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This is the largest of Alberta stoneflies. The species is distinguished by its large size (male length = 40 mm; females = 60 mm), and the presence of gills (nymphs) or gill remnants (adults) on all thoracic segments and the first two abdominal segments. Male genitalia have the ninth sternum straight near the tip; the epiproct is large and flattened with its tip expanded. Female subgenital plate is straight, or with two small projections extending just to the edge of the ninth sternite. Nymphal females have the projection on the tenth tergum projected postero-dorsad to a point; nymphal males have the projection extended postero-ventrad with a peg on the caudal surface. Mature male nymphs have a nearly rectangular projection posterad on the ninth abdominal sternum.

The life cycle is at least two years in Wisconsin, and three years in Saskatchewan. Adult longevity is inversely related to the temperature at which nymphs are maintained. Emergence is greatest at water temperatures of 15°C. Females reared at 15°C produced, on average, 475 eggs, but at 20°C fecundity declined by approximately 60% (Nebeker, 1971a; Nebeker, 1971b).