124 Field Columbian Museum — Zoology, Vol III. 



It is quite evident that the rivers in Sonera have gotten their 

 fauna from the Gila River and tl^e Rio Conchos (or Rio Grande 

 System). 



Ptychocheilus lucius, Agosia crysogaster, Pxcilia occidentalism 

 Lcuciscus nigcr and Gila i/iinacce hdiMe probably migrated or resulted 

 from migrations from the Gila River. 



Mr. John P. Ramsey of El Paso, Tex , tells me that trout are 

 found in Chihuahua on the west slope of the Sierra Madre moun- 

 tains. The species is not known. As no trout are known from 

 the Gila River it is quite safe to predict that this species is Salmo 

 clarki pleiiriticus or a closely related species. 



Pautostciis plcbius, Leuciscus nigresccns and Leuciscus purpiu-eus 

 are apparently equally related to the fauna of the Rio Grande and 

 the Gila River, leaving 8 species which have migrated or resulted 

 from migrations from the Rio Grande system. Of the 4 species 

 known from the Rio Sonora, 3 belong to the Gila River. 



The fishes of Sonora and of that portion of Chihuahua which 

 belongs to the Pacific slope, are migrants from the Rio Grande 

 and the Gila River, the greater number from the former. When 

 and how this migration occurred can be discovered only by a 

 careful study of the topography and geology of this region. It 

 evidently took place within recent geological times. 



Southern Mexico. 



There are at present 10 species of fishes recorded from the 

 Valley of Mexico: 



Algaitsea tincella Zoogoneticus miniatiis 



'■'■'Astecula azteca *Skiffia variegatas 



'^Evarra eigeiunaui Chirostovia jordani 

 *Ez'arra tlaJmaceiisis Cliirostoma Jmmboldtianioii 



GirardiiiichtJiys imioiiilnatus Cliirostoma estor 



Four species (marked"'^) have so far not been found else- 

 where. All of the other species belong to the Rio Lerma fauna. 

 One species Algansea tincella, has been found in the Rio Mocte- 

 zuma, an upper tributary to the Rio Panuca. Azieciila inexicana 

 has been taken only in the Rio Moctezuma, and Aztecula lerincB 

 only in Lake Lerma, near the head waters of the Rio Lerma. 

 These two species are very closely related to Aztecula azteca. Of 

 the three species taken in the Rio Moctezuma, one species, Al- 

 gansea tincella, is found in the Rio Lerma and in the Valley of 

 Mexico. A second species, Goodca cnliente, is found in the Rio 

 Lerma. Aztecula inexicana, the third, is found in neither of these 



