May, 1953 
the Heptageniidae and Baetidae. The adult 
wing venation is typical for the Hepta- 
geniidae, resembling most closely that of 
Rhithrogena, fig. 320, but the hind tarsus 
has only four clearly differentiated seg- 
ments. The abdomen is quite long and slen- 
der, and the ninth sternite of the female 
has a median indentation on the posterior 
margin, fig. 307. The male genitalia are 
quite similar in structure to the genitalia of 
the jejuna group of species in the genus 
Rhithrogena. The median caudal filament 
is vestigial in the adults of Pseudiron. 
Each of the nymphs has a somewhat flat- 
tened, heptageniid-like head, with the eyes 
dorsal in position; in addition, the head is 
slightly elevated on the meson between the 
antennal bases, faintly suggesting the baetine 
head form. The mouth-parts evidently are 
fitted for predatism (Spieth 1938a:3). The 
tarsal claws, fig. 301, are longer than the 
tibiae. The gills, fig. 304, are elongate and 
slender, with a small fibrillar tuft near 
the base on the ventral side and a narrow, 
flagellum-like appendage near the center of 
the posterior margin, also on the ventral side 
of the gill. This type of gill occurs in no 
other known member of the order Ephem- 
eroptera. 
Spieth (1938a:3) described a nymph 
which he had collected in southwestern In- 
diana and thought to be the nymph of 
Pseudiron. A nymph, apparently of the same 
species, has been collected in Illinois. In my 
opinion, this nymph can be accepted as that 
of Pseudiron without further question de- 
spite the fact that an actual rearing from 
nymph to adult has not yet been accom- 
plished. The tarsal characters place it in 
the Ametropidae and the wing venation 
visible in the nymphal wingpads, as well as 
the form of the abdomen, are in agreement 
with the adult Pseudiron characteristics. 
Furthermore, this nymph and the adults of 
Pseudiron have been collected at the same 
location in Illinois. 
Pseudiron centralis McDunnough 
Pseudiron centralis McDunnough (19314:91). 
Matve.—Length of body and of fore wing 
12 mm. Head light yellow, with red-brown 
shading on face and on vertex between com- 
pound eyes; each antennal scape and pedicel 
red-tan, flagellum light yellow; compound 
eyes of living insect dark gray. Dorsum of 
Burks: THe Mayr ies or ILiiNois 149 
thorax reddish brown, with narrow, yellow 
stripes on lateral sutures of mesonotum; 
pleura and sternum yellow. Legs markedly 
long and slender, yellow-brown, with a dark, 
red-brown crossband present at middle and 
at apex of each femur, each tibia and tarsal 
segment darkened at apex; wings hyaline, 
each brown stained in stigmatic area, veins 
and crossveins brown. Abdomen with broad, 
dorsomedian, longitudinal, brown stripe, 
edges of this stripe extended to lateral mar- 
gin at posterior margin of each tergite; ab- 
dominal sternum yellow, with ganglionic 
areas faintly brown-stained; genitalia, fig. 
310, yellow-brown; caudal filaments yellow, 
with basal two or three segments shaded 
with brown, articulations light brown, be- 
coming colorless toward the apexes of the 
filaments. 
FEMALE.—Length of body 12-13 mm., of 
fore wing 13-14 mm. Coloration almost 
identical with that of male except that dor- 
sum of thorax is mostly yellow-brown; stig- 
matic area of fore wing not brown stained, 
veins and crossveins of hind wing almost or 
quite hyaline; ninth abdominal sternite in- 
cised on meson of posterior margin, fig. 307; 
caudal filaments white, basal articulations 
light brown. 
NympH.—Length of body 12-13 mm. 
Head broad, flattened dorsally, but slightly 
elevated on median area between antennal 
bases, thus somewhat intermediate in form 
between typical heptageniid and_ baetid 
nymphal heads. Pronotum with lateral mar- 
gins expanded laterally as thin, platelike pro- 
jections, reminiscent of the pronotum in some 
Palaeodictyoptera. Legs long, slender, fig. 
301, with each tarsal claw longer than re- 
spective tibia; wingpads showing venational 
pattern typical for this genus. Abdomen 
long, slender, with lateral margins flaring; 
platelike, posterolateral angles acute on seg- 
ments 8 and 9, rounded on more anterior 
segments; gills, fig. 304, with a small fibril- 
lar tuft near base and a flagellum-like pro- 
jection near middle of posterior margin; 
apex of gill lanceolate; cerci each with a 
fringe of long setae on inner side only, 
median caudal filament bearing long setae 
on both sides. 
Known from Illinois, Indiana, lowa, Kan- 
sas, Manitoba, and Missouri. Evidently de- 
velops in rivers that are fairly rapid and 
of moderate size. 
Illinois Records.—CENTRALIA: at light, 
