TRIBE ARCACEA. 155 



grooves : extremities of the hinge gibbous and callous : beaks 

 oblique, approximated and but little prominent. Jt. 



A. Irudina. Lam. 23. Oval, tumid, with decussated striae, 

 scaly at the margin and anterior extremity : beaks approximated 

 and oblique. ^. — (Closely resembling Venerupis Irus.) 



A. Lacerata. Lin. mus. I'essin. p. 116. no. 2. §' t. 16. f. 1. 

 —D.p. 229.— Lam. 38.— W. t. 9.f. 10.— Ch.f. 536, 7.—E. t. 

 309. f. 2. Transversely subovate, depressed, very inequilateral, 

 brown under a greenish epidermis, with longitudinal radiating striae, 

 which are ragged and ciliated, granular and unequal, the elongated 

 hair of the epidermis disposed on them at regular distances : margin 

 subcrenated and closed, ligamental area so narrow that the beaks 

 touch . 2 . — In dia . 



A. Reticulata. Gmel. 3311.— D. p. 237.— Lam. 39.— Ch. 

 f. 540. — W. t. 9. f. 25. Ovate, rhomboidal, very inequilateral, 

 somewhat compressed, white under a brown epidermis, with fine 

 equal decussated striae ; umbones minute and approximated ; area 

 between the beaks narrow, and finely grooved. — India. 



A. Gaimardii. Payr. Cat. p. 61. t. 1. /. 36. to 39. Small, 

 whitish, quadrilateral, and equilateral, heart-shaped, ventricose, 

 covered with a fine net work of longitudinal and transverse striae; 

 beaks large, approximated and recurved, and the area between them 

 forming a narrow deep channel. — Corsica and Sicily. 



A. Gradata. Brod. fy Sow. Z. J. 4. — Beechey. Zool. t. 43. 

 f. 1 . Oblong, anteriorly angulated : with concentric ribs which are 

 radiatingly imbricated, forming as it were steps down to the ventral 

 margin. -£$. . 1. — Mexico. 



A. Pacifica. — Byssoarca P. Sow. Z. P. 1833. Oblong, pale 

 variously streaked with brown ; with radiating ribs : contracted in 

 the middle, and the ribs smaller : umbones far apart : posterior 

 side the shorter, acuminated dorsally, the ribs for the most part 

 larger, wrinkled, the ventral margin sloping : anterior side very 

 large, anteriorly emarginated, an obtuse keel from the umbo to the 

 ventral margin : ligamental area very large, the margins broad : the 

 gape in the ventral margin large. 2 T 3 ¥ . . 4. — W. Columbia. 



A. Divaricata. — Byssoarca D. Sow. Z. P. 1833. Oblong, 

 whitish, with transverse grooves, which are radiatingly decussated; 

 posterior side subangulated dorsally, the anterior with a spinous 

 keel from the umbo to the ventral margin, and divaricating striae, 

 which are elegantly decussated ; ligamental area narrow. ±±. . 1 . 

 — Pacific. 



A. Solida. — Byssoarca S. Sow. Z. P. 1833. Squarish- 

 ovate, thick, solid, equilateral, with radiating striae, most minutely 

 decussated ; posterior side rounded, anterior obtusely angulated ; 

 dorsally and obsoletely carinated ; ligamental area elongated, the 

 ligament rhomboid, central. § . . f . — Peru. 



