PHOLAS. PIDDOCK. 145 
much resembles the former, is known by the want of 
cells on the back, by being furnished with only one lan¬ 
cet-shaped dorsal valve, and more especially by the rounded 
tubercles placed on the inner-margin of the hinge. These 
tubercles, from some misunderstanding of the exact mean¬ 
ing of Montagu, have been represented as supporting the 
teeth: “ Cardinis dente ex tuberculo ort o/* Maton and 
Rackett. “ Hinge with a tooth sjjringing from a tubercle,” 
Wood. “ The teeth of the hinge issuing from a tubercle,” 
Dilkcyn. The teeth, however, are inserted under the inner 
margin of the hinge, as in the other species, and have no 
attachment or connexion whatever with the tubercles, 
which are seated on the centre of the margin and remote 
from the insertion of the teeth. Ph. bandida is a much more 
delicate and transparent species, rounded at the top and 
without the sloping beaks, in consequence of which it has 
\ very little frontal gape when closed ; the transverse striae 
i are more regular and at remoter distances, visible on the in- 
I dde, and not so strongly crossed by the longitudinal ones, 
by which means it is not so much echinated or spinous; 
the back, with its single dorsal valve and want of cells, is 
formed like Ph. paiwa; and its characteristic mark, inde¬ 
pendent of its outline, is a single sharp curved supple¬ 
mental tooth seated on the middle of the hinge, in the left 
1 hand valve only, and locking into a groove of the opposite 
valve. Of this strong specific mark, neither Maton and 
Rjckett nor Dill wyn have taken any notice ; and Mr, Wood, 
in whose left hand figure this tooth is remarkably well re¬ 
presented, calls it a folded process, and asserts that it is 
found in both valves. 
The philosophy of their natural history may probably be 
of no very difficult solution. The rock in which they are 
imbedded is a cementation of the finest sand and lime, of 
so very soft a substance when first taken from its bed, as to 
be easily cut with a knife into any form, and sufficiently 
absorbent to afford moisture for the purposes of life and 
their peculiar action. The animals themselves abundantly 
secrete a mild phosphoric solution, as may be seen by its 
illuminating in the dark whatever is moistened with it, suf¬ 
ficiently powerful to decompose the rock by the slow con¬ 
tact of their gradually increasing bulk. The atmospheric 
