172 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 



Trygon hrachyurus and T. reticulatus, recently described by Dr. Giinther, 

 belong to the genus Potamotrygon. The species redescribed and figured by 

 Dr. Steindachner in 1878 as Tceniura magdalence also belongs to that genus. 

 It needs but a slight knowledge of the anatomical differences existing between 

 the Potamotrygones and the Tceniurce proper to convince any one that both 

 cannot be retained in the genus Tceniura. 



Cambridge, October, 1880. 



M 



