INTRODUCTORY REMARKS. XI 



power as of some (though not of the highest degree of) importance, 

 group together the species possessing it, as comprehending of them- 

 selves one distinct subsection of the Phytophaga. 



This, the general question, we need hardly here consider, inas- 

 much as we have another and a more valuable character, which is 

 common to all that portion of the Halticidae that is the subject of 

 this Catalogue, the globular and bladder-like inflation of the posti- 

 cal claw. This, so far as we know, is a specialty affecting only this 

 group of insects ; it is unique, and seems not only to have (it may 

 be) a greater value, as the basis of arrangement, than the incras- 

 sated posterior femora, but to possess sufficient importance to per- 

 mit us, by means of it, to unite together forms of these saltatorial 

 Halticidae that in external facies are not otherwise than dissimilar 

 the one to the other. 



The thought at once suggests itself (if we have satisfied ourselves 

 as to the soundness of this basis of arrangement), that if among these 

 saltatorial Halticidae we can discover a character (this globular in- 

 flation of the postical claw) which is sufficiently striking and perma- 

 nent to bring together many different forms, included in the group, 

 and which at the same time does not introduce any single species 

 (from among the other sections of Phytophaga) that does not possess 

 this saltatorial power, whether some other character may not be dis- 

 covered among the remaining forms of Halticidae which is common to 

 them, and to them alone ; and whether it does not, to some extent, 

 supply an argument in favour of our seeking to unite together, as 

 one subsection of the Phytophaga, all species, however dissimilar in 

 form, that possess this saltatorial power. 



But to return to the more immediate subject before us : we believe 

 that this globular inflation of the postical claw so far holds good as 

 the basis of arrangement, that genera and species which possess it 

 (although they may differ considerably inter se in general external 

 form) are really, by means of it, more closely related to each other than 

 they are to others which (with a greater appearance of resemblance) 

 are deficient in this peculiar structure. When, however (having 

 satisfied ourselves as to the questions, what are the natural limits of 

 the group ?, what forms ought to be included, and what excluded ?), 

 we begin to investigate seriatim the species from different countries 



