TRIBE ARCACEA. 165 



Arca Eqtjilatera. Gmel.—JD. p. 240.— Ch. f. 562. — E. t. 

 11. 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. If. — W. Indies. 



P. Pectiniformis. Lam. 16. — Reeve. Ic. f. 11. — Arca 

 Pectunculus. Lin. 1142.— J), p. 238. — W. t. 9. /. 29.— Ch. 

 f. 568. — E. 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, lg. — Asiatic and American Seas. A slight incurvation 

 of the anterior margin. 



P. Pectinatus. Lam. 17. — Reeve. Ic. f. 28. — Arca P. 

 Gmel. 3313.— B. p. 239.— Ch. f. 5/0, l.—E. t. 311. /. 6.— - 

 IV. 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. f . — W. Indies. — Variety from Brazil. White 

 with rufous spots. 



P. Radians. Lam. 18. Suborbicular, transverse, inequilateral, 

 rufous the umbones very white, with very numerous line, 

 longitudinally striated ribs. — Variety. With the ribs broader. 

 ]^. — New Holland. 



P. Vitreus. 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. 1-|. — South Seas. 



P. Multicostatus. 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. 1^. — South 

 America. 



P. Parcipictus. Reeve. Z. P. 1843. — Reeve. Ic. f. 14. 

 Rather obliquely heart-shaped, radiately ribbed ; ribs flat, often 

 grooved up the middle, interstices deep ; white sparingly variegated 

 with yellowish chesnut undulated zones and patches : interior 

 white with a purple posterior stain. 1. — " The ribs are peculiarly 

 firm and squarely grooved out." 



P. Aurifluus. Reeve. Z. P. 1843.— Reeve. Ic. f. 17. 

 Orbicularly heart-shaped, inequilateral radiately ribbed, ribs broad 



