988 



FRESH-WATER BIOLOGY 



68 (69) Shell thick and solid; operculum concentric, inner edge simple. Animal 

 with the foot very large, much produced beyond the snout. 

 Teeth of the radula simple or only minutely crenulate. 



Catnpeloma Rafinesque. 



This genus is peculiar to North America and the several 

 species are usually very abxmdant, when found. Though norm- 

 ally dextral, sinistral examples are not uncommon. They range 

 from the Mississippi Valley east to the Atlantic and from the St. 

 Lawrence Valley south to the Gulf. Example, C. subsolida Anth., 

 (Fig. 1450). 



Fig. 1450. 



69 (70) Shell turreted; operculum with a subspiral nucleus. 



Lioplax Troschel. 



This genus is also peculiar to this country. The several species are restricted 

 to the states east of the Mississippi and south of Ohio and New Jersey. Type, 

 L. subcarinata Say, (Fig. 1451)- 



Fig. 145 1. 



70 (67) Shell (typically) large, solid, imperforate; spire elevated; operculum 

 concentric, with the inner margin reflected, forming an ele- 

 vated, marginal fold Tulotoma Haldeman. 



This genus is peculiar to North America and is restricted to the 

 Alabama River and its tributaries in Alabama. The two leading 

 species are remarkable for their heavy, nodulous, or tuberculated 

 shell. Type, T. magnifica Con., (Fig. 1452). 



Fig. 1452. 



71 (72) Shell small, spiral, dextral, turbinate, or subdiscoidal; aperture entire, 



circular; operculum round, multispiral. No basal denticles 



on the central tooth of the radula. . Family Valvatidae. 



Only one genus Valvata Miiller. 



The several species of this genus are usually found in great numbers and 

 are of general distribution. Example, V. tricarinata Say, (Fig. 1453 ; X 4). 



Fig. 1453. 



