The nymphs have streamlined bodies with platelike gills on abdominal segments 1 to 7, 2 to 7, or 1 to 5. They lack mandibular tusks, have double front tarsal claws, and the outer pair of tails have hairs only on the inner side.
Adults have 2 tails. The lateral ocelli are 1/10 to 1/4 the size of the compound eye. The hind tarsus has 3 or 4 clearly defined, moveable segments. Abdominal segments 6 and 7 are not wider and higher than the adjacent segments. The forewings of the adult have 1 or 2 long, basally detached cubital intercalary veins accompanied by free marginal veinlets, and lack long intercalary veins between MP2 and CuA. Vein MP2 is not bent near its base. The hindwings are small or absent.
This genus is of little importance to the fly fisher.
