Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
I'm just guessing Neoleptophlebia on this one. It could easily be Paraleptophlebia.
This mayfly was collected from the Neversink River in New York on September 5th, 2006 and added to Troutnut.com by Troutnut on October 3rd, 2006.