132 INVERTEBRATA OF MASSACHUSETTS. 



most common shells found in the stomachs of fishes caught in 

 Massachusetts Bay. The shell is not often so large as above 

 mentioned. 



Its rounded-oval and regularly convex form, with its radiating lines, 

 forbid that it should be confounded with any other shell except an En- 

 glish species, the Crenella elliptica of Brown, ( Conch, lllust. of Great 

 Brit., 4c. pi. 31, f. 12 to 14,) the My'tilus decussdtus of Montagu. 

 For my own part, in comparing a small specimen of this shell with 

 one of ours of a similar size, I must confess I can discover no differ- 

 ence, though Mr. Sowerby supposes they are distinct. In giving the 

 dimensions I have supposed the shell to be placed in the ordinary po- 

 sition of other species, with the beaks placed laterally. 



FAMILY PECT&NIDES, LAM. 



Ligament interior or half interior. Shell in general regular, compact, not 

 foliated. 



GENUS PECTEN, TURTON. 



Shell rounded, inequivalve, eared ; superior margin straight ; 

 beaks contiguous. Hinge toothless, with a triangular internal 

 pit for the cartilage. 



PECTEN MAGELLA'NICUS. 



Shell orbicular, inequivalve, upper valve more convex than the 

 lower ; exterior surface everywhere marked with closely arranged 

 radiating lines', interior surface without ribs; ears small and 

 equal. 



State Coll., No. 152. Soc. Cab., No. 2028. 



6'strea Magellanica, GMELIN ; 3317. No. 9. CHEMN. ; Conch., vii. t. 62, f. 597. 



DILLWYN; Catal., 250. 

 Pecten Magellanicus, LAM.; An. sans Vert., vii. 134. DESHAYES; Encyc.M&th., 



Vers, iii. 718, pi. 208, f. 5. CONRAD ; Amer. Mar. Conch., pi. I, f. 1. 



Shell orbicular, rather higher than long, thin and translucent 

 when young, thick, strong, and opaque when mature, equilateral, 

 inequivalve, the lower valve being nearly flat, and not attaining 

 the edge of the upper valve by an eighth of an inch or more ; 



