270 THE ENTOMOLOGIST. 



in Scotland, as indeed has Rhamni. That some of these occur in 

 South Scotland is not improbable, but the chief interest their 

 apparent absence possesses is from the belief, held by many- 

 naturalists, that Ireland derived its fauna from Scotland. If such 

 be the case, and these species were once inhabitants of Scotland, 

 it may have been in the more genial climate of middle post-glacial 

 times, and that they perished in the less genial period which 

 followed. Flourishing as they do in the mild and humid atmo- 

 sphere of the South-west of Ireland, it seems clear that they are 

 not dependent on a "continental" climate, as we have supposed 

 some of the species absent alike from Scotland and Ireland to be. 



The distribution of the species which occur in Scotland, but 

 are absent from Ireland, must now be considered. They are five 

 in number; and if it be the case that Heliantheinum vulgare 

 is the food-plant of Astrarche (as it certainly is of its variety 

 Ai'taxerxes), then the absence of that species can be accounted 

 for. I believe, however, that it also feeds on Erodium cicutarium, 

 which, unlike the Heliantheinum, is an Irish plant. 



Of the five Scottish species not found in Ireland three {Selene, 

 Ewphrosyne and Astrarche) are arctic, one (Lucina) occurs in 

 South Sweden, and the remaining one {Mthiops), though a 

 species of central Europe, has so wide a distribution in Scotland 

 that its absence from Ireland is very remarkable. So far as can 

 be seen there is no climatic reason by which the absence (if such 

 be really the case) of these species can be explained. We are, 

 therefore, driven to supj)ose that the land connection with Ireland 

 must have been severed before the}^ were able to establish them- 

 selves, and that no friendly wind has since wafted them across the 

 narrow sea, and so implanted them in the Emerald Isle. 



In connection with the whole group of the British butterflies 

 there is a question of much interest, but one to which we can 

 scarcely hope to get a satisfactory answer. It is this. In what 

 order relativel}' did the various species come to Britain ? There 

 is also another matter on which the exotic distribution (that is 

 the distribution in other countries than Britain) throws a certain- 

 light, and that is the relative antiquity of each species. 



We will first briefly discuss the latter question. 



It may be taken for granted that, unless circumstances {e. g., 

 human agency, conscious or unconscious), have been exceptionally 

 favourable, species which have the widest distribution are probably 



