TRIBE ARCACEA. 161 
A. Emarernata. Sow. Z. P. 1833. Oblong, subcylindrical, 
inequivalve, white, with radiating ribs : posteriorly short with the 
ribs narrower, and wrinkled; anteriorly elongated, with the ribs 
broader and smooth: anterior dorsal margin emarginated, liga- 
mental area narrow ; epidermis brown and bristly in the grooves. 
4..13.—C. America. 
A. Tusercutosa. Sow. Z. P. 1833. Oval, turgid, oblique, 
subauriculated, with numerous radiating ribs armed especially pos- 
teriorly with scattered tubercles : umbones close, ligamental area 
narrow: anterior side the longer. 2-15..24.—S. America. 
A. Carpirormis. Sow. 4 P. 1833. Inequivalve, suboval, 
rounded posteriorly, on the anterior side ventrally angulated : ven- 
tricose, whitish with radiating ribs which are smooth except on the 
posterior side where they are wrinkled, the interstices on the larger 
valve very narrow: lateral edge sloping : ligamental area small 
and subequal. 1,15 .. 2.—Californza.—Aspect of the common 
Cockle. 
A. Murticostata. Son. Z. P. 1833. Ovate-rhombic, pos- 
terior side angulated dorsally, and rounded ventrally ; anterior side 
angulated dorsally, lateral edge sloping; a rounded keel running 
from the umbo to the base of the anterior margin : white under 
a brown almost satin-like epidermis, with numerous radiating mi- 
nutely decussated rounded ribs, which posteriorly are subgranular : 
the grooves rounded, the ligamental area broadish. 22..24,.— 
C. America. 
A. Noposa. Wood. S. t. 2. f. 8. Equilateral, tumid, ob- 
liquely subrhombic, white; hinge margin angulated at both ends, 
very obliquely so anteriorly ; rayed with about twenty-six flat ribs 
which angulated at their sides are rather broader than the simple 
interstices, and are decussated, except on the anterior slope, with 
transyerse straight raised lines: ventral edge arcuated : ligamental 
arearhombic broad and short. 2.—S. America ? 
A. Transversa. Say. Journ. A. N.S. Phil. 2. p. 269.— 
Gould. Mas. p. 97. Oblong, rhomboidal, with from thirty-two 
to thirty-five ribs as wide as their interstices, apices separated by 
a long narrow area (on which one or two angulated lines diverge 
from the apex) and situated at one-third the distance from the 
posterior end of the hinge margin which is angulated at each end ; 
of the anterior edge the superior half rectilinear, posterior edge 
rounded, ventral edge nearly straight. 43..11.—U. States. 
'See also the Compianata of Ch. f. 544, 5. (D. p. 228.— 
W.t. 9. f. 8.) and his Plicata f. 2008 (D. p. 227. and f.—W. 
rg: F763) 
M 
