abundant in the Mediterranean. 

 \Vhon the animal is touched, it diffuses a thick fluid of a deep 

 violet colour that dyes the surrounding water. 



NERITA, Lin. \\ 



The culumella of the Xeritje being in a straight line, renders the 

 aperture semicircular or semi-elliptical. This aperture is generally 

 larue in comparison with the shell, but is always furnished with an 

 iiluin which completely closes it. The spire is almost effaced, 

 and the shell semi-globular. 



* Which ni'i-t ,- Mrefalij :i-tiui:iiMied from the Actions of Oken that appear to 



lu- :illiol to tin- li 



f Ynli'ln tonmtilis, and Itfiuciala, L.Martini. II, xliii. 442. 44:5 ; V. M/.'co/fl, 

 :m.| V. WiWii/.i, Ib., 440, 441 ; V. Jiammeu, ib., 439; '. flara, Ib. 444 ; T. 

 pusiiltt, Ib. 446. 



* Trorhns il<>ll;itus t L. Chemn., V, clxvii, It 63, 1064; B*li nvs ttrdelhm, 

 Hn'iir.. I/.-t., S4t, 73. 



This genii.- form-, tin- family of the OXY6TOM*, Blainv. 



!| M.de Blniuville forms his family of the HEMKYOLOSTOM,* , from this geaus. 



