﻿Contribution from the Zoological Laboratory of Indiana Uni- 

 versity, No. 181. 



The Fishes of the Rivers Draining the Western 

 Slope of the Cordillera Occidental of 

 Colombia, Rios Atrato, San 

 Juan, Dagua, and Patia 



By Carl H. Eigenmann 



The rivers mentioned in the title, and many others between 

 them or tributary to them, with one exception, rise in the western 

 Andes of Colombia and flow westward, for a space, at least. The 

 Patia forms the exception. It has cut thru the western Cordillera, 

 rising in and draining the inter-andean parks between Popayan 

 and Tulcan. The Cordillera Occidental is the oldest of the Cordil- 

 leras and extends from near Cartagena, on the northern coast of 

 Colombia, to Cape Horn. For the most part the western slope 

 of this Cordillera within Colombia is extremely wet. 



A. THE ATRATO AND SAN JUAN 



The particular interest in this region centers in the Rios Atrato 

 and San Juan. They flow between the Cordillera Occidental 

 to the east of them, and the coastal Cordilleras to the west of 

 them. They rise on the western slope of the western Cordil- 

 leras, flow westward for a space, and then the Atrato turns north, 

 gathering many tributaries to flow into the Caribbean Sea. The 

 San Juan turns south, also gathering many tributaries, and 

 empties into the Pacific. The continental divide, separating their 

 headwaters at Istmina, is little more than 300 feet above sea-level. 



A general subsidence of but 300 feet would drown the Atrato 

 valley, extending the Gulf of Uraba to Tambo, just north of 

 Istmina, and would extend the Gulf of Buenaventura to above 

 Istmina. The Atlantic and Pacific would be separated by a ridge 

 less than 5 miles wide and less than 50 feet high. The tributaries 

 of the Atrato and San Juan would be reduced to short mountain 

 torrents. 



In a general program for the investigation of the freshwater 



