24 Bryant Walkdr 



Type : Nerita urceiis Miill. 



Example: A. paludosa Say, fig. 70. Radula, fig. 71. Animal, fig. 72. 



Family VIVIPARID^. 



Shell moderately large, turbinate, imperforate, or subperf orate; whorls 

 convex; aperture entire, subcircular or somewhat angled above; lip simple; 

 operculum convex, concentric, nucleus subcentral, sometimes subspiral. 



Animal with a long snout, not divided into tentacular lobes; tentacles 

 long and slender, in the male the right one is shorter, truncated and forms 

 a sheath for the verge; eyes on peduncles on the exterior base of the 

 tentacles; mantle with two cervical lobes, of which the right is the larger, 

 forming with the mantle distinct tubular conduits for the ingress and egress 

 of water for respiration; jaws two; radula with the teeth simple or denti- 

 culate, central tooth large, broad, without basal denticles, laterals large, 

 subtrigonal, marginals narrow, elongated. Ovoviviparous. 



Key to the Genera of Vhiparidce. 

 { Operculum wholly concentric 2. 



[ Operculum with subspiral nucleus Lioplax. 



{ Reiiected apices of the lateral teeth simple Campeloma. 



[ Reflected apices of the lateral teeth denticulate 3. 



r Inner margin of the operculum simple Viviparus. 



3. ] Inner margin of the operculum reflected, forming an ele- 



[ vated marginal fold Tulotoma. 



Genus VIVIPARUS Montfort, 1810. 



Shell dextral, spiral, subconoidal; rather thin, smooth, imperforate or 

 slightly umbiHcate; light green or olivaceous, unicolored or banded with 

 brown or tinged with purple; whorls convex, aperture entire, subcircular; 

 lip simple, acute; columellar and parietal margin not usually thickened; 

 operculum concentric, inner margin simple, not reflected. 



Fig. 73 Fig. 74 



Animal with foot of moderate size, not produced beyond the snout. Teeth 

 of the radula multicuspid. 



Type : Helix vivipara L. 



Example: V. intertextus (Say), fig. 73. Radula, fig. 74. 



