6 
My experience of the habits of the Pkolas in boring into 
rocks or other bodies is very limited, in fact the only in- 
stance which has come under my observation, is that of the 
Pholas Candida in the stiff clay, at low water mark, on 
the beach of Blackpool. During the last summer, my 
attention was directed to the black limestone, forming the 
lowest portion of the carboniferious strata, a little north of 
Scarlet, and Port St. Mary, both near Castletown, in the Isle 
of Man. At the former place at low water mark, the lime- 
stone on its surface is pitted with countless holes, made by 
marine worms and a small bivalve, the Saxicava rugosa, 
specimens of which are now exhibited; but no trace of 
a Pholas could be met with in the rocks after diligent search 
on this, and other parts of the shores of the Island; 
and the holes made by the Saxicava and worms, were, so 
far as I could observe, only to be met with in a limestone 
rock, and not in the trap ash or clay slates adjoining it. 
The holes made by the bivalves were various, some being 
at right angles to the surface of the rock whilst others were 
at different angles. The depth of the holes observed was 
one and a half inches, aud their diameter half an inch, their 
form at the base being pear-shaped, and not cylindrical. 
The largest shell found in the holes measured one inch 
by three eighths of an inch. Looking at these holes and 
the shape of the shells found in them, it is difficult to deter- 
mine whether they are the result of boring by the inhabi- 
tant of the shell, or the dissolving or softening of the rock 
by an acid acting on the carbonate of lime, or by a com- 
bination of the two. Certainly in the localities observed by * 
me the holes were found only in calcareous rocks, but the 
shape of the holes always at the base agreed with the form 
of the shell. 
