TRIBE NAYADES. 209 
reddish brown and wrinkled ; cardinal teeth small, lateral thin and 
lamellar. 1-1, ..24.—Mewico. 
U. Moptouirormis. Lea. Tr. Am. Ph. 5. t. 13. f. 40.— 
U. Detumpis. Conr. Elongated-ovate, very thin, inflated, trans- 
verse, rounded at both ends, very narrow and short posteriorly : 
dilated anteriorly ; beaks small, ligament rather long and thin ; 
cuticle brown and shining, rays indistinct, nacre slightly purple, 
very irridescent : cardinal teeth small, compressed, the lateral long 
and curved. 13..2,%,.—S. Carolina. 
U. Tenrerus. Rave.—Trenesrosus. Conr. F. W.S. p. 42. 
t.7. f. 1. Elliptical, ventricose, thickish posteriorly, beaks pro- 
minent, anteriorly dilated, the edge descending oblique and recti- 
linear from the ligament, and subtruncated at the extremity, ventral 
edge simple and little rounded ; cuticle olivaceous with linear rays: 
the margins dark brown, nacre irridescent bluish or pink, teeth 
moderately thick.— Virginia. 
U. Tappanianus. Lea. on U. 2. p. 62. t. 17. f.55. Ovate, 
rather inflated, inequilateral, thin, anteriorly dilated, ventral margin 
subincurved, umbonal slope rounded and inflated ; beaks somewhat 
prominent, with double undulations, ligament slender and shortish; 
cuticle yellowish brown, with dark rays and the border dark ochre- 
brown, nacre somewhat salmon-coloured : cardinal teeth compressed 
and curved, lateral thin. 1,4, ..2.—Hollidaysburg. 
U. Conrravens. Lea. on U. 2. p. 75. t. 18. f. 58. Ovate, 
rather inflated, inequilateral, thin, smooth, ventrally and posteriorly 
rounded, obtusely angulated anteriorly, and the dorsal edge elevated ; 
beaks rather prominent and undulated, ligament thin and longish : 
cuticle yellowish green becoming green on the anterior slope, nacre 
white and irridescent: cardinal teeth linear, the double one in the 
right valve, the lateral thin and somewhat curved. 1-15. . 1.9. 
U. Srramineus. Conr. in Sil. J. 25. t. 1. f. 6. Suboval, 
convex, anteriorly longer, wider and rounded above and below, ven- 
tral edge incurved in the middle, beaks slightly prominent, with 
irregular undulations, umbones convex ; concentric lines remarkably 
coarse and prominent: cuticle straw colour, rayed only on the ante- 
rior slope, nacre pearly white and irridescent; cardinal teeth double 
in both valves and subcompressed. 2}.—. Alabama. 
t+tttttt+tt+ Arcuated. 
U. Crassissimus.  Fer.—Sinvata. Lam. 1.—Desh. (not 
Pfeif. nor Blainv.)—Drap. p. 132. t. 10. f. 17. to 19.— EL. t. 248. 
J: 1.—Rossm.f. 195. Ovate-oblong, ponderous, thick, dark brown, 
breadth about twice the length, very inequilateral, posteriorly 
rounded, anteriorly obliquely and obtusely subtruncated, ventral 
edge retuse, dorsal arcuated: cardinal teeth thick, the lateral 
P 
