MAY, 1902. THE ICHTHYOLOGY OF MEXICO MEEK. 69 



de Patzcuaro has no outlet, and its waters have become some- 

 what brackish. 



Lago de Zirahuen is a small, deep mountain lake. Its drain- 

 age area is small, and the lake is' about one mile in diameter. A 

 portion of its shore is sandy and muddy, while much is fringed 

 with vegetation. This lake also has no outlet. The fishes from 

 it are very dark in color. In this respect they are much like the 

 fishes in Lago de Chalco. Commercial fishing is carried on here 

 to some extent. 



The Drainage System of the Valley of Mexico. 



Lago de Texcoco is a large shallow lake in the valley of 

 Mexico. Its size varies much during the year. It is connected 

 with all of the other lakes in this valley by canals which carry off 

 much of the filth of the City of Mexico as well as of other cities 

 near by. 



Lago de Chalco is deeper and smaller than Texcoco. This 

 lake supports an immense amount of vegetation. Not far from 

 Tlahuac, in the bed of the lake, is a large spring. The water is 

 about 20 feet deep, and can be seen boiling up through the sand 

 on the bottom over an area of more than 100 feet square. Our 

 collections from this lake were made at Chalco and Tlahuac. 



Lago de Xochomilcho is much like Lago de Chalco. The 

 few fishes in our collection from this lake were purchased from 

 fishermen in the markets of the City of Mexico. 



The Balsas System. 



The Rio Balsas is south of the Rio Lerma and is the second 

 largest river wholly within Mexico. We visited this river at 

 Balsas, a small village almost directly south of the City of 

 Mexico. The river at close of the dry season, at this place, was 

 about 100 feet wide and 10 to 15 feet deep. The mountains on 

 either side rise almost from the water's edge, forming a sort of 

 canon. The current was very swift, while at intervals of a mile 

 or so were rapids or cascades. In the bed of the stream are a 

 few small bayous and cut-offs, and in these most of our fishes 

 were collected. The Rio Balsas in the wet season is for a while 

 one of the great rivers of this continent. Its water in the dry 

 season is so brackish that the natives seldom use it. 



The Rio Cuculo is a small stream tributary to the Rio Balsas 

 at this place. It contained no running water. The few deep 

 holes near its mouth furnished an excellent place to collect fishes. 



