TRIBE NAYADES. 189 
_ shghtly elevated and without undulations at the tip; ligament 
short and thick: cuticle yellowish covered with irregularly in- 
terrupted rays, nacre pearly white and irridescent : cardinal teeth 
elevated, the lateral larger near their termination. 1,9,..37)5.— 
Tennessee. 
DoPrctrorosus. .Conr., N.y Bey Wages fest. 6) fo Le» Oval, 
ventricose, not thick, anteriorly obtusely biangulated and longer ; 
umbonal slope subangulated, the space behind flattened, with an 
impressed line from the beaks to nearly the middle of the anterior 
margin: ventral edge arcuated and entire; umbones wide and 
prominent, beaks slightly elevated ; cuticle brownish olive rayed 
with angular spots, nacre white: cardinal teeth direct, subpyrami- 
dal, prominent. 3.—T'ennessee. 
U. Venrricosus. Barnes. Sil. J. 6. t. 14. f. 14. Large, 
thick, triangularly ovate, transverse, convex, the umbones large 
round and prominent, the beaks recurved, and the cavity capa- 
cious: smooth, anteriorly very broad and subtruncated, anteriorly 
rapidly narrowed, ventral edge entire and arcuated ; anterior slope 
longitudinally waved: cuticle yellowish olive becoming chesnut 
brown on the umbones (rayed when young with green) nacre dull 
white, cardinal teeth broad, prominent and obliquely flattened, 
the lateral broad elevated and abruptly ending anteriorly. 33.. 43. 
—North America, 
U. Occipens. Lea. on U. 1. p. 49. (§ Tr. Am. Ph. 3.) 
t. 10. f. 16.—Ventricosus. Say. Am. 6. t. 32. Inequilateral, 
transverse, ventricose, thick, rounded at both ends, posteriorly very 
narrow, anteriorly very broad ; beaks large, rounded, approximate, 
prominent, subundulated and rarely decorticated : ligament rather 
short and thick: cuticle olive yellow with oblique greenrays, which are 
more crowded anteriorly, nacre white: teeth elevated. 2,5,..32. 
—- Ohio. 
U. Dotasrzrormis. Lea. on U.2.p. 103. (§ Tr. Am. Ph.) 
t. 24. f. 113. Elliptical, transverse, inequilateral, thick ; dorsal 
edge incurved, posteriorly much lower and angulated at its extremity, 
ventral edge straightish in the middle ; beaks inflated and prominent: 
umbonal slope somewhat carinated and obscurely rayed : cuticle 
brown and finely wrinkled, nacre white and irridescent : cardinal 
teeth somewhat lamellar, the lateral long and lamellar. 3..43.— 
Georgia in America. 
U. Guososus. Lea.—Sympnonota G. Trans. Am. Ph. 
5. t. 4. f. 12. Transversely obovate, very globose, inequilateral, 
thinnish, pellucid, ventral edge much arcuated, hinge margin 
much curved and angulated at the extremities ; beaks very round, 
ineurved ; cuticle very smooth and pale yellow, nacre pearly white 
and irridescent ; teeth lamellar, the lateral elevated. 22..34.— 
Ohio. 
