72 



VALVATID^. 



VALVA'TA^, Miiller. PI. III. f. 13, 14, 15. 



Eyes nearly sessile : operculum horny and thin. 



1. Valvata piscina^'lis t, Miiller. 



Nerita 2>isci7ialis, Miill. Verm. Hist. pt. ii. p. 172. V. piscinalis, F. & H. 

 iii. p. 19, pl.lxxi. f.9, 10. 



Body of a clear yellomsh'gTey, with small and indistinct 

 milk-white specks : snout long, narrow, and transversely 

 wrinkled : tentacles long, cylindiical, rather close together, and 

 slightly recurved at the point : eyes large and round, but not 

 prominent: foot separate from the snout and six times as 

 broad, deeply cleft in front and rounded behind; its tail 

 nearly covered by the operculum : hrancliial plume transparent, 

 bearing on each side fourteen slender offsets, which are placed 

 at right angles to the stalk : branchial appendage of the same 

 size and length as the tentacles. 



Shell forming a depressed cone, subglobular, rather solid 

 and opaque, brownish-yellow, closely and regularly striate 

 transversely, and more or less distinctly ridged in a spiral 

 direction, which often gives the surface an elegantly reticu- 

 lated appearance : whorls 6, rounded and convex, the last being 

 rather less than one-half of the shell : spire compressed and 

 blunt : suture nearly straight and very deejD : mouth circular : 

 outer lip rather thick and reflected : inner lip quite separate 

 from the columella and continuous with the outer lip, so as to 

 form a complete peristome : umbilicus round, not large, but 

 very deep, exposing nearly all the interior of the spire : oper- 

 culum circular, slightly compressed in the middle, forming a 

 concentric spire of from 10 to 12 whorls, the outer edges of 

 which are thickened and raised so as to project over and 

 partly overlap the succeeding whorl of the operculum. L.0-25. 

 B. 0-275. 



Yar. 1. clepressa. Shell having the spire more depressed and 

 the umbilicus consequently larger. V. depressa, C. Pfeiffer, 

 Deutsch. Moll. i. p. 100, pi. ii. f. 33. 



Yar. 2. subcylindrica. Shell having the spire more produced, 

 and flattened at the top : imibilicus small. 



* Closed by a valve, or operculum. 



f Inhabiting fish-ponds. 



