HASEMAN, GEOGRAPHICAL DISTRIBUTION IN SOUTH AMERICA 57 



static distribution offers only hypothetical evidence of the shakiest kind 

 for any theory. 



Iclithyological Faunal Regions 



In the first part of this thesis, the writer briefly outlined the principal 

 environmental complexes in which the sum total of the natural condi- 

 tions was about equal in each complex. In the following pages, I pro- 

 pose to analyze the changes which have been wrought by the environments 

 on the distribution of the fishes; but before making the analysis, it is 

 first necessary to consider the range of the fishes. 



The Siluridae are found everywhere in South America: The Cichlidse 

 and Characinidse are found everywhere north of Patagonia and east of 

 the Andes. A few Characinidse and Cichlidse are found on the western 

 slope of the Andes of Peru and Central America, and a few are also 

 found in the West Indies. Two species of Characinidse are also found in 

 northern Patagonia. 



The few species found in the West Indies diminish in number of 

 genera the farther the islands are from the mainland There is thus a 

 suggestion that the Cichlidse and Characinidse came directly from South 

 America by way of the sea. I have no doubt that this is true, since by 

 actual experiment I have determined that certain of these genera will 

 live for some time in sea water. 



The Characinidse have never been completely revised, and consequently 

 the genera cannot be of equal value. Notwithstanding this lack of re- 

 vision, the following summary of the genera is instructive. Of the 129 

 genera of Characinidse which have been described, 94 are found in the 

 Amazon Valley, 50 are widely distributed, 60 are found in the Paraguay, 

 64 in the Guianas, 58 in the Orinoco, 54 in the La Plata, 41 in the Sao 

 Francisco and 37 in the coastwise streams of southeastern Brazil. The 

 Paraguay harbors about 60 genera of Characinidse, 58 of which are found 

 in the Amazon. The species belonging to these genera are not usually as 

 similar as are the genera, for example, of the 118 species of Characinidse 

 reported by Eigenmann from the Paragua}', only 63 are found in the 

 Amazon, while 45 of his 47 Paraguayan genera are found in the Amazon. 

 Do the above data indicate a direct connection between the Paraguay and 

 the Amazon ? No, and for the following reasons : 



1. There is at the present day no connection and no indication of an 

 ancient connection, at least since the present iclithyological fauna has 

 developed, at such an altitude as to be favorable for lowland forms to 

 cross from one basin into the other. 



2. No connection is known to exist between the rivers of Guiana and 



