74 VALVATIDJS. 



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

 distended, bursts, and about 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, when 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, Mull. 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 : branchial 

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

 stalk: branchial appendage 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 owing 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 : 

 umbilicus very large and open, fully exposing 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 branchial plume. 



