Family AMNICOLIDAE 



Shell small, usually conical; aperture rounded; Vv'ith eyes on the 

 outside of the bases of cylindrical tentacles; operculum various, 

 concentric (Bythinia) to spiral 



Common genera — Amnicola Lyogyrus 



Bythima Horatia 



Somatogyrus Lyrodes 



Fluminicola Gillia 



Pomatiopsis Cochlwpa 



Littoridina Clappia 



Tryonia Pyrgulopsis 



Paludestnna Hoyia 



Family VALVATIDAE 



Shell small, with low spire; aperture ovate; gill with filaments 

 on both sides (exceptional in this order) ; with stalked eyes on 

 the inner sides of the bases of cylindrical tentacles; operculum 

 with multispiral markings 

 Common genus — 'Valvata 

 Family VIVIPARIDAE 



Animal viviparous; with stalked eyes on the outside of the bases 

 of slender tentacles; operculum largely with concentric mark' 

 ings; gill present, no lung 



Common genera — \liviparus LiopJax 



Campeloma Tulotoma 



Family AMPULLARIIDAE 



Aquatic or amphibious; with stalked eyes on the outside of the 

 bases of slender tentacles; operculum with concentric markings; 

 with both gill and respiratory sac 

 Common genus — Pomacea 

 Family PLEUROCERATIDAE 



Shell usually elongate; aperture with slight channel below; eyes 

 on the outside of the bases of the tentacles; operculum subspiral 

 Common genera — ■ Pleurocera Anculosa 



lo Gyrotoma 



Goniohasis Eurycaelon 



Lithasia l^itocris 



Class PELECYPODA (or LAMELLIBRANCHIATA) 



With two opposing valves joined by a hinge ligament; animal without 

 a distinct head 



Order EULAMELLIBRANCHIATA 



With gill filaments joined to form continuous lamellae 



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