THE MOLLUSCA 



987 



65 (66) Shell large, globose-turbinate ; umbilicate; operculum corneus, con- 

 centric. Animal with the respiratory chamber divided into 

 two parts, one being the lung and the other containing a gill. 



Family AMPULLARIIDAE. 

 Only a single genus Ampullaria Lamarck. 



The Ampullarias are the largest of our fresh- 

 water snails. Two or three species occur in 

 Georgia and Florida. Example, A. paludosa 

 Say, (Fig. 1448). 



FIG. 1448- 



66 (71) Shell of moderate size, dextral, turbinate, imperforate, or subperforate; 

 operculum corneus. Animal branchiferous. 



Family VIVIPARIDAE . . 67 

 Four genera: 67, 68, 69, 70 



67 (68) Shell rather thin; operculum concentric, inner margin simple. Animal 

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

 Teeth of the radula multicuspid. . . Viviparus Montfort. 



Several species are found in the Mississippi Valley and 

 from Ohio and Indiana south to the Gulf. They are 

 usually to be distinguished from the Campelomae by the 

 thinner and more globose shells and convex whorls. Ex- 

 ample, V.intertextus Say, (Fig. 1449; 



FIG. 1449. 



