192 TESTACEOUS MOLLUSCA. 
pressed, thinnish, 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. 14..2}.— Tennessee. 
U. Venustus. Lea. on U. 2. p. 4. t. 2. f. 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.. 145.—Missouri. 
U. Crassus. Say. Am. C. t. 8.—Barn. in Sil. J. 6. f. 1.— 
U. Ligamentina. Lam.—E..ipticus 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 angulated 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. 31..44+.—N. America. 
U. Orsicuntatus. Hildr. in Sil. J. 14.—Asrvurrtus. Say.— 
Crassus. Conr. Mon. 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. 23.—U. States. 
U. Ausrratis. Lam. 46. Transversely ovate, subsinuated 
in the middle, lateral extremities rounded: cardinal tooth small, 
compressed, and rather acute. 21:—New Holland. 
U. Hypranus. Lea. on U.2.p. 14. t. 6. f. 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. 12..23.— Louisiana. 
U. Cuarrsornensis. Lea. on U. 2. p. 105. t. 24. fi 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..15%,.—R. 
Alabama.— Clairborne. 
U. Lureotus. Lam.—U. Siriqvoipes. Barnes.—Con. Am. 
6. ¢. 10. f. 1.—Inruarus. 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 
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