992 



FRESH-WATER BIOLOGY 



91 (92) Shell large, fusiform; base of aperture prolonged in a long canal. 



lo Lea. 



This group of large, striking species is confined to the rivers of east- 

 ern Tennessee. They are found only in very rapidly running water. 

 Example, /. spinosa Lea (Fig. 1469). 



FIG. 1469. 



92 (94) Shell globose-conic; columella callously thickened above and below; 

 aperture shortly channeled below. 



Lithasia Haledman . . 93 



The Lithasiae form a very distinct group characterized by the colu- 

 mella thickened by deposits of callus above and below and the short canal 

 at its base. With the exception of three species, which extend as far 

 north as the Wabash River, Indiana, the group is restricted to Ken- 

 tucky, Tennessee, and Alabama. Type, L. geniculata Con. (Fig. 1470). 



FIG. 1470. 



93 Shell similar to Lithasia, but with the basal canal more produced. 



Section Angitrema Haledman. 



This group connects Lithasia with lo. Type,' Lithasia armigera Say 

 (Fig. 1471). 



FIG. 1471. 



94 (95) Shell obovate, thick, solid; spire short; body- whorl large; columella 

 callously thickened above, incurved below and subtruncate. 



Eurycadon Lea. 



This genus, when restricted to the species grouping about the 

 confined to the rivers of the Tennessee drainage system. Type, E. 

 Budd (Fig. 1472). 



FIG. 1472. 



