366 Mr. Osler on the burrowing 
should be produced where the soluble portion of a stone has 
been dissolved, and the insoluble particles are left projecting 
from the surface ; and even stronger facts may be adduced. 
Specimens are at all times to be obtained in which the shell has 
been extensively acted on by others ; while the cuticle, which 
had necessarily been exposed to the same agent, remains un- 
injured, and overhanging the breach. 
In Montagu's Testacea Britannica, it is stated on the 
authority of Pulteney, that Venerupis irus (Donax irus of 
Linnaeus) has been found in clay ; and the author affirms 
that he himself possessed specimens of Mya pholadia in stones 
not calcareous. Facts presenting so serious an exception to 
the general habits of the animal to bore into lime, would be 
fatal to the theory of a solvent, did they not admit of full 
explanation. The young animals, in seeking a convenient 
spot, almost invariably fix themselves in holes or crevices 
which afford them immediate shelter. Hence, they are oc- 
casionally found lodged among the roots of fuci ; and they 
will sometimes find a shelter in stone, upon which they are 
unable to act. I have met once with a Mya distorta, and re- 
peatedly with Saxicava rugosa and prascisa, lodged in soft 
argillaceous stone ; but in every such case the hole had 
clearly been made by a pholas, the remains of whose shells 
were generally found in it more or less dissolved by the 
Saxicava. The specimens I observed were in masses of rock, 
honeycombed by the pholas ; which, having probably been 
brought among ballast, have for many years formed part 
of the boundaries of the oyster banks in this neighbourhood, 
and which are within a very short distance of rocks abound- 
ing with Lithophagi. I have often found Mytilus edulis, and 
