THE MOLLUSCA 



1003 



126 (127) Shell smooth, elliptical; hinge edentulous; beak sculpture consisting 

 of a few fine, concentric ridges. . . Anodontoides Simpson. 



The type, A. ferussaciana 

 Lea (Fig. 1496; X I), is of 

 general distribution in the St. 

 Lawrence, Ohio, and Mis- 

 sissippi drainage areas. The 

 concentric undulations of the 

 beaks are characteristic. 



FIG 1496. 



127 (128) 



Shell small, solid, thick in front, with two radial ridges extending 

 from the beaks to the biangulated posterior end. Pseudo- 

 cardinals solid; laterals wanting Pegias Simpson. 



A single species, P.fabula Lea (Fig. 1497), from the Cum- 

 berland and Tennessee river systems, is the only one known. 



FIG. 1497. 



128 (129) Shell large, inflated, subrhomboidal, with two radiating rows of 

 knobs; beak sculpture coarse, continuous with that of the 

 surface which consists of oblique folds and wrinkles; pseudo- 

 cardinals large; laterals short and blurred. 



Arcidens Simpson. 



The typical and only species, A . confragosa Say (Fig. 1498; X$), is common throughout the 

 Ohio and Mississippi drainage systems and southwest to Texas. 



FIG. 1498. 



