THE NEARCTIC REGION 



167 



2. Nearctic — those not found beyond the limits of the 

 Nearctic Region. 



3. Neogean — those found in the New, but not in the 

 Old World. 



4. Arctic and Palxogean — those which are found in the 

 Old World, and only in the Canadian Sub-region of the 

 New ; and, finally — 



5. Neogean and Palmogean — containing the most 

 widely distributed forms. 



Section V. — The Western or Arid Sub-region 



This Sub-region is, on the whole, the richest of the three, 

 both as regards the total number of genera found within its 

 limits and also as regards the number of genera peculiar 

 to it, which amounts to seven out of fifty-three, as com- 

 pared with four out of forty in the Canadian, and one out 

 of forty in the Eastern. 



The Western Sub-region shares with the Eastern the 

 only representative of the Marsupials found in North 

 America, the Virginian Opossum. Just extending, too, to 

 within its limits occurs the only member of the Order 



