TRIBE NAYADES. 223 
lowish bands towards the base :) beaks not elevated: hinge margin 
rectilinear compressed posteriorly, and anteriorly compressed 
almost to a wing, ligament almost concealed: posterior margin 
rounded, anterior a little prominent obtusely angulated, ventral 
much arcuated ; inside as much undulated as without, pale bluish 
varied with pale flesh. 4..5-3;.—N. America. 
D. Wide. 
A. ELroneata. Swain. Z. Il. 1st. ser. Transversely elongated 
oblong, convex, thick, posteriorly very short and rounded above and 
below, anteriorly produced compressed attenuated but rounded at 
the tip, ventral edge little arcuated and incurved subcentrally ; 
cuticle fulvous, nearly smooth, umbones convex, remarkably thick 
and deeply eroded : inside pearly and irridescent with a tinge of 
flesh colour, hinge plate rather convex. 14..23.—S. America? 
A. Enstrormis. Spix. Test. Braz. t. 24.—D’ Orb. Trans- 
verse, four times as broad as long, posteriorly rounded and very short, 
anteriorly produced into a long attenuated beak, thick, transversely 
furrowed, ventral edge incurved ; beaks retuse, decorticated, um- 
bones depressed ; cutile olive, nacre bluish and _ irridescent. 
12..43.— Brazil. 
A. Cytinpracea. Lea. on U. 2. p. 45. t. 13. fi 40. 
Subcylindrical, very transverse, posteriorly very short and rounded, 
anteriorly produced and rounded biangular, the ligamental edge 
straight and long, ventral incurved and little rounded: thin, the 
cuticle dark brown covered with capillary rays: umbonal slope 
rounded : beaks somewhat prominent : nacre blue and irridescent. 
13,-.225-—Vera Cruz. 
A. Suscytinpracea. Lea. on U. 2. p. 106. t. 24. £117. Elhp- 
tical, twice as broad as long, subcylindraceous, very thin, posteriorly 
short and rounded, anteriorly produced and obtuse, ligamental and 
ventral edges nearly straight, the latter subincurved : beaks some- 
what prominent and minutely undulated at the tip: cuticle brown 
and rayless: nacre bluish and irridescent. 21.— New York. 
A. Bucuanensis.' Lea.on U. 2. p. 47. t. 14. f. 23. Trans- 
verse inflated, thin, subcylindrical, posteriorly short and rounded, 
anterior very produced and obtuse, ventral edge incurved, sides flat- 
tened ; umbonal slope elevated and rounded; beaks somewhat 
prominent and minutely undulated : cuticle greenish, darker on 


1 Add likewise the A. Arcuata of Ferussac, the A. Esuza of 
Cristofori and Jan’s Catalogue (Jridina E. of D’Orbigny) and the 
A. Georgine of Gray figured (Mollusca. t. i9. f. 23.), but not 
described in Griffith’s edition of Cuvier. 
