34 INVERTEBRATA OF MASSACHUSETTS. 



valve. Hinge having the teeth seated upon the base of the rib ; 

 in the left valve three ; the first strong, ascending and curved.^ the 

 second still stronger and widely branched, one branch being erect, 

 the other nearly prostrate, the third very much compressed, 

 delicate, at right angles with the first and directed parallel to the 

 margin, just under the ligament ; on the other valve two teeth, the 

 first prominent, a little oblique, the other very thin and oblique, 

 entering between the middle and last tooth of the opposite valve. 

 Ligament quite protuberant. Height 1} inch, length 2^ inches, 

 width I inch. 



Not unfrequently taken from the stomachs of cod-fish caught on 

 the Banks, and sometimes ofi:'our shores. 



This species differs from all its co-species by the inclination of the 

 rib towards the longer side of the shell, and also by its apparent back- 

 ward curvature. It is, however, very closely allied to the shells 

 figured by Wood and Conrad. 



It is very rare to find all the teeth entire. The two thin teeth next 

 the ligament are almost always broken ; but a careful examination 

 will discover their vestiges ; and they never seem to be obsolete. 

 The erect tooth of the left valve is not unfrequently broken, and per- 

 haps one of the branches of the bifurcated tooth. The large tooth of 

 the right valve is most constant. 



Mach^'ra costa'ta. 



Shell thin, smooth, shining; epidermis greenish, zoned and 

 radiated with livid-violaceous ; internal rib inclining forward. 



Figure, see Wood-cut, page 24. 



State Coll., No. 239. Soc. Cab., No. 1716. 



Solen costktus, Say ; Journ. Acad. JVat. Sc.,u. 315. 



Solecurtus costatus, Say; £mer. Conch., p]. 18. Conrad; Amcr. Mar. Conch., 

 21,pl.4, f. 2. 



Shell ovate-elliptical, thin, fragile, smooth, and diaphanous ; 

 beaks very minute, placed at the anterior fourth of the shell ; pos- 

 terior side very little pointed, its upper margin compressed and 

 somewhat crested ; basal margin sometimes a little contracted ; 

 elsewhere regularly arcuated. Epidermis very smooth and shin- 

 ing, of a light yellowish-green color blended with livid-violaceous 



