PREFACE. V 



by himself and others in earlier works, in which his new system 

 is employed. This point, however, docs not practically affect 

 the nomenclature of Odonata. 



Specific names rejected as synonyms, and subsequently applied 

 to other species of the same genus, appear to me as objectionable 

 as preoccupied names of genera, and have been discarded. 



Specific names unaccompanied by descriptions, which were 

 the bane of Entomology fifty years ago, and the use of which 

 has been retained in Odonata longer than in most other groups 

 of insects, have usually been rejected, with the following excep- 

 tions : — 



(1) 'When the characters of the genus, combined with the 

 locality, are sufficient to identify the species intended (e. g. 

 Anax Imperator, Leach). 



(2) When a genus has been characterized, and the species 

 belonging to it have been provisionally named, but not described 

 (e. g. Acanthaschna Victoria and Uniformis, Selys) . 



(3) In the case of fossil species ; for the names applied to 

 these, in the present state of our knowledge, often relate rather 

 to individual specimens in Museums than to readily obtainable 

 and identifiable species. 



(4) "When j\IS. names have been adopted by a later author 

 reference is sometimes made to the MS. name. 



Subgenera are not used; all such are here treated as genera. 



The limits of a genus are always variable, and its characters 

 subject to modification, both according to the increase of our 

 knowledge, and to the divergent views of different entomologists ; 

 hence, although no generic name ought to be issued v.ithout a 

 description, yet the fixing of a type, which must always be an 

 identifiable species placed in it when the generic name is used 

 for the first time, appears to be even more important ; for no 

 real certainty can be obtained without. In fact the fixing of the 

 type of a genus is to the description what the figure of an insect 

 is to the description of a species. Hence when Baron De Selys- 

 Longchamps first })ublished the name Agriocneniis without a 

 description, and placed in it two undescribcd and one described 



