THE ENTOMOLOGIST 



Vol. XXX.] JUNE, 189 7. [No. 409. 



ON THE GEOGRAPHECAL DISTRIBUTION AND POST- 

 GLACIAL DERIVATION OF THE PAL^ARCTIC AND 

 NEARCTIG ALPINE RHOPALOCERA FAUNAS. 



Bv W. IIarcourt-Bath. 



In studying the intricate and complex themes which con- 

 stitute the subject-heading of the present essay, a good deal 

 will be gained from obtaining a preliminary insight into the 

 theories of those botanists who have contributed treatises on 

 the distribution and derivation of the alpine floras in the exten- 

 sive regions under consideration. 



The geographical and vertical distribution of the Rhopalocera 

 in a very great degree is so intimately connected with the distri- 

 bution of their pabula that it is reasonable to suppose they have 

 closely followed the various migrations of the flora upon which 

 they are so dependent, both antecedent to and after the termina- 

 tion of the glacial period. It follows therefore that, in order to 

 intelligently comprehend their present distribution, as well as 

 their post-glacial derivation, we must possess a certain know- 

 ledge of the closely kindred science of pbyto-geography. 



We will flrst of all take a glance at the geographical distri- 

 bution of the alpine Rhopalocera fauna which exist at the 

 present day upon the different and diverse mountain systems in 

 the two regions under consideration. As the genus Erchia is 

 the most extensive and typical group among the alpine butter- 

 flies, it will serve to illustrate with a certain degree of accuracy 

 the facts relating to the whole. 



In the Pala3arctic and Nearctic Regions combined this genus 

 numbers nearly sixty species,* all but seven or eight being con- 



-■• These and the following figures only profess to be approximatelj^ correct. 

 BNTOM. — JUNE, 1897. O 



