i)2 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



Hydrophlox rubricroceus, Plwtogenis galacturus, and Catostomus nigricans, 

 both in the Tennessee and Savannah, will illustrate this. Neither of the 

 two first-named species are as yet known from any other river-basins. 



VI. When the watershed between two streams is a swampy upland 

 instead of a mountain-range, the same species may be found in the head- 

 waters of both, although the species inhabiting the lower courses may be 

 different. In case the one stream flows northward and the other south- 

 ward, the common fauna will be nearest like that of the northern stream. 



In Northern Indiana, the same species are found in the waters of Saint 

 Joseph's, Mauinee, Wabash, and Illinois Bivers, although these streams 

 discharge their waters in widely different directions. The swampy water- 

 shed between them is often overflowed in the spring, affording to the 

 smaller fishes an easy means of migration. 



VII. In any river-basin, many of the species inhabiting small streams 

 are different from those occurring in the river-channels. Among the 

 brook species may be mentioned Eucalia incomlans, Pcecilichthys apecta- 

 bilis, Xenotis lythrocliloris, Xenisma stelliferum, SalveUnus fonlinalis, 

 Ericyniba buccata, Semotilus cbrporalis, Chrosomus crythroyaster, the 

 species of RhinicUthys, etc. Of channel species, Haptoidonotvs, Hyodon, 

 Dorosoma, Pomolobus, Roccit8 chrysops, all the " Buffalo fishes", and the 

 larger Siluridce, Ichtliculurus pvnctatm, Peludichthys olivar-is, Amiunis 

 nigi -leans, and the like, will serve as examples. 



Vlli. Many species inhabiting the upper course of a stream are differ- 

 ent from those of the lower. This subject has been ably discussed by 

 Professer Cope, but further investigations, especially of the rivers of the 

 Southern States, are very desirable. 



IX. This difference between the upper fauna and the lower is due to 

 differences in the character of the river itself, such as climate, condition 

 of water, character of river-bed, supply of food, etc. 



X. Hence, if in the same river basin there are two streams flowing 

 into a larger stream, the one near its source, the other near its mouth, 

 if the two streams are similar in all known physical respects, their 

 faunaB will be similar, and if dissimilar, they will have different fauna3. 

 The general identity of the faunas of Elk River and Powell's Eiver 

 may be noticed in this connection. 



XI. Some species of fishes are confined strictly to a single river-basin, 

 while other species, with apparently no better means of diffusion or of 

 defense, are widely distributed, inhabiting many rivers. In illustration 

 of this, the limited range of each of the species of Codoma may be com- 



