: 
May, 1953 
femur with broad, brown band at base and 
near apex, dark brown mark at apex of 
tibia and each tarsal segment; middle and 
hind legs yellow, with brown markings as 
in fore leg. Abdominal tergum white, with 
faint, brown shading on tergites 2-6, ter- 
gites 1 and 7-9 almost completely dark 
brown; venter white, ganglia and two small, 
lateral spots on each sternite may be brown 
stained; sternites 1 and 9 completely dark 
brown; male genitalia, fig. 309; the two 
well-developed caudal filaments white, the 
articulations brown. 
FEMALE.—Length of body 12-14 mm., 
of fore wing 14-15 mm. Color almost iden- 
tical with that of male, except that wings 
completely lack brown staining at bases, and 
brown shading of abdominal tergites is usu- 
ally more intense; abdominal sternum al- 
most completely white, with sternite | largely 
brown and sternites 7-9 heavily shaded with 
brown; caudal filaments similar to those of 
the male. 
NympH.—Length of body 15-16 mm., of 
caudal filaments 5-6 mm. Thorax yellow 
and brown on dorsum, yellow on venter. 
Abdominal tergum yellow, with varying 
brown markings and with tergites 1, 6, and 
9 almost completely brown; venter yellow, 
with three longitudinal, brown stripes; gills 
single on segments 4-7, those on segments 
1-3 each with a minute, recurved ventral 
flap; caudal filaments each with a brown 
crossband near tip. 
Known from Illinois, Indiana, Manitoba, 
and Minnesota. Develops in fairly rapid, 
moderate-sized rivers. 
Illinois Records.—ILirnois: 1¢. Ha- 
VANA: Chautauqua Park, April 29, 1914, 
1g. Momence, Kankakee River: May 5, 
1938, Ross & Burks, 32; May 8, 1940, 
Mohr & Burks, 22, 1 N. Rock ISLAND: 
536, 22 (Walsh 1862:369). 
HEPTAGENIIDAE 
This family, as limited here, corresponds 
to the family Heptageniidae in Traver’s 
classification (1935a:293) and is similar to, 
but not identical with, Ulmer’s family Ecdy- 
onuridae (1933:212). 
In the family Heptageniidae, the male 
adults have large compound eyes, but these 
eyes show no obvious division into upper 
and lower portions. The upper portion of 
each eye is, however, composed of facets 
Burks: THE Mayer ies oF ILLINors 
Pd 
which are slightly smaller and usually less 
heavily pigmented than are those in the 
lower. The line that divides these two 
portions is quite obscure. The fore tarsus 
in the males is longer than the fore tibia 
in all genera except the rare Anepeorus. 
In all genera, the hind tarsus has five clearly 
defined segments, figs. 17, 19. Each fore 
wing invariably has four cubital intercalary 
veins, all of which are free at the bases, figs. 
317-321. The hind wing has veins R, and 
R, diverging at or near the center of the 
wing, figs. 317-320, except in Arthroplea, in 
which R, and R. are fused for their entire 
length, fig. 321. The male genitalia consist 
of a pair of four- or five-segmented forceps 
and a pair of variously modified penis lobes, 
figs. 331-356, 363-380, 387-389, 391-393. 
The median caudal filament is invariably 
vestigial in the adults. 
In the nymphs, figs. 360, 383-386, 390, 
394, 395, the body is flattened, the head is 
broad, almost or quite flat, with the eyes 
located dorsally and the mouth-parts ven- 
trally. The labrum is always much wider 
than long, each mandible has two canines, 
and each maxillary and labial palp has two 
segments. The mouth-parts in all but one 
genus are fitted for a diet of vegetable mat- 
ter, such as diatoms, and animal and vege- 
table detritus. The exception is a nymph, 
tentatively placed as that of Anepeorus, fig. 
394, which has mouth-parts clearly fitted for 
predacity. Almost all heptagenine nymphs 
have seven pairs of dorsal abdominal gills, 
each of which is composed of a dorsal, plate- 
like member and a ventral, filamentous tuft. 
In Rhithrogena, however, the filamentous 
tuft is dorsal and the platelike element ven- 
tral, in Arthroplea the filamentous portion 
of each gill is wanting entirely, and in the 
supposed nymph of Anepeorus the gills are 
ventral and each gill consists of a narrow, 
elongate, anterior member and a posterior, 
fimbriate member. All heptagenine nymphs 
have three well-developed caudal filaments. 
The differentiation and separation of the 
genera in this group can hardly be said to 
be on a firm and rational basis. The nymphs 
and the male adults can be segregated gen- 
erically, but the females usually cannot. 
Pending the discovery of generic characters 
which will serve for the segregation of the 
females, also, I am using the generic char- 
acters employed by Traver (1935) and UI- 
mer (1933). 
