TRIBE ARCACEA. 165 
Arca EquinaTeRA. G'mel.—D. p. 240.—Ch. f. 562.—E. t. 
ll. f. 2—W. t. 9. f. 32. Orbicular, subequilateral, chesnut, 
mottled with white, with numerous longitudinally striated ribs, 
which become obsolete towards the beaks which are not inclined ; 
within white. 13.—W. Indies. 
P. Pectinirormis. Lam. 16.—Reeve. Ic. f. 11.—Arca 
Pecruncutus. Lin. 1142.—D. p. 238.—W. t. 9. f. 29.—Ch. 
J. 568.—#. t. 311. f. 5. Suborbicular, thick, moderately convex, 
somewhat eared, whitish more or less tinged with flesh colour, and 
marked with brown wavy riband-like stripes, or spots, the ribs 
and interstices both broad and the surface roughened by fine raised 
transverse wrinkles ; beaks small and not inclining: within white 
stained with chesnut at the hinge and near the beaks, the margin 
plaited. 13.—Asiatic and American Seas. A slight incurvation 
of the anterior margin. 
P. Pectinatus. Lam. 17.—Reeve. Ic. f. 28.—Arca P. 
Gmel. 3313.—D. p. 239.—Ch. fi 570, 1.—. t. 311. f. 6.— 
W.t. 9. f. 30. Lenticular, rather depressed, whitish with wavy 
brown transverse markings or small spots, and numerous smooth 
rather flattened ribs and narrow interstices : white within and the 
margin crenated. }.—W. Indies.—Variety from Brazil. White 
mith rufous spots. 
P. Raprtans. Lam.18. Suborbicular, transverse, inequilateral, 
rufous the umbones very white, with very numerous fine, 
longitudinally striated ribs.x—Variety. With the ribs broader. 
11.—New Holland. 
P. Vrrreus. Lam. 19. Orbicular depressed, somewhat eared, 
thin, pellucid, with transversely striated almost granular longitu- 
dinal ribs, white with a few orange dots; beaks small and acute :. 
the hinge formed of two straight lines which almost form a right 
angle at the beaks and are each furnished with from twelve to 
fifteen oblique teeth. 12.—South Seas. 
P. Mutricostatus. Sow. Z. P. 1832.—Reeve. Ic. f. 26. 
Suborbicular, white mottled with chesnut, rust-colour, and ashy- 
grey; with numerous radiating small rounded ribs which are 
transversely striated : umbones posteriorly inflected. 13.—South 
America. 
P. Parctercrus. Reeve. Z. P. 1843.—Reeve. Ic. f. 14. 
Rather. obliquely heart-shaped, radiately nbbed; ribs flat, often 
grooved up the middle, interstices deep ; white sparingly variegated 
with yellowish chesnut undulated zones and patches: interior 
white witha purple posterior stain. 1.—‘* The ribs are peculiarly 
JSirm and squarely grooved out.” 
P. Aurirtuus. Reeve. Z P. 1843.—Reeve. Ic. f. 17. 
Orbicularly heart-shaped, inequilateral radiately ribbed, ribs broad 
