DESCRIPTIONS OF TWO NEW NAIADS. 



By Paul Bartsoii, 



Assistant Curator, Dirision of MoUusks. 



Among- the Unionid* received by the United States National Museum 

 in the past two years are two undescribed species, which are here 

 diagnosed. 



NEPHRONAIAS FLUCKI, new species. 

 Plates XXVII-XXIX. 



Description. — Shell elliptical, moderately inflated, attenuated pos- 

 terio-ventrally; sloping gently and evenly dorsally from a line extend- 

 ing from the umbones to the posterior ventral angle. Dorsal line 

 evenly arcuate, curving a little more abruptly anteriorly than at the 

 posterior end; ventral margin almost straight or slightly concave. In 

 some, presumably the females, the shell is somewhat drawn out ven- 

 tralh' at the posterior margin, and in such the ventral outline neces- 

 sarily appears more concave. Surface marked by numerous very 

 strong concentric lines of growth and crinkly radiating rays which are 

 most pronounced on the anterior end and gradually fade out from the 

 middle of the shell posteriorly. Periostracum shining, dark brown 

 at the umbones, fading gradually to greenish yellow at the edge. 

 Umbonal cavity moderately deep. Pseudocardinal of the right valve 

 strong, triangular, deepl}^ notched (almost bifid by the deep vertical 

 A-shaped notch in old specimens), with numerous tine secondary notch- 

 ings. Pseudocardinals of the right valve rather slender, finely notched, 

 inclosing a A-shaped cusp between them, which corresponds to the 

 A-shaped notch in the other valve. Laterals narrow, slightly arcuate 

 and obliquely ridged. Dorsal muscle scars feeble. Nacre bluish white 

 at the margin, shading to livid olive dorsally. 



There are four specimens of this species before me, all with more or 

 less eroded umbones. They measure: 



a Type. 



Proceedings U. S. National Museum, Vol. XXX— No. 1454. 



H9H 



