OYSTERS AND SMALL CLAMS 57 



Stomach between the two shells of its victim and 

 digesting him alive; various "drills," or small sea- 

 snails, which bore their way through the shell and 

 attack a vital spot; also mud, which may be washed 

 in in time of freshet and then bur}^ the helpless crea- 

 tures; also frost, which may occur during cold morn- 

 ings in the winter when the tide is low and the beds 

 of oysters are left exposed to the lull influence of 

 the weather. This last enemy is not much feared in 

 California, but is liable to cause extensive damage 

 farther to the north. 



The native oysters reproduce rapidly, but experi- 

 ments with the imported species have not been alto- 

 gether satisfactory. It is certain, however, that some 

 of their young do survive and grow, and the subject 

 needs further investigation. Large oysters always 

 command a high price upon the Pacific coast, and 

 this fact has led to a great trade in canned oysters, 

 put up on the other side of the continent. Some at- 

 tempts have been made to introduce living Japanese 

 oysters upon the northern coasts of California. The 

 whole subject is one of great interest, and in a finan- 

 cial way, is perhaps the most important problem 

 connected with our study of western mollusks. 



We now come to a very different family 

 of mollusks, and the}^ are far more regular^ 

 in shape than those that we have just been 

 considering. Figure 26 gives a good idea ^'^-^e 

 of the Little Heart-shell, Cardita subquadrata, 

 Cpr. The name is very much longer than the shell, 

 and even the little picture is too large for ordinary 

 specimens. It is a firm, hard little shell, however, 



