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rior part obliquely truncated; shell 

 rather thick; epidermis brown, blackish, 

 olive and gold coloured ; tooth small, 

 rugose. Length 4 diam. f axis of 

 the breadth. 

 Unio pictorum, &c. 



Second Sub-genus LEPTODEA. 



Cardinal tooth entire and smooth, that of the 

 right valve simple ; contour not thickened ; liga- 

 ment membranaceous ; lamellar tooth slightly 

 curved. 



SPECIES V. Unio leptodon (Elliptio leptodon.) 



Shell elliptical, much compressed, attenuated 

 posteriorly, thin and fragile, somewhat rugose ; 

 epidermis brownish ; nacre violaceous ; cardinal 

 tooth small, obtuse^ smooth, tubercular; lamellar 

 tooth thin and long. Length ^ diam. J- axis 

 i of the breadth. 



Common in the lower part of the Ohio, mostly 

 small, for its shell is so fragile, that it easily be- 

 comes the prey of its enemies ; notwithstanding 

 this, it sometimes attains to three inches in 

 breadth. The muscular impressions are slight ; 

 fossule apparent, confluent ; animal whitish. 

 Var. 1. olivacea olive epidermis. 

 3 



