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, Miiller. 



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 

 scars 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 08TREA, 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. 



Jl. 0. VIRGINIANA, Lister. Figs. 528, 529. 



Conch., t. 2QO, f. 34. 1686. 



Ostrea Virginica, Gmel. Syst. Nat., 3336. 1790. 

 Ostrea Canadensis, 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 New York, where it is replaced by 

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



