Status of some historically unfamiliar American mayflies (Ephemeroptera)

The status of each of 10 American species of Ephemeroptera that have not be en reported for at least the past half century is evaluated. Isonychia dive rsa Traver and Siphlonurus luridipennis (Burmeister) are declared recently extinct, and Ephemera compar Hagen and Pentagenia robusta McDunnough are co nfirmed as such. The documented extirpation of the closely related European Palingenia longicauda (Olivier) may be indicative of the disappearance of P. robusta in North America. Ephemera triplex Traver, Ephemerella ora Burks , Isonychia notata Traver, Leptophlebia grandis (Traver), Nixe otiosa (McDu nnough), and N. rodocki (Traver) are shown to be new junior synonyms of cer tain other, better known congeneric American species.