192 TESTACEOUS MOLLTJSCA. 



pressed, tliinnisli, inequilateral, ventral edge somewhat rounded : 

 beaks somewhat prominent and undulated : cuticle fulvous, covered 

 with numerous rather large green rays, nacre pearly white and irri- 

 descent : cardinal teeth small and erect, the lateral long and nearly 

 straight. \^. .2^.— Tennessee. 



U. Venustus. Lea. on U. 2. p. 4. t. 2. /. 4. Elliptical, 

 transverse, somewhat compressed, inequilateral, thickish, dorsal edge 

 posteriorly sloping, ventral posteriorly subincurved : beaks scarcely 

 prominent : cuticle yellowish with green somewhat sinuous rays, 

 nacre pearly white and irridescent : cardinal teeth small, the lateral 

 rather curved. 1 . . l^^o- — Missouri. 



U. Crassus. Say. Am. C. t. 8.— Barn, in Sil. J. 6./. 1.— 

 U. LiGAMENTiNA. La.m.. — Ellipticus and Carinatus. Barnes. 

 — Mya Gravis. Wood. S.f. 6.— U. Fasciatus. Conr. Varying 

 in form, usually more or less oval, very thick and tumid, light 

 brown , rounded posteriorly, slightly augulated anteriorly : surface 

 waved, beaks projecting, nacre pearly white and irridescent ; car- 

 dinal teeth direct, very thick, lobed, angulated and deeply sulcated; 

 posterior cicatrix deep and rough. 3^ . . 4^. — N. America. 



U. Orbiculatus. Hildr. in Sil. J. 14.— Abruptus. Say. — 

 Crassus. Conr. 3Ion. U. t. 16. Suborbicular, anterior margin 

 broad and slightly rounded, posterior short and narrow: discs much 

 inflated ; ligament thick elevated and passing between the beaks, 

 which are broad, somewhat elevated and directed backwards ; 

 cuticle changing from dark chesnut on the discs to light brown, 

 nacre flesh colour and irridescent : cardinal teeth elevated and 

 angulated. 2\. — U. States. 



U. Australis. Layyi. 46. Transversely ovate, subsinuated 

 in the middle, lateral extremities rounded: cardinal tooth small, 

 compressed, and rather acute. 2^. — New Holland. 



U. Hydianus. Lea. on U. 2. p. 14. /. 6./. 14. Elliptical, 

 transverse, very inequilateral, subinflated, thickish ; ventrally sub- 

 incurved, rounded at both ends : cuticle yellow, covered with dark 

 green rays, nacre white and irridescent: cardinal teeth elevated, 

 lateral long and separate. lf..2|. — Louisiana. 



U. Clairbornensis. Lea. on U. 2. p. 105. t. 24. y. 115. 

 Elliptical, subinflated, inequilateral, thick; beaks somewhat promi- 

 nent ; ligament rather long and thin: cuticle yellow, smooth, with 

 a few obsolete rays : nacre white and irridescent: cardinal teeth 

 small and compressed, lateral long and lamellar. 1 . . 1^'^. — R. 

 Alabama. — Clairborne. 



U. LuTEOLUs. Lam. — U. SiLiauoiDES. Barnes. — Con. Am. 

 6. t. 10. y. 1. — Inflatus. Barnes. Elliptical, ventricose, mode- 

 rately thick, glabrous, olive yellow, with numerous green rays vary- 

 ing much in size ; posteriorly rounded, not very short; anterior 

 edge forming an angle with the almost direct and straight ligamental 



