Mayfly Species Siphlonurus marginatus (Gray Drakes)

Another medium-sized brownish species with a black mid-ventral line.

Head yellowish brown. No dark band across median carina, but a dark spot beneath each antenna. Thorax bright yellowish brown, the scutella darker. Pleural sclerites dark brown. Fore leg pale brown, tip of tarsus greyish white; femur with indistinct band. Middle and hind legs whitish; joinings brown; femora banded. Wings hyaline; longitudinal veins of fore wing brown, other veins pale yellow or whitish. Costal cross veins indistinct, almost invisible before the bulla; in stigmatic area, tend to anastomose. Stigmatic area, in costal and subcostal spaces, opaque white.

Abdomen olive brown dorsally, pale ventrally. Lateral triangles of tergites dark brown, much reduced in size; oval spots brown. Anterior pale triangles extended to occupy a large part of each tergite. Posterior margins dark brown. Pattern less distinct on apical tergites. Ventrally, a black median line extends continuously from sternites 1 to 9, widened near the posterior margin of each sternite. A small black dot on each side of median line, very near it, at the center of each sternite. Another oblique dark mark anterior to the dark dot, and laterad of it.

Forceps and forceps base yellowish brown. Penes as in fig. 123. Tails yellowish white, joinings dark reddish brown.

The nymph has double gills on segments 1 and 2 only. Legs yellowish; middle and hind femora with a brownish band, which is absent from the fore femur. Ventral markings are those of the imago. Usual black band across the tail beyond the middle.