TRIBE NAYADES. 211 
large, the umbonal slope acutely carinate, the anterior slope very 
much flattened, having an indistinct furrow along the edge of the 
carina, cuticle dark green, with numerous green rays over the whole 
surface, nacre bluish: teeth lamellar and irregular.— Georgia in 
America. 
U. Marernata.—Mare. M. Lea. Tr. Am. Ph.6.—Varicosa. 
Lam.—Mya Rucutosa. W. 8S. f.7.—Axasmoponta M. Say. 
in J. A. N.S. Phil. 1.—Barnes in Sil. J. 6.— Gould. Mass. p. 
116. f. 77. Transversely ovate, thin, inequilateral, gaping ante- 
riorly, posteriorly narrow, rounded at both extremities above and 
below ; ligamental edge scarcely sloping, ventral subincurved in the 
middle ; umbonal ridge elevated and well defined, anterior slope 
with coarse rounded wrinkles running obliquely dorsally and ante- 
riorly, beaks at the posterior third, rather smal! but elevated : cuti- 
cle olivaceous, shining, obscurely rayed with broken lines : nacre 
bluish white, with a chalky white margin ; tooth small, compressed, 
looking backwards. 1-1, ..2.—Massuchusets, Sc. 
U. Rueosa.—Axasmoponta R. Barnes in Sil. J. 6. t. 13.f. 
21.—Kat. § Hild.—U. Aspucra. Say. Oblong, thick, rounded 
at both ends, posterior side not quite so long nor broad as ante- 
rior, ligamental edge nearly straight, not sloping, ventral edge 
little curved, anterior slope with deep divergent folds, the ridge 
little elevated, the folds indenting the edge; cuticle chesnut with a 
silky lustre; nacre flesh colour, becoming at the margin pearly 
white, with a narrow margin of dark chocolate: teeth large and 
elevated with afold behind. 2..33,.—N. America. 
Section B.—Smooth. 
U. De.roipea.—Mare. D. Leu. on U, 2. p. 43. t. 13. f. 38. 
Ovate, inequilateral, compressed, thin, obliquely rounded posteriorly, 
obtuse anteriorly, the anterior ventral margin incurved ; beaks pro- 
minent, undulated at the tip and devoid of the green rays which 
elsewhere adorn the yellow cuticle: cardinal teeth erect, the lateral 
obsolete: nacre white and irridescent. -9,.. 12.— Ohio. 
U. Unpurata.—Atasmoponta U. Say. Am. C. t. 16.— 
(Young.) A. Scutpritis. Say.—Mya Unpuxata. Wood. S.t. 
1. f. 5.—U. Grasratus. Sow. Transversely ovate, inequilateral, 
strong, much inflated, widely gaping, anteriorly attenuated and 
angulated, posteriorly and at the ventral edge rounded; beaks 
tumid elevated and undulated: cuticle shining dark green, with 
obscure linear rays alternately yellow and dark, nacre white; one 
cardinal tooth in each valve supported by a strong internal rib. 
12..2.—Massachusets, §c. 
U. Swananoensis.—MarcG. Raveneviana. Lea. Trans. Am. 
Ph. 5, t. 17. f. 50. Transverse, oblong, anteriorly longer and 
Pp 2 
