This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
This species is known in older taxonomies under the former name Baetis pygmaeus.
It is a diminutive baetid with distribution across every region. It is reported to have localized hatches of occasional importance.
This is a very rare mayfly in western Montana. The shape of the last gill is a key to its identification. I have collected this species in only one location.