238 ILLIno1is NATURAL History SURVEY BULLETIN 
and Nemocapnia, (4) addition of Claas- 
senia to the Perlidae, (5) addition of Dic- 
tyopterygella to the Perlodidae, (6) the 
recognition of Diploperla as the generic 
name for a group of species formerly for 
the most part placed in Perla (s./.), and 
its placement in the family of Perlodidae, 
(7) erection of a new family, the Isoper- 
lidae, for the genus Isoperla, which I 
formerly placed in the Chloroperlidae, 
(8) recognition of Oroperla as a genus of 
Perlodidae and (9) removal of Isoperla 
from Chloroperlidae and the addition to 
this family of Hastaperla. 
Some of the now accepted genera repre- 
sent rather homogeneous groups of species, 
whereas other genera are quite hetero- 
geneous and may contain several more or 
less minor complexes. Acceptance of these 
minor complexes within the larger generic 
units as subgenera will serve most nomen- 
clatorial and classificatory needs. For in- 
stance, Brachyptera represents a genus 
containing several smaller complexes, most 
of which (Nephopteryx, Obipteryx, Oem- 
opteryx, Rhabdiopteryx, Strophopteryx, 
etc.) have already been named and some- 
times considered as genera. No _ phylo- 
genetic relationships are lost or obscured 
by use of subgeneric names for such 
smaller complexes as Ocemopteryx, for 
example, and the treatment of general 
entomological literature is often improved. 
The same applies to such genera as Ne- 
moura and Perlodes. Isoperla (s.l.), as I 
now recognize it, contains several sub- 
genera, some named and others unnamed. 
Almost any genus containing a number of 
species can be broken into finer subgeneric 
groups or complexes, but it is not the pur- 
pose of this article to go into detail con- 
cerning such classifications. Revisional 
papers dealing exhaustively with single 
families or genera are the best places for 
such lesser groupings to be defined and 
evaluated. 
The groupings of the above species are 
subject to the personal factor in evalua- 
tion by individual specialists, and, like an 
accordion, the skeletal organizational 
scheme can be pulled out or contracted. 
Some students of stoneflies prefer to group 
the nemourids, leuctrids, capnids and 
taeniopterygids as subfamilies of a single 
large family, the Nemouridae. I prefer, 
however, at least for the present and until 
the world fauna is better known, to con- 
Vol. 22, Art 
sider them as separate families. “The actual 
problems of ready identification and keying 
remain the same regardless of which policy 
is followed. Future and broader studies 
of the world stonefly fauna will inevitably 
exert influences for some changes in exist- 
ing classificatory systems. 
REVISED KEY TO FAMILIES 
of the Plecoptera of North America 
(Figures illustrating almost all of the charac- 
ters used in these keys may be found in Frison 
1935a) 
ADULTS 
1. Anal area of forewings with two or 
more rows of crossveins; basal ab- 
dominal sternites with remnants of 
nymphal gills ye «Sree Pteronarcidae 
Anal area of forewings entirely without 
crossveins or with but one row; basal 
abdominal segments without remnants 
of nymphal) gills?.>22) 2 ee 2 
2. Cerci short, not longer than greatest 
width of the pronotum: 17). ) 2. 3 
Cerci long, much longer than greatest 
width of the pronotum.]:.) 27.) 7 
3. Forewings with numerous costal cross- 
veins; the pronotum, as viewed from 
the side, lies at a downward sloping 
angle to the otherwise general hori- 
zontal plane of the mesothorax and 
metathorax; some species with gill 
remnants at least on sides of meso- 
thorax and metathorax above bases 
of legs...) 4 ee Peltoperlidae 
Forewings with no or few costal cross- 
veins; the pronotum, as viewed from 
the side, lies in the same general hori- 
zontal plane as the mesothorax and 
metathorax; without any gill remnants 
on sides of mesothorax and metathorax 
above bases of legs... 7232 5.20uuaee + 
4. Second tarsal segment about as long as 
other tarsal segments... 7099): ee 
Me. Taeniopterygidae 
Second tarsal segment much shorter than 
other tarsal segments....... eee 5 
5. Cerci with five or six segments.......- 
Rehr Capniidae (Eucapnopsis only) 
Cerci one segmented 6 
6. Apical marginal space beyond tip of sub- 
costa with an oblique crossvein; some 
species with gill remnants in cervical 
region... 0. 0... 0. ens oo NTO 
Apical marginal space beyond tip of sub- 
costa without oblique crossvein ; no gil 
remnants ever present in cervical re- 
gion. ...... o... 0a 
7, First tarsal segment long, about as long 
as the third tarsal segment; remnants 
of thoracic or submental gills never 
present; forewing with no or few 
median and cubital crossveins; fe- 
males with a narrow or broad, pale, 
weakly sclerotized, median, longitudi- 
nal band on basal abdominal tergites 
distinctly contrasting with strongly 
sclerotized lateral margins; labium 
