138 INVERTEBRATA OF MASSACHUSETTS. 



the margins are generally more or less plaited or scolloped, en- 

 tirely bony in the lower valve, but membranous and somewhat 

 flexible in the upper one. The hinge differs from the preceding in 

 having the beaks less prolonged, and the upper valve, instead of 

 having a lengthened, pyramidal ridge extending backwards to the 

 apex, has only a transverse ridge, abrupt behind, and sloping into 

 the shell, like a mere partition, behind which the cartilage is at- 

 tached. The muscular impression is also dark-violet. Interior, 

 either chalky or greenish-white. 



This species also grows to a great size. A specimen before 

 me measures a foot in length, and 6 inches in breadth. A com- 

 mon size is five and six inches in length. 



This is the common New York oyster, and, although they are 

 said to have been once abundant in various parts of Massachusetts 

 Bay, especially within Cape Cod, yet the Boston market is now 

 chiefly dependent for its supply on the oyster-beds in the vicinity 

 of New York and in the Chesapeake. In those parts of Buzzard's 

 Bay which border upon Sandwich, the native oyster is still 

 found in great abundance. 



The oystermen maintain that our shell is identical with the En- 

 glish O. edulis ; and there are certainly forms in which the Ameri- 

 can and European specimens could not be distinguished. 



GENUS ANEMIA, LAM. 



Shell irregular, inequivalve, one valve convex, the other flattened 

 or concave, perforated near the beak for the passage of a muscle, 

 by which it adheres. 



ANOMIA EPH'IPPIUM. 



Shell rounded, margin irregular ; surface scaly, variously 

 wrinkled and undulated ; beaks pointed, not quite reaching the 

 margin ; aperture ovate. 



State Coll., No. 146. Soc. Cab., No. 2060. 



6streum parvum, LISTER ; Conch., t. 204. 



An6mia ephippium, LIN. ; Syst. JVctf., 1150. GMELIN ; Syst., 3340, No. 3. GUALT. ; 

 Test., t. 97, f. B. D'ARGENV. ; Conch., t. 19, f. C. PENNANT ; Brit. Zool, iv. 

 t. 62, f. 70. CHEMN. ; Conch., viii. t. 76, f. 692, 693. MONTAGU ; Test. Brit., 

 155. WOOD ; Lin. Trans., vi. pi. 18, f. 11, 12. MATON and RACKETT ; Lin. 



