74i VALVATID^E. 



twelfth day after they have been laid^ the capsule^ being 

 distended^ bursts^ and abont two -thirds of the fry emerge 

 and enter on their career of life. The capsule then re- 

 sumes its former shape, and retains the rest of the fry 

 for four days longer, w hen they are, in their turn, hatched 

 or emancipated. 



Both Draparnaud and Montagu were aware that this 

 species was furnished with the branchial plume ; but the 

 former included it in the heterogeneous assemblage of 

 species which he called Cyclostoma, assigning the next 

 species to Valvata; and our countryman referred one 

 species to Helix and the other to Turbo. The present 

 species is the Nerita obtusa of Studer ; and Draparnaud 

 adopted his specific name. 



2. V. crista'ta"^, Miiller. 



V. cristata, Miill. Verm. Hist. pt. ii. p. 198 ; F. & H. iii. p. 21, pi. Ixxi. 

 f. 11, 12, 13. 



Body dark grey or brown, with a few small black specks on 

 the upper part, slate- colour underneath : snout prominent, 

 rather narrow and curved, faintly wrinkled : tentacles long, 

 slender, close together but recurved at their points : eyes small 

 and round : foot quite separate from the snout, and resembling, 

 in proportion to its size, that of the last species : hranchial 

 jilume transparent, bearing about 15 offsets on each side of the 

 stalk : hranchial ap^endaye rather shorter than the tentacles. 



Shell forming a flat coil, concave beneath, rather solid, 

 semitransparent, yellowish or greyish-horncolour, closely and 

 regularly striate transversely : epidermis very thin : whorls 5, 

 the last exceeding in breadth all the rest put together : spire 

 flat, or slightly concave omng to the convexity of the whorls : 

 mouth circular ; outer lip thin and slightly reflected : inner lip 

 separate from the columella and continuous with the outer lip : 

 umhilicus very large and open, fully exjiosing the interior of 

 the spire : operculum circular, concave like an inverted pot- 

 lid, forming a concentric spire of about a dozen whorls, the 



* Crested ; so called from its brancldal plume. 



