I. THE FISHES OF THE RIO BENI BASIN, BOLIVIA, 
COLLECTED BY THE MULFORD EXPEDITION 1 
By Nathan Everett Pearson, Assistant in Zoology, 
Indiana University 
As a part of the general plan for the study of the fishes of 
the eastern slope of the Andes the author was enabled to join 
the “Mulford Expedition” 2 3 to Bolivia. The field expenses 
were paid by the Mulford Expedition. The expenses to La 
Paz, Bolivia, and from Manaos, Brazil, home were provided 
by grants from the University of Michigan, the Bache Fund 
of the National Academy of Sciences, 2 and Indiana University. 
The equipment was provided by Indiana University. 
I sailed from New Orleans on May 25, one week before the 
rest of the Mulford Expedition. The extra time was spent 
collecting in the lower Tambo River in southwestern Peru, 
one of the few rivers on the Pacific slope of South America 
not previously examined by. members of the expeditions of 
Indiana University to western South America. 4 
Landing at Mollendo, I went by rail to Ensenada and from 
there to Chucarapi by mule. Chucarapi is about twenty miles 
from the coast. The valley here is about three-quarters of a 
mile wide. On each side of the valley the foothills rise about 
three hundred feet. The river is swift and narrow but cut- 
off streams and irrigation ditches offered fishing opportuni- 
ties. Altho strenuous efforts were made, only two species 
1 Contribution from Zoological Laboratory of Indiana University, No. 203. 
? In order to further the search for medicinal plants in South America, the H. K. 
Mulford Drug’ Company turned over to Dr. H. H. Rusby, dean of the College of Phar- 
macy of New York City, Columbia University, ( a sum of money to be used for such work 
as he saw fit. Dr. Rusby was well acquainted with neotropical life in general. He 
invited a few other men to accompany the expedition and work in their particular fields. 
During the winter 1920-21 I was selected to cover fishes and batrachians. 
3 Grant No. 220 from the Bache Fund of the National Academy of Sciences to C. H. 
Eigenmann. The present paper is a report on that grant. 
4 For accounts of expeditions to Panama, Colombia, Ecuador, Peru, and Chili see 
“The Fresh Water Fishes of Northwestern South America, including Colombia, Panama, 
and the Pacific slopes of Ecuador and Peru,” etc., Mem. Carnegie Mus., IX, Oct. 1922, 
and “The Freshwater Fishes of Chili,” Mem. Nat. Acad. Sci., 1925. 
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