May, 1953 
ment, a forceps. Each mandible bears, at 
the apex, two long incisors, a large, tufted 
lacinia, and a broad, molar surface provided 
with numerous, lamellate teeth. The hypo- 
pharynx is large—about one-half as wide as 
the labrum—and has a pair of broad, thin 
parapsides. 
The entire thoracic notum is fused and 
modified to form a carapace, which covers 
the thorax and the first five abdominal ter- 
gites, as well as the anterior part of the 
sixth abdominal tergite. The legs are rela- 
tively short and stout, with long, slender, 
edentate claws which are almost as long as 
the tibiae. Each of the abdominal segments 
1-6 bears a pair of platelike, fissured gills, 
fig. 175. These gills normally are completely 
concealed by the thoracic carapace. Ab- 
dominal tergite 6 has a median, truncated, 
pyramidal lamina against which the apex 
of the carapace fits. Each of abdominal 
segments 6-9 has a pair of blunt, postero- 
lateral projections. Tergite 9 has also a 
median dorsal spine on the posterior margin. 
Tergite 10 has a median notch on the pos- 
terior margin; this tergite is completely 
surrounded posteriorly and laterally by the 
incised ninth tergite. Sternite 9 is produced 
posteriorly and has a median notch on the 
posterior margin in both males and females. 
There are three relatively short caudal fila- 
ments, each of which bears a dense fringe 
of setae on both the inner and outer margins. 
Baetisca was revised by Traver (1931c: 
45), and the nymphs were keyed out by 
McDunnough (19324: 213). Both nymphs 
and adults were again treated by raver 
(1935a:558), and, since the appearance of 
Traver’s and McDunnough’s comprehensive 
papers, three additional Nearctic species 
have been described, viz., bajkovi Neave, 
rogersi Berner, and thomsenae ‘Traver. 
Specific characters for the females of this 
genus have not yet been found. 
KEY TO SPECIES 
Apvutt MALEs 
1. Wings partly or almost entirely washed 
‘Altea et oy Sea ees A 1. rubescens 
WAS Gea yal Nei cae Notes) tw sir Plece ls sume > 2 
2. All longitudinal veins of fore wing brown; 
caudal filaments white, with articula- 
tions brown . Ai SN ats 2. laurentina 
Longitudinal veins of fore wing posterior 
to R; hyaline; veins C, Sc, and R, 
lightly shaded with yellow, and bases 
stained with brown; caudal filaments 
Burks: THE Mayr ties or ILLINOIS 77 
usually entirely white, basal articula- 
tions sometimes b 
3. Abdominal venter almost completely 
shaded with brown......... 3. obesa 
Abdominal venter white or very pale 
Vella water eee ees ae 
4. Middle abdominal tergites light brown; 
fore tibia white, shaded brown at apex; 
fore wing 10 mm. long...... 4. bajkovi 
Middle abdominal tergites dark red- 
brown; entire fore tibia tan; fore wing 
Simm Ones epee oe 5. lacustris 
Nympus 
1. Mesonotum with both lateral and dorsal 
SPINE Sere Ree eee Da ee ah ee 2 
Mesonotum with lateral spines only, as 
EE TSAI RS eS SU ane ae 3 
2. Frontal tubercles of head reduced, virtual- 
ly wanting, fig. 179....2. laurentina 
Frontal tubercles of head relatively well 
developed, fig. 180.......... 3. obesa 
3. Frontal projections of head reduced; 
genalsshelf-smally figs 17725. 3....4- 
Pe ages or eer ue ea 5. lacustris 
Frontal projections of head relatively well 
developed; genal shelf well developed, 
Inga | gto ete Aopen creleeie ae ae ae 4. bajkovi 
1. Baetisca rubescens (Provancher ) 
Cloe unicolor Provancher (1876:267), 
not Hagen. Misidentification. 
Cloe rubescens Provancher (1878:127, 144). 
New name. 
Mav.e.—Length of fore wing 8-9 mm. 
Base and costal area of fore wing and most 
of hind wing flushed with a pink stain; 
thoracic notum dark red-brown, abdominal 
tergites red-brown, and abdominal sternites 
lighter reddish or yellowish brown; genital 
forceps and caudal filaments white or pale 
yellow. 
The nymph is unknown. 
The species is known from Quebec. 
2. Baetisca laurentina McDunnough 
Baetisca laurentina McDunnough 
(1932b: 214). 
Mace.—Length of fore wing 9-10 mm. 
Compound eyes in life yellow in upper 
portion, darker yellow, with brown flecks, 
in lower portion; head and antennae yellow- 
brown. Mesonotum dark chestnut brown, 
darker brown at apex of scutellum; meso- 
pleura light brown, sternum dark brown. 
All legs yellow-brown, with each fore leg 
slightly darker than others; wings hyaline, 
with all longitudinal veins of fore wing light 
brown and crossveins hyaline. Abdominal 
tergites dark brown; sternites light brown 
