266 MICHIGAN SURVEY, 1908. 



more especially of the eastern part of this area), largely north of the 

 U. S. boundary. There is also a marked transcontinental tendency. As 

 these forms do not now occur abundantly even in the mountain regions 

 of the west, it is likely that many have spread northwest in post- 

 Glacial times with tlie Northeastern Biota, rather than from the regions 

 south of the western glaciated area with its relatively arid climate. 



Of these seven species the following four: Cordulia aetiea (C schurt- 

 loffl), Leucorhinia hudsonica and Lihellula quadrimaoulata, are Asiatic 

 (Northern) and European — thus circumpolar. As to the geographic 

 origin of these forms very little can be said, as the taxonomic relations of 

 the Odonata, from a geographic and ecologic standpoint, has never been 

 attempted. Attention, however, should be called to the fact that so far 

 as known, these are all forms that frequent quiet waters. 



There is an interesting correlation between the geographic range of 

 the genera Leucorhinia and Syrnpetrum and the geographic development 

 of the habitat conditions which they frequent. Both are circumpolar 

 in the subarctic region. This same area (especially in America) also 

 furnishes the greatest almost continuous tract of lake, pond and swamp 

 conditions found upon the earth. In North America at least, the base 

 leveling of the region, its imperfect drainage due to glaciation, and its 

 cool climate are the important or dominant factors in, the production 

 of this extensive area of favorable habitats for these genera. It is very 

 probable that many animals, dependent upon such conditions, will show 

 a similar correlation. 



. The powerful Alight of the larger species suggests that the present 

 distribution of the above listed circumpolar species may have taken 

 place under conditions similar to those which exist today. Thus 

 the habitat preferences and the present geographic distribution of the 

 species all suggest a faunal interchange via Alaska and Siberia. Such 

 a change might have occurred during Glacial, inter-Glacial or post-Gla- 

 cial times, but at present we have no criteria or evidence by which to 

 determine such relations. 



The migratory habits of certain species of dragonflies also has a 

 direct bearing upon the extensive range of certain species. One Isle 

 Royale species, Lil)eUiila quadrimaculata, has long been known to mi- 

 grate (cf. Dragon Flies and Mosquitoes, 1890, p. 161). 



REFERENCES. 



Calvert, P. P. 



1893. Catalogue of the Odonata-Dragonflies of the "Vicinity of Phil- 

 adelphia, with an Introduction to the Study of this Group 

 of Insects. Trans. Am. Ent. Soc, 20, pp. 152a-272. 



1905. The Fauna of New England. No. 6. List of Odonata. Occ. 

 Papers Bost. Soc. Nat. His. VII, pp. 1-43. 

 Currie, R. P. 



1901. The Odonata (Alaska Harriman Expedition). Pro. Wash. 

 Acad. Sci., 3, pp. 217-223. 



1905. Dragonflies from the Kootenay District of British Columbia. 

 Proc. Ent. Soc. Wash., 7, pp. 16-20. 



