174 Mr. Barnes on the Genera Unio and Alasmodonta. 



extremity pointed, posterior rounded ; epidermis greenish 

 brown ; surface striated, glabrous ; cardinal teeth slender; 

 lateral tooth long and thin ; naker bluish-white varied with 

 wax-yellow, and sometimes tinged with violet, and irides- 

 cent ; cavity of the beaks, scarcely any. 



Remark. — This cannot as M. Lamarck supposed be his 

 Unio J^asuta, for it has no sinuses on the basal margin, is 

 not " crooked" nor " obliquely attenuated." 



27. Unio Gracilis. — Shell ovately triangular, very 

 thin and fragile, hinge margin elevated ; valves 

 connate ; ligament concealed. 



Unio Alatus. Mr. Say. 



Inhabits the Wisconsan. Mr. Schoolcraft. 



And the Lakes. Mr. Say. 



Cabinetof the Lyceum. 



My Collection. 



Diam. 1-0— 1-2 Length 2-2— 2-5 Breadth 3-1— 4-1. 



Beaks depressed, and placed far back; ligament between 

 the valves, and covered; anterior lunule distinct and obso- 

 letely ribbed ; hinge margin elevated into a large wing ; 

 epidermis sea-green, wrinkled and striated transversely ; 

 obscurely radiate and glabrous ; cardinal teeth very small, 

 scarcely projecting ; lateral teeth very thin and finely stria- 

 ted ; channel just sufficient to admit the point of the thumb 

 nail ; naker bluish-white tinged with violet, and beautifully 

 iridescent. 



Remarks. — This shell differs from Unio Alatus in being 

 much thinner, broader in proportion, lighter color both in- 

 side and outside, produced and somewhat pointed behind ; 

 anterior slope in a straight line with the alated projection. 

 It differs entirely in the shape and proportion of the teeth. 



28.U.,oP.Kvus. Fig.l8. } -f- »:• 



Shell oblong-ovate, small, convex, sides round- 

 ed ; beaks slightly elevated, inside pearly white, 

 iridescent. 



