242 DESCRIPTION OF 



Read June 1 8ih, 1841. 



Unio argenteus. Plate 25, Fig^. 57. 



Testa obliqud, oviformis, valde compressd, valde incequilaterali, postice subangulata; valvulis sub- 

 crassis; natibus subprominentibus ; epidermide luteo-fuscd, polita; dentibus cardinalibus suhgrandibus ; 

 lateralibus longis subcurvisque ; margaritd argented et iridescente. 



Shell oblique, oviform, much compressed, very inequilateral, subangular behind ; valves rather thick : beaks 

 somewhat prominent; epidermis yellowish brown, polished; cardinal teeth rather large; lateral teeth long 

 and somewhat curved; nacre silver white and iridescent. 



Hab. Holston River, East Tenn. Dr. Troost and Mr. S. M. Edgar. 

 My Cabinet, and Cabinets of Dr. Troost and Mr. Edgar. 

 Diam. .8, Length 1.6, Breadtli 2.5 inches. 



Shell oblique, oviform, much compressed, very inequilateral, subangular 

 behind, and regularly rounded before, with two compressed lines behind the 

 umbonial slope, substance of the shell rather thick, thinner behind; beaks 

 somewhat prominent; ligament rather long and thick; epidermis brown, po- 

 lished and shining on the superior portion, with regular and somewhat distant 

 lines of growth; cardinal teeth rather large, not much elevated; lateral teeth 

 long, rather thick and slightly curved; anterior cicatrices distinct; posterior 

 cicatrices distinct ; dorsal cicatrices placed on the under side of the plate be- 

 tween the cardinal and lateral teeth ; cavity of the shell very shallow, cavity of 

 the beaks very shallow and angular ; nacre silver white and iridescent. 



Remarlcs. — In a box sent to me by Dr. Troost and Mr. Edgar from the 

 waters of East Tennessee, there was a single specimen of this shell. In form it is 

 most nearly allied to U. oviformis, Con., but it differs in being rather more com- 

 pressed. In colour it differs entirely, being much darker and being devoid of 

 rays. 



Uxio sPARSus. Plate 25, Fig. 58. 



Testa sparsim tuberculatd, triangulari, subinflatd, subequilaterali, postice emarginatd, ad Idtus pla- 

 nulatd; valvulis crassis; natibus elevatis; epidermide luteold; dentibus cardinalibus grandibus, late- 

 ralibus brevissimus rectisque; margaritd albd et iridescente. 



