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^%. . 4-J^.—Missisip]n. 



U. Parallelopipedon. Lea. Trans. Am. Ph. 5. t. 8./. 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 and irridescent ; cardinal teeth oblique, crested, 

 the lateral long and straight. 1^..2-J^. — R- Parana, South 

 America. 



U. Platyrrhinchus. Kossm. 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. — Qej^many.^ 



U. TuMiDus. Z?e^^.*— RossM./. 70, 202, 3, 4.— Mya Ovata. 

 Don. t. 122.— D. p. 50.— TF. t. 2. f. 27.— Mysca Solida. Turt. 

 B. t. 16. /. 2. §• 3Ian.f. 13.— (U. Nodulosa. 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 

 round the umbones. Germany, Sj'c. 



U. PiCTORUM.* Lam.Z2.—Drap.t.\\.f. A.—lsi\K V. Lin. 

 1112. D.p. 49.— Tr. t. 2./. 26.— Mysca P. Turt. Man. f. 11.— 

 U. Rostrata. Lam.Z\. — U. Manca. Lam. 43. — U. Turtoni. 

 Payraud. — Capigliolo. Payr. — Elongatula. 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. — LJnrope. 

 /cc/ U. Elongatus. Pfeif." 



'\ U. Productus. Conr. Mon. U. t. 14. fi. 1. p. 31. Narrow- 

 elliptical, rather compressed, posteriorly very short and rounded (the 

 hinge subterminal,) anteriorly produced and obtusely acuminated 



^ Add likewise the U. Caillaudi of Ferussac. 

 - I find no species of this name in PfeifFer. His Elongatulus 

 (fide Gray,) is but a variety of Pictorum. 



