180 



UNIONID^. 



It greatly resembles the A. cygnea of Europe, and is chiefly distin- 

 guished by the latter having the beaks less central, and not at all 

 elevated. From the next species the most obvious distinctions are, 

 the bright green-color, together with the thinness of the shell. It 

 is very difficult, if not impossible, to draw the line between our shell 

 and some of the species of the western waters. They seem, most 

 of them, to be mere variations in size. 



Anodon implicata. 



Fig. 78. 



Shell transversely oblong, sub-oval, variable in proportions, thick and strong, 

 exterior coarse ; epidermis yellowrish-olive ; nacre flesh-colored. 



Anodonta implkatn, Say, New Harmony Disseminator, 340 (1829); Mrs. Say's reprint, 

 11; Binney's reprint, 138. — Conrad, Synops. in Proc. Ac. Nat. Sc. vi. 264. — 

 Lea, Synops. 3d ed. 50. — Stimpson, Shells of New England, 1.5. 



Anodonta Neivloniensis, Lea, Trans. Amer. Phil. See. (N. S.) vi. 79, pi. 21, tig. 66 (1839). 



Anodonta marginata? Say (young), Nicholson's Encyc. Amer. ed. iv. pi. 3, fig. .5. 



Anodon implicata, Gould, Inv. 118, fig. 78. — De Kay, Nat. Hist. New York, 202. 



Shell transversely-oblong, sub-oval, almost as broad as high, sub- 

 cylindrical, thick, opaque, strong and heavy ; beaks removed about 



Fig. 481. 



A- implicata. 



two fifths of the length of the shell from the anterior end, rather 

 elevated, obtuse ; breadth of shell greatest behind the middle ; 

 hinge-margin a little curved, forming an angle at both its termina- 

 tions ; the backward slope from this angle is usually a little curved, 



