THE FRESH-WATER (J LAM 



233 



Fig. 222. — On the mud-flat, digging the soft-shell clam. 



naria, which is the commonest species, and is most abundant 

 south of Cape Cod. It owes its name " mercenaria " to the 

 fact that the purple-colored patch seen on the margin of the 



Fig. 223. — Venus mercenaria, the hard-shelled clam. At the left the foot 

 protrudes from the shell ; at the right the siphons. Nat. size. FromVerrill, 

 " Invertebrates of Vineyard Sound." 



