324 THE ENTOMOLOGIST. 



that the chain under consideration, by reason of its peculiar 

 physical configuration, proves an effectual barrier to the dis- 

 persal, north and south, of lowland forms existing on the lower 

 slopes upon either side. Unlike the more elevated mass of the 

 Alps, there are no transverse valleys and passes at a compara- 

 tively low elevation which would provide the passage to and fro 

 of such Austral or lowland types. All communication between 

 France and Spain is thus completely severed, except in the case 

 of those species existing in the immediate vicinity of the snow- 

 line. Spain similarly in proportion to its southern latitude 

 possesses a comparatively poor Rhopalocera fauna. In this 

 case, however, less is possibly to be attributed to the effects of 

 the glacial period than to the isolated position occupied by the 

 Iberian peninsula ; at the same time it undoubtedly has made 

 its influence felt to a great extent. 



At about the climax of the glacial epoch geologists assert 

 that the land connection between Southern Spain and the 

 northern parts of Africa was severed, and has been so ever 

 since. This theory entirely accounts for why so few species 

 inhabiting the southern shores of the Mediterranean have been 

 able to extend their area of distribution to the north, where 

 they could easily find a congenial home in the subtropical climate 

 of Andalusia. At the same time no alpine forms inhabiting 

 Europe, I believe, are found upon any of the mountains in North 

 Africa. This would seem to suggest a date anterior to the 

 climax of the glacial epoch for the discontinuity of the two 

 continents. Geologists suppose that when the ice-cap attained 

 its greatest dimensions the climatological and phyto-geographical 

 conditions of the South of Europe must have been very similar 

 to those which reign supreme in Scandinavia at the present day. 

 If this was the case it must have harboured many of the alpine 

 forms of butterflies existing then. So that, unless the dis- 

 continuity between the two continents did not take place at a 

 date anterior to the climax, I do not understand the reason why 

 some of them should not be retained at the present day at high 

 altitudes upon the Atlas Mountains in Morocco and Algeria, 

 to whence they would have retreated upon milder conditions 

 ensuing. For if the disconnection took place before the climax, 

 when the climatological conditions were not so severe, the alpine 

 butterflies would not have retreated sufficiently far south in order 

 to secure a foothold upon the African continent. The only other 

 contingency I could see is that these conditions were not quite so 

 severe at the climax as geologists have pictured, which is indeed 

 supported by the fact that very few alpine forms occur upon the 

 elevated chain of the Sierra Nevada, in the extreme south of the 

 Iberian peninsula. 



Another important item to be taken into consideration in 

 order to account for the comparative paucity of the Rhopalocera 



