300 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



The Rio Mezquital south of the Presidio contains : 



N Ameiuriis pricci (Rutter). 



N Pantosfe?/s p/ebchts[^2i\vd & Girard). 

 *N Moxostoma mistrinnni Bean. 



N HybognatJiiis episcopits (Girard). 



N Leucisc2ts nigrescens (Girard). 



N Notropis oruatiis (Girard). 



M C/inracodo)t garmani ]ord2in & Evermann. 

 *M C/iaracodon fnrcidens ]ovd2in & Gilbert. 



T Cyprinodon latifasciatits Gar man. 

 *M Chirostonia niezqtn'fa/MQ&k. 



N Etheostonia pottsii (Girard). 

 As Meek points out, all but three of these species (marked *) belong 

 to the Rio Grande basin and were probably captured from it. There are 

 no distinctly South American elements in this river system as far as ex- 

 amined ; it belongs to the north. But no collections have been made 

 below the Mexican plateau and the tropical elements would naturally 

 occur in the lowlands. 



Skipping the Rio Grande de Santiago and its tributary the Lerma, whose 

 basin embraces the greater part of the Mexican plateau, the Rio Balsas 

 belongs distinctly to the transition zone containing Tetragoiioptcnts niexi- 

 caiius and CicJilasonia istlarius as (S) South American intrusives ; Istla- 

 riits, Aztecitla and A^ofropis as (N) North American intrusives, the first 

 two of which have become generically distinct from their North American 

 relatives and might therefore be classed as transition genera. The rest 

 are transition genera (T) with the one exception of the Mexican Goodea. 

 This river is almost equal in size to the Lerma. It contains only about 

 one-fourth as many fishes. Its basin is larger than the basin of the Panuco. 

 It was fished from about 1400 feet to 6000 feet in elevation. In this 

 area the number of species is less than half the number found in the 

 Panuco. 



N Istlarius balsaniis Jordan & Snyder. 

 N Aztecula vittata (Girard). 

 N Notropis boucardi (Giinther). 

 S Astyanax mexicanus (Philippi). 

 T Gambusia gracilis (Heckel). 

 M Goodea whitei Meek. 



