270 Mr. Barties on the Genera Unio and Alasmodonta. 



straight ; cavity of the beaks small and rather shallow, na- 

 ker pearly white and iridescent, surface smooth and polished. 

 Variety (a) shell less, more ovate, broader before, hinge 

 margin more elevated. 



Remarks. -This is a beautiful and elegantly formed shell. 

 It somewhat resembles a pea-pod; hence its name. It 

 agrees in color and surface with the Unio Ventricosus, but 

 differs in being of smaller size, longer in proportion, more 

 cylindrical, less inflated, beaks much less elevated, and cav- 

 ity less capacious. 



22. Unio Ovatus. — Shell roundish-ovate, convex, 

 umbones elevated, beaks recurved, anterior lu- 

 nule flattened ; teeth crest-like elevated. 



Unio Ovatus. Mr. Say. 



Unio Ovata. M. Lamarck. 



Inhabits the Ohio. Mr. Collins. 



Maumee, at Fort Wayne. Mr. Scars. 



Mr. Collins' Collection. My Collection. 



Diam. 1-6— 2-0 Length 2-3— 3-0 Breadth 3-3— 4-0. 



American Conchology, plate 2, fig. 7. 



Shell usually broader before, and narrower behind the 

 beaks ; but in the figure referred to above, the contrary is 

 •observed ; thin when young, and not remarkably thick 

 when old; disks swelled; umbones prominent; ligament 

 partly concealed ; anterior lunule flattened, and fuscous, 

 somewhat waved with striae and wrinkles becoming lamel- 

 lar; hinge margin making- an angle with the anterior and 

 posterior dorsal ; epidermis yellowish, or horn color; sur- 

 face glabrous, deeply wrinkled, wrinkles appearing on the 

 inside ; cardinal teeth crest-like, elevated and compres- 

 sed ; lateral teeth elevated ; in some specimens, short, 

 crooked, and apparently deformed; in others, straight; 

 cicatrices smooth and polished ; cavity large and rendered 

 somewhat angular by the flattening of the anterior slope ; 

 naker pearly, bluish white ; surface, in old specimens, pa- 

 pillous, in young, smooth. 



Remarks. — The angular appearance produced by the 

 fattening of the anterior slope, readily distinguishes thi? 



