CHIEFLY OF THE UNITED STATES. 267 



Shell sulcate, triangular, somewhat inflated, nearly equilateral, biangular behind 

 and obliquely rounded before; valves very thick, thicker before; beaks prominent; 

 epidermis olive color, roughly sulcate, obscurely raj^ed ; cardinal teeth thick, rugose 

 and raised; lateral teeth rather long, rather thick, lamellar and slightly curved ; 

 nacre silvery white and iridescent. 



Proc. Acad. Nat. Sci. 1866, p. .33. 



Hah. — Central America, Don. Patricio M. Paz. 



My cabinet and cabinet of Don. P. M. Paz. 

 Diara. 1-4, Length 2-2, Breadth 3 inches. 



Shell sulcate, triangular, somewhat inflated, nearly equilateral, biangular behind 

 and obliquely rounded before ; substance of the shell very thick, thicker before, 

 with a broad and thickened border; beaks prominent, rather pointed ; ligament rather 

 large and light brown ; epidermis olive color, darker on the umbones and posterior 

 slope, with distant, indistinct marks of growth ; umbonial slope angular; posterior 

 slope narrow elliptical, with an indistinct furrow on each valve ; cardinal teeth large, 

 thick, rugose, raised and obtusely pointed ; lateral teeth rather long, rather thick, 

 lamellar and slightly curved; anterior cicatrices distinct, very large and well im- 

 pressed ; posterior cicatrices confluent, very large and slightly impressed ; dorsal cica- 

 trices placed above the centre of the cavity of the beaks ; cavity of the shell rather 

 deep and wide ; cavity of the beaks obtusely angular and somewhat deep ; nacre 

 silvery white and iridescent. 



Remarks. — There were two specimens, nearly of the same size, sent to me by Don 

 P. M. Paz. The species is very distinct, and belongs to that sulcate group which 

 generally prevails with the Central American species. The specimens were marked 

 as coming from the United States, but I have no hesitation in saying that this must 

 be an error ; the species having all the analogous characteristics of the Central Ameri- 

 can species. It has some resemblance to U. Kitahrooldanus (nobis), but is much thick- 

 er, higher in the beaks, more sulcate and darker colored. It is allied to Neiocomhi- 

 anus (nobis), from Lake Nicaragua, and might be taken for tlie old of that species, 

 but it is very much larger, very much heavier, more inflated, has a much more cor- 

 rugate surface and is not so lenticular. In the rugosulcatus the nacre is of a remarka- 

 bly pure pearly white, and on the umbones and beaks the olive color is nearly i-e- 

 placed by a greenish brown color. 



Unio firmus. pi. 34, fig. 82. 



Testa Itevi, elliptica, subiuflata, valde inrequilaterali, postice et antice rotuudata ; valvulis crassiusculis, 

 antice aliqiianto crassioribus ; natibus proniinulis ; epidermide viridi-fusca, eradiata ; dentibus car- 

 dinalibus subcrassis, compressis, in utroque valvule duplicibus ; lateralibus longis, laracllatis sub- 

 curvisque ; margarita argentca et valde iridescente. 



68 



