The nymphs are sprawling forms with bodies, legs and head that are strongly flattened. The head is large in relation to the body. Eyes are also large and are located on the dorsal surface of the head. Gills are present on abdominal segments 1 to 7. Adults have two tails and five freely moveable joints in the hind tarsus. Two pairs of cubital intercalary veins are present in the fore wings, while both fore and hind wings display heavy veination. The males have large spherical eyes that are normally light in coloration during the day and black at night.
Various species of this genus create some of the better hatches of the season in the East and West. These mayflies are in the 7-11 mm size range. Nymphs can easily be differentiated from those of other family members by their possession of only two tails. In the adult stage, the first segment of the fore tarsus is as long as or longer than the second.