found on th-e Sea-Coast near Edinburgh. 101 



do so by the rotatory motion of their valves, or by means 

 merely mechanical ; while others suppose, from the apparent 

 fragility of the shell, that they must have the power of secret- 

 ing some solvent fluid, capable of decomposing the substances 

 in which they burrow. That the first of these hypotheses is 

 the one most conformable 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 opposes obstacles to its reception not easily 

 to be got over. Any acid or solvent fluid that would act with 

 effect on the calcareous stones in which the Pholades lodge, 

 would, it is evident, act equally on the shell of the animal it- 

 self; 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 uncover- 

 ed 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 Candida, were procured alive, in great num- 

 bers, and of all ages. When the tide recedes, they withdraw 

 their tube within the perforations, 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 Myae and Solenes are disturbed in their haunts. 

 The Pholades are found at various depths in the stone, cor- 

 responding 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 inter- 

 mediate distances, the youngest being merely covered by a 

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

 species on some coasts, occurs most plentifully ; but both spe- 

 cies 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 widen as they recede downwards, corresponding to the 

 animal's growth. The Pholas itself is found in an inverted 



