TRIBE NAYADES. 191 
obliquely rounded, ventral edge somewhat rounded: beaks some- 
what prominent, undulated at the tip; cuticle yellow with green 
rays nearly over the disc; nacre white and irridescent; cardinal 
pas large and erect, lateral long and straight. 1 1,..21.—New 
ork. 
U. Perovaris. Conr. N. F. W. S. p. 43. t. 2. f. 2. Shortish, 
oval, moderately thick, inflated, transverse, inequilateral: anterior 
side obtusely truncated obliquely, ventral edge arcuated and entire; 
umbonal slope rounded ; cuticle olivaceous, obscurely rayed, wrin- 
kled on the margins ; nacre whitish and irridescent anteriorly: teeth 
prominent and granulated.—Var. Reddish brown, nacre rosy. 
2.—h. Alabama. 
U. Capsarormis. Lea. Tr. Am. Ph. 5. ¢.2. f. 4, Trans- 
versely elliptic, shorter and rounded posteriorly, subangulated 
above and below, anteriorly convex, ligamental edge straight, beaks 
slightly elevated, ligament short and thick; cuticle yellow with 
numerous short green rays, nacre white and irridescent anteriorly ; 
teeth elevated, the cardinal double in both valves, the lateral lamel- 
Jar. 1,8,.. 195-—N. America. 
U. Greentt. Conr. N. F.W.S.32.t.4.f- 1. Subovate, trans- 
verse, thickish, posteriorly not very short rounded, ligamental edge 
sloping, obtusely angulated at its end; beaks slightly prominent 
umbonal slope straight, subangulated : cuticle wrinkled, olivaceous, 
rayed anteriorly ; nacre bluish white ; a short obtuse elevation pas- 
sing obliquely from beneath the cardinal teeth which are thick, the 
lateral striated and minutely granulated. 13.—#. Alabama. 
U. Prerus. Lea. Trans. Am. Phe dit. 11s. f- 32.) Trane- 
versely elliptical, dilated and produced anteriorly, thinnish; beaks 
compressed and finely undulated at the tip, ligament short and rather 
thick ; cuticle yellow, with numerous oblique interrupted rays 
which are strongly pencilled at the commencement of each stage 
of growth, nacre pearly white and irridescent : cardinal teeth small, 
the lateral long and slightly curved. 13..23.—Tennessee. 
U. Taniatus. Conr. N. F. W.S. 26. t. 4. f. 2. Transverse, 
regularly convex and elliptical, the beaks slightly prominent, the 
umbonal slope rounded, ligament slope with a slightly impressed 
line, ventral edge rounded: cuticle wrinkled olivaceous, with green 
interrupted rays, nacre bluish white, teeth prominent. 2.—&. 
Alabama. 
U. Interruptus. Lea. on U. 2.p. 15. Transverse, elliptical, 
compressed, inequilateral, thickish, ventral edge rounded, posterior 
dorsal sloping ; beaks somewhat compressed, rather prominent, 
the umbones flattened ; ligament shortish ; cuticle yellow, rather 
smooth, covered with broad green interrupted rays, nacre white ; 
lateral teeth rather long and curved. 13. .23.— Tennessee. 
U. Mennianus. Lea. on U. 2. p.76. Elliptical, rather com- 
