8 KEY TO FAMILIEs. 
* Operculate. Fluviatile. 
Family AMPULLARIIDA. 
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 VivipaRIp&. 
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 AMNICOLIDA. 
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. 
