Figures: 27, 97-98, 111, 191, 195, 242
In addition to the Heptageniinae characteristics, the following combination of characteristics will identify the genus:
Larvae of Stenonema are characterized by the combination of having long, narrow lamellae with tracheation but no fibrils on gills 7 (Fig. 98) and a submarginal anal rib on gill lamellae 1-6. Furthermore, the lamellae of gills 1-6 are rounded apically and the costal rib is absent (Fig. 97).
Adults of Stenonema are differentiated from those of other Nearctic Heptageniinae by having abdominal terga 3-8 each with a median black dot and a pair of dark transverse dashes on the posterior margin (Fig. 195).
Nearctic (Fig. 242).