GASTEROPODA. 



99 



rusac and Rang, though the snout is longer, and the edge 

 of the mantle fringed : according to Quoy and G uimard 

 there is only one rigid, cylindrical, compound thread-like 

 gill existing. — About 200 species; also fossil. 



Found in a great many parts of the world ; abundant 

 in Asia, but rarer in Europe. They inhabit rivers, streams, 

 and lakes. 



Philippi includes the following as sub-genera: — An- 

 cylotus Say ; Paludomus Sw. ; Melanopsis Fer. ; Faunus 

 Montf. ; Jo Lea ; Melafusus Sw. ; Tricula Benson. 



LlTlOPA. Rang. (Bombyxinus Belanger.) — Shell not 

 very thick, horny, with a slight epidermis, rather 

 transparent, conical, with whorls somewhat round- 

 ed, the last being larger than all the rest together ; 

 the apex pointed, whorls longitudinally grooved ; 

 aperture oval, with the lips disunited, the right lip Litiopa 

 simple, separated from the left by a rather in- 

 distinct notch, the left lip slightly reflected backwards ; 

 no operculum? Animal with a small foot formed for 

 creeping on the fuci on which it dwells ; the head is 

 lengthened into a long snout, and bears two conical awl- 

 shaped tentacula, the eyes placed at the base. Several 

 species ; also fossil. 



Sowerby says that the animals of this shell have the 

 power of suspending themselves from the sea-weed on 

 which they live, by a thread resembling a spider's web. 

 They arc found in the Atlantic and Pacific Oceans. 



Plan axis. Lam. — Shell small and oval ; 

 aperture oval, and having a half-formed notch ; JWm 

 left lip flattened, and thickened at the upper f V-djj'- 

 part ; right lip rayed or grooved in the interior ; • 

 operculum horny. Animal, foot short and thick ; 

 head proboscis-shaped, with two long tentacula ; 



H 2 



