NOTES INTRODUCTORY AND EXPLANATORY TO PART II 
The remainder of this book is a condensed account of the North 
American species of Odonata, with brief diagnostic descriptions and 
figures, and with all that is known about their habits. Here we offer 
a few suggestions that are intended to aid the beginner in its use. 
Confusion of names:—The reader who would make use of the litera- 
ture cited in this book (if unacquainted with the intricacies of zoological 
nomenclature) will need to know two things: 
1. That the older authors used fewer and more inclusive group 
names. The tendency has been and is to multiply subdivisions, creating 
new families, subfamilies and genera, and to name them all. 
2. That the Law of Priority adopted by the international zoological 
congress required the restitution to present day use of older names, 
even to the displacement of many that had obtained general currency. 
This law was first applied to the whole order by W. F. Kirby in his 
Catalogue of the Neuroptera-Odonata in 1890. Its application wrought 
great confusion in our literature through the transfer of names from 
one group to another. For example, the family name Agrionidae was 
long applied to a different family from that which the Law of Priority 
demands that it shall designate. The principle sources of such con- 
fusion are the following: 
Names used by the older 
authors and by 
non-conformists 
Names used by others 
since Kirby 
Calopteryx, which equals Agrion, whence 
Calopteryginae Fe Agrioninae, and 
Calopterygidae 3 Agrionidae. 
Agrion, which i Caenagrion, whence 
Agrioninae Caenagrioninae, and 
Agrionidae = Caenagrionidae. 
Diplax 3 Sympetrum 
Aeschna* = Aeshna 
Progomphus* az: Gomphoides 
Gomphoides* . Negomphoides 
Herpetogomphus Erpetogomphus 
Hoplonaeschna : Oplonaeschna 
* We follow the older usage here. 
46 
