TRIBE NAYADES. 197 
what prominent ; ligament small; cuticle black or dark brown 
(sometimes rayed), nacre purple; cardinal teeth rather large and 
elevated, lateral straight and lamelliform. +.. 143; —Ohio. 
U. Divaricatus. Lea. Trans. Am. Ph. 5. t. 9. f. 24. 
Transversely elliptic, rather compressed, thin, ligamental edge 
straight and parallel to the ventral edge ; beaks with beautiful 
divaricating folds ; ligament rather short and slender ; cuticle 
greenish smooth, nacre white and irridescent ; cardinal teeth small, 
compressed, the lateral long and rather thin. 2, .. 12.—Hgypt. 
U. Fasa. D’Orbig. Mag. de Z. 1835. Ovate-oblong, com- 
pressed, thin, smooth, greenish brown, anteriorly subangulated and 
broad, posteriorly short and rounded; beaks radiated or smooth ; 
nacre bluish white; cardinal tooth thin, lamellar bifid, the lateral 
elongated and thin. 7..14.—S. America. 
U. Burrovenranus. Lea. Trans. Am. Ph. 5. t. 10. f. 27. 
—D’ Orb. in Mag. de Z. Obovate, transverse, compressed, thick- 
ish, anteriorly subbiangular and longer, posterior end dorsally sub- 
angulate, obliquely rounded below ; beaks with oblique folds and 
rather prominent ; cuticle smooth, dark brown with yellow lines of 
growth : nacre pearly white and irridescent ; cardinal teeth large 
elevated and lamelliform, the lateral nearly straight. 14. .22— 
R.*Parana. S. America. 
U. Discus. Lea.on U. 2.(Tr. Am. 6.) t. 18. f.57.  Ellipti- 
cal, very much compressed, inequilateral, thick, posteriorly rounded, 
anteriorly much attenuated and biangular; beaks prominent, liga- 
ment long and thick ; cuticle blackish, nacre purple and irridescent ; 
cardinal teeth large, the lateral long and separate. — India. 
U. Simus. Lea. on. U. 2. (and Tr. Am. 6.) p. 26. t. 8. f. 20. 
Ovate, transverse, compressed, inequilateral, obliquely angulated 
anteriorly, ventral edge not much rounded, thickish, beaks somewhat 
prominent, ligament shortish ; cuticle yellowish and indistinctly 
rayed, nacre white and irridescent ; cardinal teeth small, lateral 
long and thick. 1.. 1/5.—TZennessce. 
U.Corrvueatus. Lam. 34.—Mya C. Muller.—G mel. 3221. 
—D. p. 52.—Ch. f. 22.—W. t. 2. f. 31.—Myvya Rucosa. Ginel. 
3222.—D. p.53.—Ch. f. 1649.—M. Nopvosa? Gmel.—Spurta ? 
Gmel.—U. Spurta. Lam. (fide Lea.) Ovate-rhombie, thin, 
green, the umbones with angularly flexuous sublongitudinal wrin- 
kles. 14.— Coromandel. 
U. Nitoricus. Cail. voy. d Meroe. 2. t. 61.f. 8, 9.—Desh. 
1 T may not venture to differ from such an authority as Mr. Lea, 
but as the figures of Gmelin’s Mya Rugosa (W. ¢. 2. f. 33.) and 
Nodosa (W. ¢. 2. f. 34.) differ in many particulars from Corrugata, 
I have given copies of them. 
