May, 1953 
flight, almost immediately after emerging 
from the nymphs. 
Most adult specimens of Caenis intended 
for study should be killed with cyanide and 
mounted dry on pins or points; a few speci- 
mens of a series may also profitably be 
preserved in alcohol for ease in studying 
the genitalia. The colors of the specimens 
in alcohol fade seriously, but the characters 
of the male genitalia can be seen plainly in 
uncleared specimens preserved in alcohol. 
The male genitalia of dry specimens can be 
cleared in KOH for study, but the clearing 
technique is difficult. Specimens of Caenis 
are both small and fragile, which makes 
them difficult to handle without breakage 
during staining and clearing operations. 
A revision, based on adult specimens of 
this dificult genus, was made by McDun- 
nough (193le) ; all subsequent North Amer- 
ican workers have leaned heavily on_ his 
work. Specific characteristics for females 
and nymphs of Caenis have not been found. 
KEY TO SPECIES 
Aputt MAtes 
1. Vertex of head entirely and uniformly 
Shadede with darkenay. 2s... 04.0. 2 
Vertex of head partly or completely white 
Ompelemyellowsss ents. fishes fac costes 5 
Hind femur freckled with numerous, mi- 
nute, black dots........1. punctata 
Hind femur without numerous, minute, 
black dots; white, with an apicodorsal 
black spot or subapical black band. .3 
3. Apex of hind femur completely encircled 
by a black band........2. diminuta 
Apex of hind femur with only a dorsal 
DIAGKES DOR Ia eee eins cine ts ool 4 
4. Genital forceps short and stout, fig. 105; 
body and fore wing each only 2 mm. 
i) 
loners ote ie ia Ae Ss 3. amica 
Genital forceps moderately long and 
curved, fig. 106; body and fore wing 
each 3.5—4.0 mm. long... .4. simulans 
5. Abdomen lacking spiracular dots or 
SENSORS p hg bisa PSN ae ae ae 6 
Abdomen with spiracular dots or pereales 
6. Mesonotum light red-brown; genital for- 
ceps short, fig. 107, apexes straight; 
vertex of head almost entirely white, 
shaded with purplish gray only at 
margins and near ocelli....5. anceps 
Mesonotum light yellow; genital forceps 
moderately long, fig. 111, apexes 
hooked; vertex of head heavily shaded 
with purplish gray near ocelli, light 
OnlventiMcentete wa <1 7-4... ae 6. ridens 
7. Abdominal segments 7-9 only with gray- 
brown spiracular streaks; segments 1-6 
without spiracular dots or spots 
7. hilaris 
Burks: THe Mayrties oF ILLINnots 51 
~ 
Abdominal segments 1-6 with spiracular 
GOES Or SHOTS yes neath Ae 
8. Vertex of head almost entirely white, with 
purplish-gray shading present only at 
anterior and posterior margins and 
occasionally near lateral ocelli; length 
ofibady 2 mmeterc tas eas: 8. gigas 
Vertex of head dark gray-purple in entire 
anterior two-thirds, posterior third 
light yellow or white; length of body 
1. Caenis punctata McDunnough 
Caenis punctata McDunnough (1931¢:259). 
Mave.—Length of body and of fore wing 
3 mm. Vertex of head completely covered 
with purplish gray; mesonotum  yellow- 
brown; fore femur with dark purplish-gray 
shading in middle and near apex; middle and 
hind femora peppered with minute, black 
dots, each also with a dark gray band near 
apex; abdomen pale yellow, almost white, 
with extensive gray shading on tergites; spi- 
racular marks present on all abdominal seg- 
ments; each sternite with a pair of black, 
lateral dashes, sternites 1-6 each with a pair 
of sublateral, black dots, and sternites 7-9 
each with two pairs of sublateral, black dots; 
genital forceps, fig. 110, short and stout. 
Known from New York, Ontario, Quebec, 
and Wisconsin. 
2. Caenis diminuta Walker 
Caenis diminuta Walker (1853: 584). 
Mate.—Length of body and of fore wing 
3mm. Vertex of head slightly but uniformly 
shaded with gray; mesonotum dark chest- 
nut brown; fore femur shaded with gray 
and with a darker, transverse band near 
apex; fore tibia uniformly shaded with faint 
gray; middle and hind femora white, with 
a black band encircling each near apex; 
abdomen white, with extensive gray shading 
on tergites 1-6; spiracular dots present on 
segments I—-8 or —9; sternites 2-6 each with 
a pair of slender, lateral, black lines; two 
pairs of minute dots sometimes present on 
each abdominal sternite, those on sternites 
7-9 always darker than anterior ones; gen- 
ital forceps, fig. 112, short, stout, and mark- 
edly divergent. 
Known from Florida, Georgia, Ontario. 
