THE PIDDOCKS. 



435 



THE two upper figures are examples of some very curious and common shells, 

 popularly called PIDDOCKS, and found in profusion along the sea-coast. 



The common Piddock may be found in vast numbers in every sea-covered chalk rock, 

 into which it has the gift of penetrating so as to protect itself from almost every foe. 

 The two specimens on the upper left of the engraving belong to this species, and are 

 represented so as to give two views of the same shell, the one to show the peculiar 

 curve of the shell and the protruding foot, and the other to exhibit the umbonal valves. 



Every one is familiar with the beautiful white shell of the Piddock, crossed by a 

 series of elegantly curved projections, something like the teeth of a file. According to 

 some writers, it is by means of these projections that the creature is able to burrow in- 



PIDDOCK.-PAo/as dactylas. PAPER PHOLAS.-PAo/as.-PAo/as papyracea. 



WATERING-POT SHELL. Asperglllum pulchellum. 



to the rock ; and the possibility of such a feat has been proved by the simplest possible 

 means, namely, by taking a Piddock into the hand and boring a similar hole with it. 

 Mr. Robertson, who kept these creatures alive in their chalky burrows, devoted much 

 time to watching them, and finds that during the process of burrowing they make a 

 half turn to the right and then back to the left, never turning completely round, and, in 

 fact, employing much the same kind of movement as is used by a carpenter when boring 

 a hole with a bradawl. 



Mr. Woodward remarks very justly, that " the condition of the Pholades is always 

 related to the nature of the material in which they are found burrowing ; in soft sea- 

 beds they attain the largest size and greatest perfection, whilst in hard and especially 

 gritty rock, they are dwarfed in size, and all prominent points and ridges appear worn by 

 friction. No notice is taken of the hypothesis which ascribes the perforation of rocks, etc. 



