Pelecypoda. 119 



end. There is but one adductor muscle ; the foot is yet 

 undeveloped, but from the foot region project long threads, 

 the "byssus," by which it becomes attached. At the tip 

 of each valve there is an incurved hook by which the little 

 clam usually catches hold of the fin or gill of a fish, 

 whereby it is protected from enemies and kept in fresh 

 water. Soon after it thus becomes attached it is covered 

 by a growth of the skin (a diseased growth) which still 



FIG. 73. YOUNG CLAM, STILL WITHIN THE EGG MEMBRANE. 



m, adductor muscle ; t, hooks by which it attaches itself to the gills or fins of fishes ; b, byssus ; 

 s, sense organs. 



further protects the parasite. When sufficiently mature, 

 the young clam drops off, soon becomes like the adult in 

 form, and shifts for itself. 



Salt-water Clams. Although several kinds of marine 

 clams are used as food, there are two that are more largely 

 eaten in this country. One is Venus mercenaria, found 

 from Texas to Cape Cod, but rare north of that point ; the 

 other Mya arenaria, found generally along the coasts of 

 the Eastern states, but rather distinctively more Northern 

 than the other. So when Massachusetts people speak of 

 clams they mean the Mya, commonly designated elsewhere 

 as the "soft clam," "soft-shelled clam," "long-necked 

 clam," or "long clam." Whereas, when New Yorkers 

 mention clams, without any qualifying adjective, they have 



