FRESHWATER FISH FAUNA 203 



cene time the North American species Catostomiis catostomus re- 

 crossed to eastern Siberia. The recency of that crossing is indicated 

 by the common occurrence, in Siberia and western Arctic America, 

 of the same subspecies (Walters, 1955, pp. 295-296). 



It is rather generally held that the suckers are ancestral to (or at 

 least more primitive than) the minnows, family Cyprinidae, but a 

 comparative study of the upper jaw mechanism in the bony fishes 

 led Eaton (1935, p. 168) to conclude that suckers undoubtedly 

 descended from minnows. And, after studying skeletal features of 

 two groups of Asiatic minnows and comparing them to those of 

 certain catostomids, Ramaswami (1955a, pp. 152-153; 1955b, p. 

 236; 1957) found certain catostomid skeletal features in members of 

 the gudgeons, a subfamily of minnows inhabiting China, and con- 

 cluded: "... it is not likely that the Catostomidae could have given 

 rise to the Cyprinidae." The weight of present evidence thus indi- 

 cates (Fig. 11) a cyprinid prototype as probably ancestral to this 

 family. 



The carps and minnows comprise the largest of all freshwater fish 

 families, the Cyprinidae, with an estimated 250 genera and up- 

 wards of 2,000 species, inhabiting all the continents except South 

 America and Australia. The group attains its greatest number of 

 species and diversity of form in southeastern Asia, where the most 

 generalized types also are found. Relatively, the family is not very 

 richly represented nor is it particularly diverse in the New World, 

 where there are only about 40 genera and 250 species, and the 

 paleontological evidence indicates that minnows arrived here in 

 comparatively recent times, not prior to the Miocene epoch. Whereas 

 a number of distinct subfamilies are recognized in the Old World, 

 for example in China (Chu, 1935), it is probable that all of the New 

 World cyprinids belong to a single subfamily, the Leuciscinae 

 {Notemigonus is possibly a member of the Abramidinae, but its 

 relationships to that Old World group are in need of critical study). 

 Not only lack of basic morphological diversity but also the readiness 

 with which most American minnows hybridize (Hubbs, 1955) sup- 

 ports the evidence that the group has not been here long enough to 

 develop strongly divergent lines. 



About 27 genera and 58 species of cyprinids live in western North 

 America. Of the genera 15 (or 56 per cent) are monotypic. Twenty 



