66 NEW UNIONID.E 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. 



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

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

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



Unio exactus. pi. 4, fig. 210. 



Testa licvi, elliptica, compressa, postice rotundata, insequilaterali ; valvulis subcrassis ; natibus prominulis ; 

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

 utroque valvulo duplicibus ; lateralibus sublongis, lamellatis subrectisque ; margaritil alba et iridescente. 



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. 



Eah. — Neuse River, six miles from Ealeigh, 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, inequilateral ; 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. 



Bemarks. — This belongs to the compJanatus 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 turgidulus. PI. 5, fig. 211. 



Testa Isevi, elliptica, subsquilaterali, ad latere vel paulisper planulata vel impressa; valvulis crassis, antiee 

 cra.ssioribus ; 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 ; uiargarita alba et iridescente. 



