TRIBE NAYADES. 181 



3, 4.— D. p. 52.— W. t. 2. /. 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. f. 5. — Tr. Am. 

 Ph.3.t.5. — Eaton. — Verrucosus Albus. Hildr. 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. If . . If. — Ohio. 



U. Dromas. Lea. Trans. Am. Ph. 5. t. 10. /. 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. If . . 1 t 9 q. — Tennessee. 



U. ^sopus. Green. Cont. of Mac. Ly. 1827. t. 3.— U. 

 Cicatricosus. 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 striae 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. I. p. 100. t. II. f. 20. — Cicatri- 

 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 . . 4f. — Ohio. 



U.Perplexus. Lea. on U.l.p. 122. t. 17./.42. — Tr. Am. 

 Ph. 4. t. 7.f. 42. — Gibbosus. 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- 



