528 POPULAR SCIENCE MONTHLY 



The origin and distribution of the fresh-water fishes of tropical 

 South America have come about as follows : In the earliest tertiary 

 tropical America consisted of two land areas, Archiguiana and 

 Archamazona, separated by the lower valley of the Amazon, which was 

 still submerged. There was a land mass, Helenis, between Africa and 

 South America, possibly in contact with Guiana in South America 

 and some point in tropical Africa. 1 



This land mass was inhabited, among other things, by Lepidosiren- 

 idas, Pceciliidse, Characinida?, Cichlidae and Siluridse. This land-mass 

 sank beneath the surface of the ocean, forcing the fauna in two direc- 

 tions, towards Africa and towards South America, exterminating all 

 types not moved to the east or the west. From these two rudiments 

 have developed the present diverse faunas of Africa and South America, 

 each reinforced by intrusives from the ocean and neighboring land 

 areas and by autochthonous development within its own border. The 

 one fauna can not be said to have been derived directly from the other. 



The connection between Africa and South America existed before 

 the origin of present genera and even before the origin of some of 

 the present subfamilies and families, some time before the earlier ter- 

 tiary. There has never been any exchange between Africa and South 

 America since that time. 2 There must have been an intimate con- 

 nection between these two continents, for there is no evidence such as 

 identical species or genera on the two coasts to indicate an occasional 

 or accidental exchange of types across the Atlantic since the formation 

 of existing genera, therefore such an interchange across the ocean prob- 

 ably never took place. The east Brazilian land mass south of the 

 Amazon (Archamazona) must have become stocked from the western 

 end of Helenis, or Archiguiana, very early, for it contains many genera 

 peculiar to the region, indicating a long separation, and tertiary fresh- 

 water deposits in this area contain existing genera of fresh-water fishes. 



When, later, the Cordilleras arose out of the ocean at a distance 

 from Archiguiana and Archamazona too great to be traversed by colo- 

 nists from them, their developing streams and arms of the sea, con- 

 nected with brackish, and, later, fresh-water lakes, all became populated 

 with marine types. In the north where they later came into competi- 

 tion with immigrants from Archiguiana most of them were extermi- 

 nated with the continued elevation of the land. On the south, which 

 was not, or not so easily, reached by immigrants, Orestias, Gastropterus 

 and Protistius remain in the high Cordilleras of southern Peru as 

 relicts of these marine species. Later, as the distance between the 



1 This paragraph is an outline of part of von Ihering's Archiplata-Arch- 

 helenis theory. 



2 There has been a remarkable parallelism in the evolution of genera of 

 cichlids, characins and catfishes on the two continents that I hope to take up 

 in another place. 



