48 I-ttinois NATURAL History SuRVEY BULLETIN 
1¢. Rocxron: Rock River, June 11, 1948, 
Burks, Stannard, & Smith, 1 é. WuILMING- 
TON: at light, Aug. 3-4, 1937, Ross & Burks, 
70 & ; Aug. 6, 1947, Burks & Sanderson, 3 6. 
3. Tricorythodes peridius new species 
This species agrees with atratus in having 
the antennae almost completely white, in 
having a subapical, red-brown band on each 
of the femora, which are extensively shaded 
with black, and in having abdominal seg- 
ments 3-7 shaded with black only on the 
dorsal meson and at the _ posterolateral 
angles of the tergites. The two differ in 
that peridius is larger and generally much 
lighter in color, with the vertex of the head 
mostly yellow instead of entirely black, as in 
atratus; in peridius, also, the apical margin 
of the genital forceps base has a relatively 
broad, shallow median excavation. 
Mare.—Length of body 4.0-4.5 mm., of 
fore wing 4.5-5.5 mm. Head yellow-brown, 
shaded with black near posterior margin of 
vertex; eyes and ocelli black; antennae 
white, each usually shaded with tan and 
black on pedicel. Pronotum completely 
shaded with dark gray, mesonotum and 
metanotum brown, pleura slightly lighter 
brown, venter same color as mesonotum at 
lateral margins, color paling to white on 
meson; all coxae and trochanters dark 
brown; femora light brown, shaded with 
black, and with a subapical, red-brown 
band on each; fore tibia gray, middle and 
hind tibiae light yellow or white, with black 
shading in middle; fore tarsus light gray, 
middle and hind tarsi white; wings hyaline, 
veins Sc and R, shaded with gray, veins 
and crossveins in anterior half of each wing 
brown. Abdomen mostly light yellow or 
white, tergites 1 and 2 washed with gray. 
Tergites 3-7 shaded with gray on meson 
and at lateral margins, apical tergites uni- 
formly washed with gray; sternites faint 
gray-tan, often almost white; caudal fila- 
ments white, basal four to six segments of 
each filament shaded with gray. Genitalia, 
fig. 99, white, with vague, gray shading along 
lateral margins of structures, apical margin 
of forceps base with a broad, shallow median 
indentation. 
Holotype, male.—Wilmington, Illinois, 
at light, Aug. 6, 1947, Burks & Sanderson. 
Specimen in alcohol. 
Paratypes.—ILLiINois: Same data as for 
Vol. 26, Art. 1 
holotype, 11¢. Sr. CHarves: at light, 
July 8, 1948, Ross & Burks, 1¢. All 
specimens in alcohol. 
10. BRACHYCERCUS Curtis 
Brachycercus Curtis (1834: 122). 
Oxycypha Burmeister (1839:796). In part. 
Eurycaenis Bengtsson (1917:186). 
The species of Brachycercus consist of 
small mayflies with broad thoraxes. All 
species have the mesonotum and metanotum 
various shades of brown, and the head, 
pronotum, and abdomen white, with black 
or gray markings. Each antennal pedicel 
is markedly long, three times as long as the 
scape. In both sexes, each lateral ocellus is 
two-thirds as large as one of the compound 
eyes. The wing venation, fig. 97, does not 
Fig. 
nymph, dorsal aspect. 
113.—Brachycercus lacustris, mature 
