When in doubt, go with a rusty spinner. As far as the dun pattern, if we new what kind of nymph it was, you may get more dun patterns than you would know what to do with. There are a few on the board who may be able to figure what nymph that is, I certainly can not.
In their winged stages, they are a very stout little mayfly with big wings. There is only one N. American genus (Baetisca), and three species in NY, Baetisca lacustris, B. laurentina and B. obesa.
