144 AMERICAN MARINE CONCHOLOGY. 
very minute. Surface smooth and diaphanous, the epidermis very 
shining. Pale violaceous, passing into olive towards the margins; 
the violet disposed in faint broadening rays. Within white, faintly 
iridescent, the transverse rib white. 
Length 2, height .8 inches. 
New England to New Jersey. 
This species is more southern in distribution than S. squama ; 
it is smaller, more fragile, and readily distinguished by its purple 
rays. 
Family MACTRID A. 
Animal with the mantle more or less open in front; siphonal 
tubes united, orifices fringed; foot compressed; gills not pro- 
longed into the branchial siphon. 
Synopsis of Genera. 
Shell thick, nearly equilateral; anterior hinge-tooth A shaped, with some- 
times a small laminar tooth close to it ; lateral teeth doubled in the right 
valve. MactTRaA. 
Shell thin, cordate, ventricose, slightly produced and rather gaping behind ; 
hinder slope keeled, narrow. RAETA. 
Genus MACTRA, Linnzus. 
Syst. Nat., edit. xii. 1125. 1767. 
The mactras inhabit sandy coasts, where they bury just beneath 
the surface; the foot can be stretched out considerably and 
moved about like a finger, it is also used for leaping. The ani- 
mal is eaten by star-fishes, whelks, pigs, and men. 
1. M. sonipisstmaA, Chemnitz, 336, 337. 
Conch. Cab., x. 350, t. 170, f. 1656. 
Mactra similis, Say, Journ. Philad. Acad., ii. 809. 1822. 
Mactra Raveneli, Conrad, Am. Mar. Conch., 65. 1881. 
Shell large, solid, subovate, or subtriangnular; cardinal fosset 
very large, cordate; lateral teeth transversely striated; muscular 
impressions very large ; epidermis dirty-brown. 
» Whole Coast. 
American authors have generally considered the M. similis dis- 
tinct from the above. It is said to be smaller in size, more trian- 
gular in outline, and to replace the solidissima on the Southern 
coast. Having collected these shells in large numbers at Atlantic 
City, N. J., a locality where northern and southern forms inter- 
