2 Merriam — (JcograpJiic JJistrtbidion of Life. 



Page. 



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



Lists of Boreal genera and snbgenera 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 Eegion (comprising Upper and Lower Sonoran Zones) 26 



Lists of genera and subgenera of Sonoran ]\lanunals 2G 



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 IMammals 34 



Table showing the Geographic Distribution of North American Genera 



of non-pelagic Mammals occurring north of Mexico SO 



Boreal Genera. 30 



Sonoran Genera 3(5 



Tropical Genera 3() 



Transition Zone Genera 30 



Genera inhaliiting hcAh Boreal and Sonoran Eegions 30 



Distinctness of the Tropical Eegion from the Sonoran 37 



The Sonoran not a Transition Eegion 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 



Eemarks respecting some of Wallace's Fallacies 49 



Mountains as ))arriers to dispersion .*• 50 



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



evidence on which they are based 50 



Pahearctic and Nearctic Eegions 58 



Peculiar Genera of ]\Iannnals inhabiting North America north of 



Mexico 01 



Of Boreal origin '>1 



Of Sonoran origin 01 



Principles on which Bio-Geographic Eegions should be estab- 

 lished 04 



Introductory Remarks. 



Nine years ago the Biological Society listened to an address 

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

 Principles of Zoogeogra})hy,'' or the science of the geographical 

 distribution of aninuils.'^~ Professor Gill assembled the oceans of 

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



*Proc. Biological Societv of Washington, vol. II, 1884, 1-39. 



