58 NEW UNIONIDiE OF THE UNITED STATES. 



under the cardinal teeth; cavity of the shell deep and nearly round; cavity of the 

 beaks deep and angular; nacre white and iridescent. 



Remarks. — This does not seem to be a rare species in North Carolina, having re- 

 ceived it from several habitats. It is a small species belonging to the group of which 

 castaneus (nobis) may be considered the type. It is also near to nux (nobis) and pul- 

 vinulis (nobis). The junior specimens have numerous minute rays, and some have a 

 tint of salmon color in the cavity of the beaks. It was first called to my attention 

 by F. A. Genth, M. D., to whom I with great pleasure dedicate it. 



Unio gracilentus. PL 3, fig. 205. 



Testa laevi, valde transversa, valde compressa, ad latere planulata, valde insequilaterali, postice obtuse bian- 

 gulata ; valvulis tenuibus, natibus vix prominentibus, ad apices undulatis ; epidertuide tenebroso-fusca, 

 striata, postice obsolete radiata ; dentibus eardinalibus parvis, crenulatis, in utroque valvulo duplicibus ; 

 lateralibus prselongis, lamcllatis rectisque ; margarita cEeruleo-alba et valde" iridescente. 



Shell smooth, very transverse, very much compressed, flattened at the sides, very 

 inequilateral, obtusely biangular behind ; valves thin ; beaks scarcely prominent, 

 undulate at the tips; epidermis dark brown, striate, obsoletely radiate behind; cardi- 

 nal teeth small, crenulate and double in both valves; lateral teeth very long, lamellar 

 and straight ; nacre bluish white and very iridescent. 

 Proc. Acad. Nat. Sci. 1857, p. 85. 



jM,._Catawba River, Gaston Co., N. C. C. M. Wheatley. 



My cabinet and cabinet of Mr. Wheatley. 

 Diam. -5, Length 1-1, Breadth 2-8 inches. 



Shell smooth, very transverse, very much compressed, flattened at the sides, very 

 inequilateral, obtusely biangular behind; substance of the shell thin, very slightly 

 thicker before; beaks scarcely prominent, undulate at the tips; ligament long, thin 

 and dark brown ; epidermis dark brown, striate, obscurely rayed behind ; umbonial 

 slope very slightly raised, obtusely angular; posterior slope very narrow, raised into 

 a carina, much compressed ; cardinal teeth small, crenulate and double in both valves ; 

 lateral teeth very long, lamellar and straight; anterior cicatrices distinct, rather small, 

 moderately well impressed ; posterior cicatrices confluent, rather large and slightly 

 impressed ; dorsal cicatrices well impressed and placed nearly in the centre of the 

 cavity of the beaks ; cavity of the shell very shallow and wide ; cavity of the beaks 

 very shallow and obtusely angular ; nacre bluish white and very iridescent. 



Rcmarhs. — Several specimens are before me of different ages. It has some of the 

 characters of percoarctatus, herein described, but it is not quite so compressed, and is 

 wider and more pointed at the posterior margin. In outline it reminds one of rostriform is 

 and perstriatus. The nacre is white in the adult, in my possession, but in the }~oung 

 disposed to reddish brown. The stria? on the whole surface is disposed to be rough. 



