found on the Sea-coast near Edinburgh. 433 



shell, that they must have the power of secreting some solvent 

 fluid, capable of decomposing the substances in which they bur- 

 row. That the first of these hypotheses is the one most confor- 

 mable to appearances, no one who has seen the living animals 

 can doubt, and accordingly, it has been adopted by most recent 

 observers ; while that supported by MONTAGU and others op- 

 poses .obstacles to its reception not easily to be got over. Any 

 acid or solvent fluid that would act with effect on the cal- 

 careous stones in which the Pholades lodge, would, it is evident, 

 act equally on the shell of the animal itself; and a solvent which 

 possessed the power of dissolving stone, would be little likely to 

 have the same effect on the fibres of submerged wood. 



Some years ago, while residing at Portobello, I discovered, on 

 the coast at Joppa Salt-pans, where the rocks are uncovered at low 

 water, numerous perforations in the shale or clay-rock, which I 

 ascertained to be the work of Pholades. On breaking the stone 

 in different places two species of Pholas, P. crispata and candi- 

 da, were procured alive, in great numbers, and of all ages. 

 When the tide recedes, they withdraw their tube within the per- 

 forations, but when covered by the water, its rounded mouth is 

 visible above the upper surface of the rock. On striking the 

 rock with a hammer, near any of the holes, a spirt of water is 

 ejected, similar to what occurs when the Mya? and Solenes are 

 disturbed in their haunts. The Pholades are found at various 

 depths in the stone, corresponding to the age of the animal ; the 

 largest, and of course oldest, specimens being found at from four 

 to six inches, or even more, under the surface ; others at all in- 

 termediate distances, the youngest being merely covered by a 

 thin layer of the clay. The Pholas Candida, not a common spe- 

 cies on some coasts, occurs most plentifully ; but both species are 

 frequently found together. 



The perforations in the rock at the surface are not much 

 larger in diameter than a quill ; many are much smaller, but they 



