IO02 



FRESH-WATER BIOLOGY 



123 (124) Shell thin; hinge edentulous; beak sculpture consisting of several 

 more or less doubly -looped parallel ridges, often slightly nod- 

 ulous on the loops Anodonta Lamarck. 



This genus is the only one of the North American Naiades that has a general distribution 

 from the Atlantic to the Pacific. Numerous species are recognized. They are easily distin- 

 guished by the edentulous hinge and double loop of the beak sculpture. Example, A. grandis 

 Say (Fig. i493JXi). 



124 (125) 



FIG. 1493. 



Shell smooth, elongated, rather thin, inequilateral, compressed; 

 epidermis shining, often rayed; a single, imperfect pseudo- 

 cardinal in each valve and sometimes vestiges of laterals. 



Lastena Rafinesque. 



Only a single species is 

 known, L. lata Raf. (Fig. 

 1494 ; X I), and is found in the 

 Ohio, Cumberland, and Ten- 

 nessee river systems. 



FIG. 1494. 



125 (126) 



Shell smooth, elongated, subtriangular, with usually a high, sharp 

 posterior ridge; hinge with a rudimentary pseudocardinal 

 and lateral in each valve. . Gonidea Conrad. 



This genus, represented 

 by a single species, G. an- 

 gulata Lea (Fig. 1495; Xf), 

 as usually found, is remark- 

 able for the sharp posterior 

 ridge and more or less 

 flattened posterior region. 

 It is a characteristic west 

 coast species and ranges 

 from central California 

 north to British Columbia, 

 and east to Idaho. 



FIG. 1495. 



