The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
This one seems to lead to Couplet 35 of the Key to Genera of Perlodidae Nymphs and the genus Isoperla, but I'm skeptical that's correct based on the general look. I need to get it under the microscope to review several choices in the key, and it'll probably end up a different Perlodidae.
Described by Newman, E.A. (1839) On the Synonymy of the Perlites, together with brief charaters of the old and of a few new species. Art. IV. Magazine of Natural History 3, 32–37, 84–90.