2 THOMAS SAY FOUNDATION 
Since the publication of the Monograph of the Plecoptera of 
North America by Needham and Claassen (27), the writer has 
devoted some time to the study of the morphology, biology and 
taxonomy of the immature forms of stoneflies, and within this 
paper are embodied the results of this investigation. Descriptions 
and notes on the nymphs of sixty-eight species are included, and 
these represent all the genera of the order except Kathroperla, a 
rare Western genus; Perlyomyia, a very close ally of Leuctra; 
and Capnura, a genus closely related to Capnea and containing 
only one known species. 
Probably one of the most striking results obtained from the 
study is the fact that the nymphs of only one family, the Perlidae, 
are essentially carnivorous, while the nymphs of all other families 
are herbivorous. Peltoperla, which has heretofore been included 
in the family Perlidae, is here placed in a separate family, 
Peltoperlidae. This seems desirable since the nymphs of Peltoperla 
are true herbivores, and in structural characters differ markedly 
from the nymphs of any of the other genera now included in the 
family Perlidae. 
In addition to the many structural characters which have been 
used in separating genera and species, the color patterns of the 
nymphs, especially those of the Perlidae, have been found remark- 
ably reliable for use in identifying different species. However, in 
the Pteronarcidae, Peltoperlidae, Nemouridae, and Capnidae, 
where the nymphs are almost wholly concolorous, and where 
closely allied nymphs do not exhibit structural differences, specific 
identification is often very difficult or impossible. 
ACKNOWLEDGMENTS 
In this investigation the writer has been aided in various ways 
by his colleagues and students at Cornell University. The draw- 
ings of the nymphs were made by Elizabeth K. Burkmyer. Naomi 
Argo and Sid Robinson assisted in the rearing work of the insects, 
and the drawings of plates one to ten are largely the work of Mr. 
Robinson. Mr. Yuanting T. Chu has also assisted materially in 
this study. The photographs were made by the author with the 
assistance of Mr. Robinson. A grant from the Heckscher Research 
Council has made possible the pursuance of the work and as- 
sistance in the publication of the manuscript. 
The frontispiece is a photograph which was colored by Ellen 
Edmonson. 
Nymphs have been received from the following individuals: 
Virgil Argo; H. S. Barber; C. Betten; S. C. Bishop; P. J. Chap- 
