146 
PHOLAS. PIDDGCK. 
air also seems to be occasionally necessary to this process, 
as they are always found in situations which are left dry 
for a short period by the recess of the lowest tides, its oxy- 
gene perhaps serving by its union with this secretion to 
form a phosphorous acid. In confirmation of this belief we 
have affixed them, when fresh taken, to a smooth piece of 
the same rock, by the frontal gape, occasionally moistening 
them with seawater; and in a few days have found, that at 
the place of contact an evident waste of substance had been 
made by the decomposition of the lime, and a deposition 
of sand in the finest grains. It may reasonably be supposed 
that all the borers of rocks and wood, even the Teredo, 
act in this manner by their peculiar and appropriate sol¬ 
vents. 
4. Pholas crispata. Curled Piddoch. 
Lister, pi. 436. f. 27.9— Pennant , pi. 43. f. 2— Da Costa , 
pL 16. f. 4— Donovan, pi. 62— Wood, pi. 15. f.3, 4, and 5 
—Dorset Cat . pi. 3. f. 4. 
The young shell. 
Pholas Candida. Donovan, pi. 69. 
Shell strong, gibbous, somewhat oval, much rounded at 
one end and narrower at the other, and very open at both, 
whitish or rust-color, marked by a longitudinal furrow from 
the hinge to the margin, which divides the shell into two 
nearly equal parts 5 one of which is smooth, except a few 
transverse stria?; the other rough with strong transverse 
undulate or indented raised scale-like folds; inside white, 
with a longitudinal rib in the middle answering to the furrow 
on the outside : hinge smooth, white, forming a furrow on 
the back at the anterior end which is obliquely truncate: 
teeth long, flat, much curved: length nearly two inches; 
breadth almost three. 
We have never been able to discover this species in its 
natural habitation, nor have we met with any one whoever 
had: the dorsal valve has consequently not been described 
by any writer. It is said to be imbedded in hard clay and 
limestone. Maton and llackett, and Mr. Wood, have er¬ 
roneously described the groove or furrow which divides the 
shell into two parts, extending from the binge to the mar¬ 
gin* ss a transverse one. v. m. 
5. Pholas 
