ANODON. 



179 



Amdonta cataracta, Sat, Nicholson's Encyc. (Amcr. ed.) iv. pi. 3, fig. 4 (1816). 

 Aiwdonla Jltwiatilis, Lea, Trans. Amer. Thil. 8oc. (new series) vi. 138; Syuops. Naiad. 



51. — Stimpson, Shells of New EngUmd, 15. 

 Mijtilus illitiis, So LANDER, Portland Caial. 1G.3. 

 Lister, Conch, t. 111'. 



Shell transversely sub-oval, sub-cylindrical, thin, fragile, inflated; 

 beaks at the anterior two fii'ths of the shell, tumid, somewhat ele- 

 vated, and minutely undulated at tip. Hinge-margin straight ; an- 

 terior imperfectly angular above, nearly as high as behind 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 compressed into a sort of 



A. Jluvialilis. 



crest ; basal margin a good deal curved ; surface undulated some- 

 what 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 l)ehind and above, and 

 obscurely radiated. Nacre silvery, or tinged with bluish or yellow- 

 ish, margin greenish ; cavity of the beaks not deep, large ; hinge 

 edge very thin, rounded, scarcely curved. Length, four and one 

 half inches ; height, two and three fourth inches ; breadth, one and 

 one half inches. 



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, Charlestown. 



