OSTRACEA. MOLLUSCA. OSTREA. 137 



O'strea rostrata maxima, CHEMN. ; Conch., viii. 38, t. 73, f. 677. 



O'strea elongata, SOLANDER; Mss. . 



O'strea Canadensis, LA.M.; Jin. sans Vert., vii. 226. 



Shell narrow, elongated, gradually widening, moderately curv- 

 ed, for the most part with a long and pointed beak at the apex, 

 and rounded at the other extremity. Upper valve the smallest, 

 flattest and smoothest, surface, when not worn, presenting every- 

 where leaf-like scales, of a somewhat leaden-color. The hinge 

 presents the usual channel in the beak of the lower valve, longer 

 or shorter according to the age of the shell, and marked with lines 

 exhibiting the successive removes of the cartilage ; and in the up- 

 per valve we have the corresponding elevation, which is also con- 

 tinued back to the point of the shell. The muscular impression 

 is nearly central, of a dark-chestnut, or sometimes dark violet- 

 color. It often measures 12 or 15 inches in length, but seldom 

 more than 3 inches in breadth. 



This is the common oyster of the Chesapeake Bay. It is oc- 

 casionally found in the vicinity of Boston, and also about Prince 

 Edwards' Island, at the mouth of the St. Lawrence. Its dis- 

 tinctive characters are its narrow, elongated form, and the length- 

 ened, pyramidal hinge ridge along the beak of the upper valve. 

 The O. Canadensis is either a variety of this, or the next species, 

 most likely of this. 



O'STREA BOREA'LIS. 



Shell somewhat rounded, curved, scaly , greenish ; beaks rather 

 short, considerably curved ; hinge having the furrow in the lower 

 valve from the apex, but having in the opposite valve merely a 

 transverse ridge, not extended backwards. 



State Coll., No. 149. Soc. Cab., No. 2055. 



O'strea borealis, LAM.; An. sans Vert., vii. 220. 



O'strea Canadensis, BRUG. ; Encyc. M6th., pi. 180, f. 1 to 3. 



O'strea edulis, LIN ; &c. 



Shell somewhat obliquely rounded-ovate, usually curved, up- 

 per valve smallest, flattest ; the beaks are never greatly prolong- 

 ed, more curved than in O. Virginica. The surface is very 

 irregular, displaying loosely arranged flakes of a greenish-color ; 

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