THE NEOTROPICAL REGION 75 



The inspection of this table will show at a glance that 

 the Central- American Sub-region is predominantly " Neo- 

 tropical " as regards its mammals, but has received a small 

 immigration of Nearctic forms, and possesses only few 

 endemic types. 



Section VI. — The Guiano-Brazilian Sub-region 



This extensive area, in which is combined three of the 

 Sub-regions usually allotted to Birds, is the largest and by 

 far the richest of the four divisions of the Neotropical 

 Region adopted in the present article. It extends from the 

 Isthmus of Panama in the north to about 30° south 

 latitude. But the southern frontier between this and the 

 Patagonian Sub-region is very undecided, the Fauna of 

 Uruguay and the northern part of the Argentine Republic 

 containinsr forms characteristic of both Sub-regions. The 

 western boundary is formed by the well-watered and 

 forest-clad western slopes of the Andes, the waterless 

 eastern slopes, together with the western slopes of Peru and 

 Bolivia from the neighbourhood of the Equator downwards, 

 being referable to the fourth or Patagonian Sub-region. 



The greater part of the Guiano-Brazilian Sub-region 

 consists of forest, and the Mammalian fauna, though 

 tolerably abundant, is not nearly so profuse as that of the 

 Birds and Insects, which are here both developed in far 

 greater luxuriance than in any other part of the world. 



This Sub-region is more especially the home of the 

 peculiar Platyrrhine monkeys, the arboreal Sloths, and 

 other tree -loving Mammals. 



Beginning at the bottom of the list, we find that nearly 



