14 



Of the six hundred species of fishes found in the rivers of 

 the United States, about two hundred have been recorded from 

 the basin of the Mississippi. From fifty to one hundred of 

 these species can be found in any one of the tributary streams 

 of the size, say, of the Housatonic river or the Charles. In 

 the Connecticut river there are about eighteen species perma- 

 nently resident ; and the number found in the streams of Texas 

 is not much larger, the best-known of these, the Rio Colorado, 

 having yielded but twenty-four species. 



The waters of the Great Basin have not yet been fully ex- 

 plored. The number of species now known from this region is 

 about seventy-five. This number includes the fauna of the 

 upper Rio Grande, the Snake river, and the Colorado, as well 

 as the fishes of the tributaries of the Great Salt Lake. This list 

 is composed almost entirely of a few genera of suckers [Catos- 

 iotnus, Pantosteus, Chasmistes), minnows {Sgua/tus, Gila, Pty- 

 chocheilus, etc.), and trout [Salmo mykiss and its varieties). 

 None of the catfishes, perch, darters, or sunfishes, moon-eyes, 

 killifishes, and none of the ordinary Eastern types of minnows 

 (genera Notropis, Chrosomiis, etc.) have passed the barrier of 

 the Rocky Mountains. 



West of the Sierra Nevada, the fauna is still more scanty, but 

 fifty species being enumerated. This fauna, except for certain 

 immigrants (as the fresh water surf-fish \^Hyst€rocarpus traskt] 

 and the species of salmon) from the sea, is of the same general 

 character as that of the Great Basin, though most of the species 

 are different. This latter fact would indicate a considerable 

 change, or " evolution," since the contents of the two faunae 

 were last mingled. There is a considerable difference between 

 the fauna of the Columbia and that of the Sacramento. The 

 species which these two basins have in common are chiefly those 

 which at times pass out into the sea. The rivers of Alaska con- 

 tain but few species, barely a dozen in all, most of these being 

 found also in Siberia and Kamtschatka. In the scantiness of its 

 faunal hst, the Yukon agrees with the Mackenzie river, and 

 with Arctic rivers generally. 



There can be no doubt that the general tendency is for each 

 species to extend its range more and more widely until all local- 



