TRIBE NAYADES. 219 
straight subparallel to the ventral which is scarcely at all arcuated : 
_ beaks flattened and minutely undulated : cuticle very smooth, green 
and olive green with obsolete rays (the three anterior more distinct) 
nacre bluish white and irridescent, scars nearly perceptible. 13... 31. 
— Ohio. 
A. Newronensis. Lea. on U. 2. p.79.t. 21. f. 66. Narrow 
elliptical, inflated, thick, ventral edge entire, inequilateral ; beaks 
somewhat prominent and rather largely undulated at the tip: liga- 
ment rather short : cuticle dark brown, shining, apparently ray- 
less: nacre white, sometimes salmon 2,%,..43.— New Jersey. 
A. Mortoniana. Lea. Am. Ph. Tr. 1837. t. 13. f. 37.— 
A. Curquitana. D’ Orb. in Mag. de Z. 1835. Transversely sub- 
elliptical somewhat inflated, thick, the ventral and ligamental edge 
nearly parallel and scarcely curved, anteriorly subbiangulated, pos- 
teriorly very short and narrow : grooved along the umbonal slope ; 
beaks retuse and scarcely prominent : cuticle intensely brown and 
slightly wrinkled ; nacre silvery white and irridescent. 12. .3.— 
R. Parana, S. America. 
A. Ovata. Lea. on. U. 2. p. 2. t. 2. f. 2. Ovate, somewhat 
compressed, transverse inequilateral, thinnish, ventral edge rounded; 
beaks somewhat prominent and granular at tip; ligament rather 
short : cuticle greenish brown, wrinkled, apparently rayless ; nacre 
white or bluish. 24..4.—Ohio. 
A. Purana. Lea. Am. Ph. Tr. 1837. t.7.—Decuivis. Conr. 
Ovate-oblong, inequilateral, thick, rather compressed, anteriorly 
subangular, dorsal line slightly curved, ventral edge but slightly 
arcuated, posterior side but little narrower ; beaks elevated, granular 
at the tip; cuticle smooth, olive to dark green, brighter on the 
beaks, rays obsolete; nacre white (rarely salmon near the beaks, ) 
sears perceptible. 3,1,..52.—Lowisville, N. America. 
A. Decora. Lea. on U. 2. p. 64.t.20.f. 63. Elliptical, thin, 
nearly straight on the dorsal margin, inequilateral, angular an- 
teriorly ; beaks rather prominent and undulated in a double series at 
the tip; ligament rather long and straight; cuticle smooth and 
shining, rayed with green beyond the subcentral dark band; 
anterior slope dark, with three rays: nacre white just tinged with 
salmon in the cavity. 24..3-9,.— Ohio. 
A. GiganTEa. Lea. on U. 2. p.1. t. 1. Ovate oblong, inflated, 
thick, posteriorly broad, anteriorly very produced and subcuneiform 
from the great slope of the lgamental margin ; beaks prominent, 
granular at tip ; cuticle dark brown, smooth ; ventral edge incurved 
anteriorly; nacre white and richly pearly. 44..74.—-Port Gibson.! 
A. OrEGONENSIS. Lea. on U. 2. p. 80. t. 21. f. 67. Some- 

1 Add likewise the A. Susvexa of Conrad. 
