196 



VALVATA, 



helix piscinalis. — Gmelin. 



Muller and Draparnaud have described this genus of 

 fresh water shells under its present name, which La- 

 marck therefore preserves. It is quite distinct from the 

 G. Planorbis, although its form is rather discoid : as the 

 animal only breathes water, and has an operculum, it 

 more nearly approximates the G. Paludina; but the 

 spiral cavity of the Valvata is complete, that is, not mo- 

 dified by the previous whorl, and the aperture is round- 

 ed, and not angular at the summit. Shell widely um- 

 bilicated, rather oblong, obtuse, cylindrical; whorls 

 but slightly connected, and not limiting the spiral cavi- 

 ty; aperture rounded, entire, and sharp; the operculum 



is orbicular. 



Valvata piscinalis. 



PALUDINA. 



HELIX VIVIPARA. Gmcllll. 



This genus, of which the various species have been 

 confounded with the genera Bulimus, Cyclostoma, and 

 Turbo, by various authors, Lamarck has properly 

 classed by itself. It generally inhabits fresh water, 



