OBSERVATIONS OX LIVING SOLENOMYA. 265 



If burrowing posterior end downward is a common habit of 

 Soknomya it forms an exception to all lamellibranchs that 

 burrow. So far as I know all lamellibranchs that burrow in 

 sand, mud, wood or stone penetrate the substance anterior end 

 first, and in that position they rest. Indeed the foot is the 

 primary instrument used in effecting this penetration. Solen- 

 omya is unique in this respect. 



As before stated the creature, resting on its back, thrusts out 

 its foot in a pointed shape, presses the bottom of the dish, then 

 immediately withdrawing it at the same time expands the 

 fimbriated disk which unfolds in a graceful manner, and in that 

 expanded condition swings back and forth a few times in the 

 pedal opening which is widely distended. The overlapping 

 periosteum then folds abruptly within the shell, which closes at 

 the same time as the thick foot is drawn in between the polished 

 w r alls of the periosteum. The creature then falls over on its 

 side and remains in that position until the valves again open 

 which is almost immediately. The method of swimming has 

 been accurately described by Drew. The act consists in thrust- 

 ing out the foot, promptly expanding it and then suddenly with- 

 drawing it, at the same time closing the shell and expelling the 

 water from the siphonal end. These motions are often repeated 

 a number of times without the animal moving at all. When 

 these movements are made with sufficient vigor, however, the 

 animal seems to leap or dart in the water, anterior end forward, 

 going three or four times the length of the shell at each leap. 



Stimpson says: 'The thinness of the shell enables the animal 

 to make surprising leaps and I have seen it leaping or swimming 

 about the water for some time without touching the bottom. 

 The leap is performed by suddenly drawing in the umbrella- 

 shaped foot, at the same time that water is expelled from the 

 posterior opening by the closing of the valves." I counted the 

 number of darts made by different individuals and, though the 

 specimens I had were probably enfeebled by their long trans- 

 portation in a small glass vessel, I found the following result 

 22, 24, 31 and 36 darts respectively were made before the creature 

 fell to the bottom of the dish. The 36 darts were made by a 

 young individual. The darts w'ere vigorous, and w r ere made at 

 the rate of 90 to 100 a minute. 



