202 TESTACEOUS MOLLUSCA. 
U. Paranensis. Lea. Tr. Am. Ph. 5. t. 14. f.42.—U. Sot- 
s1aAnA.—D’Orb. in Mag. de Z. Subrotund, inequilateral, com- 
pressed, thickish, umbonal slope flattened; beaks rather elevated, 
longitudinally folded and retuse, ligament thin ; cuticle wrinkled, 
shining, greenish becoming brown towards the margin, with very 
obscure curved rays which sweep from the beak towards the pos- 
terior side, nacre pearly white and irridescent: cardinal teeth 
recurved, double in both valves, the lateral rather long and curved. 
3..33.—H. Parana. 
U. Mempranacea. Lea.—Myrtitus M. Maton.—Lin. Tr. 
10. ¢. 24. f. 11, 12.—U. Marontana. D’ Orbig. 8. Am. t. 71. 
Jf: 1, 2. Roundish, subinflated, posteriorly shorter and rounded, 
anteriorly angulated, dorsal edge straight, very thin, smoothish, 
greenish rufous, with very small ribs diverging from the beaks, 
inside bluish or pink : cardinal tooth thin straight and solitary, the 
lateral tooth anteriorly very long and elevated. 2..22.—S 
America. 
U. Variapinis. Lea.—Mya V. Maton in Lin. Trans. 10. t. 
24. f. 4, 5,6, 7.—W. t. 3. f. 38.—D. p. 53.—U. Rorunpuvs. 
Wagn. in Spix. Braz. t. 26. f. 3, 4. Subrhombie gibbous, the um- 
bones longitudinally wrinkled ; transversely striated, the wrinkles 
gradually disappearing, cuticle greenish brown, dorsal edge nearly 
straight, and subangulated at its extremities, ventral edge poste- 
riorly very obliquely rounded ; nacre bluish: hinge with two teeth 
diverging at the apex and inserted in linear receptacles. 1..1— 
S. America. 
U. Personatus. Say.—U. Cariuuaris. Lea. Trans. Am. 
Ph. 5. t. 2. f. 2. Obtusely subquadrate, broader than long, ven- 
tricose, thickish, subangular and longer anteriorly: beaks thick and 
elevated, ligament short and thick; cuticle dark and finely wrinkled, 
smoother towards the beaks, rays numerous capillary and spread- 
ing, nacre pearly white and irridescent: cardinal teeth much 
elevated, the lateral lamellar and inclined to curve upwards. 
1} ..1,9,.— Ohio. 
U. Rerusus. Lam.—Conr. Mon. U. t. 8.—Torsa. Raf. in 
Ann. de Sc. Phy. 5. t. 82. f.1, 2, 3.—Haton. Obtusely sub- 
triangular, ventricose, with concentric furrows : beaks subcentral, 
retuse, umbo very prominent and leaning posteriorly ; ligament 
long and prominent; umbonal slope rounded and undefined ; pos- 
terior and ventral edges regularly rounded; anterior side with a 
slight furrow ; ligamental edge curved and very oblique : within 
dark purple margined with white: cuticle olive. 21, .2— 
N. America. 
U. Esenus. Lea. Tr. Am. Ph. 4. t. 9. f. 14.—Mytinorpes. 
Conr. (not Raf.) Obliquely obovate, inequilateral, very ventricose, 
very thick; beaks nearly terminal and much elevated, ligament 
