6 PREFACE. 
The following grouping is the best that can be made at present : — 
Mask flat (agreeing with Agrionina),— all Aischnina and Gomphina (except Cordu- 
legaster). 
Mask, spoon-shaped (agreeing with Libellulina), — Cordulegaster. 
Antenne, four-jointed and flattened, — Gomphus and Allies. 
Antenne filiform and seven-jointed, — Cordulegaster and A%schnina, excepting two 
aberrant genera having six and five joints. 
All legs with tarsus three-jointed, — A‘schnina and Cordulegaster. 
All legs with tarsus two-jointed, — Ictinus. 
The two anterior pairs of legs with tarsus two-jointed, — Gomphina. 
These general characters are sufficient to determine the place of any nympha. 
Aveust, 188]. 
