May, 1953 
sternites white; middle and hind legs en- 
tirely white. Abdomen white, without spi- 
racular spots or streaks; genital forceps, fig. 
111, stout and moderately long. 
FEeMALE.—Length of body and of fore 
wing 2.5-3.0 mm. Head almost entirely 
white, with faint gray shading extending 
across middle of vertex only; fore femur 
with gray shading at apicodorsal angle; ab- 
dominal tergites 1 and 2 each with a pair 
of sublateral, transverse dark spots. 
Known from Illinois, Kansas, Michigan, 
Ontario, and Wisconsin. Develops appar- 
ently in eddies in small rivers. 
Illinois Records.—Avrora: at light, 
July 17, 1927, Frison & Glasgow, 222,42. 
LAKE Forest: J. G. Needham, 19 (Traver 
1935a: 653). Oakwoop: at light, July 10, 
1927, Frison & Glasgow, 53 ¢, 219. 
7. Caenis hilaris (Say) 
Ephemera hilaris Say (1839:43). 
Mave.—Length of body and of fore wing 
2.0-2.5 mm. Head white, faint lavender 
shading present on vertex near lateral 
ocelli; antennae white. Pronotum white, 
with faint gray-brown shading at each an- 
terolateral angle; a fairly large, gray-brown 
spot present on outer side of each fore coxa; 
fore leg white, with gray shading at apex of 
femur; meso- and metanotum light yellow, 
with a prominent, gray-brown spot near 
apex of mesoscutellum, this spot often ex- 
tending forward onto mesoscutum; meso- 
and metapleura white, with vague gray- 
brown shading around coxal cavities; all 
thoracic sternites white; middle and hind 
legs white, with a black spot on dorsal side 
near apex of each femur. Abdomen white, 
with gray shading on first tergite and prom- 
inent, gray-brown spiracular lines on tergites 
7-9; genital forceps, fig. 109, short and stout. 
FEMALE.—Length of body and of fore 
wing each 2.5-3.0 mm. Coloration identical 
with that of male except that vertex of head 
is slightly darker, each fore femur has a 
dorsoapical, black spot, and spiracular lines 
may be present on tergites 5 and 6 as well 
as on apical tergites. 
Known from the eastern and central 
states. Develops in eddies of moderate-sized 
and large rivers. 
Illinois Records.—Dixon: June 27, 
1935, DeLong & Ross, 17¢. ELIZABETH- 
TOWN: June 22, 1932, Dozier & Park, 9°. 
Burks: THE MAyrtigs oF ILLINOIS 53 
Foster: Mississippi River, July 22, 1939, 
B. G. Berger, 82. Futon: July 20, 1927, 
Frison & Glasgow, 2¢. Homer: Aug. 10, 
1925, T. H. Frison, 22. Jackson ISLAND, 
in Mississippi River opposite Hannibal, Mo.: 
Sept. 6, 1940, G.-T. Riegel, 14,129. 
KANKAKEE: Aug. 16, 1938, Ross & Burks, 
34,52. Mackinaw: July 4, 1939, Ivabel 
Johnson, 32. Momence: Aug. 16, 1938, 
Ross & Burks, 3¢. Montezuma: at light, 
Oct. 9, 1931, C. O. Mohr, 362. OQuawKa: 
Sept. 26, 1947, H..H. Ross, 18:4; 3@¢ : 
Orecon: at light, July 18, 1927, Frison & 
Glasgow, 2904, 212; July 2, 1946, Burks 
& Sanderson, 5446, 7092. Rock Is_Lanp: 1 4 
(Walsh 1862: 381). SAVANNA: Mississippi 
River, July 23, 1892, S. A. Forbes e¢ al., 12. 
8. Caenis gigas new species 
This species resembles hilaris in being very 
small and having the vertex of the head 
almost entirely white. The two differ in 
that gigas has spiracular dots or streaks on 
abdominal segments 2-9 rather than on 
segments 7-9 only, as in hilaris; gigas also 
has longer and more slender genital forceps 
than does hilaris. 
Matce.—Length of body and of fore wing 
each 2 mm. Head white, vertex white, with 
a narrow, gray-purple line at anterior and 
posterior margins, occasionally faint, gray- 
purple shading present on vertex near lateral 
ocelli; antennae white, each pedicel twice 
as long as scape, flagellum five times as long 
as pedicel. Pronotum white, with purplish 
shading at margins; propleura and sternum 
white; each fore coxa shaded with purplish 
gray at base, fore femur almost completely 
shaded with gray, fore tibia gray, tarsus 
white, with purplish gray shading at articu- 
lations; mesonotum light yellow-brown and 
with a narrow line of gray shading at princi- 
al sutures; mesopleura yellow-brown, with 
fairly extensive, gray-purple shading, meso- 
sternum white; wings hyaline, costal shading 
typical for genus; metathorax white, with 
gray shading around coxal cavities; middle 
and hind legs white, shaded on coxae and on 
dorsal sides, near apexes, of femora. Ab- 
domen white, tergites with extensive, dark 
gray shading on median area and at pos- 
terior margins of tergites 1-6; tergite 7 
with gray shading covering median and 
anterolateral areas; tergite 8 with gray 
shading in anterolateral areas; tergite 9 with 
