TRIBE PHOLADARIA. i 
rounded off subtruncation, smooth ; posterior ventral margin with a 
very large gape: accessory valve solitary and posterior : lanceolate 
and acuminated posteriorly. 4..1%.—W. Columbia. Very like 
Parva. 
* * Valves divided hy an indented radiating groove. 
P. Crispata.* Lin. 1111.—D. p. 40.—Lam. 7.—Ch.f. 872, 
3, 4.—Don. t. 62.—Wood. G. C. t. 15. f. 4, 5.—Mont. p. 23.— 
Turi. B. p. 6.—W. t. 2. f. 5. Oval, gibbous, whitish, rounded 
at one end, and forming a short beak at the other ; a longitudinal 
furrow in the middle, on the posterior side of which the shell is covered 
with muricated striz, on the anterior transversely wrinkled: gape 
wide. 14..21.—N. and W. Europe. 
P. Cravara.* Lam. 9.—P. Pustra. Lin. 1111.—D. p. 33.— 
Ch. f. 867,8, 9.—P. Striata. Lin. 1111.—W. t. 2. f. 7.— Wood. 
G. C. t. 16. f. 1, 2, 3,4, 8.—Don. t. 116.—Reeve. t. 24. f. 2.— 
Sow. G. f. 2.—D. p. 37. Oblong, rounded, white, and of a re- 
markably conoid shape; the broader end strongly reticulated by 
arched strie, the other parts except a smooth triangular space at 
the posterior ventral margin faintly striated: the shield which 
covers the hinge heart-shaped, and beneath it a narrow plate joined 
to the membrane which connects the valves; a narrow ventral plate 
and membrane which seems to prevent the shell from opening except 
at the ends. 3..1.—America, §c. 
P. Ovum. Grayin W. S. f. 4. Sub-cuneiform, posteriorly 
inflated, rounded and somewhat gaping, anteriorly attenuated : 
valves.divided by a longitudinal groove, anterior to which the shell 
is nearly smooth ; the posterior dorsal portion with minute raised 
oblique wavy wrinkles crossing the more or less distinct radiating 
riblets, posterior ventral portion with distant divaricating striz ; 
hinge margin raised, reflected : accessory valve sub-rotund, dorsal 
and posterior : teeth thin and flattened ..14.—The young without 
the posterior ventral portion. The sulcus forms a distinct tooth 
at the interior ventral edge. 
P. Fatcata. Wood. G. C.t. 16. f. 5, 6, 7.—D. p. 39.—W. 
t. 2. f. 8. Suboval, ventral margin posteriorly much incurved, 
divided by a longitudinal groove, the posterior compartment being 
very tumid, short, and rough with sub-dentated strize, the anterior 
compressed, with simple transverse strie: whitish, the gape wide, 
the hinge with a forked tooth. +.—Shape of Crispata. | 
P. Catva. Gray. Z. P. 1834. Ovate, posteriorly retuse, 
anteriorly sub-acuminated, gaping ; each valve divided into 3 sur- 
faces, the posterior one roughish, the middle one with a horny 
epidermis and concentrically striated, the anterior one with horny, 
imbricated, smooth scales, which gradually become less, and are 
anteriorly rounded : the posterior ventral space smooth and closed: 
