144 
PHOLAS. PIDDOCK. 
gape when closed, rough with spinous excrescences, which 
decrease towards the smaller end where it is nearly smooth: 
hinge reflected, without cells, with a single oblong plate at 
the bach, hut none below the hinge ; and on the internal 
margin of the hinge above the insertion of the tooth is a 
rounded knob or protuberance in each valve: length three 
quarters of an inch ; breadth an inch and a half. 
Burrowed in sandstone and clay. v. v. 
4 3. Pholas Candida. White Piddock . Fig. 79. 
Lister, pi. 435. f. 2/S—Penrnnt , pi. 42. f. 2— Donovan. 
pi. 132 — Wood, pi. 14. f. 3, 4 —Dorset Cat. pi. 1. f. 12. 
Shell very thin, oblong, white or yellowish-white, trans¬ 
parent, rounded and not eloping to a beak at the broader 
end where it is nearly closed when shut, rough with points 1 
all over except close to the cartilage on the back, with sc- ( 
veral rows of prickles on the broad end from the hinge to 
the margin : hinge smooth, white, reflected, without cells, 
with a single oblong somewhat curved strong plate on the 
back, hut none connecting the Yalves below the hinge; 
teeth slender, curved, and in one valve only there is an ad- 
ditional tooth placed upon the interior margin of the hinge, 
which is pointed, curved towards the cartilage and leaning 
towards the elongated end, locking into a groove of the 
opposite valve: length three quarters of an inch ; breadth 
an inch and a half. v. v. 
Masses of rock, taken at the mouth of the river just be¬ 
low the town of Tcignmouth in Devonshire, and inclosing 
vast numbers of these three species indiscriminately and 
collectively, are now before us while we are describing 
them. The writers who have succeeded Montagu do not 
seem to have well understood their peculiar differences, or 
to have distinctly discriminated them. The manner of their 
reticulation, as adopted by Linnc, is by no means sufficiently 
clear to form intelligible specific distinction. Ph. Dactylns 
is at once known by the cells at the back of the hinge, a 
circumstance mentioned by Mr. Wood only, and when in a 
perfect state by the four dorsal valves, two of which cover 
the cells, the triangular one which supports these two, and 
the narrow elongated one beneath this last. PL parva, 
which in its outline, large frontal gape, and elongated beak, 
much 
