Geographic and Geologic Relations 



417 



masses, is it possible to reach correct understanding of 

 present often puzzling distributions. 



The Cyprinidae, with about 1300 species, contrasts 

 markedly with the Siluridae in geologic relation and evi- 

 dent lines of geographic evolution. The chart (Fig. 70) 

 sets forth the areas now occupied by species of the four 

 sub-families Catostominae, Cyprininae, Cobitidinae, and 

 Homalopterinae. At a glance the chart would indicate 

 that the entire family evolved as a northern temperate- 

 region group. It further indicates that the Catostominae 



Fig. 70. Chart of distributional areas gradually occupied by 

 sub-families of the Cyprinidae. The arrows indicate the lines of 

 travel from the primitive N. American centre. 



and Cyprininae, specially the latter, have been the "domi- 

 nant" divisions. We may now try to learn how such has 

 resulted. 



The sub-family Catostominae must have been abundant 

 in such genera as Amyzon and Catostomus over consider- 

 able reaches of N. America during early Eocene times. 

 This is partial indication that at least in late Cretaceous 

 beds of that region, more primitive types might be expected. 

 These, and evolving Cyprininae, seem gradually to have 



