No. 034] UTILIZATION OF ECHINODERMS 



421 



which it carries in its mouth, and by use of which it drills 

 into the clam or whatever mollusk it may encounter, kill- 

 ing the same. This, it is claimed, is a common habit of 

 members of the family Naticidse of which the genera 

 Natica and Lunatica are best known. Daugherty (1912) 

 says: 



in the sand for clams and bores a hole with its radula, rotating its own 

 body in the action. 



Agersborg (1918), during the summer of 1916, observed 

 a number of specimens of Polynices in the actual act of 

 killing and eating clams. At low-tide, when rowing along 

 the shores of Dyes Inlet near Chico, Washington, a large 

 number of Polynices was found. As the tide was very 

 low it was possible to pick them up by using a dip-net. 

 Some of them, however, were not so easily removed from 

 the bottom as others, holding to the same by means of the 

 enormous foot, or having sucked down into the sand to 

 the depth of about ten centimeters, leaving only part of 

 the shell uncovered in the middle of a pit. It was soon 

 found that there was a definite cause for their holding on 

 to the bottom so firmly; these individuals of Polynices 

 were feeding. The process of feeding was found to be 

 somewhat different from that described by Keep, and 

 Daugherty. 



As Polynices crawls along the bottom it kills any clam 

 it encounters by suffocation. The soft-shelled clam, Mya 

 arenaria, which is quite numerous in the bays of Puget 

 Sound, is a common victim. Hard-shelled clams, Paphia 

 staminea, Cardium corbis, are also an easy prey for this 

 ravener. In the case of Mya, the gasteropod sucks itself 

 over the syphon down into the sand until its victim is dead 

 from suffocation, and then when the clam has opened, 

 Polynices simply sends its proboscis between the valves 

 and devours the content. As for the hard-shelled clams, 

 the process of feeding is similar to that used when eating 

 a Mya but the method of killing is different. In this 

 case the prey is held in the "sole" of the foot until the 



