TRIBE NAYADES. 193 
ventral edge simply arcuated ; umbones not prominent, umbonal 
slope undefined ; beaks with flexuous undulations; inside bluish 
white, cardinal teeth oblique, lateral slightly decurved anteriorly. 
1t..2!,.—Delaware, 5c. N. America.' 
U. Putcner. Lea. on U. 2. (and Tr. Am. Ph. 6.) p. 6. t. 3. 
J. 6. Elliptical, transverse, somewhat compressed, inequilateral, 
thickish, ventral edge rounded; beaks irregularly undulated; cuticle 
yellow, covered with numerous dark green well defined rays, nacre 
pearly and pink: cardinal teeth erect, lateral enlarged near their 
termination. 1,3,..21.— Tennessee. 
U. Raptatus. Lam. 13.—U. Virerntana? Lam. 39.—Mya 
Rapiata. Gmel. 3220.—D. p. 51.—Mya Ostoneata. Wood. 
J. 2.—Ch. f. 7. Obovate, thin, convex-depressed, very finely striated 
transversely, the anterior side very broad, cuticle yellowish and lon- 
gitudinally rayed. 23.—Sarratoga. 
U. Mepetumnus. Lea. on U. 2. (and Tr. Am. 5.) p. 39. 
t. 12. f.34. Elliptical, transverse, rather compressed, inequilateral 
thinnish, ventral margin subincurved centrally ; much narrower 
and obliquely rounded posteriorly ; beaks rather prominent, ligament 
rather long and slender: cuticle yellowish covered with green rays, 
nacre white and irridescent : cardinal teeth small, lateral long and 
somewhat curved. 153,..2-3,.—Vera Cruz. 
U. Noratus. Lea. on U. 2.(Tr. Am.6.) p. 28. t. 8. f. 22. 
Elliptical, compressed, transverse, inequilateral, anteriorly subbian- 
gular, thin, posteriorly obliquely rounded: beaks rather prominent : 
ligament shortish: cuticle reddish brown, covered with interrupted 
rays, nacre salmon coloured and irridescent: cardinal teeth small, 
lateral long and slightly curved. 1. .14.—Tennessee. 
U. Vanuxemensis. Lea. on U. 2. (and Tr. Am. 6.) 11. f. 
31. Elliptical, transverse, compressed, inequilateral, thick, ventral 
edge straightish, anterior edge incurved: beaks somewhat pro- 
minent: cuticle dark brown and (apparently) rayless, nacre salmon 
coloured and irridescent : cardinal teeth large, the lateral long and 
somewhat curved. 11..1-2,.—Tennessee. 
U. Nasuvinturanus. Lea. Trans. Am. Ph. 5. t. 14. f. 43. 
Transversely elliptical, thickish, posteriorly rounded and short, ante- 
riorly produced and subacuminated, ventral and ligamental edges 
little arcuated: beaks slightly elevated and minutely undulated ; 
ligament shortish: cuticle dark brown, obscurely rayed, nacre 
pearly white: cardinal teeth lamelliform and double in both valves, 
the lateral nearly straight. 12..2}.—Ohio. 
U. Ziecuerianus. Lea. on U. 2.(Tr. Am.6.) p. 32. t.10. f. 
27. Elliptical transverse, inequilateral, smooth, thickish, somewhat 

1 Add likewise the U. Carnprent.—Gray. 
e 
