There has been some discussion here before about Epeorus
identification, especially the distance between the eyes of the adult males, which is one identifying characteristic. The keys say that the distance should be "less than the width of the median ocellus," but I have collected a few male duns that didn't quite fit that requirement.
We figured they were Epeorus
anyway, so it's not a big deal, but a new specimen I collected sheds a bit of light on the question.
I collected a dun whose eyes were also a bit far apart, which you can see here:
Then it molted into a spinner:
The spinner's eyes were really almost touching, well within the description of the genus. So that answers our question: the duns may have a little wider spread and the gap will close up in the spinners.