TRIBE NAYADES. 191 



obliquely rounded, ventx'al 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 lai'ge and erect, lateral long and straight, IxV • • ^i' — -^<?w 

 York. 



U. Perovalis. Conr. N. F. W. S. p. 43. t. 2./. 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. — M. Alabama. 



U. Capsaformis. Lea. Tr. Am. Ph. 5. t.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- 

 lar. l-^3_ ^ ^ i^__ — jv". America. 



U. Greenii. Conr. N. F. W. S. 32. t. 4./. 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 

 latex'al striated and minutely granulated. 1^. — ^. Alabama. 



U. PiCTUs. Lea. Travis. 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. 1|^ . . 2-|. — Tennessee. 



U. T^NiATus. 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 rovmded: cuticle wrinkled olivaceous, with green 

 interrupted rays, nacre bluish white, teeth prominent. 2. — li. 

 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^ . . 2|. — Tennessee. 



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



