TRIBE NAYADES. 205 
tenuated ; beaks slightly prominent, ligament long narrow and 
nearly straight : cuticle yellowish, very smooth and shining, anterior 
slope fuscous, nacre pale salmon or white ; cardinal teeth double in 
both valves and very erect; the lateral long, slightly curved and 
separate. 1,9,.. 4445.—Missisippi. 
U. Parattevorreepon. Lea. Trans. Am. Ph. 5. t. 8. f. 20.— 
D Orb. in Mag. de Z. Oblong, transverse, subcylindraceous, 
thickish, dorsal and ventral edges parallel, posteriorly short and 
obtuse, anteriorly inflated and obliquely angulated dorsally ; liga- 
ment long and thin, umbones flattened, umbonal slope carinated ; 
beaks somewhat elevated, retuse ; cuticle wrinkled and almost black, 
nacre pearly white andirridescent ; cardinal teeth oblique, crested, 
the lateral long and straight. 14..27,.—R. Parana, South 
America. 
U. Praryrruincuus. Rossm. f.130. Transverse, elongated, 
wedge-shaped, inequilateral, anteriorly produced in a compressed 
beak which points downwards, ligamental edge very long, very short 
and rounded posteriorly: the umbones tumid; olive with brown 
zones: cardinal teeth very compressed, bladed. 3.—Germany.1 
U. Tumipus. Retz.*—Rossm. f. 70, 202, 3,4.—Mya Ovara. 
Don. t. 122.—-D. p. 50.—W. t. 2. f. 27.—Mysca Souipa. Turt. 
B.t. 16. f. 2.§ Man. f.13.—(U. Noputosa. Lam. fide Lea.) 
Transverse, inequilateral, ovate, elongated, the anterior side wedge- 
shaped tumid produced and attenuated, thick, brown, ventral edge 
arcuated ; umbones prominent and rugose ; posterior teeth thick, 
high, triangular, strong, left anterior strong: nacre white, (rarely 
pale salmon,) the young with irregular concentric nodulose ridges 
roundthe umbones. Germany, ge. 
U. Picrorum.* Lam. 32.—Drap. t.11.f.4.—Mya P. Lin. 
1112. D. p. 49.—W. t. 2. f. 26.—Mysca P. Turt. Man. f. 11.— 
U. Rosrrata. Lam.31.—U. Manca. Lam. 43.—U. Turront. 
Payraud.—CarierioLto. Payr.— Evoneatuta. Pfeif. t. 8. 
f. 5, 6. Oval-oblong, ventricose, anteriorly produced into a bluntly 
truncated beak, yellowish green, brownish zoned, greenish anteriorly, 
dorsal edge nearly straight, ventral rather retuse ; hinge teeth very 
much compressed, arched and crenated, anterior teeth of the left 
valve small or evanescent ; nacre white. 3.—dHurope. 
U. Exvoneatus. Pfeif.? 
U. Propuctvus. Conr. Mon. U.t. 14. f. 1. p. 31. Narrow- 
elliptical, rather compressed, posteriorly very short and rounded (the 
hinge subterminal,) anteriorly produced and obtusely acuminated 


1 Addlikewise the U. Cariiavuni of Ferussac. 
2 I find no species of this name in Pfeiffer. His ELonGaruLus 
(fide Gray, ) is but a variety of Picrorum. 
