CHAP. XVIII.] 
BIRDS. 
331 
African Psittams , have been found. But the origin of so wide- 
spread, isolated, and varied a group, must be far earlier than 
this, and not improbably dates back beyond the dawn of the 
Tertiary period. Some primeval forms may have entered the 
Australian region with the Marsupials, or not long after them ; 
while perhaps at a somewhat later epoch they were introduced 
into South America. In these two regions they have greatly 
flourished, while in the two other tropical regions only a few 
types have been found, capable of maintaining themselves, among 
the higher forms of mammalia, and in competition with a more 
varied series of birds. This seems much more probable than 
the supposition that so highly organized a group should have 
originated in the Australian region, and subsequently become 
so widely spread over the globe. 
Order IV.—COLUMBM 
Family 84.— COLUMBID.E. (44 Genera, 35o Species.) 
General Distribution. 
Neotropical 
Sub-regions. 
N EARCTIC 
Sub-regions. 
Pa t..*: arctic 
Sub-regions. 
Ethiopian 
Sub-regions. 
Oriental 
Sub-regions. 
Australian 
Sub-regions. 
1 . 2 . 3.4 
1 . 2 . 3 .4 
1 . 2 . 3 .4 
1 . 2 . 3 .4 
1 . 2 . 3. 4 
j 1 . 2 . 3 . 4 
The Columbidse, or Pigeons and Doves, are almost universally 
distributed, but very unequally in the different regions. Being 
best adapted to live in warm or temperate climates, they dimin- 
ish rapidly northwards, reaching about 62° N. Latitude in North 
America, but considerably farther in Europe. Both the Neuro- 
tic and Palsearctic regions are very poor in genera and species 
of pigeons, those of the former region being mostly allied to 
Neotropical, and those of the latter to Oriental and Ethiopian 
types. The Ethiopian region is, however, itself very poor, and 
several of its peculiar forms are confined to the Madagascar sub- 
region. The Neotropical region is very rich in peculiar genera, 
though but moderately so in number of species. The Oriental 
