CHIEFLY OF THE UNITED STATES. 47 



anterior cicatrices distinct, rather large and deeply impressed; posterior cicatrices 

 confluent, large and slightly impressed ; dorsal cicatrices placed in the centre of the 

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

 beaks shallow and obtusely angular ; nacre very purple and iridescent. 



Bemarhs. — Two specimens of this small species were presented to the Academy of 

 Natural Sciences by Mr. Anthony. They were labelled U. Vanuxemii, (nobis,) but 

 they certainly are not that species, which is wider and not so dark in the nacre or 

 the epidermis. Both the specimens have a dark purple nacre. It is very near to 

 fuscatus (nobis) in outline, but is not quite so transverse, is a thicker and darker 

 shell. The fine hair-like rays on the posterior portion remind one of Troost'd, (nobis), 

 but it cannot be confounded with that species! 



Unio biemarginatus. pi. 16, fig. 45. 



Testa Isevi, triangiilari, innsquilaterali, postice biangulata, ad latere sulcata, ad basim et postice emargi- 

 nata ; valvulis suborassis, antice crassioribus ; natibus prominentibus, compressis ; epidermide rufo- 

 fusca, valde radiata ; dentibus cardinalibus parvis, valde crenulatis, subconicis, in utroque valvule 

 duplieibus ; lateralibus curtis, crassis rectisqiie ; margarita alba et iridescente. 



Shell smooth, triangular, inequilateral, biangular behind, sulcate on the side, 

 emarginate at the base and behind; valves rather thick, thicker before ; beaks some- 

 what prominent and compressed; epidermis reddish brown, very much rayed; 

 cardinal teeth small, very crenulate, somewhat conical, double in both valves; 

 lateral teeth short, thick and straight ; nacre white and iridescent. 

 Proc. Acad. Nat. Sei., 1857, p. 83. 



Eah. — Florence, Alabama, Rev. G. White. 



My cabinet and cabinet of Mr. White. 

 Diam. -64, Length 1-10, Breadth 1-41 inches. 



Shell smooth, triangular, inequilateral, biangular behind, sulcate on the side, 

 emarginate at the base and behind ; substance of the shell rather thick, thicker be- 

 fore ; beaks somewhat prominent and compressed ; ligament short, rather thick and 

 brown ; epidermis reddish or yellowish brown, very much rayed, with distinct and 

 rather distant marks of growth ; umbonial slope raised and biangular ; posterior 

 slope somewhat flattened, cordate, with a wide groove from the beaks to the margin ; 

 cardinal teeth small, very much crenulate, somewhat conical and double in both 

 valves ; lateral teeth short, thick, straight, thicker towards the end ; anterior cica- 

 trices distinct, small and well impressed ; posterior cicatrices confluent, large and 

 very slightly impressed ; dorsal cicatrices placed over the cavity «of the beaks and 

 along the case of the cardinal tooth ; palleal cicatrices emarginate ; cavity of the 

 shell shallow ; cavity of the beaks rather deep and obtusely angular ; nacre silvery 

 white and iridescent. 



