﻿ANODONTA 



395 



There seems to be almost no limit to the variation of this 

 species. It may be smooth or rough, shining- or dull, light or 

 dark, and it varies greatly in the degree of its inflation and 

 elongation. Its most constant distinguishing character is the 

 very full, rounded ridge or inflation that starts with the beaks 

 and is carried outward, then downward and backward towards 

 the posterior termination of the shell. The greatest degree of 

 inflation of this is in front of the posterior ridge. 



Group of Anodonta imbccillis. 



Shell thin, elliptical, sometimes slightly produced near the 

 center of the base, pointed behind, with a slight posterior 

 dorsal wing ; area of the beaks generally flattened, though 

 often full ; beak sculpture consisting of several rather delicate, 

 irregular ridges, which show a tendency to break into nodules ; 

 epidermis bright and smooth, often marked with l>eautiful, del- 

 icate, capillar}' rays ; nacre bluish. Animal sometimes highly 

 colored ; gills nearly alike in size, having a distinct border of 

 dififerent texture ; eye-spots on branchial opening generally 

 perceptible. 



Anodont.v iMiucciLLis Say. 



Shell oblong, thin, with dorsal and ventral lines nearly par- 

 allel, pointed behind at or above the median line, inequilateral, 

 convex or inflated ; beaks compressed or flattened, not pro- 

 jecting above the nearly or quite straight dorsal line, their 

 sculpture consisting of a few rather feeble, irregular, broken 

 ridges, which are sometimes faintly doubly looped : posterior 

 ridge low. curved down in the middle ; epidermis generally 

 smooth, yellowish-green or blue-green, often banded and feebly 

 rayed, with two or more wide, ill-defined, dark rays, on the 

 posterior slope ; muscle scars scarcely visible : nacre pale blue 

 or bluish-white. 



Length f)2. height 45. diam. 35 mm. 



Length 75, height 38, diam. 25 mm. 



