FISHES OF SOUTH AND MIDDLE AMERICA 527 



13. Ci •hlasoma bimaculaturn L. 



14. Crenicichla saxatibs L. Two Members of the CiCHLm.K, of which there are about 150 

 known species between the bjrders of the United States and Patagonia. 



ding the valley of the City of Mexico and the Lerma basin draining to 

 the west, and the Eio San Juan, a tributary of the Panuco, draining 

 to the east. While containing intrusive elements from the north, it 

 contains none from the south, and its fauna is so distinct from either 

 that there is slight hesitation in considering it as equivalent to the 

 American, South American and Patagonian faunas. 



The third, the South American fauna, is sharply divisible into the 

 Brazilian and Andean. The Brazilian occupies the rivers from South- 

 ern Mexico to Buenos Aires and from Para to Callao, exclusive of the 

 high Andes. This fauna is the richest in species in the world. From 

 this region about ten per cent, of all the known fishes have been re- 

 corded. The Andean, from 3,000 to 5,000 feet and over above sea- 

 level, while possessing some forms in common with the Brazilian, is 

 quite distinct. The species inhabiting this region would cause sur- 

 prise if found at Manaos ; those of the Pacific slope would not. 



The Patagonian fauna is among the poorest in the world. It 

 occupies the Rio Negro basin, and everything lying south of it and a 

 line joining it with Valparaiso. Its fauna has been considered in 

 detail. 



For convenience these faunal areas may be enumerated as the 

 following ' regions ' of unequal value. (1) Transition. (2) Mexican. 

 (3) Brazilian. (-1-) Andean. (5) Patagonian. I am not sure but 

 that the Titicacan basin constitutes a ' region ' distinct from the 

 Andean north of Titicaca. 



