OBSERVATIONS ON PECTEN DISLOCATUS. 26 1 



The slight flatness of the left valve does not serve to make them 

 settle always upon the same side. 



THE FUNCTIONS OF THE FOOT. 



The foot lies just opposite the notch in the right valve. It 

 appears to be functionless in adult specimens, or rarely used by 

 them, but is made use of to good advantage by the young. 

 Specimens were often seen to extend the foot anteriorly to a 

 remarkable distance, attach it at the tip to the bottom and then, 

 by a powerful contraction, draw the body forwards to the point 

 of attachment. The foot is cylindrical and seems very small to 

 carry such a load ; and frequently, after it has been extended 

 and attached, the valves are opened and clapped together, at the 

 same time the foot contracts, the body thus being drawn forward 

 with much less strain upon that organ. This method of loco- 

 motion is a combination of swimming and creeping. The force 

 of the current of water expelled from the mantle chamber serves 

 to raise the body and propel it forwards as far as the attached 

 foot will permit. At the same time, the foot contracts and the 

 body lands close to the point of attachment. When this method 

 of locomotion is used, the foot, instead of being extended directly 

 outwards, anteriorly, is usually directed more ventrally, so that 

 the point of attachment is more nearly in line with the force ex- 

 erted by the swimming movement. Except for the notch in the 

 right valve, this sort of performance would not be possible, be- 

 cause by the closure of the valves, the foot would be crushed. 



The foot is, also, frequently used in turning the body over, 

 when placed upon the left valve ; it is extended anteriorly from 

 the body and attached ; the valves are opened and clapped 

 together vigorously ; the body, as a result, is raised and shot 

 forwards, but the weight of the foot and the resisting pull from 

 its attachment cause it to swing over upon the foot as a pivot, 

 the scallop landing upon the other valve, having turned through 

 an arc of 180 degrees. 



The above method of turning over, is usually, if not quite uni- 

 versally, used by specimens when placed upon the left side for 

 the first time. After a little handling, however, they become 

 much more irritable, seeming to be excited, and at such times, they 



