8 KEY TO FAMILIEb. 



* Operculate. Fluviatile. 



Family Ampullariid^. 



Rostrum bi-lobed in front, tentacles long and 

 filiform, with eyes pedunculated at their outer 

 bases. Mantle with an elongate siphon on the 

 left side. Operculum annular. Shell generally 

 globosely turbinate, spiral, large, aperture en- 

 tire. Distribution tropical and sub-tropical. 



Family Viviparid^. 



Rostrum entire in front, tentacles short, 

 stout, tapering, with eyes on tubercles at their 

 outer bases. Mantle simple in front. Oper- 

 culum annular, the nucleus sometimes spiral. 

 Shell turbinate, spiral, of smaller size, aperture 

 entire. Distribution universal. 



Family Amnicolid.e. 



Tentacles elongated, with eyes at their outer 

 bases. Operculum sub-spiral or concentric. 

 Shell small, globular or elongated, spiral. 

 Aperture broadly oval, lip continuous. Gener- 

 ally umbilicated. 



Inhabit fresh waters in all parts of the world. 



