?Kam. 30.] NATUKAL HISTORY SOCIETY. lOS 



The foot is used, in a curious and beautiful way, for leaping and 

 swimming backward and forward through the water without 

 touching bottom ; it is also used for burrowing. Usually found 

 buried, in mud or sand near low water mark ; more abundant 

 in bays. 



1. Soknomya velum, Say. Shell very thin and fragile, oblong, 

 •ends rounded, the front end longer and wider; umbones not 

 elevated at all, but having a i3it behind them; surface radiated, 

 with about 15, slightly impressed, double lines; epidermis ex- 

 tends about 2 mm, beyond the edge, and is thinned or notched 

 at the radiations. Epidermis yellowish-brown or chestnut color, 

 the radiating lines lighter; interior of shell bluish-white. Size, 

 including epidermis, L. 25; H, 12; W. 8; U. f.— Whole coast. 

 .Not rare. 



2. Solenomya boreaUs, Tot. , Similar to the last but larger, 

 thicker and with the epidermis more projecting, more decidedly 

 notched and darker in color. L. 50; H. 22; W. 14; U. f.— 

 Whole coast. Rare, 



Family 29. CORBULID/E. 

 Shell small, inequivalve, thick, gaping in front; hinge consist- 

 ing of one recurved tooth in one valve, fitting into a notch in 

 the other. Animal with mantle closed except in front, the 

 narrow opening notched; siphons short, united, fringed. Liv- 

 ing in sand or mud. 



1. CoRBULA, Brug. 



Shell small, inequivalve, thick; umbones nearly central; 

 about one tooth in each valve and an internal cartilage between 

 them. Animal with short, united siphons ; orifices fringed ; foot 

 thick. 



1. Corbida contrada, Say. Shell small, ovate-globose, solid; 

 anterior end shorter, broader, rounded and gaping; posterior 

 somewhat pointed ; left valve shutting within the edge of the 

 right at the bottom ; gonial ridge distinct ; one cardinal tooth in 

 each valve and the cartilage between them ; surface beautifully 

 marked with regular, smooth, rounded, concentric ridges. Shell 

 white, epidermis brctwn. L. 10 ; H. 6 ; W. 5 ; U. a little nearer 

 anterior end. — Cape Cod and south. 



Family 30 MYID/E. 

 Shell rather strong, opaque and gaping ; left valve with a spa- 



