590 MOLLUSCA 



cm. ; width 7 cm. : Labrador to Cape Hatteras ; common on sandy bottoms 

 in shallow water; sometimes used for food; Europe. 



M. lateralis Say. Shell small, triangular, very convex; color white, 

 with a brown periostracum ; length 15 mm.; height 12 mm.; width 10 

 mm.: Nova Scotia to Texas; West Indies; in shallow water on muddy 

 bottoms; often very abundant, especially in Long Island Sound. 



2. LABIOSA Schmidt. Shell oblong, widely gaping, with the poste- 

 rior dorsal border reflexed and with a distinct ridge below: about 2 

 species on the Atlantic coast. 



L. lineata Say. Shell oval, the surface unequally and slightly 

 wrinkled; color white; length 7 cm.; height 5 cm.; width 28 mm.: New 

 Jersey to Texas; West Indies; in shallow water. 



SUBORDER 3. VENERACEA. 



Shell round, oval, or elongate ; usually thick and solid ; mantle edges 

 usually open below; siphons usually short and more or less united; pal- 

 lial sinus present; 2 adductor muscles: 3 families, all marine. 



Key to the families of Veneracea here described: 



di Shell regular and thick 1. VENEBIDAE 



a, Shell more or less irregular and thin 2. PETBICOLIDAE 



FAMILY 1. VENEBIDAE.* 



Shell regular, heavy ; ligament external ; hinge usually with 3 diverg- 

 ing teeth in each valve ; laterals not constant ; pallial sinus usually small ; 

 mantle open below: several hundred species, in all seas, those in the 

 tropics often very brightly colored. 



Key to the genera of Veneridae here described: 



Oi Margin of shell crenulated. 



6j Shell large with a rough surface 1. VENUS 



6, Shell small and smooth 2. GEMMA 



a. Margin not crenulated. 



&! Shell ovate 3. CALLOCABDIA 



6, Shell round, as high as long 4. DOSINIA 



1. VENUS L. Shell thick and round or ovate, inner lower margin 

 minutely crenulated; cardinal teeth 3 in each valve; laterals absent; 

 lunule distinct; ligament prominent; siphons short, unequal, and more 

 or less separated ; mantle margins fringed : numerous species, in all seas. 



V. mercenaria L.f Hard-shell clam. Round clam. Quahog (Fig. 

 930). SJiell ovate or heart-shaped; anterior end short and truncated; 



* See "Synopsis of the Family Veneridae and of the North American Recent 

 Species," by W. H. Dall, Proc. U. S. Nat. Mus., Vol. 26, p. 335, 1902. 



t See "Clam and Scallop Industries of New York," by J. L. Kellogg, Bull. 43, 

 N. Y. State Museum, 1901. "Feeding Habits and Growth of Venus Mercenaria," by 

 same, Bull. 71, same. 



