Moved from Choroterpes basalis.

See comments here.

Another new species for the guide. I try to get the wings in focus on these mayflies, and this time it payed off. Even if there aren't any official records for Massachusetts, we know they're here:-)

This specimen caused me to take another look at the one that I had previously suggested was something in Leptophlebiidae (here)--they are nearly identical. (One is missing two tails, the other only one.) What threw me about the first one was that I seemed to be seeing a costal "bump" on the hindwing. That bump is even clearer on this specimen (on both hindwings). Leptophlebia and Paraleptophlebia lack that trait.

From the position of the costal bump (near the midpoint), the banding of the femurs, and what can be seen of the venation of the wings, I believe that both specimens are probably female Choroterpes basalis imagoes (Leptophlebiidae). I couldn't find that species in the collection record for MA (which seems sketchy), but it is listed for CT.