196 TESTACEOUS MOLLUSCA. 
rays; nacre bluish white, anteriorly irridescent: cardinal teeth 
direct, prominent, pyramidal. 2.—R. Alabama. 
U. Muutre toranus. Lea. Tr. Am. 6. f. 36. p. 41. Elliptical, 
rather compressed, transverse, inequilateral, thickish, rounded at 
both ends, ventral and anterior dorsal edge straightish : beaks rather 
prominent, finely undulated : cuticle yellowish with dark green rays 
anteriorly, nacre white and irridescent ; cardinal teeth rather small 
and erect, lateral long and erect. 1-3, . . 2;3,.— Tennessee. 
U. Cresservus. Lea. on U.2. (and Tr. Am.6.) p. 33. t. 10. 
J. 28. Subelliptical, very transverse, very inequilateral, thickish, 
ventral edge little rounded and rather sinuated, anterior dorsal 
edge straightish, anterior edge incurved ; beaks rather prominent 
and undulated at the tip, retuse: cuticle dark green, obscurely 
rayed : cardinal teeth small and elevated, the lateral obscure ; nacre 
white. 12..2,7.—Tennessee. 
U. Grasper. Lea. on U. 2. (and Tr. Am. 6.) 34. t. p. 10. f. 
29. Hiliptical, transverse, compressed, smooth and shining, inequi- 
lateral, thin; beaks somewhat prominent, with fine nearly parallel 
undulations at the tip ; ligament short: cuticle smooth yellow with 
numerous fine rays over nearly the whole disc: cardinal teeth small 
and elevated, the lateral long. #. .14.—Tennessee. 
U. Hiupreruianvus. Lea. Trans. Am. Ph. 5.t. 3. f. 8.— 
U. Amspieuva? Say. Narrow elliptical, subcylindraceous, very 
transverse, thin, rounded at both ends, ventral edge little arcuated, 
incurved, subparallel to the dorsal, cuticle dark brown, nacre above 
brown, below white ; ligament long and thin ; cardinal teeth single 
in each valve, no lateral. 51,.. 13.—Ohio. 
U. Fasauis. Lea. on. U.1. p. 96. (and Tr. Am. Ph. 4.) 
¢. 10. f. 16.—U. Capiuius. Say. Transylv. Jour.—ULariiuvs. 
Say. Am. Conch. t. 41. Subelliptical, transverse, inequilateral, 
thick, rounded at both ends ; ventral margin incurved in the middle ; 
ligament short ; beaks slightly prominent ; cuticle dark, with green 
hair-like undulating rays (especially anteriorly) ; nacre pearly white 
and irridescent ; cardinal teeth small, the lateral short thick and 
enlarged anteriorly. 2..1.— Ohio. 
U. Parvus. Barnes, Sil. J. 6.—Haton.—Conr. Mon. U. t. 
6. f. 1. Oblong-ovate, convex, rounded at the sides, thinnish ; 
beaks slightly elevated and placed at one-fourth the distance from 
the posterior end ; ligament very narrow, and slope distinct and 
obsoletely ribbed; ventral edge little rounded ; cuticle brownish, 
an obtuse slightly elevated anterior ridge; nacre pearly white and 
irridescent ; the lateral tooth rectilinear, rounded at the end and 
parallel to the base. 3..11.—Foa River, North America. 
U.Guans, Lea. on U. 1. p. 92. (and Tr. Am. Ph. 4.) t. 8. 
J. 12. Ovate elliptical, transverse, inequilateral, inflated, rather 
thick, rounded at both ends; ventral edge rounded ; beaks some- 
