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. f.. 1^ — Ohio. 



U. Divaricatus. Lea. Trans. Am. Ph. 5. t. 9. /. 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. -f-Q . . If. — Egypt. 



U. Faba. D'Orbig. 3Iag.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. -J. . If. — S. America. 



U. Burroughianus. 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. If . . 2f — 

 JR.'Parana. S. America. 



U. Discus. Lea. on U. 2. (TV. Am. 6.) t. 18./. 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. (andTr. Am. 6.)/;. 26. t. 8./. 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-^. — Tennessee. 



U. Corrugatus. Lam. 34. — Mya C. Muller.— Gmel. 3221. 

 — D. p. 52.— Ch.f. 22.— W. t. 2. f. 31.— Mya Rugosa. Gmel, 

 3222.— D. p. 53.— Ch.f. 1649.— M. Nodosa ? Gmel— Spuria ? 

 Gmel. — U. Spuria. Lam. (fide Lea.) Ovate-rhombic, thin, 

 green, the umbones with angularly flexuous sublongitudinal wrin- 

 kles, lj. — Coromandel. 1 



U. Niloticus. Cail. voy. d Meroe. 2. t. 61./ 8, 9. — Desh. 



1 I may not venture to differ from such an authority as Mr. Lea, 

 but as the figures of Gmelin's Mya Rugosa (W. t. 2. / 33.) and 

 Nodosa (W. t. 2. f. 34.) differ in many particulars from Corrugata, 

 I have given copies of them. 



