62 NEW . UNIONIDJE OF THE UNITED STATES. 



over the centre of the cavity of the beaks ; cavity of the shell rather deep and wide ; 

 cavity of beaks rather shallow and obtusely angular ; nacre white and iridescent. 



Remarlcs. — This species has an outline of a nearly regular ellipse. It reminds one 

 of Hgamentmus, Lam., having the same yellowish, shining epidermis, but it has not 

 the rays over the whole disk, as that species usually has. 



Unio exactus. PL 4, fig. 210. 



Testa lrevi, elliptica, coinpressa, postice" rotundata, insequilaterali ; valvulis subcrassis ; natibus prominulis ; 

 epidermide tenebroso-fusca, striata, obsolete radiata; dentibus cardinalibus parviusculis, crenulatis, in 

 utroque valvulo duplicibus ; laterulibus sublongis, lamellatis subrectisque ; margarita alba et iridesceDte. 



Shell smooth, elliptical, compressed, rounded behind, inequilateral ; valves rather 

 thick ; beaks a little prominent ; epidermis dark brown ; cardinal teeth rather small, 

 crenulate and double in both valves ; lateral teeth rather long, lamellar and nearly 

 straight ; nacre white and iridescent. 



Proc. Acad. Nat. Sci. 1858, p. 41. 



Eab. — Neuse River, six miles from Raleigh, N. C. Prof. Emmons. 



My cabinet and cabinet of Prof. Emmons. 

 Diam. -6, Length 1-3, Breadth 2-3 inches. 



Shell smooth, regularly elliptical, compressed, rounded behind, inecpuilateral ; sub- 

 stance of the shell rather thick, very slightly thicker before ; beaks a little prominent ; 

 ligament rather short, thin and brownish ; epidermis dark brown, obscurely rayed, 

 with rather distant marks of growth : umbonial slope slightly raised and subbiangular ; 

 posterior slope narrow, slightly raised, with obscure impressed lines from the beaks to 

 the 'margin ; cardinal teeth rather small, crenulate, double in both valves ; lateral 

 teeth rather long, lamellar and nearly straight ; anterior cicatrices distinct, rather 

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

 dorsal cicatrices placed immediately above the cavity of the beaks ; cavity of the shell 

 very shallow and wide ; cavity of the beaks very shallow and rounded ; nacre white 

 and iridescent. 



Remarlcs. — This belongs to the com-planaius group. It is remarkable for its exact 

 ellipse. There was only a single specimen received ; this was white in the nacre. 

 Others may be found to be purple or salmon, but I suspect that it will usually be a 

 clear white. 



Unio tuegidulus. PL 5, fig. 211. 



Testa lsevi, elliptica, subsequilaterali, ad latere vel paulisper planulata vel impressa; valvulis erassis, antice 

 crassioribus ; natibus tumidis, subelevatis incurvisque; epidermide luteo-olivacea, crebre virido-radiata ; 

 dentibus cardinalibus subgrandibus, elevatis, subconicis, crenulatis, in utroque valvulo duplicibus; late- 

 ralibus curtis, subcrassis subrectisque ; margarita alba et iridescente. 



