private collection, and also for work on the keys to the genera 

 of imagos. We are under special obligation to Dr. P. P. Calvert, 

 of Philadelphia, for aid given Mr. Adams in the revision of 

 keys and in the determination of doubtful species, and for notes 

 on dragon-flies in Illinois made by Mr. Harry Walker at Belvi- 

 dere, Mr. Shafer at Mt. Pulaski, and Mr. E. J. Kuegeman at 

 Ravenswood and Edgewater. Data relating to collections in 

 Illinois have been furnished us by Mr. Maurice Ricker, of Bur- 

 lington, la., and by W, E. Longley, and others, of the Entomo- 

 logical Society of Chicago. 



Of the twenty-eight recognized Illinois species of the fami- 

 lies of Anisoptera herein treated, we have here described the 

 nymphs of twenty-four (six of them for the first time), repre- 

 senting all our eleven genera. To these have been added by 

 Professor Needham descriptions of ten nymphs of extralimital 

 species. Thirty-four nymphs are thus described in all, fourteen 

 of them for the first time. 



Much careful study has been given to the preparation of 

 the keys. In all cases the linear arrangement is according to 

 the principles suggested by Comstock, the more generalized 

 group or species being followed by the divergent ones in the 

 order of the direction and amount of specialization. The de- 

 scrii3tions of the nymphs are drawn up from full-grown exam- 

 ples unless otherwise stated. The newly hatched insect quickly 

 takes on the form and structure of the full-grown nymph, and 

 may usually be recognized while still very young by the char- 

 acteristic sculpture and armament of its species. 



