116 Intinois NaturAL History SuRVEY BULLETIN 
recurved ventral flap. These ventral gill 
flaps decrease in size from front to rear, 
so that the recurved flap borne by each gill 
of segment 3 is almost as large as the gill 
itself, while the recurved flap of each gill 
of segment 7 is so small as to be easily 
overlooked, fig. 226. There are three equally 
long caudal filaments; the cerci are fringed 
with long setae on the mesal side only. 
Many of the species of this genus are said 
to be ovoviviparous. 
This genus includes about 20 Nearctic 
species, 3 of which occur in Illinois. 
Characteristics for the separation to spe- 
cies of the females of this genus in both 
adult and nymphal stages have not yet been 
found. 
KEY TO SPECIES 
Apvutt MALeEs 
1. Crossveins in fore wing in area posterior 
to vein R, relatively few in number, 
forming a single row across disc of wing, 
and with none located very near outer 
wing margin, fig. 221....1. fluctuans 
Crossveins in fore wing in area posterior 
to vein R; relatively abundant, forming 
two irregular rows across disc of wing, 
and with many located close to outer 
WINE MARIN, NO ee: ev oeie, ecth rca 2 
Costal margin of fore wing hyaline...... 
LANES ERAY 45> aha -aper ny Sa 2. ferrugineus 
Costal margin of fore wing partly or com- 
pletely shaded with brown or tan... .3 
3. Fore wing shaded with brown at base 
a ih pane ise are eae Ans 3. brevicostatus 
Fore wing shaded with light tan in costal 
area from base to apex of wing........ 
Sep utah tepescinne wie ees oak 4. skokianus 
te 
Mature Mare Nympus 
1. Length of body 12-13 mm..4. skokianus 
Length of body not over 10 mm........ 2 
Claw of fore leg relatively long and 
slender, the length more than five times 
greatest thickness, fig. 265; abdominal 
gills of seventh pair double.......... 
EAE oR EL TORE ee ee 2. ferrugineus 
Claw of fore leg relatively short and stout, 
the length less than four times greatest 
thickness, fig. 264; abdominal gills of 
seventh pair single....... 1. fluctuans 
ht 
1. Callibaetis fluctuans (Walsh) 
Cloe fluctuans Walsh (1862: 379). 
This species was described from the fe- 
male only, and the types are lost. 
Mae.—Length of body 5.5-7.0 mm., of 
fore wing 6-8 mm., of caudal filaments 
10-12 mm. Head, fig. 257, brown, light 
yellow around bases of antennae and on 
Vol. 26, Art. 1 
lateral areas of frontal shelf; eyes brown 
when insect is alive; each antennal scape 
and pedicel brown, flagellum light yellow. 
Dorsum of thorax brown, venter almost en- 
tirely light yellow, with only a few brown, 
punctate dots on mesosternum; wings hya- 
line, fig. 221, without any coloration, all 
veins and crossveins hyaline; costal cross- 
veins of fore wing wanting entirely or vestig- 
ial, stigmatic crossveins not anastomosed, 
slanting, 5-7 in number; crossveins in disc 
cf wing relatively few, fig. 221, marginal 
intercalaries on outer margin usually single, 
sometimes double; legs light yellow, fore 
leg faintly stained with brown near apex 
of femur and at base and apex of tibia; 
middle and hind legs each with faint brown 
staining near apex of femur and with a 
minute, brown dot at apex of each tarsal 
segment. Abdomen light yellow, with brown 
shading: tergite 1 dark brown on meson; 
tergites 2-9 each completely shaded with 
light brown except for a narrow, longi- 
tudinal, pale streak on meson, a fairly large 
spot at anterior margin near each antero- 
lateral angle, and a narrow line crossing 
tergite at posterior margin; a pair of dark 
brown, submedian dots at anterior margins 
of tergites +10, a pair of short, curved, 
dark brown dots near anterolateral angles 
of each abdominal tergite, and a pair of 
longitudinal, dark brown marks at lateral 
margins of tergites 1-7; abdominal sternum 
light yellow, with a pair of short, curved, 
submedian, dark brown marks near anterior 
margin of each sternite, and usually a mi- 
nute, dark brown dot at anterolateral angles 
of each sternite. Genitalia light yellow; 
caudal filaments white, articulations not 
darkened. 
FEMALE.—Length of body 6-8 mm., of 
fore wing 7-9 mm., of each caudal filament 
9-10 mm. Coloration much as in male, but 
brown shading of dorsum of thorax more 
restricted. When insect is alive, pink stain- 
ing visible on vertex, on dorsal area of 
pronotum, and on mesonotum anterior to 
wing bases; wings hyaline, brown stained 
in costal, subcostal, and first radial inter- — 
spaces, this staining often extending on mem- — 
brane slightly posterior to vein R, at apex 
and in basal area of wing, and on veins as 
far back as M, ; brown staining interrupted 
around crossveins; in living insect, pink — 
staining present in wing on basal two-thirds 
of veins Sc and R, and on crossveins in this 
