144 AMERICAN JOURNAL 



DESCRIPTIONS OF NEW AMERICAN FRESH WATER 



SHELLS. 



BY JOHN G. ANTHONY. 



1. Anobon McISTielii, Anthony. — t. 6, f. 1. 



Description. — Shell smooth, elliptical, somewhat inflated, 

 rounded before and biangular behind ; substance of the shell 

 thin and diaphanous; epidermis remarkably smooth and pol- 

 ished, of a pale yellowish-green color over the umbones, be- 

 coming darker and rougher on the posterior slope; beaks 

 prominent, rugose at tip, the wrinkles occupying nearly the 

 entire surface of the earliest growth; hinge margin slightly 

 curved, with ligament long and slender ; marks of growth dis- 

 tant and distinct, but not very broad, three only on each 

 valve; anterior and posterior cicatrices scarcely perceptible ; 

 nacre silvery white and iridescent. 



Dimensions. — Diam. 1 inch, length 2 7-10ths inches, breadth 

 1| inches. 



Habitat. — Michigan. 



Collection Mus. Comp. Zoology, Cambridge, Mass. 



Observations. — Without presenting any very prominent 

 characters, this shell seems perfectly distinct ; its texture is 

 remarkably thin and diaphanous, and it has a strong but not 

 very sharp carina on the umbonial slope; the basal edge is 

 curved upward behind, giving the shell rather a cuneate 

 appearance. 



2. Anodon subgibbosa, Anthony. — t. 6, f. 2. 



Description. — Shell smooth, inflated, subquadrate, inequi- 

 lateral, and very thin ; epidermis of a dull olive color and 

 without rays; marks of growth not distant but distinct, about 

 4 on each valve, indicated by a rather broad darker line; 

 beaks not very prominent, having coarse elevated rugae at tip; 

 anterior slope rounded, posterior slope obscurely angulated and 

 somewhat excavated ; anterior and posterior cicatrices both 

 very indistinct ; nacre bluish in color, but somewhat iridescent. 



