rNTBODTJCTTON. Xlll 



be expected of those large tracts of country where there has 

 never been a resident collector, or of the many square miles of 

 mountain and moor in which an entomologist has never set 

 foot. Many Lepidoptera are almost ubiquitous, and others 

 appear to occur wherever there is a suitable habitat. Some 

 species are restricted in their range by reason of their food 

 plant being confined to a narrow area. Others are equally 

 restricted without any apparent reason. They will occur in 

 one corner only of a moor or wood, or even of an open field, or 

 by a single hedge side, and such species may be sought else- 

 where altogether in vain. Then the period of their appearance 

 in the various stages is but of short duration, and it is often 

 exceedingly difficult to find them when we know they exist 

 there. Except the butterflies, which appear on the wing during 

 the chief part of a sunny day, the flight of Lepidoptera is 

 generally of very short duration, and much influenced by causes 

 of which we have little knowledge. The delay of a single 

 hour, a change of wind, or many other trivial things may 

 prevent the capture of an expected species for a whole season, 

 even when we know it is there. What can be said then of the 

 species we do not know to be there, or of whose habits we 

 are ignorant? This Catalogue should be but the starting 

 point for future entomologists, and I trust all will strive to 

 find species not enumerated here, and additional localities for 

 those given. 



I do not propose to enter into any account of the Geology or 

 Botany of the two counties. This has been exhaustively done 

 in the second volume of these Transactions by writers who had 

 special knowledge of the subjects. It will be sufficient for me 

 to speak in very general terms on the character of the ground 

 surface. It must always be remembered that the Lepidoptera 

 of a district depend on the plants growing there, and that the 

 plants depend to some considerable extent on the geology. 

 Chalk appears to be most productive, and limestone next ; but 

 we do not look for limestone plants on sandstone, nor sandhill 

 plants on trap rock. 



