TRIB NAYADES. 203 
rather short and thick: cuticle blackish brown before the beaks 
and at their tip, on the second growth yellow, nacre pearly white: 
cardinal teeth large, lateral large and curved. 13 ..13.—Ohio. 
U. Macutatus. Conr. N. F. W. S. p.30.t. 4. f.4. Sub- 
triangular, compressed, thickish ; cuticle much wrinkled except on 
the smooth umbones, brown olive with a few very broad and narrow 
intervening interrupted green rays; a slight broad and oblique 
furrow from the prominent beaks to the base: umbonal slope sub- 
angulated, behind which the shell is cuneiform, ligament edge ob- 
lique, rectilinear, anterior edge obliquely subtruncated : cardinal 
‘teeth nearly transverse, subcompressed: nacre very white and irri- 
descent. — Tennessee. 
U. Kirxxuanpianus. Lea. Trans. Am. Ph. 5. t.14. fi 41. 
Rounded-subquadrate, broader than long, thick, compressed, ante- 
rior and ligamental edges little arcuated ; beaks somewhat elevated, 
ligament thick and rather short; cuticle wrinkled, dark brown 
but yellowish near the beaks, with interrupted rays not reaching 
the well rounded ventral edge, nacre pearly white and irridescent : 
cardinal teeth thickish, the lateral short and slightly curved. 
2..23,.—Ohio. 
U. Susrotrunnus. Lea. Tr. Am. Ph. 4. t. 18. f. 45.—Po.t- 
tus? Say.—Suborbicular, subventricose, thick, subequilateral, 
beaks thick and elevated, ligament thick and shortish; cuticle 
yellow and smooth towards the beaks, becoming brown and finely 
wrinkled towards the margin, with interrupted rays about the 
umbones, nacre white and irridescent: cardinal teeth thick, the 
lateral short and slightly curved. -Diameter, 12.—Ohio. 
U. Inrueatus. Conr. F. N. W.S. p. 45. t. 3. f. 2. Trans- 
versely obovate, compressed ; anteriorly dilated, the margins 
slightly oblique, obtusely rounded or subangulated at its extremity; 
umbones wide, not prominent, beaks greatly eroded; umbonal slope 
subangulated and hardly curved: cuticle black, nacre pearly white: 
cardinal teeth direct, pyramidal.— Georgia in America. 
U. Coccineus. Lea. on U. 2. (and Tr. Am. 6.) p. 12. t. 5. 
J. 12.—Conr. Mon. U.t. 13. f. 1.—Caritius. Conr. Mon. U. 
t.13. f. 2. Subtriangular, oblique and slightly compressed, thicker 
posteriorly, posterior dorsal edge very short and sharply angulated ; 
beaks rather elevated retuse, with one or two undulations; lga- 
ment rather long and curved: cuticle dark reddish brown, nacre 
bright red: cardinal teeth thick, the lateral thick and somewhat 
curved. 2..21.—Ohio. 
ttttttt Wide. 
U. Sueparpianus. Lea. Trans. Am. Ph. 5. t. 13. f. 38.— 
Very elongated transversely, thickish, short and rounded poste- 
