116 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,’ Minnows,? and Trout.8 
None of the Cat-fishes, Perch, Darters, or Sun- 
fishes, 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, but fifty 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. This latter fact would indicate a con- 
siderable change, or “evolution,” since the con- 
tents of the two faune were last mingled. There 
1 Catostomus, Pantosteus, Chasmistes. 
2 Sgualius, Gila, Ptychocheilus, etc. 
3 Salmo mykiss and its varieties. 
4 Genera WVotropis, Chrosomus, etc. 
5 As the fresh-water Surf-fish (Aysterocarpus traski) and the 
species of Salmon. 
