l6o HISTORY OF THE EUROPEAN FAUNA. 



moths (Macro-lepidoptera}\ even those of Siberia have 

 been fairly well investigated. The interesting facts ob- 

 tainable from their distribution are therefore of special 

 value. No less than 243 species of Lepidoptera are 

 mentioned by Moschler as being common to North 

 America and Europe. It is extremely probable that 

 a fair number of these have either migrated direct 

 from America to Europe or vice 'versa, though many 

 may be of Asiatic origin, and have wandered east 

 and west from their original home. The following 

 twelve species are mentioned by Petersen (p. 38) 

 as occurring in Arctic Europe and also in Arctic 

 North America, but not in Asia : Colzas nastes, 

 Colias hecla, Syrichthus centaurece, Pachnobia carnea, 

 Plusia parilis, Anarta Richardsoni, Anarta Schon- 

 herri, Anarta lapponica, Anarta Zetterstedti^ Cidaria 

 frigidaria, Cidaria polata, Eupithecia hyperboreata; 

 and these, as he remarks, point to the possibility 

 of a former direct land-connection between Europe 

 and North America. 



Mr. Petersen believes that the chief immigration 

 into the Arctic area of Europe is post-glacial and 

 took place from Siberia, since the majority of the 

 species are still to be found in that country at the 

 present day (p. 57). He also draws particular atten- 

 tion to a fact, which I shall discuss more fully in the 

 next chapter, namely, that the most characteristically 

 Arctic forms of Northern Europe, which also partly 

 occur in the Alps, are entirely absent from the 

 Caucasus. 



