BIVALVES V KNITS. 41 



longitudinal or transverse stria.*, sometimes nitli Loth, 

 which net unfrequently terminate in foliations near the 

 margins. 



The interior of the shells of this genus is often adorned 

 with rich coloring,* as in the Venus mercenaria or wam- 

 pum clain, uiiicli in fine specimens is of a rich purple. 

 It is from these shells thai the North American Indians 

 make their wampum or money. Tlic same sliell, in a fossil 

 state, is often found in the Swedish mountains. 



The hinge of the Venus, with scarce any exception, 

 contains three teeth, all approximate or close to each 

 other; besides these tlirce, tliere is a lateral tooth, not 

 unfrequently divergent at the tip, the iimer margin of the 

 sliell is sometimes crcnuhite. Some of tlie species, though 

 rarely, gape. 



Almost all parts of the world supply specimens of this 

 genus. The American, African, Eastern, and Western 

 Oceans abound with them. The Mediterranean, Caspian, 

 and Southern Sras likewise produce some species; as also 

 do the European and more northern oceans. 



Several species are Ibund in a fossil state. 



VENUS. 



A. Shell somewhat heart-shaped, 

 Dioue (Pi'lckbj mouthed V-) J^apicida, 

 Paphia , Divergens. 



Marica. *Casina (Broad ribbed.) 



Dysera. Cancellata. 



Bajana. *Gallina. 



Excavata. (ruineeusis. 



*Vcrrurosa (GUI tcoman.) Pctulca. 



