Synopsis FrEsh-Water Moelusca 



27 



Animal dioecious ; tentacles long, slender, cylindrical ; eyes sessile on the 

 internal bases of the tentacles; snout long; foot large, bilobed in front; gill 

 external, plumose, protected by a long, slender pallial appendage ; verge ex- 

 terior, placed on the right side, at the base of and below the tentacle; jaws 

 two ; lingual teeth multicuspid, no basal denticles on the central tooth. 



Genus VALVATA Miiller, 1774. 

 The characters of the genus are those of family. 



Type : V. cristata Miill. 



Example: V. tricarinata (Say), fig. 86. Animal, fig. 87. Radula, fig. 88. 



Fig. 86 Fig. 87 Fig. 88 



Family AMNICOLID.^. 



Shell small, spiral, dextral, conical, imperforate or umbilicated ; uni- 

 colored; aperture entire, lip simple, acute; operculum concentric, spiral or 

 subspiral. 



Animal with a long snout ; tentacles long, cylindrical, with the eyes at 

 their outer bases ; foot oblong, truncate before, rounded behind ; gills inter- 

 nal; verge exserted, placed on the back, some distance behind the right 

 tentacles ; jaws two ; central tooth of the radula multicuspid and with one or 

 more basal denticles ; laterals hatchet-shaped, multicuspid ; marginals 

 slender, multicuspid. 



Key to subfamilies of Ainuicolidcc. 



\ Opercuhun multispiral Lyogyrincu. 



I. ^ Operculum concentric BytJiinincr. 



[ Operculum paucispiral 2. 



C Foot divided Pov.iatiopsincr. 



Foot simple 3. 



3- 



f Shell thin, subglobose to elongate ; columella not thickened 



! Amnicolhuc. 



Shell tliick, short, body-whorl very large ; columella thick- 

 [ ened LitJioglypliincr. 



Subfamily P.YTHINTN.F: Stimson, 1865. 



Shell small, spiral, de.xtral, turbinate, spire produced ; operculum cal- 

 careous, concentric. 



Foot simple ; central tooth of the radula with several basal denticles. 



