156 AMERICAN MARINE CONCHOLOGT. 



Genus CEKONIA, Gray. 



1. C. ARCTATA, Conrad. Figs. 385, 386. 



(Mactra.) Journ. Philad. Acad., yi. 257, t. 11, f. 1. 1830. 

 Mactra deaurata, Conrad, Am. Mar. Conch. 59^t. 14, f. 1. 

 Mactra subtriangulata, Wood, Index Suppl. t. 1, f. 10. 



Shell subtriangular, wedge-shaped, thick and strong, smooth 

 and covered by a thin yellowish epidermis. Hinge with a Y-shaped 

 primary tooth and a long straight lateral tooth on either side, ' 

 partially double in the left valve and their articulating surfaces 

 striated. 



Length 37, height 25 mill. 



New York to Labrador. 



2. C. DEAURATA, Turton. Fig. 387. 



(Mactra.) Conch. Dithyra Brit., 71, t. 5, f. 8. 1822. 

 Mactra denticulata, Gray, in Wood Suppl., t. 1, f. 9. 

 Mesodesma Jauresii, Joannis, Mag. de Zool., t. 54. 1834. 



Shell ovate, triangular, thick, very rough with coarse concentric 

 ridges ; lateral teeth very strong, curved, faintly striated. 

 Length 43, height 26 mill. 



New Foundland, Gulf of St. Lawrence. 



This species is larger, more ovate in form, flatter, rougher than 

 C. arctata, and differs internally in its curved lateral teeth and 

 their obsolete striation. 



Genus ERVILIA, Turton. 

 Brit. Bivalves, 56. 1822. 



1. E. CONCENTRICA, Gould. 



Proc. Bost. Soc. Nat. Hist., viii. 280. 1862. 



Shell minute, *oblong-ovate, pellucid, shining, crowded with con- 

 centric raised striae ; umbones a little posterior, anterior more 

 acute than the posterior extremity. 

 Length 6-J-, height 4, diam. 3 mill. 



Dredged off the Coast of North Carolina. 



This little shell, which seems to be abundant along the whole 

 Southern coast, is quite different from anything before described. 

 GOULD. 



Family VENERID^E. 



Animal free, locomotive, rarely byssiferous or burrowing ; man- 

 tle with a rather large anterior opening ; siphons unequal, more 



