176 TESTACEOUS MOLLUSCA. 
U. Trapezorpes. Lea. on U. 1p: 79.t. 3. 7. VU. 
Inrerruptus. Say. Ann. C. t. 33.—U. Crassipens. Var. 
A. Lam. 3. Trapezoidal, inequilateral, thick, transverse, ante- 
riorly angular above and below, posteriorly obliquely rounded ; 
anterior portion with oblique subparallel large plaits, its slope 
large and keeled; beaks slightly prominent, incurved : cuticle 
black and wrinkled, nacre purple and irridescent: cardinal teeth 
double in both valves, lateral, curved, and lamelliform. 22. .4%5. 
— Louisiana.} 
U. Fouratus. Hildreth. in Sil. J. 14. f. 16.—U. Friex- 
vosus. Conrad. in text.—Foutatus in plate 4 Monog. Com- 
pressed and shaped like a grape-leaf, the posterior ventral margin 
having a projecting lobe, on either side of which the edge is 
incurved anteriorly, rounded posteriorly, beaks flat and eroded, 
ligament more elevated than the beaks and passing between them ; 
dorsal margin curved: two elevated ridges from the beaks pro- 
jecting on the anterior dorsal and ventral margins: cuticle dark 
olive, waved transversely, and obscurely rayed with green across 
the waves: cardinal teeth small, that in the right valve deeply 
suleated, the lateral teeth short and thick: nacre greenish white. 
2.—United States. 
U. Purcirerus. Lea.gn U.2.p. 61. t. 17. f. 53. Elliptical, 
inequilateral, somewhat inflated, with numerous small folds on the 
anterior side and slope, thicker posteriorly: ligament short and 
light horn coloured, cuticle blackish green, nacre purple: teeth 
rather large, the lateral straight. 14. .25.—Mewico. 
U. Muttisrriatus.. Lea. on U. 1. p. 101. t. 12... 22. 
Subrectangular, transverse, inequilateral, slightly compressed and 
rounded nearly alike at both ends, rather thin; beaks slightly 
prominent, surrounded by wrinkles forming acute angles with each 
other: ligament linear; cuticle dark brown and wrinkled, nacre 
bluish white : cardinal tooth oblique, lamelliform, single in the left 
and double = ee valve, the lateral long and nearly straight. 
1... 129;.— Brazil. 
U. Susrentus. Say. J. A. N.S. Phil. 5. §& Am. Con. t. 15. 
Oblong-oval, subcompressed, slightly contracted at the middle of 
the base, dull yellowish brown; beaks not prominent, decorti- 
cated: dorsal edge regularly arcuated, without any appearance 
of an angle: anterior margin with numerous slightly reflected 
ribs. 14..31.—North America. 
U. Conrapicus. Lea.-Trans. Am. Ph. 5. t..9. f. 23. 
Elongated-elliptic, transverse, rounded and short posteriorly, attenu- - 
ated anteriorly, ligamental edge straight, ventral entire and little 

1 Lamarck’s CasTaL1& belong to this section. 
