PELECYPODA 



591 



Fig. 930 Venus mercenaria 

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

 3, ligament. 



posterior end bluntly pointed; umbo directed forwards; surface dirty 



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



lower margin violet or purple; length 11 



cm. ; height 9 cm. ; width 6 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: 1 



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 



Gemma 



gemma. 



(Gould). 



Fig. 932 Callocardia 

 convexa (Gould). 



