IV INTRODUCTION. 



first applied to the species : as far as regards the specific 

 names, there is comparatively little difficulty in the applica- 

 tion of this simple rule ; but generic names have been used 

 by different authors in senses so widely different, and the 

 groups which they were meant to designate have been so va- 

 riously extended and restricted, that it was no easy matter to 

 determine, where several names had been used, which of them 

 ought to be preferred. 



If the generic name adopted be different from that first 

 employed for the species after the establishment of the Lin- 

 nean system of nomenclature, the name under which it was 

 first described follows as a synonyme, and where the specimen 

 has received more than one specific name, those names are 

 also given, as being sufficient for all purposes of identifica- 

 tion ; and to facilitate this kind of reference, the specific 

 names used will be all referred to in the Index, followed by 

 an indication of the genus to which they belong. 



These are followed by a reference to the best original 

 figures of the species. 



In those cases where the two sexes of the same species, or 

 any particular individual state or variety belonging to it, have 

 been differently named, the name or figure exclusively apper- 

 taining to the state or individual is placed after the indication 

 of the specimen to which it applies. 



Great care has been taken by Mr. Adam White in the 

 determination of the species, the verification of the synonymes, 

 and in arranging them into generic groups, in accordance 

 with the present state of the science. 



The specimens collected by my friend and predecessor, Dr. 

 W. E. Leach, may be considered as the nucleus of this col- 

 lection, and great attention has been paid to the published and 



