TRIBE NAYADES. 181 
3, 4.—D. p. 52.—W. t. 2. f. 29. Suboval, thick, covered with 
tubercular knobs uniting into waved masses near the margin ; 
cuticle bottle green, umbones decorticated ; nacre pearly white, 
hinge with a clumsy strong crenated tooth ; scars deep, crenated. 2. 
U. Irroratus. Lea. on U. 1. p. 11. t. 5. ff. 5.—Tr. Am. 
Ph. 3.t.5.—Haton.—Verrucosus Atsus. HMildr. Suborbicular, 
longitudinal, inequilateral, extremely thick and swollen, dorsal edge 
rounded ; ventral rounded and slightly emarginated : beaks some- 
what elevated, recurved, decorticated ; cuticle really yellow but so 
covered with dark green radiating spotted lines as to appear olive ; 
discs transversely and deeply wrinkled, with a slight radiating 
furrow; tubercles slightly raised numerous and generally seated 
on the wrinkles : nacre pearly white and silvery : termination of 
the lateral tooth abrupt. 14 ..13.—Ohio. 
U. Dromas. Lea. Trans. Am. Ph. 5.t. 10. f. 29. Subtri- 
angularly suborbicular, suboblique, gibbous, very thick, very short 
posteriorly ; irregularly and transversely folded at the stages of 
growth, an oblique furrow before the umbonal slope ; beaks thick 
and elevated, ligament short and dark, umbones with a gibbosity ; 
cuticle yellow with numerous dark green dotted rays and posteriorly 
with about six rather broad ones, nacre pearly white: cardinal 
teeth wide, the lateral short and thick. 14.. 1-9,.— Tennessee. 
U. Msorus. Green. Cont. of Mac. Ly. 1827. t. 3.—U. 
Crcatricosus. Conr. (not Say.)—U. Varicosus. Conr. (not 
Lea.) Ovate, compressed attenuated and obtusely angular anteriorly, 
rounded and short* posteriorly, ventral edge anteriorly sinuous : 
transversely striated and wrinkled on the disc; beaks decorticated 
and not prominent; a nearly central radiating gibbosity or 
nodulous ridge produced by the striz at that point becoming thick 
and tuberculated : cuticle glossy, tawny (in the young spotted 
and rayed with brown) nacre white and pearly: teeth thick and 
striated.—N. America. 
U. Varicosus. Lea. on U. 1. p. 100. ¢. 11. f. 20.—Crcatri- 
cosus? Say. Subelliptical, oblique, thick, anteriorly compressed, 
varicose, with transverse concentric elevations ; beaks nearly terminal, 
elevated, incurved ; ligament long and large ; cuticle reddish 
brown, nacre pearly white: cardinal teeth rather small, the lateral 
long large and nearly straight. 3..41.—Ohio. 
U.Perpiexus. Lea. on U.1.p. 122. t. 17. f.42.—Tr. Am. 
Ph. 4. t.7.f.42.—Gisposus. Conr. Ovate, oblique, inequilateral, 
thick, having an irregular nodulous line near the middle which 
stretches obliquely from the beaks to the ventral margin: umbonal 
slope irregularly wrinkled, posteriorly to which is a wide slightly 
impressed furrow; beaks prominent rounded and close to the 
posterior end: ligament slender and rather long : cuticle smooth 
shining, yellowish, with numerous small crowded green rays cover- 
