The status of Asthenopus Curtus (Hagen) (Ephemeroptera: Polymitarcyidae) (Study of a series of reared adult male and female mayflies in the genus Asthenopus from the Amazon demonstrated that males had been described by Hagen as A. curtus and females as A. amazonicus. As only a single species is represented by the strongly sexually dimorphic males and females, all should be designated as A. curtus (Hagen) and A. amazonicus (Hagen) is, therefore, a synonym.