DESCRIPTION OF FIFTY-TWO SPECIES OF UNIONID.E. 41 



The specimen from Virginia seems to be a male, while the others are generally 

 females, judging from the enlargement of the umbonial slope. 



Unio attenuatus, pi. 14, fig. 38. 



Testa Isevi, lata, attennata, ad latere subcompressa, valde inasquilaterali, postice sabbiangulari, antice 

 oblique rotundata ; valvulis crassiusculis, antice parnm crassioribus ; natibus prominulis, fere 

 terminalibus; epidermide tenebroso-fusca, aliquanto nigra, radiata; dentibus cardinalibus parvis, 

 compressis, crenulatis, obliquis, in utroque valvulo-duplicibus ; lateralibus pr^longis, lamellatis 

 subrectisque ; margarita alba et valde iridescente. 



Shell smooth, wide, attenuate, somewhat compressed at the sides, very inequi- 

 lateral, subbiangular behind and obliquely rounder before; valves somewhat thick, 

 slightly thicker before; beaks slightly prominent, nearly terminal; epidermis dark 

 brown, somewhat blackish, radiated ; cardinal teeth small, compressed, crenulate, 

 oblique, double in both valves; lateral teeth very long, lamellar and nearly straight; 



nacre white and very iridescent. 



Proc. Acad. Nat. Sci., 1812, p. 151. 

 Hab. — Savannah River, Geo., Dr. Barratt ; and Beaver Creek, Houston Co., 



Geo., J. Lewis, M.D. 



My cabinet and cabinet of Dr. Lewis, 

 Diam. -7, Length 1, Breadth 2-7 inches. 



Shell smooth, wide, attenuate, somewhat compressed at the sides, very inequi- 

 lateral, almost terminal, subbiangular behind and obliquely rounded before ; sub- 

 stance of the shell somewhat thick, slightly thicker before; beaks slightly promi- 

 nent; ligament long, thin and brown; epidermis dark brown, somewhat blackish,, 

 radiated, with very distant marks of growth; umbonial slope obtusely angular; 

 posterior slope subcarinate, narrow elliptical; cardinal teeth small, compressed, 

 crenulate, oblique, double in both valves ; lateral teeth very long, lamellar, nearly 

 straight ; anterior cicatrices distinct, somewhat large and moderately impressed ; 

 posterior cicatrices confluent and slightly impressed ; dorsal cicatrices placed nearly 

 in the centre of the cavity of the beaks ; cavity of the shell wide and subcylin- 

 drical ; cavity of the beaks shallow and obtusely angular ; nacre white and very 

 iridescent. 



Remarks. — There are five specimens before me. That which is figured is from 

 Beaver Creek, Geo. It is the most perfect and the whole disk is covered with 

 small dark green rays. The old specimens are quite black and without rays. The 

 nacre in all these is white and finely iridescent. None were perfect enough in the 

 beaks to display undulations at the tips. It is very near in outline to rostriformis 

 and Hazlehurstianus (nobis). 



11 



