May, 1953 
abdominal tergum, this band often inter- 
rupted at each suture, a large, dark brown 
spot present near either anterolateral angle 
of each tergite; abdominal sternum lighter 
yellow-brown than dorsum, each sternite with 
a pair of submedian, parenthesis-shaped, 
brown marks; genitalia, fig. 260, yellow to 
white; caudal filaments white. 
FEMALE.—Length of body 9-10 mm., of 
fore wing 10-11 mm. Head and body gen- 
erally lighter in color than those of male. 
Head yellow to almost white, with tan 
shading, face below antennal sockets always 
white. Thorax yellow to tan, dorsal, longi- 
tudinal, median stripe light brown, legs 
white; all femora usually vaguely washed 
with tan, brown shading at apexes of all 
tarsal segments; wings hyaline, longitu- 
dinal veins of each fore wing anterior to M 
tan, first three interspaces of fore wing 
shaded with chestnut brown, this shading 
interrupted at crossveins, brown shading 
also extending over small part of basal area 
of posterior radial, median, and cubital 
interspaces; hind wing not shaded. Dorsum 
of abdomen light brown, thickly sprinkled 
with dark brown, punctate dots; venter tan 
to almost white; caudal filaments white. 
NympH.—Length of body 12-13 mm. 
Head light yellow to white, with brown 
shading on frons, between eyes, and ventral 
to ocelli between antennal sockets. Thorax 
light yellow, with brown shading on mesono- 
tum and on wingpads; legs white, tarsi 
tinged with brown. Abdomen mostly light 
yellow on dorsum, a median, interrupted, 
longitudinal, brown stripe usually present, 
this brown area spreading on tergites 2 and 
3 to cover most of exposed dorsal area; 
gills hyaline, tracheae brown; gills on seg- 
ments | and 2 triple, those on 3—7 double, 
ventral lobe on seventh gill greatly reduced; 
caudal filaments darkened near apexes. 
Callibaetis skokianus is known from Illi- 
nois, Minnesota, Missouri, New York, 
North Dakota, and Ontario. It was orig- 
inally described from a very long series of 
specimens collected over a 4-year period at 
the turn of the century from a pond on the 
campus of Lake Forest College located on 
the shore of Lake Michigan north of Chi- 
cago. This pond has now disappeared, and 
intensive, recent collecting and rearing in 
that area has failed to yield additional speci- 
mens, but a few scattered ones have been 
taken elsewhere in the state. 
Burks: THE Mayr ties or ILLINOIS 119 
Illinois Records.—Avurora: July 17, 
1927, Frison & Glasgow, 19. East Du- 
BUQUE: at light, July 21, 1927, Frison & 
Glasgow, 12. Freeport: at light, June 10- 
11, 1948, Burks, Stannard, & Smith, 19 ; 
Aug. 4, 1948, Burks & Stannard, 19. Ha- 
vVANA: April 14, 1894, Hart & Hempel, 1 ¢ ; 
April 17, 1894, Hart & Hempel, 1 2 ; April 
18-19, 1894, C. A. Hart, 2¢. Lake Forest: 
in pond on college campus, April-May, 1899, 
J. G. Needham, 29%; May, 1902, J. G. 
Needham, 64, 292, nymphs. PmINcREE 
Grove: May 9, 1939, Ross & Burks, 4¢. 
30. CENTROPTILUM Eaton 
Centroptilum Eaton (1869:132). 
In this genus, the stalk of each turbinate 
eye in the males is quite low, so that the 
lower portion of the eye is almost in con- 
tact with the faceted upper portion. ‘The 
width of the vertex separating the compound 
eyes in the females is only slightly greater 
than the length of one eye. Typically, the 
head and thorax in the males are dark 
brown, with the abdomen light, but often 
strikingly marked on the dorsum with red 
or red-brown; the females are generally 
light in color, the abdominal tergites heavily 
marked with black tracheal lines. Each 
fore wing has relatively few crossveins and 
the marginal intercalary veins are single. 
The hind wing is long and slender, with a 
hooked, costal, subbasal projection; with 
two longitudinal veins and sometimes with 
vestigial third vein; the crossveins are want- 
ing or vestigial. The male genital forceps 
are four segmented, the first segment being 
short and broad, the second also short and 
broad with, typically, a prominent tubercle 
on the mesal margin, the third segment is 
slender and usually not strongly bowed, and 
the fourth segment is often three or four 
times as long as broad; occasionally, the 
fourth segment is only as long as broad. 
There is a large, variously shaped penis 
cover between the bases of the forceps arms. 
The nymphs are streamlined, vigorously 
swimming forms, typically developing in the 
shallow, rapidly flowing water of brooks 
and creeks. The nymphal labial and maxil- 
lary palps have each three segments. The 
claws are long and slender, and lack ventral 
denticles. The abdominal gills are platelike 
and usually single on all segments; in some 
species each gill borne by the basal segments 
