TRIBE NAYADES. 189 



slightly elevated and without undulations at the tip ; ligament 

 short and thick : cuticle yellowish covered with irregularly in- 

 terrupted rays, nacre pearly white and iri'idescent : cardinal teeth 

 elevated, the lateral larger near their termination. 1-^^ . . 3-^^. — 

 Te?inessee. 



U. Pectorosu?. Co7ir. N. F. W. p. 37. t. 6. f. 1. Oval, 

 ventricose, not thick, anteriorly obtusely biangulated and longer ; 

 umbonal slope subangulated, the space behind flattened, with an 

 impressed line from the beaks to nearly the middle of the anterior 

 margin : ventral edge arcuated and entire ; umbones wide and 

 prominent, beaks slightly elevated ; cuticle brownish olive rayed 

 with angular spots, nacre white : cardinal teeth direct, subpyi-ami- 

 dal, prominent. 3. — Tennessee. 



U. Ventricosus. Barnes. Sil. J. 6. t. 14. f. 14. Large, 

 thick, triangularly ovate, transverse, convex, the umbones large 

 round and prominent, the beaks recurved, and the cavity capa- 

 cious : smooth, anteriorly very broad and subtruncated, anteriorly 

 rapidly narrowed, ventral edge entire and arcuated ; anterior slope 

 longitudinally waved : cuticle yellowish olive becoming chesnut 

 brown on the umbones (rayed when young with green) nacre dull 

 white, cardinal teeth broad, prominent and obliquely flattened, 

 the lateral broad elevated and abruptly ending anteriorly. 3| . . 4^. 

 — JVorth America. 



U. Occidens. Lea. on U. 1. p. 49. (.j- Tr. Am. Ph. 3.) 

 t. lO.y. 16. — Ventricosus. Say. Am. 6. t. 32. Inequilateral, 

 transverse, ventricose, thick, rounded at both ends, posteriorly very 

 narrow, anteriorly very broad ; beaks large, rounded, approximate, 

 prominent, subundulated and rarely decorticated : ligament rather 

 short and thick : cuticle olive yellow with oblique green rays, which are 

 more crowded anteriorly, naci-e white: teeth elevated. 2j^q . . 3f . 

 — Ohio. 



U. DoLABR^FORMis. Lca. 071 U. 2. p. 103. (Sf Tr. Am. Ph.) 

 t. 24. f. 113. Elliptical, transverse, inequilateral, thick; dorsal 

 edge incurved, posteriorly much lower and angulated at its extremity, 

 ventral edge straightish in the middle ; beaks inflated and prominent : 

 umbonal slope somewhat carinated and obscurely rayed : cuticle 

 brown and finely wrinkled, nacre white and irridescent : cardinal 

 teeth somewhat lamellar, the lateral long and lamellar. 3 . . 4^. — 

 Georgia in America. 



U. Globosus. Lea. — Symphonota G. Trans. Am. Ph. 

 b.t.A.f. 12. Transversely obovate, very globose, inequilateral, 

 thinnish, pellucid, ventral edge much arcuated, hinge margin 

 much curved and angulated at the extremities ; beaks very round, 

 incurved ; cuticle very smooth and pale yellow, nacre pearly white 

 and irridescent ; teeth lamellar, the lateral elevated. 2v . . 3\. — 

 Ohio. 



