62 NEW Ui\IONID.E OF THE UNITED STATES. 



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

 beaks deep and angular; nacre white and iridescent. 



Remarhs. — 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 

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

 rlimJh (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. pi. 3, fig. 205. 



Testa la3vi, valde tratisvevsa, vuKlC' couipres-vfi, ad latere pknulatri, valJc inse pilaterali, postiee obtuse bian- 

 gulata ; valvulis tenuibus, natibus vis prorainentibus, ad apices undulatis ; epidermide tcnebroso-fusca, 

 striata, postiee obsolete radiata ; dentibus cardinalibus parvis, crenulatis, in utroque valvulo duplicibus ; 

 lateralibus prcelongis, latuellatis rectisijue; margarita casruleo-alba et vald(^ 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. 8i3. 



/^,(i._Catawba River, Gaston Co., N. C. C. M. Wheatley. 



My caljinet and cabinet of Mr. Wheatley. 

 Diam. -5, Length 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 conflnent, 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 wdiite and very iridescent. 



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

 characters oi percoarctatns, herein described, but it is not quite so compressed, and is 

 Avider and more pointed at the posterior margin. In outline it reminds one of rostriformis 

 and 2J^^striaius. The nacre is Avhite in the adult, in my possession, but in the young 

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



