TRIBE ARCACEA. 155 



grooves : extremities of the hiage gibbous and callous : beaks 

 oblique, approximated and but little prominent. |. 



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

 scaly at the margin and anterior extremity : beaks approximated 

 and obhque. ^. — {Closely 7'ese7nhlmg Venerupis Irus.) 



A. Lacerata. Lin. wws. l^essin. p. \16. no. 2. i^' t. 16./. 1. 

 —D.p. 229.— Lavi. 38.— TF. t. 9./. 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. — India. 



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

 f. 540. — W. t. 9. /. 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. Paijr. 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. <J' 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-f^. . 4. — W. Columbia. 



A. DivARiCATA. — Byssoarca D. So7v. 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 elougated, the 

 ligament rhomboid, central. ^. . 4- — Peru. 



