MAY, 1902. THE ICHTHYOLOGY OF MEXICO MEEK. 65 



5 or 6 miles from the lake, is a large spring, and a spring 

 branch whose waters are taken up by the sand within less than a 

 mile from the spring. C. flcgans is the only fish found here. 



At Ahumada, 9 miles from the lake, all of the water in the 

 river was taken out by irrigating ditches. A small collection of 

 fishes was made in the largest irrigating ditch. It seems that on 

 the approach of the dry season the fish in these small separate 

 river basins migrate to the head waters. A large number are 

 said to die in the lakes as these bodies of water become dry. 

 The concentration of the salts in the water due to evaporation is 

 no doubt the cause of the great mortality reported when the lake 

 has been reduced to about one-fourth of its largest size. Mr. 

 Jackson of Ahumada, who occasionally fishes for the market, 

 informed me that in June no large fishes could be found short 

 of about 20 miles up the river. 



These three river systems were probably at one time a part of 

 the Rio Grande System. 



The Conchos System. 



The Rio de los Conchos is one of the southern tributaries of 

 the Rio Grande. We visited the Rio Chihuahua, a tributary of 

 the Rio Conchos, at Chihuahua. The water was very low. This 

 stream flows with a moderate current over sandy or gravelly bot- 

 toms. The water contained a large amount of algae. This stream, 

 where visited, was well shaded by large trees and bushes. 



The Rio Santa Cruz at San Andres is a small stream with 

 sandy and gravelly bottom; by the end of the dry season it 

 contains but little running water. Our fishes were collected in a 

 few holes in the bed of the stream just below the city. There is 

 very little vegetation of any sort along this stream near San 

 Andres. This same stream at Ortiz, a considerable distance 

 below San Andres, was 'entirely dry. 



The Rio Noavaco at 'Santa Rosalia contains considerable 

 water throughout the dry season, though this is confined to long 

 deep holes with but little running water between them. 



At Jimenez the Rio Conchos was nearly dry. Our collections 

 were made from a few deep holes about 2 miles below the 

 city. These contained a large amount of aquatic vegetation, 

 which made collecting difficult and unsatisfactory. The water 

 was very clear, and in the deeper places were seen many large 

 suckers which we were unable to capture. Sunfishes were very 

 abundant. All of these streams become large and deep in the 



