Mayfly Species Heterocloeon amplum

Abdominal tergites 2-6 of male imago yellowish brown, the posterior margins hyaline whitish; hind wing two-veined, costal projection wanting.

Turbinate eyes large, almost circular; orange in color. A black mark across the face. Antennae light brown. Thorax reddish brown. Longitudinal dark brown streaks on the mesonotum, median and submedian in position. Metanotum distinctly reddish. Sternites light reddish brown. A red spot on the coxa of the fore leg; fore femur distinctly tinged with red, a band of this color near its apex. Fore tibia yellowish, tarsus yellowish white. Middle and hind legs yellowish, the femora light yellowish brown ; tarsal joinings may be very narrowly reddish. Wings hyaline, venation yellowish brown. Cross veins of the stigmatic area of the fore wing 7-8 in number; only a slight tendency toward anastomosis; almost no granulations between them. Intercalaries absent from the first interspace, well developed in other spaces. Hind wing very small (1 mm. in length), long and narrow; two veins only, the third entirely absent. Costal projection entirely wanting.

Abdominal segments 2-6 yellowish brown, tinged with grey. The posterior margins rather widely opaque, giving this part of the abdomen an annulate appearance. Segments 7-10 light reddish brown, rather darker dorsally. Basal sternites slightly paler than their tergites. Genitalia of the modified moffati type (now a synonym of Baetis tricaudatus), the second joint of the forceps being cylindrical. The distal forceps joint is relatively very long, fully three times as long as wide; it is almost one-half the length of the preceding joint.

This species is very close to B. frivolus (now a synonym ofHeterocloeon frivolum), but may be distinguished from it by the larger size, the color of the eyes and thorax, the paler abdomen and the distinctly brownish venation.