Il6 SCIENCE SKETCHES. 



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 but about eighteen species permanently resi- 

 dent; 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 explored. 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, 1 Minnows, 2 and Trout. 3 

 None of the Cat-fishes, Perch, Darters, or Sun- 

 fishes, Moon-eyes, Pike, Killifishes, and none of 

 the ordinary Eastern types of Minnows 4 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 5 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 con- 

 siderable change, or " evolution," since the con- 

 tents of the two faunae were last mingled. There 



1 Catostomus, Pantosteus, Chasmistes. 



2 Sgualius, Gila, Pfychocheilus, etc. 



3 Salmo mykiss and its varieties. 



4 Genera Notropis, Chrosomus, etc. 



5 As the fresh-water Surf-fish (Hysterocarpus traski) and the 

 species of Salmon. 



