PELECYPODA 



591 



,^,^^S. 930— Venus mercenaria 

 (Gould). 1, lunule; 2, umbo: 

 S, ligament. 



posterior end bluntly- pointed; umbo directed forwards; surface dirty 



white, witli prominent, sharp, concentric ridges; inner surface dull white, 



lower margin violet or purple; length 11 



cm.; height 9 cm.; width G cm.: Gulf of St. 



Lawrence to Texas, on sandy and muddy 



bottoms in shallow water, very common 



south of Cape Cod; used extensively for 



food; the shells were used by the Indians 



in the manufacture of wampum, the violet 



portion forming the most valuable pieces. 



V. cancellata L. Shell heart-shaped, 

 white, usually with brown spots; surface 

 with concentric ridges and radial furrows; length 4 cm.; height 27 mm.: 

 Cape Hatteras to west coast of Florida ; West Indies. 



2. Gemma Deshayes. Shell round, the umbo being nearly central; 

 3 cardinal teeth in the left and 2 in the right valve; pallial sinus long', 

 narrow, and ascending; lunule indistinct; margin crenulated within:"! 

 species on the Atlantic and Pacific coasts. 



G. gemma (Totten). Gem shell (Fig. 931). Shell small, with a 

 smooth shining surface and concentric ridges; color yellowish, white, or 

 pink ; umbo and hinder end amethyst ; length 4 mm. ; height 

 3.5 mm.; width 2 mm.: Labrador to Cape Hatteras, in the 

 sand in shallow water or between tide marks; often very 

 common; San Francisco. 



3. Callocardia Adams. Similar to Venus, but the 

 margin of the shell is not crenulated; hinge with 3 car- 

 dinal teeth in each valve and 1 or 2 laterals: numerous species; cos- 

 mopolitan. 



C. convexa Say (Fig. 932). Similar in appearance to Venus 

 mercenaria; length 43 mm.; height 35 mm.; width 24 mm.; no purple on 

 inner surface; siphons very long: Nova Scotia to 

 Florida; often common. 



4. DosiNiA Scopoli. Shell orbicular, com- 

 pressed, with concentric ridges; hinge like Cal- 

 locardia; lunule distinct; margin of shell not 

 crenulated; pallial sinus large, oblique, ascend- 

 ing; siphons united throughout: 100 species, in 

 shallow water. 



D. discus Reeve. Shell smooth, with 5 regular concentric grooves; 

 umbo pointed, with a large oblong groove underneath; muscle impres- 

 sions very large; color yellowish-white; length 66 mm.; height 61 mm.; 

 width 22 mm. : Virginia to Texas ; common. 



Fig. 931 

 Oemma 



fjemma 

 (Gould). 



Fig. 9.S2 — Callocardia 

 convexa (Gould). 



