214 ORIGIN OF BUTTERFLIES 



Pearl Skipper (E. comma), is only known upon 

 our continent by a varietal form occurring in 

 Labrador. 



Of tlie above thirteen genera we further notice 

 that the species of no less than five of them — 

 Erebia, Coenonympha, Lemonias, Cupido, and 

 Parnassius, including a dozen of the species — are 

 altogether confined to the western half of the con- 

 tinent, and show a distinct geographical relation to 

 Alaska. While on the other hand, not one of the 

 genera is confined to the eastern half ; and besides 

 this not any genus of American butterflies not 

 found in Europe, with the sole exception of Phyci- 

 odes and Basilarchia (by a single species in each 

 case), shows any special tendency to extend its 

 domain toward Alaska. The avenue of migration 

 is thus clearly marked. 



It would seem, therefore, very clear that the 

 identity or intimate resemblance which occurs in 

 certain species between the butterflies of Europe 

 and America is due altogether to their boreal char- 

 acter ; that their occurrence on the two continents, 

 looked at from a broad point of view, must be re- 

 garded as the consequence of a continuity or close 

 proximity of land during later tertiary times, when 

 a warm climate prevailed in the high north ; and 



