DESCRIBED FROM PERSONAL OBSERVATION. 255 



men, both before and while the hole at the base of 

 the cavity was gradually being enlarged, was 

 watched, and every striking and interesting feature 

 that occurred noted down at the moment. Various 

 queries were put and answered, as far as possible, by 

 direct ocular demonstration of the labours of the 

 animal in the vase before me. 



I consider myself to have been singularly fortunate 

 in being able to view the actions of the creature from 

 beneath, in consequence of the hole beingbored through 

 the rock. This circumstance allowed me distinctly to 

 see what was going on at the base of the orifice. 



My early observations have fortunately been con- 

 firmed in other captive Pholades, which at various 

 periods have been domesticated in my tank. 



I am convinced, then, that the .shell forms the 

 principal agent in boring the animal's dwelling, 

 without either acid or flinty particles. The late 

 lamented Professor Forbes held that if this were the 

 case, the rasping points on the surface of the valves 

 would soon be worn down, an appearance which, 

 he says, is never seen. With all respect for such 

 an eminent name, I must state that he was in error. 

 Not only are the edges at certain times worn, but 

 the rough surface is worn nearly smooth, appearing 

 in certain parts of a white colour, instead of a light 

 drab, as usual. 



But the reader may ask, if certain parts of the 

 valves are occasionally worn smooth, and the animal 



