PELECYPODA 577 



VENERICARDIA Lamarck. Shell with a rough periostracum ; hinge 

 with 2 large oblique cardinal teeth and 1 lateral in each valve; ligament 

 external: several species on the Atlantic coast. 



V. borealis (Conrad) (Fig. 906). Shell with about 20 rounded ribs; 

 umbo elevated and turned forwards, almost to the anterior end in old 

 shells; length 25 mm.; height and width 17 mm.: New Jersey to Lab- 

 rador; in rather deep water; Pacific coast. 



FAMILY 2. ASTABTIDAE. 



Shell thick, equivalve, with 2 or 3 strong cardinal teeth in each 

 valve ; ligament external ; laterals absent or rudimentary ; lunule distinct ; 

 a short cloacal siphon present: about 

 12 genera, all marine. 



ASTARTE Sowerby. Shell roundly 

 oval, with a smooth surface marked 

 with concentric striations: 20 species, 

 circumpolar. 



A. castenea (Say) (Fig. 907). Fig. 906 Fig. 907 



Chestnut shell. Shell thick, ovate; Fig. 906 Venericaudia borealis 



(Gould). Fig. 907Astarte casta- 

 umbo elevated and nearly central; an- nea (Gould). 



terior end slightly concave, posterior 



slightly convex ; color chestnut ; length and height 25 mm. ; width 13 mm. : 



New Jersey to Nova Scotia; in shallow water; often common. 



A. undata Gould. Like the above, with 10 to 20 strongly developed 

 concentric ridges; color brownish-olive; length 25 mm.; height 27 mm.; 

 width 14 mm. : Long Island Sound to Gulf of St. Lawrence, in shallow 

 water; common; Pacific coast. 



A. quadrans Gould. Shell triangular, smooth, yellowish in color; 

 umbo central ; length 11 mm. ; height 10 mm. ; width 5 mm. : Long Island 

 Sound to Gulf of St. Lawrence. 



FAMILY 3. CRASSATELLITIDAE. 



Shell thick, equivalve, more or less triangular; umbo towards the 

 forward end, usually concentrally striated; hinge with 1 or 2 cardinal 

 teeth; lunule distinct; ligament internal; no closed 

 siphons: about 6 genera, all marine. 



CRASSATELLITES Kriiger. Umbo nearly central, an- 

 Crassafeila terior dorsal line straight ; 2 cardinal teeth in right valve, 

 ^GtouHO? and * in the left ; ! lateral in each: 1 species on the 



Atlantic coast. 



C. mactracea (Linsley) (Fig. 908). Shell small, solid, with about 14 

 concentric ribs on the surface; color yellowish-green; 6 mm. long and 



