Pelecypoda. 



105 



times the whole shell is buried in the soil ; this seems 

 to be the case more often in the winter, when the clam 

 is less active, or after freshets which cover the clams with 

 mud. 



The Clam at Home. By watching the clam in its natural 

 habitat the position, as above described, may be observed. 

 It may be seen that the shell is slightly agape ; that a soft 

 membrane protrudes from the opened edges of the shell ; 

 that at the posterior end are two elliptical openings. It 

 may be proved that a current of water is entering one of 

 these openings and issuing from the other. If the borders 



FIG. 64. CLAM IN NATURAL POSITION. 



With foot and siphons extended. 



of these openings are touched, the soft membrane forming 

 the margins of the openings is withdrawn into the shell, 

 and the shell is tightly closed. If a clam, previously un- 

 disturbed, be quickly pulled out of the mud, a soft, fleshy 



