184 TESTACEOUS MOLLUSCA. 
angular, very thick, ventricose, umbones flattened, beaks promi- 
nent and rounded, umbonal’ slope angulated ; anterior margin flat- 
tened, a broad convex elevation marked with radiating prominent 
lines (which dentate the margin) and concentric grooves projecting 
ventrally : cuticle olivaceous and wrinkled, nacre very white : liga- 
ment very short: cardinal teeth double in both valves, thick, 
prominent sulcated and granulated. 24.—R. Alabama. 
U. Securis. Lea. on. U. 1. p. 51. t.11. f.17.—Hat.—U. 
Deprressa. af. not. Lam. Subtriangular heart-shaped, in- 
equilateral, flattened over the umbones, thick; beaks elevated, 
recurved, much compressed : ligament shortish and thick : cuticle 
olive yellow passing into olive brown, shining and transversely 
wrinkled, nacre pearly white and irridescent. 14..1-9,.— Ohio. 
U. Camexus. Lea. Trans. Am. Ph. 5.t.15. f. 45.  Trans- 
verse, subtriangular, thick; rounded, short and very attenuated 
posteriorly ; flattened over the umbones from the beaks to the 
ventral margin, which is little arcuated and incurved in the 
middle; anteriorly subcuneiform, cuticle yellowish brown with 
capillary rays, nacre white; cardinal teeth small, the lateral large 
thick and curved. 2.3, .. 32.— Ohio. 
U. Ovatus. Say. in Enc. Am. Nich.—Lam.—Conr. Mon. 
2. f. 1, 2, 3.—Barnes. Obovate, convex, not thick, deeply 
wrinkled, glossy, umbones prominent, epidermis yellowish or 
horn coloured, rayless ; anterior slope flattened and fuscous, some- 
what waved with strive, and wrinkles which become lamellar: 
hinge-margin making an angle with the anterior and posterior 
dorsal edges; nacre pearly, bluish white: beaks subcentral, 
recurved; teeth elevated, the cardinal compressed and crestlike. 
23,..343;.— Ohio. 
U. Susovarus. Lea. on U. 1. p. 128. t. 18. f. 46. Sub- 
ovate, transverse, inflated, thick, inequilateral: beaks elevated, 
incurved and undulated at the tips; ligament short and thick : 
cuticle yellowish with numerous oblique green rays, nacre white 
and very pearly : cardinal teeth double in both valves and erect, 
the lateral short and lamelliform. 3. .41—-Ohio. 
U. Crasstpens. Lam.—U. Nicer. Conr. Mon. U. t. 
26.—U. Cuneatus. Barnes. Elongated and subtriangular, 
ponderous, anteriorly narrowed wedge-shaped and compressed ; 
umbones somewhat elevated, beaks low and distant : anterior de- 
pression elongated, heart-shaped and furrowed, the ventral edge 
slightly rounded : cuticle blackish brown, somewhat ferruginous : 
an elevated ridge from the beaks anteriorly: nacre brownish 
purple and irridescent ; cardinal teeth deeply divided and suleated, 
the lateral long curved and not thick. 2,3,..34.—North 
America. 
U. Carsonarius. Lea. on. U. 2.p. 37.(f in Tr. Am. Ph.4.) 
