160 TESTACEOUS MOLLUSCA. 
at the termination of the hinge, ventral edge little rounded. 
1,3,..2.—U. States. 
A. Concinna. Sow. Z. P. 1839. Oblong, inequivalve, white, 
with radiating ribs which posteriorly are wrinkled, the interstices 
decussated ; posterior side the shorter and angulated dorsally, an- 
terior rather produced, the angle inconspicuous: ligamental area 
narrow and posteriorly crenulated on each side: ligament anterior : 
an olive epidermis which is spinous at the grooves on both ex- 
tremities. 13..13,.—Central America. 
A. Osesa. Sow. Z. P. 1833. Ovate, posteriorly shorter, 
anteriorly subangulated, ventricose, white under a brown scaly 
epidermis, with crowded smooth flattened radiating mbs : hinge 
area shortish and narrow. 151,.-143.—W. Colombia. 
A. Lasrata. Sow. Z. P. 1833. Inequivalve, short, of a rounded 
square shape, posteriorly shorter and rounded, anteriorly subangu- 
lated ; white under a brown epidermis which is setose on the 
anterior edge of the flattened radiating ribs ; these are (particularly 
on the larger valve) posteriorly wrinkled, anteriorly smooth and 
broader : ligamental area broad, subrhomboid. 1 1,..14.—eal 
_ Llegos. 
A. Nux. Sow. Z. P. 1833. Oblique, turgid, inequivalve, with 
radiating ribs which armed with granules in one valve are only so 
posteriorly in the other ; umbones distant, prominent : epidermis 
brown, horny, thin, and the anterior side of the ribs bristly. 
43, .15.—Xipixapr. 
A. Brancutata. Sow. Z. P.1833. Oblong, posteriorly shorter 
and broader, anteriorly subacuminated, lateral margin sloping ;_ ven- 
tricose, with radiating ribs, white under a bristly brown epidermis: 
dorsal margin posteriorly acute, anteriorly obtusely angulated : 
ligamental area elongated, posteriorly broader, flat. 1-3,..2.— 
W. Columbia. 
A. Formosa. Sow. Z. P. 1833. Oblong, subcylindrical, 
whitish, with radiating ribs which are numerous flattened and 
posteriorly double ; each hinge margin angulated ; posterior side 
the shorter ; hinge area broadish and elongated, epidermis in long 
pointed scales in the interstices, in bristly hairs anteriorly. 2.3,..44. 
—C. America. 
A. QuapritaTEeRA. Sow. Z. P. 1833. Quadrangular, with 
the sides angulated dorsally, the posterior dorsally rounded, the 
anterior obtusely angulated ventrally : ventricose, whitish under an 
olive epidermis, with radiating rounded ribs : lgamental area 
narrow. 437..1.—eal Llegos. 
A. Grannis. Sow. & Brod. Z. J. Obliquely subquadrangular, 
thick, white, with radiating rounded ribs, which are only crenu- 
lated at the posterior end, elsewhere unarmed ; epidermis smooth 
coriaceous. 35 ..4,3,.—Like Senilis but longer and with more ribs. 
