362 
ORIGIN OF LIFE IN AMERICA 
its nearest relations are all marine forms, its ancestors, as 
Professor Eigenmann * remarks, could only have entered the 
area when it was still a gulf of the sea. 
In the Eocene Period “ Archiguiana,” as Dr. von Ihering 
named the ancient highland of Guiana and eastern Venezuela, 
was supposed by this writer to have been isolated from the 
highland of Brazil. And, indeed, the mountain plateau of 
Guiana contains a very large number of archaic and most 
peculiar types, some of which seem to spread westward into 
Venezuela and Colombia rather than into Brazil. Yet the 
great majority of these ancient forms of Guiana also occur 
southward in eastern Brazil. One of the most noteworthy 
birds, the hoatzin (Opisthocomus hoatzin), whose young 
climb about among the branches of the trees by means of 
well-developed claws on their wings, and which have been 
placed into a distinct order by themselves, range southward 
as far as Bolivia. The chatterers (Cotingidae) comprising 
some of the most ornate and peculiar birds of South America, 
are almost equally divided between Brazil and Guiana. The 
familiar umbrella bird (Cephalopterus ornatus), the bell bird 
(Casmorhynchus niveus), the bald-headed crow (Gymnoce- 
phalus calvus), and the cock-of-the-rock (Rupicola crocea), all 
belong to genera which have spread westward from Guiana 
rather than into Brazil. In all these cases we have to deter¬ 
mine what was the original centre of dispersal. The singular 
genus of snails Ampullaria probably spread across South 
America from a Brazilian centre, and so did the fresh-water 
crab (Pseudothelphusa) and the whole family of fishes called 
Cichlidae. The snail Strophocheilus, the fresh-water mussel 
Unio, the archaic arthropod Peripatus, the family of tortoises 
Cinosternidae and others, have apparently entered Brazil from 
the north and west. As I shall endeavour to show 1 in the next 
chapter, many of the forms that have spread from the Brazi¬ 
lian highlands have near relations in Africa, while among the 
northern and western immigrants into Brazil scarcely any 
have succeeded in crossing the Atlantic area to Africa. 
Eigenmann, 0. II., “ Freshwater Fishes of South America,” p. 521. 
