AND DESCRIPTIONS OF NEW SPECIES. 75 



that conchologist says, "hinge with a primary tooth in each valve." In 

 the oriens the cardinal and lateral teeth are equally imperfect, and in 

 this respect it resembles the U. soleniformis (Nob.), though much less 

 defined. Under these circumstances, it appeared necessary to give it a 

 place with the Uniones. 



Unio Brevidens. Plate VI. fig. 6. 



Testa subtriangulari, incequilaterali, transversa ; valvulis crassis ; dentibus car- 

 dinalibus modicis, lateralibus curvis, brevibus, crassisgue ; margarita alba. 



Shell subtriangular, inequilateral, transverse; valves thick; cardinal teeth rather 

 small ; lateral teeth curved, short, and thick ; nacre pearly white. 



Hab. Ohio, William Cooper. 



My Cabinet. 



Cabinet of Lyceum of Natural History of New York. 



Diam. -8, Length 1 •2, Breadth 1-7 inches. 



Shell sub-triangular, angular behind, transverse; umbonial slope 

 curved ; sides flattened ; substance of the shell thick ; beaks slightly 

 prominent ; ligament short ; epidermis yellow, wrinkled ; rays small, 

 slightly curved and interrupted ; cardinal tooth rather small, slightly 

 elevated and widely cleft in the left valve, single and emerging from 

 a pit in the right valve ; lateral teeth curved, short and thick, posterior 

 and anterior cicatrices both distinct ; the smaller posterior one be- 

 ing placed directly over the larger and beneath the point of the lateral 

 tooth ; dorsal cicatrices situated on the under part of the cardinal tooth ; 

 cavity of the beaks arched, shallow ; nacre pearly white. 



Remarks. — For this interesting and fine species we are indebted to 

 the liberality of the members of the Lyceum of Natural History of 

 New York, who, in accordance with their known zeal in the promotion 

 of natural science, promptly passed a vote to permit their new fluvia- 

 tile shells (herein described) to be described for, and inserted in our 

 Transactions, under the impression that science would be benefited by 



