NEW UNIOXID.'E OF THE LXITED STATES. 64 



Unio percoarctatus, pi. 3; fig. '200. 



Testa liEvi, quadratri, valdi- coarctata, ad latere planulata, posticfs subbiangulata ; vilJc in;>;(iuilatcrali ; 

 valvulis tenuibus; natibus vix promiDentibus, ad apices undulatis; epi'iermide tenebroso-fusea, minute 

 ct valde striata; dentibus cardinalibus parvis, striatic, in utroque valvulo duplicibus; latjralibus pra;- 

 longis, limellatis reolisque; margaritii purpurea et valJe iridescenlo. 



Shell smooth, quadrate, very much compressed, flattened at the side^, subbiangular 

 behind, very inajquilatcral ; valves thin ; beaks scarcely prominent, undulate at the 

 tips ; ei)idermis dark brown, much and finely striate ; cardinal teeth small, striate, 

 double in both valves ; lateral teeth very long, lamellar and straight ; nacre purple 

 and very ii'idescent. 



I'loc. Acad. Nat. Sei. 1857, p. 85. 



/Z"a&.— Catawba Kiver, Gaston Co., N. C. C. M. Wheatloy and Dr. Gonth. 



My cabinet and cabinet of Mr. Wheatley and Dr. Genth. 

 Diani. -8, Length IS, Breadth ow inches. 



Shell smooth, quadrate, very much compres.'^ed, flattened at the sides, subbiangu- 

 lar behind ; substance of the shell thin, slightly thickened before ; beaks scarcely 

 prominent, undulate at the tips; ligament long, thin and dark brown; epidermis dark 

 brown, closely and finely striate; umbonial slope very slightly raised, obtusely an- 

 gular; posterior slope raised into a high carina, very much compressed and covered 

 with loose stria;; cardinal teeth small, striate and double in both valves; lateral teeth 

 very long, lamellar and straight ; anterior cicatrices distinct, large and well impressed ; 

 posterior cicatrices confluent, large and slightly impressed; dorsal cicatrices in a row 

 across the centre of the cavity of the beaks; cavity of the shell very shallow and very 

 wide; cavity of the beaks very shallow and rounded; nacre purple and very irides- 

 cent. 



Remarhs. — A number of fine specimens were given to me by Mr. "Wheatley, but 

 none were received in alcohol. This species belongs to the complanatus group, but 

 differs from them all in being more compressed, and in having the whole surface 

 covered with loose stria;. These striae are remarkable in this species, the whole 

 surface being usually covered ; and the edges being loose, a variable glossiness is 

 exhibited, except on the posterior slope, which is fuller, and here it is velvety. The 

 stria) are usually coarse and rough along the basal and anterior margins. AH the 

 numerous specimens I have seen are purple in the nacre, some of them tinged with 

 salmon color. None of the adult specimens were rayed; some of the young ones are 

 obscurely rayed. . 



Uxio .MicAxs. PI. 3, fig. 207. 



Testa licvi, eUiptica, subcomprcssa, valde inajquilaterali, poslic^ angulata; valvuli.s subtenuibus, postic6 

 crassioribus ; natibus proniinulis; epideroiide luteo-fusca, valde radiata et vald^ inicante; dentibus 

 cardinalibus parvis, cotnprcssis, ercctis crenulatisque ; lateralibus lougis, lamellutis rectisque; margarita 

 vel alba vel salmonis colore tincta et valde iridescente. 



