/Egeriidae 



miles of species which are in many cases distinctly subtropical. 

 On the high peaks holarctic genera occur, and in the valleys genera 

 which have their metropolis in Mexico. In a general sense the 

 territory may be called the Coloradan subregion. 



The Pacific subregion includes central and northern California 

 and the valleys lying between the coast and the western outliers 

 of the central Cordillera. The subregion extends northward into 

 British Columbia. There is shown here a distinct resemblance to 

 the fauna of Europe and temperate Asia. 



Beginning in Labrador on the east and 'extending across the 

 entire northern portion of the continent into Alaska is a region 

 which we may call the Holarctic subregion, in which the genera 

 and species alike of plants and animals are for the most part the 

 same which are found in similar latitudes in the Eastern Hemi- 

 sphere. In Alaska there is evidence of a distinct connection be- 

 tween the flora and fauna of Asia. Greenland and Labrador, 

 together with some of the adjacent islands, show remarkable 

 affinities to the flora and fauna of boreal Europe and the Alps. 



Various subdivisions of these broader areas have been sug- 

 gested, but in the main the subregions which the writer has 

 indicated suffice to show the differences in these tracts. 



"... From every chink 

 And secret corner, where they slept away 

 The wintry storms or rising from their tombs 

 To higher life by myriads, forth at once, 

 Swarming they pour, of all the varied hues 

 Their beauty-beaming parent can disclose. 

 Ten thousand forms ! ten thousand different tribes ! 

 People the blaze." 



THOMSON. Summer, 



390 



