382 NEW EXOTIC UNIONIDiE. 



compressed, erect, crenulate, double in both valves ; lateral teeth long, crenulate and 

 slightly curved; nacre silver-white and very iridescent. 



Hab. — Uruguay River, South America, Prof. J. Wyman. 



My cabinet. 

 Diam. 1*1, Length 1-9, Breadth 2-9 inches. 



Shell smooth, somewhat sulcate before, quadrate, compressed, flattened at the 

 sides, inequilateral, obtusely angular behind and rounded before ; substance of the 

 shell rather thick, thicker before ; beaks somewhat prominent, with diverging 

 undulations at the tips extending but a short distance ; ligament rather long, some- 

 what thick and light-brown ; epidermis dark-olive, striate, subsulcate, without rays 

 or very obscurely rayed, disposed to be darker on the posterior half, with somewhat 

 distant marks of growth ; umbonial slope slightly raised and rounded ; posterior 

 slope elevated into a well-defined carina, with one indistinct impressed line in each 

 valve from the beak to the posterior margin ; cardinal teeth compressed, erect, 

 crenulate, double in both valves ; lateral teeth long, crenulate and slightly curved ; 

 anterior cicatrices confluent, well impressed ; posterior cicatrices confluent and very 

 slightly impressed ; dorsal cicatrices placed in a row across the cavity of the beaks ; 

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

 rounded ; nacre white and very iridescent. 



Remarks. — This species is near to U. Uruguay ensis, herein described, and belongs 

 to that group of which hdeolus, Lam., may be considered the type. It is more com- 

 pressed and more quadrate than the latter, but has the same divergent undulations, 

 is of nearly the same color in the nacre and epidermis, and is about the same size. 

 The nacre is of a remarkable brilliant silvery white. The larger of the two 

 specimens before me is disposed to be trifid in both cardinal teeth ; but this charac- 

 ter will, I think, be found not to be common. I have great pleasure in naming this 

 species after my friend Prof. J. Wyman, who liberally placed in my hands all the 

 specimens of Unionidce which he collected during his voyage to Uruguay. 



Unio gratus. PI. 43, fig. 290. 



Testa laevi, subrotunda, subinflata, inasquilaterali, antice et postice rotundata ; valvulis suborassis, antice 

 aliquanto crassioribus ; natibus subprominentibus, ad apices divaricate undulatis; epiderniide tene- 

 broso-f'usca, micaute, obsolete radiata ; dentibus cardinalibus parviusculis, compressis striatisque ; 

 lateralibus sublongis subcurvisque ; margarita alba et iridescente. 



Shell smooth, subrotund, somewhat inflated, inequilateral, rounded before and 

 behind ; valves somewhat thick, rather thicker before ; ' beaks a little prominent, 

 with diverging undulations at the tips ; epidermis dark-brown, shining, obsoletely 

 rayed ; cardinal teeth rather small, compressed and striate j lateral teeth rather 

 long and somewhat curved ; nacre white and iridescent. 



