299 TESTACEOUS MOLLUSCA. 
solid, posteriorly convex and rounded, anteriorly produced, with 
an angular ridge near the depression of the anterior margin ; ventral 
margin anteriorly roundish ; disc very glossy, irridescent, pearly, 
cuticle black with green rays. Paraguay. 
A. AnserinA. Spix. Test. Braz. t. 21.  Ovate-oblong, 
anteriorly dilated, posteriorly somewhat narrowed, solid, transversely 
grooved : dorsal edge straight, the anterior slope elevated, com- 
pressed and winged, posteriorly ending in an acute angle: beaks 
decorticated and rather prominent, hinge margin ending anteriorly 
in a triangular sinus ; cuticle olive, nacre bluish and irridescent. 
1%, ..455;.— Brazil. 
A. Parisuut. Gray. Z. P. 1834. Ovate, ventricose, solid 
posteriorly compressed, somewhat produced and rather slender ; 
anteriorly expanded, dilated and rounded ; hinge margin straight, 
equalling in length the half of the ventral: disc pearly white ; 
cuticle blackish brown. 32..73}.—Paraquay. 
A. Buarnviturana. Lea. Am. Ph. Tr. 1837. t. 12. f. 35.— 
Trapeziatis. Crouch. Lam.—Irnipina F. D’ Orb. Subovate, 
transverse, inflated, thickish ; posteriorly very short and extremely 
narrow, the straight dorsal lime forming an acute angle with the 
arcuated ventral ; anteriorly much dilated, obtusely biangulated ; 
gaping at both ends; beaks somewhat prominent ; palleal scar 
broad and much incurved anteriorly ; cuticle greenish ? nacre salmon 
and pearly. 1,%..3. Chili? 
A. Crassa. Swain. Z. Ill. 1st. ser. t. 167. Oval, broad, 
thick, hinge margin subarcuated, raised anteriorly, and sharply 
angulated at both extremities ; ventral edge much arcuated, rounded 
anteriorly and meeting the posterior in an uninterrupted very oblique 
sweep; umbonal slope elevated and somewhat angulated, umbones 
thick and prominent, but obtuse at their apex ; cuticle dark grass 
green, nearly smooth, except anteriorly where the lines of growth are 
coarse. 
A. Anocuuata. Lea. on U. 2. p.97. t. 16. f. 52. Subcunei- 
form, posteriorly shorter, compressed, attenuated and rounded at 
the tip, anteriorly inflated, winged angulated above and below : 
the dorsal edge ascending, ventral edge nearly straight: cuticle 
green and smooth ; (but the anterior slope is rugged and strongly 
carinated:) nacre salmon. 2%.—California. 
C. Round. 
A. Susorpicuntata. Say. Am. Con. t. 11. Ovate orbicular, 
rather compressed, inequilateral, pale olivaceous tinted with flesh- 
colour, with very slender and numerous almost capillary obsolete 
greenish radii (sometimes with more or less obvious transverse yel- 
