lU'TTKKFLlKS OF TWO WOKI.DS. 439 



which lia.s there tor its eonipaiiioii many very ehj.sely allied speeicci. I'ierif 

 oleraeea, almost our only native speeies of Pieris, considered by many as the 

 same as Pieris napi of the Old World, has also many allies in the Old 

 World, and therefore, like Pieris raj)ae, piohahly ori<>inated there. 

 Finally Pamphila, rejn-esented in this country hy only a single species, 

 P. mandan, widely separated from all its allies, a strong flier and extend- 

 ing to Alaska, belongs to a genus represented in the Old World with 

 its immediate allies by several peculiar types, which range across the entire 

 l)readth of the continent ; we must therefore look upon this species as one 

 introduced from the Old A^'orld, but at a period of time so long ago as to 

 have become fairly distinct from the primal stock. 



If now we tiu'n our attention to the butterflies found north of our 

 boundary and not extending into it we shall find a considerable assemblage 

 of species, from twenty-five to thirty in nimiber, belonging to as many as 

 thirteen genera : and we shall at once be struck by the fact that in every 

 case these genera are represented either by the same or by allied species 

 in the Old World ; and what is more, that in all cases but one they are 

 more, often much more, bountifully supplied with distinct forms in the 

 Old World than in the New. Thus we find two species of Oeneis, both 

 of which occur in Europe, four of Ei-ebia, and two or three of Coeno- 

 nympha, all considered distinct from those of Europe, and confined to the 

 western half of our continent; five species of Brenthis, of which three are 

 looked upon as identical with those of Europe, and one of Lemonias ; one 

 each of the lycaenid genera Cupido, Agriades and Epidemia, all distinct 

 from the European species, five or six species of Eurymus, of which at 

 least two are found in Europe, one of Pontia, tw'o of Parnassius, one 

 of which is found in Europe, the same of Papilio, and finally one of 

 Erynnis, which also occurs in Europe. This last genus is the (me to 

 which we referred as being far more developed in America than in 

 Europe ; indeed, the European species, E. comma, is only known upon 

 our continent by a varietal form occurring in Labrador. 



Of the 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 

 tlie western half of the continent, and show a distinct geographical relation 

 to Alaska. AMiile on the other hand, not one of the genera is confined 

 to the eastern half ; and besides this not any genus of American butter- 

 flies not found in Europe, with the sole exception of Phyciodes 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 dear that the identity or intimate resem- 

 blance which occiu's in certain species between the butterflies of Europe 



