This is my favorite mayfly from 2004, and it appears on my popular Be the Trout: Eat Mayflies products. Check them out!
Its identification is really up in the air. It might be a late-season vitreus dun but it may very well be one of the more obscure species in that genus.
This little gal is of the usual size for Baetid mayflies, around size 20. She came with two tails, but it's kind of hard to transport size 20 mayflies without a little bit of damage.