504 EIGENMANN— ORIGIN OF FISHES OF THE 



These articles deal with the first of the faunas mentioned above. 

 I propose in the present paper to deal with the nature and origin 

 of the freshwater fishes of the Guayaquil basin of Ecuador, of the 

 rivers and lakes of Chili north of Puerto Montt and of the rivers 

 between these areas, i.e., of all the Pacific slope rivers between 

 northern Ecuador, near the equator, and Puerto JMontt, 41° 28' S. 

 The material for this study was collected by Mr. Arthur Henn of 

 the Landon Ecuadorian Expedition of Indiana University in 1913, 

 and by Dr. William Ray Allen, Dr. Adele Eigenmann and myself of 

 the Irwin Expedition of Indiana University and the University of 

 Illinois between June, 1918, and June, 1919.''' 



The Guayas Basin and its Fishes (Plate VIII.). 



North of the desert of Tumbez the coast range of Ecuador 

 consists of cretaceous formations trending from Guayaquil north- 

 westward and reaching a height of 2,300 feet. North of about 

 1° 50' south latitude the cretaceous joins tertiary hills reaching a 

 height of from 600 to 1,000 feet and extending north to the Rio 

 Santiago. North of the Rio Chone the hills approach the coast 

 and are relatively younger (late tertiary and quaternary). South 

 of the Rio Chone a wider or narrower quaternary territory extends 



■^ Several additional rivers should receive consideration at the earliest 

 moment, the Esmeraldas in Ecuador; the Santa, the largest river of Peru; 

 the lower Loa, an isolated river in northern Chili; and the Bio Bio, the 

 largest river in Chili. Betw^een Puerto Montt and Cape Horn there is a 

 series of large rivers and lakes concerning which we know nothing. It has 

 been suggested that they be searched for Cerotodus. 



The Esmeraldas drains the area immediately north of the Guayas basin. 

 Very little is known of its fauna. The Santa is the largest river of the 

 Pacific slope of Peru and may be expected to contain a more complete com- 

 plement of the ancient fauna of the Pacific slope of Peru than any of the 

 rivers examined. The Loa in northern Chili is widely separated by deserts 

 both from' the nearest rivers to the north and the nearest rivers to the 

 south. Its fishes, if there are any, should determine whether this portion of 

 Chili belonged in the past to the tropical American faunal area or to the 

 Patagonian. 



The Rio Bio Bio, the largest basin in Chili, contains all of the fishes 

 found in the rivers of Chili north of it and is " farthest north " of the 

 peculiar fauna with Australian affinities which finds its culmination in the 

 south of Chili. 



