Moved from Ephemera.
How wonderful, to get a firm species ID after all these years! Thanks.

This is a male Ephemera simulans imago. E. guttulata typically lacks dorsal markings in the imago stage, their black-and-white coloration leading to the nickname "coffin flies."

A male imago. The wing spotting and frons (face) not extending below the eyes is typical of the group. Most likely this is Ephemera simulans (Ephemeridae: Ephemerinae). E.guttata has dark terminal filaments (tails). E. varia lacks spotting on the hind wing and has a lighter abdomen. Another species of the northeast is E. triplex, and is described as having three forewing spots, none on the hind wing and a whitish dorsal abdomen. As always, this is just a best guess.