412 



most serious of all, they do not discriminate between beneficial and 

 noxious insects, but destroy both. An instance of the fact last men- 

 tioned is the recently reported feeding of Anax Junius on the honey- 

 bee. In no case, however, is it probable that the harm done overbal- 

 ances, or begins to counterbalance, the good which these insects do 

 in the destruction of biting Diptera. 



The classification of the nymphs of Zygoptera is in a backward 

 state as compared with the classification of the adults. This is due 

 especially to the fact that immature forms are not easily collected and 

 that their classification is particularly difficult. An intensive study 

 of the nymphal characters has shown that there are, within certain 

 genera, groups of nymphs the species of which are much more closely 

 related to each other than to the members of other groups of the same 

 genus. These groups correspond to groups of adult species in the 

 identification of which the characters of the anal appendages of the 

 male are mostly relied upon. Little attention seems to have been given 

 by taxonomists to the females, and where species are represented in 

 collections by females only it is exceedingly difficult to determine them. 

 Again, when studying nymphs, one is often successful in rearing a 

 number of females, but almost any amount of painstaking work may 

 fail to produce a male. In such cases still more inconvenience is 

 experienced when it is found that the reared females can not be named 

 because of the fact that the published synopses are based largely upon 

 male characters. 



It is with a view to clearing up some of the obscure features of 

 the classification and lessening the labor of determination that nymphs 

 and adults, including both sexes, have been considered together and 

 tables prepared for the separation of both. 



All obtainable biological data have been added for the sake of com- 

 pleteness; but it is fully realized that the data given here are incom- 

 plete, and can only be made complete after many years of diligent 

 study. 



Nymphs of several species which are apparently new have been 

 reared in the course of the study and are described herein for the first 

 time. Some of the remaining species which doubtless occur in Illinois 

 but which have not been collected by the writer, have been obtained 

 through the courtesy of various people, and the list has been completed 

 as far as possible in this way. 



Certain problems concerned with the nomenclature have presented 

 themselves, the most important of which concerns the adoption of 

 family names. According to the ruling of the International Commis- 

 sion on Zoological Nomenclature (Muttkowski, 'lo: 15) Agrion re- 



