Mayfly Species Penelomax septentrionalis

A species of the Ephemerella needhami group; femora and tibiae of imago very long as compared with tarsi.

Head brownish; eyes light orange-red. Thorax yellowish to olive brown dorsally; ventrally pale yellowish with reddish tinges; pleura yellow, tinged with ruddy. Legs very long; femur and tarsus of hind leg subequal in length, each being more than twice as long as the tarsus. Pale yellowish, the femora brownish at the apex. Wings hyaline, venation entirely colorless. Abdominal tergites 1-7 dull olive to smoky brown; traces of black lateral dashes often present; posterior margins narrowly darker. Tergites 8-10 bright brown with a reddish tinge. Sternites pale yellowish, hyaline except the apical segments, which are opaque and somewhat darker. An interrupted median brownish stripe may be present, sometimes extending forward on to the thoracic sternum; four dark dots on each sternite, arranged in a curving line. A small dark spot may be present at the middle of the posterior margin.

Tails yellowish white, joinings rather faintly reddish brown. Second joint of forceps somewhat swollen on the inner apical margin. Penes separated apically by a deep rounded notch; several short spines on the margin of this notch, and on each side a larger toothlike process which projects into the notch (see fig. 155).

The yellowish brown nymph is remarkable for the extreme length and slenderness of the legs, which are fringed with rather long hairs. Body yellowish, thickly sprinkled with very small brown dots. Head smooth; a tuft of hairs on each side of the occiput. Thorax smooth. Head shaded with brown along the median line; prothorax pale on median line, which is bounded on each side by a dark brown stripe. Legs yellowish; femora with three bands of dark brown; tibiae and tarsi banded near the middle, this band often lacking on the hind tibia. 11 to 12 denticles on the inner margin of each claw. Lateral extensions present on the abdominal segments; each bears a posterolateral spine. Gills present on segments 3-7. No dorsal spines, but the posterior margin is produced backward at the median line. A narrow brown median stripe the length of the dorsum, and traces of pale lateral stripes. Ventral markings consist of two dark oblique dashes on the anterior margin, and two small dark dots nearer the center of each sternite. Tails light brown at base, yellow apically; in the middle area, alternately banded with black and yellow. A whorl of spines at each joining, in the basal portion; apically without these spines, and margined with longer hairs.