A strong likelihood that this pronggilled is Paraleptophlebia debilis

I've been looking through photos I've taken of mayflies, looking for Pronggilled mayflies, and yesterday I came across this one, a picture I took in May of 2012.  If you look closely at the terga you'll note that this appears to be the same species of one of the nymphs my friend found in Sugar Hollow.

The same crescent shaped marks on the anterior edges of terga 4-6, and the markings on terga 7-10 match up as well.  Also of note, 1) the gills lack lateral branching, and 2) there are posterolateral projections on terga 8 and 9.

Those features alone -- the lack of tracheal branching and the posterolateral projections on 8 and 9 -- would lead to a Paraleptophlebia debilis ID in Mayflies by Knopp and Cormier (p. 269).   But I'd prefer to have additional confirmation.

Let's look at Donald Chandler's Key to Species of Leptophlebiidae.  Now, I no longer have a specimen that I can examine, which means I can't look at the maxillary palps, and that's a problem.  To be certain of our ID, we'd have to see palps on which -- in contrast to those we see on P. strigula and P. guttata (see the entries of 6/23 and 6/25) -- the "Segments of [the[ maxillary palpus [are] comparatively short."  But I think that that's a pretty good bet.  Why?  Because there are three species with "elongate" segments -- P. strigula, P. guttata, and P. ontario -- and we know from our previous entries that this is not strigula or guttata, and ontario has "Abdominal tergites [that] are largely yellowish with irregular brown markings."  No match there.

That takes us to dichotomy 9.

9. Abdominal tergites mottled; legs pale, barred with darker brown........paraleptophlebia debilis.
Legs uniformly brown or nearly so......10 

I'm fine with calling those terga "mottled," and the legs do look "pale [but] barred with darker brown," at least on the nymph that was found by my friend.
___________________

Not a certain ID.  But if my reasoning is solid, I think there's a pretty good chance that we've found a third Pronggilled species that inhabits our small cold-water streams.