INTRODUCTION 
The present report had its inception as a proposed Part II of The Fishes 
of Northwestern South America. Part I consisted of the studies made by C. H. 
Eigenmann, Arthur W. Henn, Charles E. Wilson, and others upon the fishes of 
Colombia, Ecuador, and the Pacific slopes of Peru (Eigenmann, 1922b). Later 
the Fishes of Chile appeared (EKigenmann, 1927), as a separate monograph. Mean- 
while the results of the studies of N. E. Pearson made on the Mulford Expedition, 
extending our work southeastward to tie up with the explorations of J. D. Hase- 
man, were published as ‘‘Part II’’ (Pearson, 1924). 
The work of the Irwin Expedition of Indiana University, in Collaboration 
with the University of Illinois, 1918-1919, was devoted (a) to the completion 
of the above-named studies on west coast fishes; (b) the Chilean monograph; 
and (c) the fishes of the highlands of the Peruvian, Bolivian, and Chilean Andes. 
The first and second-named objectives were carried out principally by Prof. Eigen- 
mann. Through the generous cooperation of the University of Illinois I was able 
to have a part in the expedition, giving my time principally to the third objective 
named above. Through the first portion of the journey Prof. Eigenmann was 
accompanied by his daughter Adele; on the second portion he was unaccompanied. 
After trying his hand at exploration in the highlands, at Oroya, 12000 feet, and 
about Cerro de Pasco, 9000-14000 feet, and descending the Urubamba from La 
Raya, 14000 down to Santa Ana, 3000 feet, Dr. Eigenmann found he must. re- 
linquish the high mountains in my favor by reasons of health. For the remainder 
of the time my apportionment was the third objective mentioned above. 
In addition to studies of fishes, I collected parasitological materials for the 
University of Illinois; earthworms and freshwater sponges being also on the list 
of desiderata. 
Later, 1920, I was sent as traveling fellow of Indiana University to continue 
exploration on down the eastern slopes of the Andes to the Amazon. Collections 
made on that, the ‘‘Centennial’’, expedition are the principal basis of the present 
volume. 
After my return some time remained which could be devoted to a study of 
certain groups. For several years these collections were given intermittent at- 
tention by Prof. Kigenmann and a number of his students. A few species were 
described by Myers, and by Eigenmann and Pearson. The Characins were 
combed through for materials to complete the monograph of that family. My 
Doradidae were studied by Eigenmann and used in his monograph of that nema- 
tognath group. 
By 1925 a not inconsiderable amount of material had been studied and par- 
tially put in writing. This included the first draft of descriptions of many new 
species, and records and notes on most of the Nematognathi. 
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