1908.] NATURAL SCIENCES OF PHILADELPHIA. 405 



this last heading. I have omitted them, however, because I have no 

 information as to the species of each, and but little as to their distribu- 

 tion. 



Thus we find the Alpine zone with no characteristic mammals, the 

 Hudsonian with three, the Canadian with none and the Transition with 

 seven, while there are six Boreal species (Cervus occidentalis, Eutamais 

 m. consobrinus, Thomomys clusius fuscus, TJiomomys fossor, SyJvilagus 

 pinetis and Neosorex palustris navigator) and one Sonoran-Boreal form 

 {Eutamias quadrivittatus) which probably do not extend much above 

 the Canadian zone, and six which seldom if ever extend below it. In 

 addition to the seven species characteristic of the Transition zone, we 

 find this zone forming the lower limit of eighteen Boreal species and 

 the upper limit of four Sonoran forms. 



While the Alpine zone possesses many characteristic plants, on the 

 mammalian side it is characterized chiefly by the paucity of its fauna, 

 possessing not a single characteristic species. The Hudsonian and 

 Canadian zones have most of their mammals in common, while of the 

 three species characteristic of the former zone, Ochotona saxatilis^^ in- 

 vades the latter to some extent, while on the other hand it occurs in 

 the Alpine zone in suitable places. 



These facts bring out very clearly, I believe, the distinctness of 

 Boreal and Sonoran regions in northern Colorado, as" based on the 

 distribution of the mammals in this territory. The Transition zone 

 is, as its name imphes, a meeting ground of these two great regions, 

 common to, and yet distinct from each. They show further the inti- 

 mate relation between Hudsonian and Canadian zones. Using the 

 mammals only as a criterion, I hardly believe w^e should be justified in 

 separating these zones from each other; their characteristics are rela- 

 tively much fewer than among the plants. 



(2) The movement of some species relative to their centers of dis- 

 persal and notes on the httle known distribution of certain forms. 



The occurrence of a species outside its proper habitat does not 

 necessarily prove a migration on the part of that species from such 

 habitat. It may, on the contrary, mean that the species formerly 

 had a more widespread distribution than at present, becoming second- 

 arily restricted to its present habitat, with the exception of a few strag- 

 glers remaining in the territory formerly occupied by it. This is a 

 question which cannot, in most cases, be settled with our present lack 



" Warren, E. R. : The Mammals of Colorado, Colorado College Publications, 

 Science Series, No. 46, p. 254, mentions the coney as occurring as low as 2,834 m. 

 near Crested Butte. 



