112 



chology. "For an opportunity to examine this spe- 

 cies, I sun indebted to Mr. Lesueur, who obtained it 

 in Bayou St. John, Dear New Orleans. It is readily 

 distinguishable from any other species." Say. 



UNIO QUADRULUS. 



l'LATK LXII. 



DESCRIPTK N 



Shell narrowed, compressed, and thin behind; short, 

 obtuse 1 , rounded, and wider before; beaks slightly 

 elevated; ligament more elevated than the beaks; 

 binge margin compressed, carinate; basal margin 

 falcate, emarginate and compressed; posterior mar- 

 gin subangulate; posterior dorsal margin subtrun- 

 cate, nearly straight; posterior basal inarL r in project- 

 ing; epidermis dark brown in obi specimens, ol an 

 olive-colour in others; surface with distinct irregular 

 transversely compressed tubercles; a broad, nodulous, 

 elevated, somewhat double ridge extending from the 

 beaks to the [>osfenor basal edge, and a furrow be- 

 hind, separating the posterior hinge and [losterior 

 dorsal margin: (animal teeth sukatcd; lateral teeth 

 striated, rough, and in th» righl valve somewhat 

 double; anterior muscular impression deep and partly 

 rough; eavit\ of the beaks angular, compressed, and 

 directed forwards under the cardinal tooth; nacre 

 pearly white, and on the posterior side iridescent. 



