302 



CHAPTER III 



(From Faune de France.) 



FIG. 56. Distribution of two species of the Carabid genus Blethisa. 



Hatched area = Blethisa multipiinctata L., in Europe and western Siberia /or?«a 

 typica, in North America sbsp. aurata Fisch.; overlapping or transgrading area in 

 eastern Siberia. 



Black dots = Blethisa eschscholtzi Zoubk. 



The figured specimen belongs to multipunctata f. typ. 



However, these are exceptions. The rule is that, provided a circumpolar species 

 is at all inclined to subspeciation, the most differing forms appear in western or 

 northern Europe on the one hand, in North America east of Hudson Bay on the 

 other. This applies to the following Carabid beetles: Agonum mannerheimi Dej., 

 Amara alpina Payk., Blethisa multipunctata L. (fig. 56), Miscodera arctica Payk., 

 Nebria gyllenhali Schnh., A'^. nivalis Payk., and Pelophila borealis Payk. 



Unfortunately, the lack of sufficient series of these species from northern Asia 

 does not permit a description of existing cline systems, but the gradients as a rule 

 seem not to be evenly sloping but to form a distinct step within a transitional zone 

 on either side of the Bering Strait: in eastern Siberia at least for Amara alpina, 

 Blethisa multipunctata (fig. 56), Nebria gyllenhali and nivalis; in Alaska or adjacent 

 parts of Canada for Miscodera arctica and Pelophila borealis. Whether this is due 

 to overlapping after previous isolation or to the transitional zone indicating the 

 original centre of the species, I am not able to decide. But the presence, at least in 

 other animal groups, of a common subspecies (Coenonympha tullia, fig. 55; also 

 the sbsp. leptura Hbs. & Schtz. of the Burbot, Lota lota L.), or of two closely 

 related subspecies (Moose, diagr. 10), on both sides of the Strait, from which other 



