100 PnOLADIDiE. 



work in tlic manner I have described ; the altered figure of 

 the shell, and the increased weight of that part of the 

 animal behind the hinge, would prevent it from raising 

 itself so perpendicularly as at first, independent of the 

 narrow space which it occupies. In the motions required 

 to enlarge its habitation, the adductors perform a very 

 essential part. The animal being attached by the foot, 

 brings the anterior part of the shell into contact. The 

 lateral muscles now contract, and, raising the posterior ad- 

 ductor, bring the dorsal margins of the valves into contact, 

 so that the strong rasp-like portions are suddenly separated, 

 and scrape rapidly and forcibly over the substance on 

 which they press. As soon as this is effected, the posterior 

 extremity sinks, and the stroke is immediately repeated by 

 the successive contraction of the anterior adductor, the 

 lateral, and the posterior adductor muscles. 



" The particles rubbed off, and which, in a short time, 

 completely clog the shell, are removed in a very simple 

 manner. When the projected syphon is distended with 

 water, the Pholas closes the orifices of the tubes, and 

 retracts them suddenly. The water, which they contained, 

 is thus ejected forcibly from the opening in the mantle ; 

 and the jet is prolonged by the gradual closure of the 

 valves, to expel the water contained within the shells. 

 The chamber occupied by the animal is thus completely 

 cleansed ; but as many of the particles washed out of it 

 will be deposited before they reach the mouth of the hole, 

 the passage along which the Pholas projects its siphon 

 is constantly found to be lined with a soft mud." 



In a valuable i>aper on the anatomy of the lamellibran- 

 chiatc mollusca published by Mr. Garner in the second 

 vol. of the Zoological Transactions, that excellent observer 

 has some short remarks on the means bv which Pholas and 



