FRESHWATER AND LAND SHELLS. 75 



render it impossible to form a correct opinion as to its appearance in 

 a perfect state. 



Unio contradens. Plate XVIIl. fig. 58. 



Testa obovata, subinflald, ina&quilaterali ; valvulis tenuibus; natibus subprominentibus 

 undulatisque ; epidermide subviridi ; dentibus cardinalibus linealis, duplicibus in valvulam dex- 

 tram ; lateralibus tenuibus subcurvisque ; margarita alba et iridescente. 



Shell obovate, rather inflated, inequilateral ; valves thin ; beaks rather prominent and 

 undulated ; epidermis greenish ; cardinal teeth linear, the double one in the right valve ; 

 lateral teeth thin and somewhat curved ; nacre pearly white and iridescent. 



Hab 



My Cabinet. 

 Diam. -7, Length 1*1, Breadth 1-9 inches. 



Shell obovate, rather inflated, smooth, inequilateral; substance of the 

 shell thin; beaks somewhat prominent, with numerous small undula- 

 tions extending on the posterior slope ; ligament rather long and thin ; 

 epidermis yellowish green over the whole disk, except the posterior 

 slope, which is green ; cardinal teeth long, linear, single in the left 

 and double in the right valve ; lateral teeth long, thin, and somewhat 

 curved ; anterior cicatrices confluent ; posterior cicatrices confluent ; 

 dorsal cicatrices placed in the centre of the cavity of the beaks ; cavity 

 of the shell rather deep ; cavity of the beaks rather shallow and angu- 

 lar; nacre pearly white and iridescent. 



Remarks.- — I am not acquainted with the habitat of this shell, having 

 purchased it of a dealer, who did not know from what waters it was 

 obtained, In the exterior and general appearance it resembles U. Tap- 

 panianus (nobis). The remarkable character of its cardinal teeth will 

 distinguish it from that and all other species with which I am acquaint- 

 ed- The single and double tooth have here changed places, the single 

 being in the left valve. They are thin, and run nearly parallel to the 

 margin. The undulations about the region of the beaks are remarka- 

 bly fine and beautiful. 



