TRIBE NAYADES. 223 



lowisli bands towards tbe base :) beaks not elevated : binge 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 t 3 q. — 2V. America. 



D. Wide. 



A. Elongata. Swain. Z. II. 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. 1^ . . 2f . — S. Amei'ica ? 



A. Ensiformis. 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. 

 \\ . .4f.— Brazil 



A. Cvltndracea. Lea. on U. 2. p. 45. t. 13. f. 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. 

 lj\.. 2^. — Vera Cruz. 



A. Subcylindracea. Lea. on U. 2. p. 106. t. 24. f. 117. Ellip- 

 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. 2-1. — New York. 



A. Buchanensis. 1 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. Esula of 

 Cristofori and Jan's Catalogue {Iridina E. of D'Orbigny) and the 

 A. Georgince of Gray figured (Mottu&ca.t. 19. f. 23.), but not 

 described in Griffith's edition of Cuvier. 



