118 INVERTEBRATA OF MASSACHUSETTS. 



hind the beaks ; upper posterior margin forming an obtuse angle 

 at the termination of the ligament, and declining in a straight line 

 to form a somewhat produced, blunted point ; this margin is com- 

 pressed into a sort of crest ; basal margin a good deal curved ; 

 surface undulated somewhat irregularly by the lines of growth ; 

 epidermis smooth and close except at the upper and posterior 

 portion, where it is loosely wrinkled ; a few radiating series of 

 wrinkles may also be seen ; color a deep grass-green, becoming 

 dusky behind and above, and obscurely radiated. Nacre silvery, 

 or tinged with bluish or yellowish, margin greenish ; cavity of the 

 beaks not deep, large ; hinge edge very thin, rounded, scarcely 

 curved. Length 4| inches, height 2f inches, breadth 1J inch. 



Inhabits ponds in the western and central parts of this State, 

 and is seldom found in any other part. Professor Adams, however, 

 assures me he has found it at Falmouth, and I have collected a 

 few specimens from clay-pits near Winter Hill, in Charlestown. 



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

 tinguished 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 IMPLICA'TA. 



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

 and strong ; exterior coarse ; epidermis yellowish-olive ; nacre 

 flesh- colored. 



FIGURE 78. 

 State Coll., No. 169. Soc. Cab., No. 2192. 



Anodonta implicata, SAY ; New Harmony Disseminator. 



Anodonta Newtoniensis ? LEA ; Trans. Amer. Phil. Soc., (New Series,) vi. 79, 



pi. 21, f. 66. 

 Anodonta marginata? SAY ; (young) Nicholson's Encyc., (Ame,r. cd.),iv. pi. 3, f. 5. 



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

 sub-cylindrical, thick, opaque, strong, and heavy ; beaks removed 

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

 rather elevated, obtuse ; breadth of shell greatest behind the 



