TRIBE LITHOPHAGI. wey 
P.Costrata.! Gray. Ann, Phil.25.—Venvus Lapicipa. Gmel. 
3269.—D. p. 190.—Ch. f. 1664, 5.—W. t. 8. f. 72. Ovate, 
somewhat heart-shaped, whitish, protuberant at the umbones ; 
anteriorly with longitudinal grooves, posteriorly with unequal 
transverse strize : hinge with two teeth in one valve, a bifid one in 
the other. 14.—Jn coral in the W. Indies. 
P. Osronea. Son. Z. P. 1834. Oblong-elliptic, palish, with 
radiating riblets: anterior dorsal edge straightish, with several 
concentric ridges which become smooth anteriorly. 4,?-—Peruw. 
P. Nivea. Gray. Ann. Phii.25.—Mytitus N. Gimel. 3358.— 
D. p. 307.—Ch. f. 734.—W. t. 12. f. 16. Oblong, sub- 
diaphanous, rounded at both ends, snow-white, coarsely striated 
longitudinally, and the margin acute: within, glossy white. 7. . 14. 
—Nicobar Islands. 
P. Dactyitus. Sow. G. f. 3.—Gould. p. 65. f. 41.—Reeve. 
t. 51. f. 3. Transversely elongated, very convex, rounded at both 
ends, concentrically wrinkled, and longitudinally ribbed at the 
short posterior extremity : white, the ventral margin rounded, the 
umbones tumid, and the anterior side very long: teeth, two in one 
valve, three in the other. 2..13.—N. America.— Bears a close 
resemblance to Chemnitz’s figure of Nivea, but the localities are so 
widely apart as to sanction their separation. 
P. Rugosa. Sow. Z. P. 1834. Oblong, pholas-shaped, whitish, 
with radiating riblets of very fine concentric striz ; the margins 
usually deformed. =',..12.—Chili. 
P. Denticutata. Sow. Z. P. 1834. Oblong, pholas-shaped, 
palish, but internally stained with blackish brown on the ex- 
tremities : posteriorly sub-rostrated, anteriorly rounded; dorsal 
edge nearly straight, ventral edge rather prominent: entirely 
covered with radiating grooves and concentric striz, which pos- 
teriorly are sub-lamellar and denticulated. 2.. 1,3;.—Peru.— 
Variety, shorter, and none of the strize sub-lamellar or denticu- 
lated. —Isle of Plata. — 
P. Tenuis. Sow. Z. P. 1834. Oblong, pholas-shaped, whitish, 
thin ; with radiating riblets, which are stronger at the sides and 
are decussated by rugulose very fine strize; posterior side very 
short. 41..1.—-Perw. 
P. Amyepatina. Sow. Z. P. 1834. Thin, sub-hyaline, yel- 
lowish, obovate, smooth ; posterior side very smooth and narrower ; 
anterior longer, broader, with some distant raised lamella. +.. 13%. 
— Gallapagos. 
P. Exvurprica. Sow. Z. P. 1834. Ovate-elliptic, reddish 

1P. Linauatuta, Lam. 13, bears so close a resemblance to 
Saxicava Rugosa as scarcely to deserve separation. 
