TRIBE NAYADES. 185 



t. 11. y. 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. 11.. 2|^. — Mexico. 



U. Gibber. Lea. on U. 2. j). 35. t. 10. /. 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 . . l-A. — Tennessee. 



U. PuMiLis. 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. ^. . lyL. — JV". Carolina. 



U. RuBiGiNOsus. Lea. on. U. \.j). 41. t. S.f. 10. — Tr. Am. 

 Ph. 3. t.S.f. 10. Inequilateral, 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. 

 2i^..2i^.-Ohio. 



U. Barnesianus. Lea. on U. 2. p. 31. t. 10. _/". 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 . . If. — Tennessee. 



U. PiLEUs. Lea. on U. 1. p. 129. t. 18./. 47. — Tr. Am. Ph. 

 4. t. 18. f. 47. Subtriangular, ventricose, thick, posteriorly 

 rounded, angular anteriorly, longitudinally furrowed in front of the 

 urabonal 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. 1 ^. . 1^. — Ohio. 



U. Sowerbiantjs. Lea. — Trans. Am. Ph. 5. t. 10./. 28. 

 Subtriangular, thick, inflated, singularly compressed on the an- 

 terior part which is filled with strise 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^^ . . l^. — Tennessee. 

 U. Trigonus. Lea. on U. 1. p- 120. (<j' in Tr. Am. 4.) t. 16. 



