120 INVERTEBRATA OF MASSACHUSETTS. 



/ 

 ANODON UNDULA'TA. 



Shell transversely ovate, rather thick ; beaks prominent, epider- 

 mis dark-brown, radiated, coarsely wrinkled ; hinge margin undu- 

 lated, and with the vestige of a tooth. 



FIGURE 79. 

 State Coll., No. 170. Soc. Cab., No. 2191. 



Anodonta undulkta, SAY; Nicholson's Encyc., (Amer. ed.), iv. pi. 3, f. 6. LEA ; 



Synops. Naiad., 50. 

 Anodon rugosus, SWAINSON; Zool. lilustr., pi. 96. 



Shell oblong-ovate, thick and strong ; beaks sub-central, 

 elevated, the points in contact, and when not eroded they exhibit 

 four or five small undulations upon them ; before them is a spear- 

 shaped pit or areola, not covered by the epidermis ; behind them 

 the margin is slightly compressed, and has two or three coarse, 

 sub-marginal furrows ; no distinct angle at the termination of the 

 ligament ; posterior end somewhat bluntly rounded ; anterior end 

 compressed, sharply rounded ; basal margin regularly curved ; 

 epidermis dark-brown, radiated in most specimens, smooth, and 

 closely adhering towards the beaks, but lying in numerous, rather 

 loose folds near the margin ; interior inclined to salmon-color, and 

 granulated centrally, bluish-white outside of the palleal impression, 

 with a broad margin of olive-color. Hinge margin waved under 

 the beaks, compressed on the right valve so as to form something 

 like an elongated cardinal tooth, which is received into a corre- 

 sponding recess in the left valve. Length 3| inches, height 2 

 inches, breadth 1J inch. 



Found in the Blackstone River and its tributaries, of large size 

 and great perfection. 



It is impossible to be certain that this is A. undulata of Say, on 

 account of the small size of the specimen he described ; but it seems 

 to be the shell which Mr. Lea regards as such. It seems to be a 

 different thing from the shell described by Hildreth under that name. 

 I apprehend that it is the same as A. edentula, Say, and A. areoldtus, 

 Swainson. If there be any difference among them, it is, that our shell 

 is less compressed, less radiated, and less fragile than A. edentula. 

 The hinge is the same, and the areola before the beaks is produced 

 by a wave-like digression of the right valve to form a peculiar tooth. 

 The young shells are thin, and much more radiated than the old ones, 



