60 ANNALS NEW YORK ACADEMY OF SCIENCES 



enter practically all of the rivers north of Patagonia and east of the 

 Andes. None of these highland genera need a direct connection between 

 the river basins, because they are fonnd not only above high waterfalls 

 which have been barriers, but also in all of the river basins, some of which 

 are distinctly separated. In this connection, I may note that I saw young 

 Hoplias swimming during a heavy rain in a trail over the highlands of 

 northern Goyaz fully two miles away from the nearest rill. 



I have already stated that the highland genera directly account for the 

 distribution of at least 33 per cent of the entire ichthyological fauna 

 without the necessity of direct connections between the different river 

 basins. Neither river connections nor the existing highland genera,, 

 however, will account directly for all of the species in common between 

 any of the rivers; nor will they explain the more difficult question why 

 so many of the common species have remained identical in river basins 

 which may or may not be connected. In order to answer this most diffi- 

 cult question, I have chosen the cichlid fishes, because they are the best 

 known of any large family of South American animals. 



In brief, the question is, Why are there more species of Cichlidas in 

 common in Guiana, the Paraguay and the Amazon than in the Parana, 

 Uruguay, the coastwise streams of southeastern Brazil and the Amazon? 

 The following list gives the genera of Cichlidse and their distribution. 

 Those marked with an asterisk (*) have few species and are more closely 

 drawn than the others. The word "general" means everywhere north of 

 Patagonia and east of the Andes. 



* Cluetobranchits, Amazon to North, 



* Clicetobranchopsis, Amazon and Paraguay, 



* Cichla, Amazon to north, Orinoco and Guiana, 



* Uraru, Guiana and Amazon, 



* Herotilapia, Lake Managua, 



* Neetroplus, eastern slopes of Mexico and Central America, 



* Acaropsis, Amazon, Guiana and Orinoco, 



* Petenia, Lake Peten, 



* Tomocichla, Costa Rico, 

 HericMhys, Texas to Guatemala, 



* Astronotus, Paraguay, Amazon and Orinoco, 



* N annacara, Essequibo, 



JEquidens, general and western Ecuador, 



Thorichthys, eastern slopes of Mexico and Central America, 



Cichlasoma, general and both slopes of Central America, 



Crenicara, Amazon and Guiana, 



Crenicichla, general, 



* -Retroculus, Amazon, 



Heterogramma, Paraguay, Amazon and Guiana, 

 Gcopliagus, general, 



