TRIBE NAYADES. 185 
t. 11. f. 32. Subtriangular, transverse, swollen, inequilateral, 
thick, ventral margin centrally incurved, anterior side rounded; 
beaks rather prominent : cuticle black and (apparently) without 
rays, nacre purple and irridescent : cardinal teeth rather large, lateral 
small and somewhat curved. 12..22.—WMexico. 
U. Gispser. Lea. on U. 2. p. 35. t. 10. f. 30. Triangular, 
compressed, inequilateral, transverse, anteriorly somewhat tri- 
angular and elevated on the dorsal edge, thickish, ventral edge 
centrally incurved : beaks rather prominent, ligament short, cuticle 
dark brown, (apparently) not rayed, nacre salmon coloured : car- 
dinal teeth small, the lateral inclined. 4. .14.— Tennessee. 
U. Pumiuis. Lea.on U.2. p. 23. t. 7. f. 17. Subtriangular, 
transverse, inequilateral, thinnish, anteriorly subbiangular and its 
dorsal edge straightish; beaks somewhat prominent: ligament 
short : cuticle dark brown, nacre white: cardinal teeth large, the 
lateral short and straight. +..1,45.—N. Carolina. 
U. Rusiernosus. Lea.on. U. 1. p. 41. t. 8. f. 10.—T'r. Am. 
Ph. 3. t.8.f.10. Tnequilateral, transverse, subventricose thickish, 
obovate, posterior and ventral edges rounded, anterior incurved, 
anterior dorsal sloping ; beaks prominent, incurved, anteriorly sub- 
angulated : cuticle rusty or salmon-yellow (wrayed when young, ) 
nacre salmon coloured; cardinal tooth large, the lateral thick. 
251,..235.— Ohio. 
U. Barnestanus. Lea. on U. 2. p. 31. t. 10. f. 36. Sub- 
triangular, compressed, inequilateral thick: beaks rather promi- 
nent: cuticle chesnut brown with interrupted green rays and 
strong marks of growth; nacre white and irridescent: cardinal 
teeth small, the lateral nearly straight. 1..12.—Tennessee. 
U. Pitevus. Lea. on U. 1. p. 129. t. 18.f. 47.—Tr. Am. Ph. 
4. t. 18. f. 47. Subtriangular, ventricose, thick, posteriorly 
rounded, angular anteriorly, longitudinally furrowed in front of the 
umbonal slope which is flattened on the ridge, the furrow causing a 
slight emargination on the ventral margin; beaks prominent and 
rounded at the tip: ligament short and thick: cuticle yellowish 
brown, wrinkled, rays numerous and hair-like, nacre pearly white 
and irridescent ; cardinal teeth large, lateral shortish and slightly 
curved. 14..14.—Ohio. 
U. Sowersranus. Lea.— Trans. Am. Ph. 5. t. 10. f. 28. 
Subtriangular, thick, inflated, singularly compressed on the an- 
terior part which is filled with strize from the anterior and the anterior 
ventral edges, the posterior part being inflated and smooth ; slightly 
emarginate at anterior ventral edge: beaks large and very prominent ; 
ligament short and thick ; cuticle bright brown, smooth and shining 
behind, striate before, nacre very light purple ; cardinal teeth large, 
the lateral thick and nearly straight. 1,7, . . 14.— Tennessee. 
U. Triconus. Lea. on U.1. p.120. (§ in Tr. Am. 4.) t. 16. 
