TRIBE ARCACEA. 155 
grooves: extremities of the hinge gibbous and callous: beaks 
oblique, approximated and but little prominent. 4. 
A. Irupina. Lam. 23. Oval, tumid, with decussated striz, 
scaly at the margin and anterior extremity: beaks approximated 
and oblique. +.—( Closely resembling Venerupis rus.) 
A. Lacerata. Lin. mus. Tessin. 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 striz, 
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.—ZIndia. 
A. Rericuntata. 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 strize ; umbones minute and approximated ; area 
between the beaks narrow, and finely grooved.—Jndia. 
A. Garmarpi. Payr. Cat. p. 61. t. 1. f. 36. to 39. Small, 
whitish, quadrilateral, and equilateral, heart-shaped, ventricose, 
covered with a fine net work of longitudinal and transverse strie; 
beaks large, approximated and recurved, and the area between them 
forming a narrow deep channel.— Corsica and Sicily. 
A. Gravata. Brod. § 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. ,9,.. 1.—Mexico. 
A. Pacrrica.—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. 2-3,..4.—W. Columbia. 
A. Drvarrcata.—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. 41. .1. 
—Pacific. 
A. Soxipa.—Byssoarca S. Sow. Z. P. 1833. Squarish- 
ovate, thick, solid, equilateral, with radiating strice, most minutely 
decussated; posterior side rounded, anterior obtusely angulated ; 
dorsally and obsoletely carinated ; ligamental area elongated, the 
ligament rhomboid, central. %..3.—Peru. 
