122 Barriers to Dispersion of River Fishes 
river basin, and it would appear that a thorough mingling of 
the upland species in these rivers has never taken place. 
The best examples of this are the following: In the Santee 
basin are found Notropis pyrrhomelas, Notropis niveus, and No- 
tropis chloristius; in the Altamaha, Notropis xenurus and Notro- 
pis callisemus; in the Chattahoochee, Notropis hypselopterus and 
Notropis eurystomus; in the Alabama, Notropis ceruleus, Notro- 
pis trichroistius, and Notropis callistius. In the Alabama, Es- 
cambia, Pearl, and numerous other rivers is found Notropts cer- 
costigma, This species descends to the sea in the cool streams of © 
the pine woods. Its range is wider than that of the others, and 
in the rivers of Texas it reappears in the form of a scarcely dis- 
tinct variety, Notropis venustus. In the Tennessee and Cumber- 
land, and in the rivers of the Ozark range, is Notropts galacturus; 
and in the upper Arkansas Notropis camurus,—all distinct species 
of the same general type. Northward, in all the streams from 
the Potomac to the Oswego, and westward to the Des Moines and 
the Arkansas, occurs a single species of this type, Notropis 
whipplei, varying eastward into Notropis analostanus. But this 
species is not known from any of the streams inhabited by any 
of the other species mentioned, although very likely it is the 
parent stoék of them all. 
Lowland Fishes.—With the lowland species of the Southern 
rivers it is different. Few of these are confined within narrow 
limits. The streams of the whole South Atlantic and Gulf 
Coast flow into shallow bays, mostly bounded by sand-spits or 
sand-bars which the rivers themselves have brought down. In 
these bays the waters are often neither fresh nor salt; or, rather, 
they are alternately fresh and salt, the former condition being 
that of the winter and spring. Many species descend into these 
bays, thus finding every facility for transfer from river to river. 
There is a continuous inland passage in fresh or brackish waters, 
traversable by such fishes, from Chesapeake Bay nearly to 
Cape Fear; and similar conditions exist on the coasts of Louisi- 
ana, Texas, and much of Florida. In Perdido Bay I have found 
fresh-water minnows* and silversidesf living together with 
marine gobiest and salt-water eels.§ Fresh-water alligator 
* Notropis cercostigma, Notropis xe@nocephalus. } Gobiosoma molestum. 
+ Labidesthes sicculus. § Myrophis punctatus. 
