TRIBE NAYADES. 199 
anteriorly ; anterior dorsal edge rather elevated, thickish, flattened 
at the umbones and sides, carinated ; beaks little prominent, undu- 
lated at the tip; ligament thin long and straight ; cuticle dark brown, 
obscurely rayed, nacre purple and irridescent ; cardinal teeth small, 
thick ; the lateral long and curved. 1-4,..3%.— Near Darien. 
U. Roanoakensis. Lea. on U. 2. (Tr. Am.6.) p. 27. t. 8. 
f.21. Oblong, transverse, inequilateral, biangular anteriorly, com- 
pressed, thick, ventral and dorsal edges little rounded, flattened on 
the umbonal slope; ligament very large and long: cuticle dark 
brown (apparently) rayless, nacre white ; cardinal teeth small, the 
lateral long and slightly curved. 21..4,%,.—N. Carolina. 
U. Jesunus. Lea. on U. 2. (Tr. Am. 6.) p.9. t. 4. f. 9. 
Oblong, transverse, compressed, thinnish, inequilateral, flattened 
on the sides, rounded posteriorly, subbiangular anteriorly; ventral 
edge little rounded, incurved in the middle: beaks compressed, 
scarcely prominent ; ligament thin and long: cuticle very dark 
brown and much wrinkled, nacre “purple or white; cardinal teeth 
small, the lateral long and straight. 14..24.—Roanoke. 
U. Cometanatus. Lea. on U. 1. p. 62.—Mya C. D. p. 51. 
—U. Purpurevs. Say § Barnes.—U. Rarisutcata. Lam.— 
U. Coarcrata. Lam.—U. Purrurascens. Lam.—vU. Ruom- 
BULA. Lam.—U. Carinirera. Lam.—U. Georaina. Lam.— 
U. Grasrata. Lam.—Svuucipens. Lam. Oblong ovate, some- 
times subrhomboidal or suboval, anteriorly broader and much longer 
more or less angular, posteriorly rounded, ventral edge little rounded 
an obtuse ridge from beaks anteriorly, surface with coarse wrinkles 
of growth, the cuticle tar-coloured or very dark green : nacre dark 
peach (at times salmon to violet pearl) cardinal teeth deeply striated, 
pyramidal. 2..33.—Massachussets. 
U. Grirritaranus. Lea. Trans. Am. Ph. 5.t. 15.f. 46. Trans- 
versely elongated-elliptic, thickish, spread out, somewhat flattened 
on the sides, rounded on the umbonal slope, ventral edge little 
arcuated, inequilateral, beaks small and scarcely elevated; cuticle 
yellowish with green rays, nacre purple salmon or white: cardinal 
teeth compressed, the lateral long and curved. 13..25.— 
Florida. 
U. Arratus. ZLea.—Nara A. Swain.—vU. Fraeizis. Srrain. 
in Z. Il. 1st ser. Transversely oval, rounded above and below at 
both extremities, thin, ventral and dorsal edge arcuated, the former 
not all incurved : moderately convex, smooth, the cuticle varying 
from black to olive green, nacre purplish near the umbones : in one 
valve two short obtuse and nearly obsolete cardinal teeth, a single 
rather sharper one in the other. 2..3.—N. America.—Liga- 

1 Add likewise the Nara Aurata of Swainson. 
