TRIBE NAYADES. 199 



anteriorly ; anterior dorsal edge rather elevated, thickish, flattened 

 at the urnbones and sides, carinated ; beaks little prominent, undu- 

 lated at the tip; ligament thin long and straight ; cuticle dark brown, 

 obscurely rayed, nacre purple and irridescent ; cardinal teeth small, 

 thick ; the lateral long and curved. 1 t 7 q . . 3-f.— Near Darien. 



U. Roanoakensis. Lea. on U. 2. (TV. Am. 6.) p. 27. t. 8. 

 f. 21. Oblong, transverse, inequilateral, biangular anteriorly, com- 

 pressed, thick, ventral and dorsal edges little rounded, flattened on 

 the umbonal slope ; ligament very large and long : cuticle dark 

 brown (apparently) rayless, nacre white ; cardinal teeth small, the 

 lateral long and slightly curved. 2\ . . 4 T 7 7 . — N. Carolina. 



U. Jejunus. Lea. on U. 2. (Tr. Am. 6.) p. 9. t. 4. f. 9. 

 Oblong, transverse, compressed, thinnish, inequilateral, flattened 

 on the sides, rounded posteriorly, subbiangular anteriorly ; ventral 

 edge little rounded, incurved in the middle : beaks compressed, 

 scarcely prominent ; ligament thin and long : cuticle very dark 

 brown and much wrinkled, nacre 'purple or white ; cardinal teeth 

 small, the lateral long and straight. 1^. . 2\. — Roanoke. 



U. Complanatus. Lea. on U. I. p. 62. — Mya C. D. p. 51. 

 — U. Purpureus. Say & Barnes. — U. Rarisulcata. Lam. — 

 U. Coarctata. Lam. — U. Purpurascens. Lam. — U. Rhom- 

 bula. Lam. — U. Carinifera. Lam. — U. Georgina. Lam. — 

 U. Glabrata. Lam. — Sulcidens. Lam, Oblong ovate, some- 

 times subrhomboidal or suboval, anteriorly broader and much longer 

 more or less angular, posteriorly rounded, ventral edge little rounded 

 an obtuse ridge from beaks anteriorly, surface with coarse wrinkles 

 of growth, the cuticle tar-coloured or very dark green : nacre dark 

 peach (at times salmon to violet pearl) cardinal teeth deeply striated, 

 pyramidal. 2 . . 3 J. — Massachussets. 



U. Griffithianus. Lea. Trans. Am. Ph. 5. t. 15.f. 46. Trans- 

 versely elongated-elliptic, thickish, spread out, somewhat flattened 

 on the sides, rounded on the umbonal slope, ventral edge little 

 arcuated, inequilateral, beaks small and scarcely elevated; cuticle 

 yellowish with green rays, nacre purple salmon or white : cardinal 

 teeth compressed, the lateral long and curved. lj..2 r %- — 

 Florida. 1 



U. Atratus. Lea. — Naia A. Swain. — U. Fragilis. Swain, 

 in Z. II. 1st ser. Transversely oval, rounded above and below at 

 both extremities, thin, ventral and dorsal edge arcuated, the former 

 not all incurved : moderately convex, smooth, the cuticle varying 

 from black to olive green, nacre purplish near the umbones : in one 

 valve two short obtuse and nearly obsolete cardinal teeth, a single 

 rather sharper one in the other. 2 . . 3. — N. America. — Liga- 



1 Add likewise the Naia Aurata of Swainson. 



