To these we may add the more or less distinct classes of (5) 

 Lake fishes, inhabiting only waters which are deep, clear and 

 cold, as the various species of whitefish and the great lake 

 trout ; (6) Anadromous fishes, or those which run up from the 

 sea to spawn in fresh waters, as the salmon, sturgeon, shad 

 and striped bass ; (7) Catadromous fishes, like the eel, which 

 pass down to spawn in the sea ; and (8) Brackish-water fishes, 

 which thrive best in the debatable waters of the river-mouths, 

 as most of the sticklebacks and the killifishes. 



As regards the range of species, we have every possible 

 gradation from those which seem to be confined to a single 

 river, and are rare even in their restricted habitat, to those 

 which are in a measure cosmopolitan,* ranging everywhere in 

 suitable waters. 



Still, again, we have all degrees of constancy and incon- 

 stancy in what we regard as the characters 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 differ- 

 ent localities. 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 recog- 

 nized species which are yearly proved to be intenable. Three 

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

 have been published by the present writer. That of Jordan and 

 Copeland, t published in 1876, enumerates 670 species. That 

 of Jordan I in 1878 contains 665 species, and that of Jordan § in 

 1885, 587 species, although upwards of 75 new species were 

 detected in the nine 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 



* Thus the chuh-sacker I Er/m^'zan sucetta) in some of its varieties ranges everywhere from 

 Maine to Dakota, Florida and Texas ; wrhile a number of other species are scarcely less widely 

 distributed. 



t Check L'st of the Fishes of the Fresh Waters of North America, by David S. Jordan and 

 Herbert E. Copeland. Bulletin of the Buffalo Society of Natural History, 1876, pp. 133-164. 



t A Catalogue of the Fishes of the Fresh Waters of North America. Bulletin of the United 

 States Geological Survey, 1878, 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 Commissioners of Fish and Fisheries for 1884 and 1885. 



