304 Barriers to Dispersion of River Fishes 



species now found being evidently an overflow from the Snake 

 River when in late glacial times it drained Lake Bonne ville. 

 This postglacial lake once rilled the present basin of the Great 

 Salt Lake and Utah Lake, its outlet flowing northwest from 

 Ogden into Snake River. The same fishes are now found in 

 the upper Snake River and the basins of Utah Lake and of 

 Sevier Lake. In the same fashion Lake Lahontan once occu- 

 pied the basin of Nevada, the Humboldt and Carson sinks, with 

 Pyramid Lake. Its drainage fell also into the Snake River, 

 and its former limits are shown in the present range of species. 

 These have almost nothing in common with the group of species 

 inhabiting the former drainage of Lake Bonne ville. 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 lobes is about 125. This list is 

 composed almost entirely of a few genera of suckers,* minnows, f 

 and trout. J None of the catfishes, perch, darters, or sunfishes, 

 moon-eyes, pike, klllifishes, and none of the ordinary Eastern 

 types of minnows have passed the barrier of the Rocky Moun- 

 tains. 



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

 only about seventy species being enumerated. This fauna, ex- 

 cept 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. 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 

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

 being found also in Siberia and Kamchatka. In the scanti- 



* Catostomus, Pantosteus, Chasmistes. 

 t Gila, Ptychocheilus , etc. 

 J Salnto clarkii and its varieties. 

 Genera Notropis, Chrosomus, etc. 



|| As the fresh- water surf-fish (Hysterocarpus traski) and the species of 

 salmon. 



