CHAPTER XIV 

 THE CLAM AND OTHER BIVALVES: PELECYPODA 



And I then engaged myself, with the other merchants, in a pearl fishery 

 in which I employed many divers on my own account. 



SINDBAD THE SAILOR, Arabian Nights. 



THE LONG-NECK CLAM 



Habitat and Distribution. The animal which is described 

 first in this chapter is commonly known as the long-neck 

 clam or the soft-shell clam. It is more accurately designated 

 by its scientific name, My 'a arena' ria (Fig. 82). As the spe- 

 cific name implies, the animal lives in the sand. It is found 

 in great abundance along our Atlantic coast, even as far north 

 as the Arctic regions. 



External Structure. The shell of the clam has the same gen- 

 eral use as the carapace of the crayfish. In both animals these 

 hard external parts protect the organs within from injury, and 

 also afford surface for the attachment of muscles. The clam's 

 shell, however, is never molted. It grows continuously from 

 the time it begins existence, at the little rounded prominence 

 called the umbo (pi., umbones), or beak (Fig. 82, l). 



Any one who has examined a dry shell of this kind can 

 tell which is the youngest portion of the shell. Probably he 

 will observe at the same time the little spoon-shaped piece 

 extending horizontally inward from one of the valves of the 

 shell. This projection is always on the left valve. It meets 

 a brown, rubber-like pad beneath the umbo of the right valve, 

 and is joined with it. As long as the two valves hold together 

 at this point, the pad, which is called the hinge-ligament, has 

 a tendency to separate the valves at an acute angle. In life 



157 



