INTRODUCTION 15 



plete, but no character of recognised importance is omitted. If 

 in the description of a family a character is attributed to tlie 

 family as a whole, this chai'acter is not afterwards repeated in 

 the descriptions of the genera ; similarly, charactei's assigned to 

 the groups are not repeated in the families. The characters 

 given are supposed to be absolute for the British fauna, but 

 exceptions occur in exotic forms, which it has not been thought 

 necessary to mention. 



In structural descrii)tions, proportional measurements are 

 sometimes briefly expressed in numbers as follows : ciliations 

 of the anteiniae are measured in terms of the breadth of the 

 stalk, thus " ciliations h " means " ciliations half as long as 

 the antennal stalk is broad " ; the length of the antennae 

 is expressed in terms of the length of the forewings, thus 

 " antennae over 1 " means " antennae longer than forewings " ; 

 the length of the palpi is expressed in terms of the breadth of 

 the eye, thus " palpi 2^^ " means " palpi two and a half times as 

 long as the eye is broad " ; the length of the tarsus is expressed in 

 terms of the length of the tibia, thus " tarsus 1^ " means " tarsus 

 half as long again as the tibia " ; the outer spurs of the tibiae 

 are ex])ressed in terms of tlie inner, thus " outer spurs f " means 

 "outer spurs | of the length of the inner"; the breadth of the 

 hindwings is expressed in terms of the forewings, thus " hind- 

 wings 1 " means " hindwings as broad as forewings " ; the length 

 of the cilia of the hindwings is expressed in terms of the breadth 

 of the hindwings, thus " cilia 6 " means " cilia six times as long 

 as the hindwings are broad." In describing the veins, they are 

 assumed to be all present and separate, except so far as they are 

 expressly mentioned to be otherwise. Generally, the absence 

 of peculiar characters is assumed unless they are mentioned 

 as present. 



In specific descriptions, the expanse of the wings (measured 

 on specimens set in the usual way) is given in millimetres (25 

 millimetres practically = 1 inch). The head and thorax may 

 generally be assumed to be coloured like the forewings, unless 

 particularly mentioned. The markings of the forewings are 

 described in accordance with a certain assumed type ; the type 

 of markings varies in difterent groups, but is explained under 

 the head of each group. Typical markings not mentioned may 

 be assiimed to be absent. All colours are descrilted as seen 

 under a lens of moderate power, which destroys optical illusions. 



Under each genus is given its geographical distribution, so 

 far as authenticated, but often the available information is very 



