A new species of Tricorythodes Ulmer (Ephemeroptera: Leptohyphidae) is described based on nymphs from the Northern Region of Brazil. Tricorythodes rondoniensis sp. n. can be distinguished from other species in the genus by the following characters: wide femora, nearly circular, with the margins covered with very long setae; tarsal claws with 5–6 marginal denticles; terga III–VII with an acute median tubercle; operculate gill ovoid and abdominal colour pattern.

Macunahyphes, gen. nov. is proposed to include Tricorythodes australis (Banks). In the present paper, the new taxon is describedan illustrated from imagos and nymphs. The unique characters present in Macunahyphes gen. nov. are: in the male imago,(1) forceps tri-segmented with first segment distomedially projected, (2) penis with very wide base, becoming thinner toward asubapical constriction, and then slightly widening again, penis lobes of each side almost completely fused except apical insicion,(3) penes with a ventral projection covered with spines, and in the nymph, (4) glossae and paraglossae almost completelyfused, with a circular outline, and (5) femora with numerous robust serrate setae.