192 AMERICAN MARINE CONCHOLOGY. 



Shell orbicular, very variable, translucent, and slightly pearly within, at- 

 tached by a plug passing through a hole or notch in the right valve ; 

 upper valve convex, smooth, lamellar or striated ; interior with a sub- 

 marginal cartilage-pit and four muscular impressions, three subcentral, 

 and one in front of the cartilage ; lower valve concave, with a deep 

 rounded notch in front of the cartilage process ; disk with a single (ad- 

 ductor)'impression. Anomia, Linnaeus. 



Shell suborbicular, regular, resting on the right valve, usually ornamented 

 with radiating ribs ; beaks approximate, eared ; anterior ears most prom- 

 inent; posterior side a little oblique; right valve most convex, with a 

 notch below the front ear ; hinge-margins straight, united by a narrow 

 ligament ; cartilage internal, in a central pit ; adductor impression double, 

 obscure ; pedal impression only in the left valve, or obsolete. 



Pecten, Midler. 



Shell equivalve, compressed, obliquely oval ; anterior side straight, gaping, 

 posterior rounded, usually close ; umbones apart, eared ; valves smooth, 

 punctate-striate or radiately ribbed and imbricated ; hinge-area triangular, 

 cartilage-pit central; adductor impression lateral, large, double ; pedal 

 sears two. small. Lima, Brug. 



Shell irregular, attached by the umbo of the right valve ; valve smooth or 

 plaited ; hinge-area obscure ; cartilage quite internal ; hinge-teeth two in 

 each valve ; adductor scar simple. Plicatula, Lam. 



Genus OSTREA, Linnaeus. 



Syst. Nat., edit. x. 696. 1758. 



Animal with the mantle-margin double and finely fringed ; the 



gills are nearly equal, united posteriorly to each other and the 

 mantle-lobes, forming a complete branchial chamber ; lips plain; 

 palpi triangular, attached ; sexes distinct. 



1. O. Virginian a, Lister. Figs. 528, 529. 



Couch., t. 200, f. 34. 1686. 

 Ostrea Vi\ inica, Gmel. Syst. Nat., 3336. 1790. 

 Qstrea ( isis, Lam. Anim. sans Vert., vii. 226. 1822. 



Shell narrowly elongated, whitish, thick-lamellar; upper valve 

 rather plane; becoming thick with age, the lower beak projecting 

 and with an inner channel transversely channelled; muscular im- 

 pression chestnut or violet-color. 



Varies from 6-12 inches in length, and 3-4 inches in breadth. 



Whole Coast. 



This is the common edible oyster of Chesapeake bay; it is 

 native about as far north as Xew York, where it is replaced by 

 the northern species 0. borealis. It is also found on the Xew 



