VII. ON FURTHER COLLECTIONS OF FISHES FROM 

 PARAGUAY. 1 



By Carl H. Eigenmann assisted by Waldo Lee McAtee and 

 David Perkins Ward. 



The fresh-water fish fauna of tropical America is by far the richest 

 in the world. It comprises about one tenth of all known fishes. It 

 is entirely distinct from the North American fauna and from the Pata- 

 gonian fauna. Its center of greatest diversity lies in the Amazons 

 about the mouth of the Rio Negro. From this point it becomes at- 

 tenuated northward until it reaches the vanishing point on the borders 

 of the United States. Southward it extends on the eastern slope to 

 somewhere, no one knows exactly where, south of Buenos Aires. On 

 the western slope it does not extend so far south. 



The key to the great diversity of the tropical American fauna is 

 to be found in the enormous single water system extending from io° 

 north to 35 ° south latitude, and from 50 to 79 west longitude, pro- 

 viding a continuous north and south water-way of more than 3,000 

 miles and an east and west course of over 2,000 miles. It embraces 

 the basin of the Orinoco, the basin of the Amazons, and the basin of 

 the La Plata, draining over 3,000,000 square miles of territory, or an 

 area about equal to that of the entire United States, exclusive of 

 dependencies. It has long been known that the Orinoco and the 

 Amazons are connected by the Cassiquiare, the waters of which at 

 times flow one way, at times another. The following is from the 

 ' ' United States of Brazil ' ' issued by the Bureau of American Republics. 



" Another remarkable phenomenon of the Paraguay is the mingling 

 of its principal head waters with those of the affluents of the Amazon. 

 An affluent of the Jauru River is sufficiently near the Guapore River 

 to be connected with the latter by a canal. The Aguapehy, another 

 tributary of this river, is separated from the Alegre by a narrow isth- 

 mus 5 kilometers wide. In the eighteenth century an attempt was made 

 to open up a canal here, and owing to the abundant rains a large canoe 

 of twelve oars succeeded in passing from the one river to the other. 

 One of the governors of the State also endeavored to open up a canal 



1 Contributions from the Zoological Laboratory of Indiana University, No. 65. 



110 



