148 IntrNors NarurAL History Survey BULLETIN 
each front wingpad, mesosternum with hook- 
like projection in center of basisternum, 
middle femur as long as tibia and tarsus 
without claw, middle tarsal claw long, slen- 
der. more than twice as long as middle tibia; 
313 
314 
Fig. 313.—Metreturus pecatonica, labrum of 
nymph. 
Fig. 314.—Metreturus pecatonica, mandible 
of nymph. 
Fig. 315.—Metreturus pecatonica, labium of 
nymph. 
Fig. 316.—Metreturus pecatonica, maxilla of 
nymph. 
metasternum with hooklike projection in 
the center, hind femur one and one-half 
times as long as tibia and tarsus without 
claw, hind tarsal claw five times as long 
as tibia. Abdomen three times as long as 
thorax, tapering toward posterior end, so 
that segment 9 is two-fifths as wide as seg- 
ment |; prominent, flat flange and projecting, 
posterolateral angle present at each lateral 
margin of tergites 1-9; a hooklike projection 
present in center of each tergite 1-9, with 
a small, median papilla present at posterior 
margin of each of these tergites; segments 
1-7 each bearing a pair of gills, each gill 
composed of a dorsal member, with a re- 
curved ventral flap, and a ventral member, 
each gill member having a stout, median 
tracheal trunk from which arise numerous, 
pinnately branching tracheae; lamina of gill 
partly eroded away between these tracheae, 
so that ventral member of each gill almost 
assumes appearance of a cluster of branch- 
ing filaments; nearly all or smaller part of 
Vol. 26, Art. 1 
upper member of each gill having a similar 
appearance, this atrophy of gill lamina of 
upper member almost complete in first gill, 
but becoming progressively less so in more 
posterior gills, the upper member of seventh 
gill with lamina eroded only at apex and 
on mesal side; caudal filaments alternately 
banded with faint yellow and light brown. 
Holotype, female nymph. — Taken by 
seining in Sugar River, one-fourth mile 
above mouth, near Harrison, Illinois, July 
6, 1926, R. E. Richardson. Specimen mature, 
taken just as molt to subimaginal stadium 
was beginning. Specimen in alcohol. 
Paratype. — ILiiNotis: Taken with dip- 
net near water’s edge at mouth of Peca- 
tonica River, near Rockton, May 8, 1927, 
R. E. Richardson, 12 nymph, about half 
grown. Specimen in alcohol. 
The streams in which these specimens 
were found have subsequently been dredged 
and straightened, but the available informa- 
tion indicates that, at the time the collecting 
was done, they were fairly rapid, shallow, 
and moderate-sized streams with sand and 
rock bottoms. Since being dredged, they have 
been sluggish, heavily silted streams with 
mud bottoms. Intensive collecting in these 
rivers in recent years has failed to produce 
additional specimens; the species probably 
has disappeared completely from them. 
38. METRETOPUS Eaton 
Metretopus Eaton (1901:253). 
In Metretopus, the wing venation is simi- 
lar to that of Siphlonurus, fig. 219, but dif- 
fers principally in that the cubital inter- 
calary veins of the fore wing consist of two 
long, straight veins instead of a series of 
short, sinuate veins decurrent from yein Cu,. 
The hind wing in Metretopus also has a 
relatively acute costal projection. The me- 
dian caudal filament is vestigial in the adult. 
Characters of the nymph, used in the above © 
key to genera, are from Bengtsson (1909: 
16). 
One Holarctic species, norvegicus Eaton 
(1901:254), has been reported from Alberta — 
by McDunnough (19254: 187). 
39. PSEUDIRON McDunnough 
Pseudiron McDunnough (1931b:91). 
Pseudiron is clearly an interstitial genus — 
showing similarity to the members of both 
