480 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



made; aud this would be fully justified by the observations published 

 in regard to European species. We would then have — 



N. JEschscholzii Mann, as a color variety or race of N. Mannerheimii 

 Esch. ; 



JV. obtusa Lee. as a color variety of W. obliqua Lee. 



Of the species thus reduced, the only ones which exhibit a close rela- 

 tionship to Palsearctic forms are the hyperborean Groups III and IV. 

 Of the latter, I am disposed to believe that N. obtusa and obliqua are 

 preGlacial Eocky Mountain species, while all the others are dispersions 

 from the later Tertiary circumpolar land, from which came aaany of the 

 forms identical, or representative, now found in the northern parts of 

 both continents. 



Groups I and V must be considered as peculiarly belonging to the 

 Pacific region, and not derived from Glacial migration. 



Group VI is similarly related to the Atlantic region. Of Group II, 

 the Californian and tht two Kocky Mountain species cannot be con- 

 nected with Glacial migration, and were, therefore, probably pre-exist- 

 ing species in situ during part of the Tertiary age ; JV". carbonaria, from 

 its resemblance to some species of Group IV, belongs to the circum- 

 polar dispersion. 



Collections made along the edge of retreating snow-fields in the 

 higher parts of the Coast Range, Sierra Nevada, and Eocky Mountains 

 will probably show the existence of other species of the groups peculiar 

 to those regions ; but as yet the materials from high mountain eleva- 

 tions are very scanty. 



