292 Dispersion of Fresh-water Fishes 



in a measure cosmopolitan,* ranging everywhere in suitable 

 waters. 



Characters of Species. — Still, again, we have all degrees of 

 constancy and inconstancy in what we regard as the charac- 

 ters of a species. Those found only in a single river-basin are 

 usually uniform enough; but the species having a wide range 

 usually vary much in different localities. Such variations 

 have at different times been taken to be the indications of as 

 many different species. Continued explorations bring to light, 

 from year to year, new species; but the number of new forms 

 now discovered each year is usually less than the number of 

 recognized species which are yearly proved to be untenable. 

 Four complete lists of the fresh-water fishes of the United States 

 (north of the Mexican boundary) have been published by the 

 present writer. That of Jordan and Copeland,t published in 

 1S76, enumerates 670 species. That of Jordan J in 1878 con- 

 tains 665 species, and that of Jordan and Gilbert § in 18S3, 587 

 species. That of Jordan and Evermann || in 1898 contains 5S5 

 species, although upwards of 130 new species were detected in 

 the twenty-two years which elapsed between the first and the last 

 list. Additional specimens from intervening localities are often 

 found to form connecting links among the nominal species, and 

 thus several supposed species become in time merged in one. 

 Thus the common channel catfish Tj of our rivers has been de- 

 scribed as a new species not less than twenty-five times, on 

 account of differences real or imaginary, but comparatively tri- 

 fling in value. 



* Thvis the chub-sucker {Erimyzon sucelta) in some of its varieties ranges 

 everywhere from Maine to Dakota, Florida, and Texas; while a number of 

 other species are scarcely less widley distributed. 



t Check List of the Fishes of the Fresh Waters of North America, by David 

 S. Jordan and Herbert E. Copeland. Bulletm of the Buffalo Society of Natural 

 History, 1876, pp. 133-164. 



I A Catalogue of the Fishes of the Fresh Waters of North America. Bul- 

 letin of the United States Geological Survey, 1S7S, pp. 407-442. 



§ A Catalogue of the Fishes Known to Inhabit the Waters of North America 

 North of the Tropic of Cancer. Annual Report of the Commissioner of Fish 

 and Fisheries for 1884 and 1885. 



!1 Check List of the Fishes of North and Middle America. Report of the 

 U. S. Commissioner of Fisheries for 1895. 



II Ictaluriis punctalus Rafmcsque. 



