THE AQUATIC VERTEBRATES 1035 



basins of Utah Lake and of Sevier Lake. In the same fashion 

 Lake Lahonton once occupied the basin of Nevada, the Humboldt 

 and Carson sinks, with Pyramid Lake. Its drainage fell also into 

 the Snake [Klamath?] River, and its former Umits are shown in 

 the present range of species. These have almost nothing in com- 

 mon with the group of species inhabiting the former drainage of 

 Lake Bonneville. Another postglacial body of water, Lake Idaho, 

 once united the lakes of southeastern Oregon. The fauna of Lake 

 Idaho, and of the lakes Malheur, Warner, Goose, etc., which have 

 replaced it, is also isolated and distinctive. The number of species 

 now known from this region of these ancient lakes is about 125. 

 This list is composed almost entirely of a few genera of suckers, 

 minnows, and trout. None of the catfishes, perch, darters, or 

 sunfishes, moon-eyes, pike, killifishes, and none of the ordinary 

 eastern types of minnows have passed the barrier of the Rocky 

 Mountains. 



" West of the Sierra Nevada the fauna is still more scanty, only 

 about seventy species being enumerated. This fauna, except for 

 certain immigrants from the sea, is of the same general character 

 as that of the Great Basin, though most of the species are different. 

 . . . The rivers of Alaska contain but few species, bareh' a dozen 

 in all, most of these being found also in Siberia and Kamchatka. 

 In the scantiness of its faunal Hst, the Yukon agrees with the Mac- 

 kenzie River, and with Arctic rivers generally." 



The fauna of the Great Lakes and of the Red River of the north 

 is essentially Hke that of the Mississippi Valley. 



The Origin of the Fresh-water Fishes. — Many of the fresh-water 

 fishes of North America have been more remotely or more recently 

 derived from the sea. Some of them, as the eel, still come from 

 the sea during each generation, to find in fresh water their range; 

 others are but seasonal visitors, entering the fresh waters from the 

 ocean as the salamanders enter them from the land, to find homes. 

 These various anadromous fishes will be considered later.^ Still 



1 The anaclromous habit may be of double origin. The various salmons, many of 

 whose relatives live in fresh water, may be fresh-water species contributed to the ocean. 

 The shad and striped perch, on the other hand, whose relatives live in the ocean, have 

 become anadromous through the general habit of many oceanic fishes to seek the shore 

 and shallow water as the breeding season approaches. 



