162 AMERICAN MARINE CONCHOLOGY. 
1. P. PHoLADIFORMIS, Lamarck. Figs. 402, 403. 
Anim. sans Vert., vy. 565. 1818. 
Petricola fornicata, Say, Journ. Philad. Acad., ii. 319. 1822.+ 
Petricola dactylus, Say (not Sowb.), Am. Conch, t. 60, f.2. 1834. 
Shell elongated, anterior side short, with strong ribs crossed by 
waved striz ; posterior side with radiating lines and gaping; teeth 
three in one valve, and two in the other. White. 
Length 37, height 17 mill. 
Whole Coast. 
Family CYPRINID. 
Animal with the mantle-lobes united posteriorly by a curtain, 
pierced with two -siphonal orifices; foot thick, tongue-shaped ; 
gills two on each side, large, unequal, united behind, forming a 
complete partition; palpi moderate, lanceolate. 
Synopsis of Genera. 
Shell large, oval, strong, with usually an oblique line or angle on the pos- 
terior side of each valve ; epidermis thick and dark ; ligament prominent, 
umbones oblique, no lunule ; cardinal teeth 2.2, laterals 0-1, 1-0, mus- 
cular impressions oval, polished. CyPRIN A. 
Shell suborbicular, compressed, thick, smooth or concentrically furrowed ; 
lunule impressed ; ligament external; epidermis dark; hinge-teeth 2.2, 
the anterior tooth of the right valve large and thick ; anterior pedal scar 
distinct. ASTARTE. 
Shell minute, triangular, furrowed ; hinge like Astarte, with lateral teeth. 
' GOULDIA. 
Shell rounded or oblong, radiately ribbed; margin toothed ; hinge-teeth 
1.2, and an elongated posterior tooth; anterior pedal scar close to ad- 
ductor. CARDITA. 
Genus CYPRINA, Lamarek. 
Extr. d’un Cours. 1812. 
1. C. Istanpica, Linneeus. Figs. 404, 405, 406. 
(Venus.) Syst. Nat., edit. xii. 1131. 1767. 
Shell large, thick, and ponderous, ventricose; beaks prominent, 
incurved, contiguous. Ligament stout and prominent; basal 
margin simple, rounded. Cardinal teeth stout and diverging, 
lateral inconspicuous. Epidermis coarse and wrinkled, blackish, 
becoming olivaceous or brownish towards the margin. 
Length 3.3, height 2.8, diam. 1.4 inches. 
Massachusetts, northward (Hur.). 
