222 TESTACEOUS MOLLtJSCA. 



(Solid, posteriorly convex and rounded, anteriorly produced, "vrith 

 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. 



A. Parishit. 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. 3| . . 7\. — Paraguay. 



A. Blainvilliana. Lea. Am. Ph. T>\ 1837. t. 12./. 35.— 

 Trapezialis. Crouch. Lam. — Iridina F. D'Orb. Subovate, 

 transverse, inflated, thickish ; posteriorly very short and extremely 

 narrow, the straight dorsal line 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. III. \st. 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 hues of growth are 

 coarse. 



A. Angulata. 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. 2f. — California. 



C. Round. 



A. SuBORBicuLATA. Say . Am. Cou. 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- 



