182 POPULAR BEITISH CONCHOLOGY. 



to cover the head. The mautle has a fold, or siphon, hmng 

 the canal of the shell. 



Perhaps the flap, or " mentum/^ may be serviceable to 

 the CeritJiojms in swimming, as it has been observed to 

 push the front of the foot with its flap far beyond the head 

 when indulging in that exercise, which is not so much the 

 case wdien the motion is that of walking. 



