30 Hjalmar Ostergren. [No. 9 



are principally arctic or principally boreal. It is usual, especially 

 when dealing- with molluscs, to conclude that a species has its real 

 home in the region, in which it attains the greatest dimensions. 

 This method can, however, hardly be adopted in this particular 

 case. Besides, I must confess that I cannot regard the results, 

 arrived at in such a way, as altogether reliable. 



