86 PROCEEDINGIS OF THE NATIONAL MUSEUM. vol.54. 



Our montane zone seems to correspond to the North European 

 lakes. The isotherm indicating the mean annual temperature at 

 this elevation in the mountains of Colorado passes through the coun- 

 tries he assigns to this zone. The agreement of faunas is also evident. 

 Certain. species, most of which do not reach into the arctic regions, 

 are common in the North European lakes and also in our montane 

 zone. Chief among these are the following: Latona setifera, Daphnia 

 longispina, Ceriodaphnia reticulata, Simoceplialus vetulus, S. serrula- 

 tus, Scapholeheris mucronata, Strehlocerus serricaudatus, Eurycerus 

 lamellatus, Camptoccrcus rectirostris, Acroperus Tiarpae, Graptoleheris 

 testudinaria, Alona guttata, Depanofhrix dentata. Tliese species are 

 common in our montane zone, though not confined to it, and do not 

 commonly reach into the alpine zone. Thus it seems that our two well- 

 defined mountain zones correspond to the two most northerly zones 

 recognized by Wesenberg-Lund. It is probable, however, that the 

 most extreme conditions met with in our alpine zone are less extreme 

 than the most extreme of the arctic zone. 



If we carry the comparison further, we may compare the plains 

 zone with the Central European lakes 'of the level country, except 

 so far as our conditions are specialized and local in their nature due 

 to the arid climate. Wesenberg-Lund comments on the very great 

 similarity (large number of common species) between the plankton 

 of Central Europe and temperate North America. 



The above writer is unable, because of the relatively small amount 

 of data, to clearly recognize in America zones corresponding to those 

 of Europe. Judging partly by the mean annual temperatures and 

 partly by the available records of the distribution of plankton Crus- 

 tacea it appears that the Hudson Bay region and Labrador correspond 

 to the arctic zone, and that the region from Lake Superior and east- 

 ward to Newfoundland represents the zone of the North European 

 lakes. Just where lines should be drawn between zones in the 

 western portion of Canada and in Alaska is not clear except that 

 the mountainous nature of this area causes the lines to curve far 

 southward. It is accordingly not possible definitely to refer the 

 different zones represented in the Colorado mountains to their posi- 

 tion in the scheme of general distribution on this continent. This 

 much is certain, that the alpine zone is a true southern extension of 

 arctic condition and of arctic fauna along the higher parts of the 

 Rocky Mountains. 



The great similarity between the fauna of the higher Rocky 

 Mountains and that of the Alps has already been pointed out. Each 

 resembles the fauna of arctic regions. There is this difference: 

 While the alpine fauna of the Colorado Rockies is a direct southern 

 continuation, without interruption, of an arctic fauna, that of the 

 Alps is separated from the corresponding arctic fauna by intervening 



