Barriers to Dispersion of River Fishes 3 i 3 



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 x&nurus and Notro- 

 pis callisemus; in the Chattahoochee, Notropis hypselopterus and 

 Notropis eurystomus; in the Alabama, Notropis c&ruleus, Notro- 

 pis trichroistius, and Notropis callistius. In the Alabama, Es- 

 cambia, Pearl, and numerous other rivers is found Notropis 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 Notropis 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 stock 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-pits 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 gobiesj and salt-water eels. Fresh-water alligator 



* Notropis cercostigma, Notropis xcenoce phalns . J Gobiosoma molestum. 

 t Labidesthes sicculus. Myrophis punctatus. 



