GEOGRAPHICAL DISTRIBUTION 325 
river whence it has its name, but the peculiarities of the lower 
portion not being observable in the higher tributaries of that 
mighty flood, its upper waters must be regarded as draining land 
that belongs to another Subregion, which, intervening between the 
Patagonian and first the Brazilian and next the Amazonian, in- 
cludes all that is left of South America, and has been named the 
“Subandean.” ‘To this also belong on the one side the Galapagos 
—ever memorable as the place where, as Darwin has told us, there 
first dawned on him, from a consideration of their Birds, the 
doctrine of Natural Selection, which has led to such fruitful and 
stupendous results—and on the other side Trinidad and Tobago, 
beside the islands on the northern coast of South America. This Sub- 
region reaches the ‘ Central American” in the Isthmus of Panama, 
and of the limits of this last none can yet speak with certainty.! 
The difficulty of distinguishing these Subregions is very great, 
and the close alliance between all but the Patagonian and Antillean 
will be plain to any one who analyzes the differences as shewn by 
the prevalence in them of the various Families of Birds peculiar 
to the whole Region.2 That the most characteristic features are 
exhibited by the Patagonian none can doubt, and indeed therein 
we find, as might be expected, the nearest resemblance to the 
Fauna of New Zealand or the Australian Region, and some of the 
best evidence of the antiquity of its population. These are the 
1 Messrs. Godman and Salvin, and there can be no better authorities, suggest 
(Ibis, 1889, p. 242) that the northern limit of certain species of Psittaci ‘‘ may 
be almost said to define the boundary between the Nearctic [Holarctic] and Neo- 
tropical Regions.” They also point out that the same limit is practically that of 
the T'rogonidz, and on the eastern side that of the Momotidz. It is also the 
termination of the Cracidz, with the exception of an Ortalis, and of the Tinamidz, 
while among the Passeres the same boundary confines Pachyrhamphus, one of 
the Cotingidz, an essentially Neotropical Family, on both sides. ‘‘ From this it 
will be seen that the line of demarcation between the two regions, so far as the 
birds are concerned, is capable of being defined with some precision, and will be 
found to coincide with the northern limits of the forests. These on the eastern 
side leave the coast a little north of Tampico, and continue in a narrow belt along 
the eastern flank of the mountains in a nearly northern direction almost to 
Monterey. On the western side a similar state of things is found, and we.meet 
with a number of southern forms extending along the western slope of the 
mountains as far as Alamos” in Sonora. 
2 It is only in deference to Mr. Salvin’s views that I do not rank the Subandean, 
Brazilian, Amazonian, and Central American areas as Provinces, and group them 
to form a single Subregion. Recognizing of course the Antillean Subregion, I 
hold the existence of a Patagonian Fauna to be unquestionable, whatever be its 
geographical limits ; but as regards the rest I am prepared to find that future 
consideration will justify the suggestion just made, so that the Neotropical 
Region will be deemed to be composed of three Subregions only, the Antillean, the 
Patagonian, and one which (comprehending the four areas above named), for 
want of a better epithet, might perhaps be called the ‘‘ Columbian.” 
