May, 1953 Burks: THE Mayr igs oF ILLINOIS 99 
SN 
== 5 S(6e aoe means 
ee 
a TA es we 
Fig. 217.—Isonychia rufa, wings. 
Fig. 218.—Parameletus midas, wings. (After 
Traver.) 
FeeSe NS eet ep 
Set rem 
1 
: 
222 
Fig. 219.—Siphlonurus quebecensis, 
Fig. 220.—Baetis propinquus, wings. 
Fig. 221.—Callibaetis fluctuans, wings. 
wings. 
Fig. 222.—Callibaetis ferrugineus, wings. 
Marure Nympus 
1. A stout, median, ventral spine on meso— 
and metasternum..... 24. Siphlonisca 
No median ventral spines on thorax. . .2 
2. A conspicuous, transverse pecten of 
spines present on margin of each max- 
Bieta OAC A <2 eo Fae. 25. Ameletus 
No pecten of spines present on maxilla. .3 
3. Apical segment of labial palp and an 
apposed, thumblike projection of penul- 
timate palp segment forming a forceps, 
foe DOE ae, ee eae: 26. Parameletus 
Labial palp not forceps-like at apex..... 
RTO, eases SLA aheas ks 27. Siphlonurus 
24. SIPHLONISCA Needham 
Siphlonisca Needham (1909:71). 
This strikingly distinct genus is at once 
recognizable because of the wide, flat lateral 
extensions on the margins of abdominal seg- 
ments 5—9 of the adults, fig. 233, and on all 
abdominal segments of the nymphs, fig. 234. 
A midventral spine is present on the meso- 
sternum and metasternum in both the 
nymphs and the adults. The abdominal gills 
of the nymphs are single and platelike, with 
the margins slightly irregular. The median 
caudal filament is well developed in the 
nymphs, but is vestigial in the adults. 
Siphlonisca most closely resembles Onisci- 
gaster McLachlan (1873:108; 1874:139), 
described from New Zealand. 
Siphlonisca aerodromia Needham (1909: 
71), known from New York, is the only 
described species. The male genitalia of this 
species are shown in fig. 232. 
