99° 



FRESH-WATER BIOLOGY 



79 (80) Shell elongated, strongly carinated on the periphery. 



Pyrgulopsis Call and Pilsbry. 



->-r^. The typical species, P. MCTOiZcKWJ Steams (Fig. 14S9; X3), is from Nevada. Others 



/i\ii v^^ have been described from the Mississippi and Tennessee valleys. 



Fig. 1459. 



80 (81) Shell ovate-conic; whorls shouldered and usually coronated with 

 spines Potamopyrgus Stimpson. 



Two species from Florida and Texas, respectively, are represented in our 

 fauna. Typically spinose, all the species are dimorphic, having both an angu- 

 late, spinose form and a smooth, ecarinate one. Example, P. corontUus Pfr. 

 (Fig. 1460; X3i). 



Fig. 1460. 



81 (75) Shell subpyramidal, rather sohd, smooth; body-whorl subangulated 

 at the periphery. . . . Littoridina Eydoux and Souleyet. 



A South American genus. A single species from Florida, L. monroensis, 

 Frfld. (Fig. 1461; X 7), has been doubtfully assigned to it. 



Fig. 1461. 



82 (88) Shell with a large body-whorl and short spire; columella usually 



callously thickened; operculum corneus, subspiral. Foot 

 simple. Central tooth of the radula with several basal 

 denticles Subfamily Lythoolyphinae . . 83 



Five genera: 83, 84, 85, 86, 87. 



83 (84) Shell depressed-conic; base concave, widely and deeply umbUicated. 



Cochliopa Stimpson. 



A Central American genus, of which one species, C. riograndensis P. and 

 F. (Fig. 1462; X 6), has been found in Texas and another (doubtfully) in 

 California. 



Fig. 1462. 



84 (8s) Shell minute, globose-turbinate, narrowly but deeply umbilicated; 

 columellar Hpthin; operculum corneus, paucispiral; nuclear 

 whorls large, slowly and regularly increasing. 



Clappia Walker. 



Only a single species, C. dappii Walker (Fig. 1463; X6J), from the Coosa 

 River, Alabama, is known. It somewhat resembles Somalogyrm in shape, 

 but can be easily distinguished by its deep umbilicus and peculiar operculum. 



Fig. 1463, 



