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^. 



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. 



Spnopsis of Oenera. 



Shell thick, nearly equilateral ; anterior hinge-tooth \ shaped, with some- 

 times a small laminar tooth close to it ; lateral teeth doubled in the right 

 valve. Mactra. 



Shell thin, cordate, ventricose, slightly produced and rather gaping behind ; 

 hinder slope keeled, narrow. Raeta. 



Genus MACTRA, Linnaeus. 

 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 b}' star-fishes, whelks, pigs, and men. 



1. M. soLiDissiMA, Chemnitz, 3.3G, 3.37. 



Conch. Cab., x. 350, t. 170, f. 1656. 

 Mactra s^imilis, Sa}^, Journ. Philad. Acad., ii. 309. 1822. 

 Mactra Eaveneli, Conrad, Am. Mar. Couch., 65. 1831. 



Shell large, solid, subovate, or subtriangtilar ; cardinal fosset 

 very large, cordate; lateral teeth transversely striated; muscular 

 impressions very large ; epidermis dirt3'-brown. 



Whole Coast. 



American authors have generally considered the 31. simihs 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- 



