1G0 TESTACEOUS MOLLTJSCA. 



at the termination of the hinge, ventral edge little rounded. 

 1 T ^..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. ±% . . \^q. — Central America. 



A. Obesa. Sow. Z. P. 1833. Ovate, posteriorly shorter, 

 anteriorly subangulated, ventricose, white under a brown scaly 

 epidermis, with crowded smooth flattened radiating ribs : hinge 

 area shortish and narrow. 1-yL . . 1-i-i. — W. Colombia. 



A. Labiata. 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 JL. . . \x, — Heal 

 L legos. 



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. 

 ii • ■ -is'—Xipixapi. 



A. Biangulata. 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^..2. — 

 TV. 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 T 3 ^ . .4^. 

 — C. America. 



A. Quadrilatera. 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 : ligamental area 

 narrow. -JJ . . 1 . — Heal Llegos. 



A. Grandis. Sow. fy Prod. Z. J. Obliquely subquadrangular, 

 thick, white, with radiating rounded ribs, which are only crenu- 

 lated at the posterior end, elsewhere unarmed ; epidermis smooth 

 coriaceous. 3| • • 4-^. — Like Senilis but longer and with more ribs. 



