196 Ittinois NATuRAL History SuRvEY BULLETIN 
extend beneath the venter at all. The me- 
dian caudal filament is slightly longer than 
the lateral ones. 
Vol. 26, Art. 1 
with the frontal margin of the head entire. 
The tarsal claws are relatively short and 
stout at the bases; each claw has only two 
Fig. 387.—Epeorus namatus, male genitalia. 
Fig. 388.—Cinygmula atlantica, male genitalia. 
Fig. 389.—Cinygma integrum, male genitalia. 
The species of Cinygmula are principally 
western and northern in distribution. C. 
altantica (McDunnough) (19246:131) oc- 
curs in New York and Nova Scotia. 
45. CINYGMA Eaton 
Cinygma Eaton (1885:247). 
In the adult males of this genus, the com- 
pound eyes are large, but do not quite meet 
on the meson; each fore leg is as long as 
the body, the femur and tibia almost or 
quite equal in length, the tarsus twice as 
long as the tibia, and the first tarsal segment 
from three-fifths to three-fourths as long as 
the second tarsal segment. In both sexes, 
the wing venation is typical for the family, 
with the stigmatic crossveins, fig. 322, nu- 
merous and anastomosed in such a way that 
a fine, slightly irregular line, parallel with 
vein C, divides the costal interspace into 
two parts; the costal crossveins of the fore 
wing in the basal area are quite weak. Vein 
M, in the hind wing diverges from M, in 
the center of the wing. The male genital 
forceps have four segments, the second of 
which is longer than the other three com- 
bined; the penis lobes, fig. 389, are broad 
and fused on the meson almost to the tips, 
and there is a small, median spine on each 
penis lobe at a point midway from the base 
to the apex. In the females, the posterior 
margin of the apical abdominal sternite is 
broadly rounded, and has a median notch. 
The nymphs are typical for the family, 
or three ventral denticles near the tip. A 
pair of gills is borne by each of abdominal 
segments 1-7; each gill, fig. 329, is composed 
of a broad and platelike, dorsal element and 
a small ventral tuft of filaments; the gills do 
not extend over the abdominal sternites; the 
three caudal filaments are all of practically 
the same length. 
The species of Cinygma known at present 
occur only in the western states. C. integ- 
rum Eaton (1885:248) is known from 
British Columbia, Oregon, and Washington. 
45. RHITHROGENA Eaton 
Rhithrogena Eaton (1881:23). 
In the adult males of this genus, the com- 
pound eyes are contiguous on the meson; 
each fore leg is slightly longer than the body, 
with the tibia one and one-third times as 
long as the femur, and the tarsus one and 
one-fourth to one and one-half times as long — 
as the tibia; the first segment of the fore 
tarsus is only one-fifth to one-third as long 
as the second segment. In both sexes, the 
wing venation is typical for the family, fig. = 
320, but the costal crossveins in the basal 
area of the fore wing are very weak, and, 
in Nearctic species, the costal, stigmatic — 
crossveins are anastomosed, fig. 323. In the 
hind wing, vein M, diverges from vein M, 
slightly basad of the middle of the wing. 
In the male genitalia, the four-segmented 
forceps arise from a base which has a shal-_ 
low, median indentation with a_ broadly 
ee 
