156 AMERICAN MARINE CONCIIOLOGY. 



Genus CEKONIA, Gray. 



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



(Muctra.) Journ. Philad. Acad., vi. 257, t. 11, f. 1. 1830. 

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

 Mactra sitMriangulata, 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 V-shaped 



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



partial!}^ 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 Snppl., t. 1, f. 9. 

 Mesodesma Jauresii, Joanuis, 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. 



JVew Foundland, Oulf of St. Latorence. 



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

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

 their obsolete striation. 



Genus EKVILIA, 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 striiB ; umbones a little posterior, anterior more 

 acute than the posterior exti'emity. 



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



Dredged off the \Joast of North Carolina. 



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

 Southern coast, is quite different from anj'thing before described. 

 — Gould. 



Family VENERID^E. 



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

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



