x BIRDS OF LA PLATA 
belongs to the Patagonian Sub-region of the Neo- 
tropical Region. 
The species known to me personally number 233, 
but many more have been added since I left the 
country. The exclusively Neotropical types in my 
list include Tanagers, Trupials, Tyrant-birds, Plant- 
cutters, Wood-hewers, Ant-birds, Gallito birds, Hum- 
ming-birds, Screamers, Courlans, Jacanas, Seed- 
snipe, Tinamus, and Rheas—in all eighty-four 
species. 
Thus in this district the exclusively South American 
forms, or families, are in a minority ; but if we take 
the whole of the Argentine country, these exclusive 
forms and the widely-distributed forms are pretty 
evenly balanced. Finally, if we take the entire 
Neotropical Region we find the exclusively South 
American forms in a majority. The Humming- 
bird family alone numbers over four hundred 
species, the Tanagers about the same number, 
while two other Passerine families, Tyrants and 
Woodhewers, count together five hundred at least. 
We have also to take into account that in the 
families that are universal in their distribution there 
are groups, genera and sub-families greatly modified 
in form. Thus, in the Thrush family we have the 
Mocking-birds, and as in the Thrush family so do 
we find divergent types in Wrens, Finches, Cuckoos 
and other families. 
To sum up. We have in the universally distri- 
buted families, groups and genera, which exhibit the 
peculiar impress of the region they inhabit (in this 
