The two new mayflies I found were both flatheaded mayflies. Both were in the lower Clark Fork River at Petty Creek. This one, genus Epeorus, species longimanus.
The genus ID was easy -- note the two tails -- and it looks just like the Epeorus nymphs we find in our own streams: pleuralis and vitreus. But what species? According to the Montana Field Guide (http://fieldguide.mt.gov/displaySpecies.aspx?family=Heptageniidae), there are four species of Epeorus that occur in Montana: albertae, deceptivus, grandis, and longimanus. As it turns out, longimanus has one very distinctive mark of identification: there are dark dots in the middle of the femora. (http://www.flyfishingentomology.com/PNW%20Mayflies.htm)
In addition, "the first and last gills meet under [the] body to form suction discs." Yes -- though one of the last gills is missing on our specimen.
You may recall that I had previously found another Epeorus -- 9/3/12 -- in a much smaller stream, Grant Creek.
At the time, I identified this one as Epeorus deceptivus. Just to be sure, I once again consulted Rohrbeck's species descriptions, and I'm pretty sure that I identified that one correctly. In any event, our ID this time was pretty easy to make: Epeorus longimanus.
The other flatheaded mayfly I found that I've not seen before was very small -- 4-5 mm -- and it was also in the Clark Fork.
Looking at the size and the shape, my guess was Leucrocuta for the genus, and I was right. The key -- no fibrilliform behind the 7th gill.
Species ID? Can't do it. Leucrocuta nymphs are very difficult to identify to the level of species. In the new book on Larvae of the southeastern USA (see the entry of 7/10) the editors key out L. thetis and L. minerva, but leave untouched, the nymphs of aphrodite, hebe, maculipennis, and juno. The Montana Field Guide (same page as noted above) notes two species of Leucrocuta that occur in Montana: maculipennis and petersi. That's as far as we can go.
Found two other nymphs that I've seen previously in my trips out in August: the small minnow mayfly Baetis tricaudatus -- female and male -- and the spiny crawler Drunella coloradensis.
I'm intrigued by D. coloradensis: it seems to come in all sorts of colors. Here are just a few that I've found in previous trips.
Pretty remarkable nymph.