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 

 teeth large and erect, lateral long and straight. lyV • • %i u — New 

 York. 



U. Perovalis. 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.— JR. Alabama. 



U. Capsaformis. Lea. Tr. Am. Pit. 5. t. 2. f. 4. Trans- 

 versely elliptic, shorter and rounded posteriorly, subangulated 

 above and below, anteriorly convex, Jigamental 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- 

 lar. 1 T 3 ^ . . 1-^y. — N. America. 



U. Greenii. Conr. N. F. W. S. 32. t. A.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. 1-|. — JR. Alabama. 



U. Pictus. Lea. Trails. Am. Ph. 5. t. 11. /. 32. Trans- 

 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. If • • 2J-. — Tennessee. 



U. Tjeniatus. Conr. N. F. W. 8. 26. t. A.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. — JR. 

 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. 1 J . . 2J- . — Tennessee. 



U. Menkianus. Lea. on U. 2. p. 76. Elliptical, rather com- 



