XXIV 



IXTRODUCTION. 



element of the fresh-water fish-fauna, but tlie generic types are comparatively few ; 



some of tlie existing European genera are represented in Oligocene and Miocene deposits. 



Tlie Nearctic Cyprininae number about 22-3 species, most of which belong to the 



I'akrarctic genus Leuciscus or to closely allied generic types, there being, perhaps, less 



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IdsTPanuTioif of CrPEisixJ!. 



diversity in this region than in any other. Consequently the generic distinctions are 

 in great part based on very trivial characters, and slight differences in the form and 

 number of the pharyngeal teeth are considered of importance. 



In Amo'rica the Cyprinini3e range from British Columbia, Saskatchewan, and Quebec 

 to the llio JJalsas in Southern Mexico. As in the Catostominse, few genera are 

 common to both sides of the Eocky Mountains, except in the case of types specially 

 ada))ted to luouiitaiu-strenms. 



Of the 40 s])ecies included in the fauna of ^lexico, 10 belong to six endemic genera, 

 of wliicli live, Ahjansed, (4 species), Falcnla (1 species), Uvarra (2 species), Xi/sirosus 

 ( 1 species), and }'nriria (1 species), are peculiar to the Lerma System and the other, 

 i^f//jiodo'n, contains a single species from Coahuila. Kotropis, with about 100 species, 

 ail from rivers east of tiie liocky Mountains and the Sierra Madre, is represented by 

 IJ in Mexico; 10 of these are from north of the Lerma and o from the Lerma System ; 



