266 



EDWARD S. MORSE. 



The violent activity of the animal in its rapid darting through 

 the water, the repeated thrusting out of the heavy pedunculate 

 foot and vigorous closing of the valves accounts for the necessity 

 of the continued absorption of food as indicated by the rapid 

 accumulation of flocculent fcecal matter in the dish. 



The thirty-nine specimens, young and nearly adult, collected 

 April 27, were placed in a white enamelled pan and showed no 

 signs of increased enfeeblement for a week or more. The water 

 was changed often. At the end of three weeks they were all 

 dead, the young ones surviving the longest. 



The individuals showed no sen- 

 sitiveness to the obstruction of light, 

 nor did they align themselves in any 

 special way in relation to the lighted 

 window. They did not seem to have 

 the sensitiveness of other lamelli- 

 branchs; the jarring of the table did 

 not cause them to close, though agi- 

 tating the water or touching them 

 with a needle ever so slightly 

 prompted them to close their shells, 

 which remained closed for a few 

 seconds, when they slowly opened 

 and repeatedly thrust out the foot. 

 In fact they became very lively after 

 agitating the water. 



As one views a specimen from 

 below with the valves wide open 

 and the closed part of the mantle 

 stretched like a drumhead from the 

 margin of the periosteum, the calci- 

 ned portion of the shell is hardly in view. The periosteum, ex- 

 tended as it is when the valves are open, shows no marked 

 shoulder or channel at its junction with the thin membranous 

 mantle, though in section a slight break is seen. The pedal 

 opening is wide and extends backward nearly to the center of 

 the body, where the free mantle edges come together, forming an 

 elongated oval opening when distended, and through this opening 



FIG. i. 



View of animal from 

 below. 



