2 Merriam Geographic Distribution of Life. 



Page. 



Boreal Region (comprising Arctic, Hudsonian, and Canadian Zones) . 22 



Lists of Boreal genera and subgenera 23 



List of Arctic Mammals 24 



List of Mammals common to Arctic and Hudsonian Zones 24 



List of Mammals of the Boreal Zone 24 



Sonoran Region (comprising Upper and Lower Sonoran Zones) 26 



Lists of genera and subgenera of Sonoran Mammals 26 



Lists of genera and species of the Transition Zone 32 



List of Tropical families of Mammals north of Panama 33 



List of Tropical genera of North American Mammals 34 



Table showing the Geographic Distribution of North American Genera 



of non-pelagic Mammals occurring north of Mexico 36 



Boreal Genera .">(> 



Sonoran Genera 36 



Tropical Genera 3(5 



Transition Zone Genera 36 



Genera inhabiting both Boreal and Sonoran Regions 36 



Distinctness of the Tropical Region from the Sonoran 37 



The Sonoran not a Transition Region 38 



Differentiation of Life from the north southward 39 



Origin of Types and Faunas Geologic Evidence 41 



Glacial Epoch 41 



Causes controlling Distribution 45 



Effects of Humidity contrasted with effects of Temperature 47 



Remarks respecting some of Wallace's Fallacies 49 



Mountains as barriers to dispersion 56 



The so-called Eastern, Central, and Western Provinces and the 



evidence on which they are based 56 



Paleearctic and Nearctic Regions .- 58 



Peculiar Genera of Mammals inhabiting North America north of 



Mexico 61 



Of Boreal origin 61 



Of Sonoran origin 61 



Principles on which Bio-Geographic Regions should be estab- 

 lished... 64 



INTRODUCTORY REMARKS. 



Nine years ago the Biological Society listened to an address 

 from its distinguished retiring President, Professor Gill, on " The 

 Principles of Zoogeography,'' or the science of the geographical 

 distribution of animals.* Professor Gill assembled the oceans of 

 the globe, as well as the land areas, into primary divisions or 



*Proc. Biological Society of Washington, vol. II, 1S84, 1-39. 



