92 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



IlydrophJox rubricrocens, Photogenis galacturus, and Catostomus nigricans, 

 both in the Tennessee and Siivannab, will illustrate tliis. Neither of the 

 two lirst-nanied spi'cios 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 si)ecies 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 

 Josei)h's, Maumee, Wabash, and Illinois Rivers, although these streams 

 discharge their waters in widely different directions. The swami)y water- 

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

 smaller tishes 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 JEucalia inconsianfi, FceciUchthyn apecta- 

 bilis, Xcnotis lijtkrochloris, Xcnisma stellifcrum, iSalvclinus fontinaliSj 

 Ericymha buccata, Semotilus corporalis, Chrosotnus erythrogaster, the 

 species of Rhinichthys, etc. Of channel species, Raploidonoivs, Hyodon, 

 J)oroso)ua, PomolobuSy Foccns chry.snps, all the " Buflalo-flshes", and the 

 larger Siluridcc, Ichthcclurus j;?/j«c<«/m.s', Fcludivhihys olivaris, Amiurus 

 nigricans, and the like, will serve as examples. 



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

 ent Irom 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 diflerence between the ujjpor 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, sui)ply of food, etc. 



X. Hence, if in the same river basin there are two streiims llowing 

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

 if the two streams are similar in all known ])]iysieiil i-espects, their 

 faun;e will be simil ir, and if dissimilar, they will have diflerent fauna'. 

 The general identity of the faniue of Elk Kiver and Tovxrirs IJivcr 

 may be noticed in this connection. 



XI. Some spi'cies of fishes are confined strictly to a single river-i)asin, 

 while other species, with apj)arently no better means of diflnsion or of 

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

 of this, the limited rauge of each of the species of Cudoma may be com- 



