TRIBE NAYADES. 201 
U. Lirrorauis. Lam. 25.—Crassus. Schr. F. 2. f. 2.— 
RuomsgorpEsa. Schr. 2. f. 3.—Breviaris, SemrruGara, and 
Nana. Lam. 14, 16, 5 17. (fide Lea).—Incurvus. Lea. on 
U. 1. p. 167. t. 13. f. 27. Transverse, oval, thick, dark brown, 
inequilateral, transversely striated, posteriorly rounded, anteriorly 
produced, ligamental edge sloping, ventral edge little arcuated, sub- 
incurved: anterior slope with a marginal groove on each side: 
beaks wrinkled: cardinal teeth thick, conical, dentato-serrated, the 
lateral thick, 23.—France, Sc. 
+t t+ + Subrotund. 
U. Circunus. Lea. Tr. Am. Ph. 3. t. 9. f. 14.—Hat.—Mya 
Rotrunpa ’—Wood. Circular, ventricose, subequilateral, thick, 
transversely wrinkled ; beaks rather elevated and somewhat re- 
curved; ligament short and thick ; cuticle dark brown becoming 
light yellowish brown anteriorly, shining and satinlike, nacre pearly 
white and irridescent : teeth large. Diameter, 14.—Ohio, §c. 
U. Lens. Lea. on U.1. p. 90. (andTr. Am. Ph. 4.) t. 8. f.10. 
Lenticular, broader than long, subventricose, equilateral, thickish, 
beaks slightly prominent, undulated at the tip, ligament short and 
thick: cuticle smooth brown but anteriorly yellowish, nacre white 
rarely rosy 3 cardinal teeth large, the lateral short and straightish. 
=, -- 14.— Ohio. 
’U. Rupetius. Conr. N. F. W. S. D. 38: t005 Jn 20 SUD 
orbicular, transverse, ventricose, thick, subequilateral, umbones 
prominent, umbonal slope rounded, margined before and behind 
by a faint angle; beaks eroded, slightly prominent ; cuticle 
reddish brown, nacre pink or purplish: cardinal teeth direct.— 
R. Alabama. 
U. Mason1. Conr. N. F. W.S.p. 34. t. 5.f.2.—Con. Mon. 
U. t. 12. f. 2. Transverse, suborbicular, discs slightly flattened ; 
umbones broad prominent, carinated behind : beaks slightly promi- 
nent : umbonal slope straight and angulated, ligament slope flat- 
tened and broad: cuticle olive, clouded with brown and polished, 
nacre bluish white : cardinal teeth prominent, compressed very 
oblique: 3.—R. Savannah, N. America. 
U. Rorunpatus. Lam.—Suporsicuuata. Lam. § Bl.— 
U. Guesutus. Say. Am. Conch. t. 34.—Suse iososus. Lea. 
Tr. Am. Ph. 5. t.2. f.3. Transverse, obovate, inflated, thick, pos- 
teriorly rounded and shorter, anteriorly subangulated, ventral edge 
arcuated and somewhat sinuated anteriorly ; beaks slightly promi- 
nent, rounded ; umbonal slope carinate, ligament thick and shortish: 
cuticle dark brown or black, nacre pearly pink ; cardinal teeth 
wide and striated, the lateral somewhat curved. 2,'4,..15%.— 
Louisiana. 
