FRESHWATER AND LAND SHELLS. 



Unio obscurus. Plate III. fig. 7. 



Testa elliptica, transversa, iiKequilaterali, subinjlata ; vahuUs subcrassis ; natibus irregu- 

 lariter undulalis; dentibus cardinalibus elevatis; lateralibus prope eorum fines majoribus; mar- 

 garita alba et purpurea. 



Shell elliptical, transverse, inequilateral, somewhat inflated; valves rather thick; 

 beaks irregularly undulated; cardinal teeth elevated; lateral teeth larger near their ter- 

 mination ; nacre purple and white. 



Hab. near Nashville, Tenn. Professor Troost. 

 Cabinet of Professor Troost. 

 Cabinet of Mr Hyde. (White nacre.) 

 Diain. "8, Length l-I, Breadth 2 inches. 



Shell elliptical, transverse, inequilateral, somewhat inflated; sub- 

 stance of the shell rather thick ; beaks slightly elevated and irregularly 

 undulated: ligament rather short; epidermis yellowish brown; rays 

 placed on the posterior part, and somewhat linear; cardinal teeth double 

 in both valves, erect, crenulate, widely cleft in the left; lateral teeth 

 rather long, straight, and enlarged near their termination ; anterior cica- 

 trices distinct; posterior cicatrices confluent; dorsal cicatrices placed 

 on the inferior part of the lateral teeth; palleal impression distinct; 

 nacre white anteriorly, purple posteriorly. 



Remarks. — I owe to Professor Troost the opportunity of describing 

 this shell. There are no very striking characters in it, but it cannot 

 be classed with propriety with any species which I know. It seems 

 to possess a resemblance to U. Nashvillianus (nobis), and to U. glans 

 (nobis), two very different species. It is however distinct, and should 

 not be confounded with either. The single specimen here noticed is 

 the only one, I believe, yet found. When more are observed, charac- 

 ters somewhat different may be noticed. 



