TRIBE NAYADES. 20f> 



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 T % . . 4 t l . — Missisippi. 



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

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

 America. 



U. Platyrrhinchus. 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. Tumidus. Retz.*— Rossm. /. 70, 202, 3, 4.— Mya Ovata. 

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

 B. t. 16. f. 2. 8f Man. 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, fyc. 



U. Pictorum.* Lam. 32. — Drap. t. II. f. 4. — Mya P. Lin. 

 1112. L>.p. 49.— W. t.2.f. 26.— MyscaP. Turt. Man. f. 11.— 

 U. Rostrata. Lam.3\. — U. Manca. Lam. 43. — U. Turtoni. 

 Payraud. — Capigliolo. Payr. — Elongatula. Pfiif. 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. — Europe. 



U. Elongatus. Pfeif. 2 



U. Productus. Conr. Mon. U. t. 14. f. \. p.3\. Narrow- 

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

 hinge subterminal,) anteriorly produced and obtusely acuminated 



1 Add likewise the U. Caillaudi of Ferussac. 



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

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



