CHIEFLY OF THE UNITED STATES. 51 



Shell smooth, wide, approaching the elliptical, intiated, very inequilateral ; sub- 

 stance of the shell thick, thicker before ; beaks rather prominent, with four or five 

 small, granular undulations at the point of the tips ; ligament rather long, broad and 

 light brown ; epidermis very smooth, shining, light straw color, with a single mark 

 of growth towards the margin, without rays ; unibonial slope raised and rounded ; 

 posterior slope rather broad, with two indistinct, impressed lines in each valve from 

 the beaks to the posterior margin ; cardinal teeth compressed, corrugate, crenulate 

 and double in both valves ; lateral teeth very long, corrugate, enlarged towards the 

 end and nearly straight ; anterior cicatrices distinct and well impressed ; posterior 

 cicatrices confluent and moderately well impressed ; dorsal cicatrices placed on the 

 upper part of the cavity of the beaks ; cavity of the shell rather deep and wide ; 

 cavity of the beaks rather deep and obtusely angular ; nacre silver white and some- 

 what iridescent. 



Remarks. — This is a well characterized species, and it is to be regretted that a 

 single specimen only should be observed, as others might present different characters. 

 It has a remarkably smooth, clean epidermis, of a clear, pale straw color. Fortu- 

 nately the tips are perfect, and present at the point very small granular undulations 

 in two rows. The single mark of growth which is presented in this specimen is 

 broad and well defined, and is placed near to the margin. I doubt if this species is 

 ever rayed, yet on one valve there are obscure indications of rays. In outline and 

 in color of the epidermis this species is very closely allied to Anodantoid&s, (nobis,) 

 from the Mississippi and Ohio basins, and particularly like the very thick ones found 

 near Cincinnati. It differs entirely in the system of the undulations of the beaks, in 

 having no rays, and in being less iridescent. Among the Asiatic species it is most 

 nearly allied to Mosulensis and to Bourguignatiamis, herein described, but it is a 

 thicker shell than the former, more transverse, and in the system of the undulations 

 of the beaks entirely different. It is a larger and thicker shell than the latter, is 

 more transverse, is less iridescent, and has not the same marks of growth. 



Unio dignatus. pi. 17, fig. 48. 



Testa Isevi, valde obliqua, inflata, ad apices tumida, valde injequilaterali, ad latere parum planulata ; 

 valvulis percrassis, antice crassioribus ; natibus prominentibus, tumidis, iacurvis, terminalibus, ad 

 apices parum granulatis ; epidermide vel lutea vel luteo-fusca, micante, eradiata ; dentibus cardinali- 

 bus erectis, compressis et crenulatis ; lateralibus prselongis, lamellatis subcurvisque ; ruargarita 

 argentea et valde iridescente. 



Shell smooth, very oblique, inflated, swollen at the beaks, very inequilateral, 

 slightly flattened at the sides; valves very thick, thicker before; beaks prominent, 

 swollen, incurved, terminal, somewhat granulate at the tips; epidermis yellow or 

 yellowish brown, shining, without rays; cardinal teeth erect, compressed and crenu- 



