﻿Contribution from the Zoological Laboratory of Indiana University, 



No. 177 



The Magdalena Basin and the Horizontal and 

 Vertical Distribution of Its Fishes 



By Carl H. Eigenmann 



The Magdalena basin lies in western Colombia and drains the 

 entire area of Colombia between the Cordillera of Bogota, also 

 called Oriental, and the Cordillera Occidental except a small 

 corner south of Popayan. Its western boundary consists of the 

 oldest (Occidental) Cordillera which extends from Cartagena 

 the entire length of the continent to Cape Horn. Nowhere in 

 Colombia does it reach the height attained by it south of Colombia. 

 Its eastern boundary consists of the much higher eastern crests 

 of the Cordillera of Bogota. The Cordillera Central separates 

 the Magdalena valley proper from the Cauca valley. The 

 Cordillera Central is older than the Cordillera of Bogota, hence 

 the Cauca flowing between the oldest chains in Colombia must be 

 the oldest part of the Magdalena basin. 



The Magdalena basin is surrounded by high mountain barriers 

 except in the northwest where low areas separate it from the basins 

 of the Sinu and of the Atrato beyond. It is the reservoir from 

 which the Atrato and thru the Atrato the San Juan to the south 

 and the Tuyra, Chepo, and Chagres to the west and north, got 

 part of the ancestors of their present fresh-water fish fauna. 

 Where did the Magdalena get its fishes? 



Physical Features of the Magdalena Basin. The Magda- 

 lena basin may conveniently be divided into five sections: 



(1) the Andean torrents flowing from the heights to the valleys; 



(2) the Upper Cauca; (3) the Upper Magdalena; (4) the Lower 

 Magdalena; and (5) the Cesar. 



The Cauca and the Magdalena rise near the second degree 

 of North latitude. They unite near 9° 30' North latitude and 

 empty near 11° north into the Caribbean Sea. 



Veatch {Quito to Bogota, 1917) says of the Cauca: 



The three great physiographic provinces between the Cordillera del 

 Choco (Occidental) and the Cordillera del Quindio (Central) are thus; 



