VIVIPARIDiE. 337 



Species of Amnicola. 



Cincinuatensis, Anthomj. marginata, Mich. 



grana, Say. Nicliliniana, Lea. 



isogona, Anton. obtusa, Whit. 



limosa, Say. orbiculata, Lea. 



lustrica, Say. porata, Say. 



Fam. VIVIPARID^. 



Tongue very short, armed with seven series of teeth 

 (3- 1-3) ; teeth laminar, longitudinal, ovate, apex recurved, 

 dentate on each side of the tips ; inner lateral tooth 

 broad. Hostrum moderate, entire ; tentacles tapering, 

 with the eyes on tubercles at their outer bases. Mantle 

 simple in front ; gill comb-like, single. 



Operculum annular, regular. 



Shell spiral, turbinate, covered with an epidermis ; 

 aperture simple in front. 



The members of this family are fluviatile, inhabiting 

 lakes and streams ; the shells of most of them are dingy 

 brown, or covered with a green, horny epidermis ; they are 

 distributed nearly all over the world. 



Genus VIVIPARA, Lamarck. 



Animal with a small lobe on each side of the neck. 



Operculum horny, annular, composed of concentric 

 elements around a central nucleus. 



Shell thin, turbinated, umbilicated ; spire produced, 

 whorls round, smooth or carinated, covered with an oli- 



VOL. I. XX 



