OP THE FAMILY OF NAIADES. 441 



Barnes does not mention, and is yellowish, not brownish. 

 This and the donaciformis are all I know which possess the 

 zig-zag markings, and they most resemble each other. 



12. Unio Patulus. Plate XII. fig. 20. 



Testa ovatd, compressd, cuneiformi, ineequilaterali, obliqud, trans- 

 versa ; umbonibus compressis ; valvulis sub-crassis ; natibus sub-termi- 

 nalibus ; dente cardinali parvo ; laterali longo et sub-curvato ; margaritd 

 alba. 



Shell ovate, compressed, wedge-shaped, inequilateral, oblique, trans- 

 verse, compressed on the umbones; valves rather thick; beaks nearly 

 terminal ; cardinal tooth small ; lateral tooth long and slightly curved ; 

 nacre pearly white. 



Hab. Ohio. T. G. Lea. 



Mji Cabinet. 



Cabinet of T. G. Lea. 



Cabinet of Prof. Vaniixem. 



Diam. -8, Length 1-4, Breadth 2-3 inches. 



Shell compressed, wedge-shaped, ovate, broad and flat ; sub- 

 stance of the shell thick anteriorly and thin posteriorly, show- 

 ing the rays through it; beaks nearly terminal, slightly pro- 

 minent, approaching, and when perfect possessing slight 

 concentric undulations, generally decorticated ; ligament not 

 large, passing from the point of the beaks ; epidermis yellow- 

 ish brown, transversely wrinkled, marked with more or less 

 broad interrupted rays, apparently formed of fasciculi of hair- 

 like lines ; cardinal tooth short, and but slightly elevated, in 

 the left valve double and deeply cleft, in the right valve 

 emerging from a pit ; lateral tooth long and slightly curved ; 

 posterior cicatrices as well as anterior cicatrices distinct ; the 

 smaller posterior cicatrix situated against the lateral tooth at 

 its termination ; dorsal cicatrices on the under part of the car- 

 dinal tooth ; cavity of the beaks not deep but rounded ; nacre 

 thick and milk white anteriorly, thin and iridescent poste- 

 riorly. 



