210 TESTACEOUS MOLLUSCA, 



lamellae thick and slightly exserted, ligamental sinus large and oval, 

 2 . . 4 — Hhine, Loire, ^'C. 



U. MoNODONTUS. Say. Am. C. t. 6 — Eat. in Tr. Jour. 3fed. 

 1831.— U. SoLENiFORMis. Lea. OTi U.l. p. 97 . Elongated, trans- 

 verse, thin, inequilateral, compressed, rounded and sloping from the 

 beaks at both ends, ventral margin strongly incurved in the middle; 

 the beaks slightly prominent : cuticle very dark brown and wrin- 

 kled, the nacre bluish white and irridesceut: cardinal tooth a simple 

 small tubercle in both valves, the lateral long straight and very im- 

 perfect. IJq . .4^3__. — Ohio. 



U. Emarginatxjs. Lea. Tran^. Am. Ph. 5. t. 9. /. 22. 

 Transversely elongated-oblong, thickish rounded and very short 

 posteriorly, anteriorly obtusely subbiangulated, ligamental edge 

 straightish, the ventral strongly incurved in the middle and com- 

 pressed ; beaks rather elevated and undulated at the tip : ligament 

 long and thin, cuticle greenish yellow, becoming green on the ante- 

 rior slope, nacre pearly white and irridescent : cardinal teeth small 

 oblique and double in both valves, the lateral long and slightly 

 curved. \^\ . . 2|-. 



Division B. 



Having one cardinal tooth. 

 Section A. — Plicate. 



U. Complanata. — Alasmodonta C. Dai'nes Sf Hild. — 

 Symphonota C. Lea. on U. I. p. 62. Triangular-ovate, inequi- 

 lateral, transversely wrinkled, compressed, thick ; anterior dorsal 

 edge winged connate and obscurely undulated at right angles to the 

 wrinkles: the beaks compressed and scarcely projecting, undulated, 

 the ligament concealed with an oblique callous plane under it: cuti- 

 cle dark brown, nacre white and irridescent : a large cardinal tooth 

 in each valve. 3 . . 5. — Ohio, Sfc. 



U. Confragosa. — Alasmodonta C. Saij. Am. Co7i. t. 21. 

 Transversely suboval, dark olive or blackish, inequilateral, anterior 

 edge forming an angle with the scarcely sloping ligamental one ; 

 convex, with oblique irregular abbreviated undulations not directed 

 towards the beak, and numerous more or less abbreviated, slightly 

 raised lines fi'om the umbo becoming obsolete towards the base, 

 those in front divaricating towards the hinge margin : beak with a 

 groove and a double series of three or four tubercles : inside white 

 margined with opaque whitish or violaceous. 3g. — iV. America. 



U. Arcula.— Marg. a. Lea. on U. 2. p. 71. t. 22. /. 69. 

 Triangular, veiy inflated, very thin, with about eight transverse 

 curved folds, dorsal edge much sinuated and angulated posteriorly : 

 ventral edge little rounded and not incurved, the umbones very 



