OP THE GENUS UNIO. 269 



beyond the margin, nearly terminal, decorticated — ligament 

 partly concealed by the beaks — epidermis reddish-brown, 

 smooth; — surface somewhat v^Tinkled — cardinal tooth thick, 

 elevated, compressed at top, crenulated ; direction same as la- 

 teral tooth — lateral tooth long, thick and slightly curved, ab- 

 rupt — posterior cicatrices distinct, as are also the anterior ones 

 - — cavity of the beaks small — nacre pearly-white, silvery and 

 iridescent in the posterior margin. 



Far. a — red inside, rare. 



Cabinet of the Academy of Natural Sciences. 

 My Cabinet. 



Remarks — The ellipsis approaches somewhat to a variety of 

 the mytiloides of Rafinesque, but is more swollen and ponde- 

 4-ous, and differs in always having an elliptical margin. 



5. Unio Irroratus. Plate V. fig. 5. 



Testa inaquilaterali, stib-orbiculatd, longitudinali, tuberculata, rugosd, 

 longitudinaliter uni-sulcatd ; dente late7'cdi abrupte terminante. 



Shell inequilateral, suborbicular, longitudinal, tuberculated, wrinkled, 

 longitudinally sulcatcd ; termination of lateral tooth abrupt. 



Hab. Ohio. T. Bakewell. 



My Cabinet. 

 Cabinet of T. G. Lea. -^ 



Cabinet of Prof. Vanuxem. 

 Cabinet of the Academy of Natural Sciences. 

 Mr Nicklin's Cabinet. 

 Diam. 1-3, Length 1-8, Breadth 1-6 inches. 



Shell extremely thick and swollen — nearly round, slightly 

 elongated — substance of the shell thick and ponderous — beaks 

 somewhat elevated and recurved, decorticated— dorsal mar- 

 gin rounded ; posterior, posterior dorsal and posterior basal 

 margins rounded ; basal margin slightly emarginate ; anterior 



VOL. III. 3 Y 



