456 
MOLLUSCA. PHOLADiE, 
Pholas. 
PHOLADiE. 
Gen. CXXXIII. PHOLAS. Shell transverse; ligament 
slender, and covered by a reflected fold of the cloak, and 
sometimes protected by calcareous plates ; hinge v^^ith a 
curved process under the margin in each valve, receding 
into the cavity. 
Valves divided hy a longitudinal groove. 
55S. P. crispata. — Transversely oblong, rounded, and gap- 
ing retrally, obliquely truncated, and open anteally. 
P. latus, List. Conch, t. ccccxxxvi. An. Ang. 192. t. v. f. 38. Anat* 
t. xix. f. 3 — P. crisp. Linn. Syst. i. 1111. 3Iont Test. Brit. 23. Turt. 
Biv. Brit. 6. — In calcareous and argillaceous rocks. 
Length 2 inches, breadth Z ; white ; a groove runs from the hinge to the 
middle of the ventral margin, where the valves come in contact, dividing 
the shell into two compartments; the anterior is very rough, with numerous 
thin waved concentric ridges, with obsolete longitudinal furrows ; the poste- 
rior is comparatively smooth ; margin of the shell at the hinge reflected, 
smooth, covered by a fold of the cloak, and strengthened by an obscure im- 
bedded calcareous plate ; projecting tooth linear ; foot or sucker large, the sy- 
phon tubes produced. 
554. P. lamellata. — An erect triangular plate at the hinge, 
placed retrally with respect to the recurved tooth. 
P. papyracea, TuH. Biv. Brit. 2. t. i. f. 1-4. — T. lamellata, U>. 4. t. i. 
f. 5, 6. 
Length half an inch, breadth an inch ; white ; anterior compartment with 
the waved ridges broken into thin denticular processes in bent longitudinal 
rows ; posterior compartment comparatively smooth ; the valves shut close 
retrally from the mesial furrow ; behind the hinge, dorsally, the margin is 
closed, compressed, and prominent ; before the hinge the margin is a little 
open, and reflected on each side into a thin, nearly erect, plate ; the anteal ex- 
tremity is obliquely truncated and open. — This is the condition of the shell 
when of a certain age (and constituting Dr Turton’s P. lamellata.) It seems 
afterwards to change its form ; the oblique truncated anteal aperture is filled 
by the deposition of shell nearly smooth, bringing the now tumid edges 
nearly in contact ; retrally the shelly matter deposited, is broadest towards 
the extremity, now become truncated and a little open, to which is attached 
a coriaceous expanding cup, divided longitudinally, and thickened at the 
margin dorsally and ventraliy ; this seems destined to be a basal sheath for 
the syphons ; anteally the margins approximate, and are thick and elevated 
before the hinge. The cloak is now closed, with only a small opening for 
the foot. In this last state. Dr Turton has described this shell as the Pholas 
papyraceizs of Solander’s MSS., and regards it as quite distinct from P. lamellata. 
A comparison, however, in reference to their mode of growth, of specimens 
of both shells, obligingly furnished to me by Mr G. B. Sowerby, has left no 
room for hesitating regarding their specific identity. The structure of the 
hinge, so different from the other species, and the singular changes of form, 
with age, would justify the erection of the genus Pholadidia., originally con-^ 
templated by Dr Goodall for its reception. 
