This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominalterga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
Cubitus: The cubitus (denoted Cu) is the fifth major longitudinal wing vein in insects, located behind the media. In stoneflies, it usually branches near the base into an anterior for Cu1 and posterior fork Cu2.
These other words reference the same concept: vein Cu, Cu vein, Cu, vein Cu1, vein Cu2, Cu2 vein, Cu2, vein Cu1, Cu2 vein, Cu2.
