I was shown a location where these mayflies were swarming in abundance. There were so many I was able to catch this one in my hand, right out of the air
Hind wing with forked second longitudinal vein, weird costal process (not shown well here). In one species the marginal intercalaries of the forewing are single in the basal half and double in the distal half (at least in the males - females that might be the same species have single the whole length of the wing). The other species appear all to have single intercalaries. Mesonotal suture is concave, unlike Centroptilum
strange maxillae. Long crest of setae, highly reduced canines, some modified setae too. Third palp segment subequal to second, unlike Pseudocentroptiloides.
you can't see it, but there is a row of fine setae on the outer margins of the tibiae and tarsi. No arc of fine setae on the femur, and I don't think there is one on the tibia (although I find that character very difficult to see sometimes).