nS AMERICAN MARINE CONCHOLOGY. 



Genus ABCA, LinnjKus. 

 Syst. Nat., edit. x. 1758. 



The animal has a long-pointed foot, deeply grooved, and heeled, 

 mantle furnished with ocelli ; palpi ; gills long, narrow, less 

 striated externally, continuous with the lips ; hearts two, each 

 with an auricle. 



The Areas with close valves have the left valve a little larger 

 than the right, and somewhat overlapping at the margin. 



There are about two hundred species ; distribution universal, 

 ranging from low-water to 230 fathoms. 



1. A. No^, Linnjeus. Fig. 404. 



Syst. Nat., edit. xil. 1140. 1767. 

 A. zebra, Swaiusou, Zool. lUust., Nc. 26, t. 118. 



Shell elongately oblong, anterior side very short, [)osterior side 

 emarginate, with a blunt keel extending from the unibone to the 

 margin; ventral margin more or less gaping; white, with waved 

 brownish streaks; radiately ribbed; ligament area flatly concave. 



North Carolina to West Indies. {Medit.) 



2. A. PONDEROSA, Say. Fig. 467. 



Journ. Philagl. Acad., 11. 267. 1822. 

 Sliell very thick and ponderous, somewhat oblique, with 25 to 

 28 ribs, eacii marked with an impressed line. Beaks distant, op- 

 posite the middle of the hinge ; lower margin nearly straight or 

 even somewhat contracted in the middle. 



Length 2.5, height 2 inches. 



Southern Coast. 



Fossil valves of this species sometimes occur on the beach at 

 Cape Ma3' and Atlantic City, N. J. 



3. A. TRANSVERSA, Say. Fig. 465. 



Journ. Phil. Acad., ii. 269. 1832. 



Shell transversely oblong, rhomboidal, with from 32 to 35 ribs, 

 umbones separated by a long narrowarea; extremities of the hinge 

 margin angulated ; epidermis chestnut-brown. 



Length 30, height 8.5 mill. 



Neio England., New York., southicards. 



4. A. LiENOSA, Say. Fig. 469. 



Am. Concli., iv. t. 36, f. 1. 1833. 

 This shell is described as fossil, and worn (probably fossil) 

 valves are found abundantly at Beaufoit, N. C. It is admitted 



