THE CANADIAN ENTOMOLOGIST. 197 



ON THE GEOGRAPHICAL DISTRIBUTION OF NORTH 

 AMERICAN LEPIDOPTERA. 



BY AUG. R. GROTE, A. M. 



(Continued.) 



The Study of the forms referable to the first or European element in 

 the North American Moths, is complicated by the circumstance of the 

 great range in the character and amount of the differences separating the 

 related species now living so widely apart. These related species are 

 found, in fact, to offer also difficulties as to their correct nomenclature. 

 We have seen that the term "representative species," like that of " pro- 

 phetic types," hides the real significance of the inter-resemblance which 

 is that of a common descent. In naming these " representative " forms 

 we must be guided by the rule that where the differences are such that the 

 species would be considered distinct if members of a common fauna, a 

 different specific title must be given them, but where these differences are 

 slight, and what, under the same supposition, would be considered only 

 varietal, the species must be considered as still identical, though separated 

 so long in time and by so wide a space. The study of those forms which 

 are practically identical is, as we have seen, further complicated by the 

 difficulty of deciding as to whether they may have been introduced since 

 the discovery of the New World by the Spaniards, or whether the species 

 have continued unaltered since the Tertiary in both America and Europe. 

 While certain species such as Scoliopteryx are undoubtedly in this latter 

 case, it is less easy to feel so sure with regard to this in instances like 

 Dipterygia Pinastri and the various identical forms of Agrotis, but on 

 the whole I am inclined to believe that the number of species artificially 

 exchanged is very small, and that these identical species have simply 

 proved more constant and are of an older type than the rest. An agent 

 which, however, must not be omitted in the interchange of species of 

 insects is the voluntary importation by collectors for purposes of acclima- 

 tization, deception, or from a desire to destroy, through the introduction 

 of injurious species, the crops of another country. It seems quite clear 

 that the Natural History of most insects precludes the idea of their im- 

 portation in an accidental way by commerce. It seems certain that the 

 Colorado Potato Beetle never found its way to Europe in cargoes of 

 vegetable provisions. Where it was found on the Continent it was evi- 



