450 Mr. Wallace on the Geographical Distribution of Birds. 
which must certainly be a mistake. You give 12,000,000 
square miles. Now Balbi gives only 8,500,000 for all Africa and 
Madagascar; and, if we estimate the part of Arabia taken from 
Asia as equal to the part of Africa given to Europe, this will be 
the true area. But I would suggest that such an anomalous 
tract as the Sahara coming between two regions should be given 
to neither; it should in fact be considered as a Sea. It is cer¬ 
tainly quite as unproductive of animal life as the sea, perhaps 
more so; and it gives quite an erroneous idea of the productive¬ 
ness of Tropical Africa to add this immense desert to it. I take, 
therefore, Africa south of the Sahara, and after reaching the Nile 
as far north as the 1st Region, following a diagonal across Arabia 
from Mount Sinai to the eastern extremity. A careful measure¬ 
ment gives me the area of this with Madagascar as 6,500,000 
square miles. 
3. Indian Region. Of this we have already defined the north 
limit, and I would add a tract of Arabia on the western shores 
of the Persian Gulf. Its south-eastern limits I draw between 
the islands of Bali and Lombok; and between Celebes and 
Borneo, and the Moluccas and the Philippines. Barbets reach 
Bali, but not Lombok; Cacatua and Tropidorhynchus reach 
Lombok, but not Bali : this I think settles that point. Ca¬ 
catua, Trichoglossus, and Scythrops in Celebes, and not in Borneo, 
settle the other. No doubt many Indian forms reach Celebes; 
but we must remember the proximity, and in the course of ages 
the only wonder is there has not been more intercommunication. 
A careful estimate of these islands, with Formosa, &c. added to the 
continental portions, gives an area of only 3,100,000 square miles. 
4. Australian Region. You have rather over-estimated this : 
with the Moluccas, &c., North Guinea, New Zealand, and the 
Pacific Islands (except the Sandwich, which I think should go 
with America), I cannot make an area of more than 2,600,000 
square miles. In the island of Batchian I have found Podargus, 
Coriphilus, and Paradisea , which shows that the several sub¬ 
divisions of this region are very closely connected. 
5 and 6. North and South American Regions. I put the 
limit between these at 22° N.; on the coast it may be further 
north, on the table-land further south, but this will be near the 
