GEOGRAPHIC DISTRIBUTION OF FISHES. 53 



Others. That certain families^ and even genera^ are 

 strictly limited,, so far as we yet know, to the shores or 

 rivers of particular countries^ is unquestionable ; and of 

 this the family of the Siluridce, upon which we shall 

 subsequently dilate, ofFers several singular proofs. The 

 most typical belong only to the equinoctial rivers of 

 America; while nearly all the sub-typical, that is, of the 

 PimelodinfE, occur in the great rivers of India : we 

 suspect, even, that such of these latter as have been found 

 in America will prove to be distinct geographic sub- 

 genera. The whole family may be considered tropical; 

 for the only species yet found in the rivers of Europe is 

 of 3 very aberrant form, and is as much related to the 

 aberrant GadiadcB as to the typical LoricarincB. The 

 GadiadcB, or cod-fish, again, seem to supply, in cold and 

 temperate regions, the place of the SiluridcB : they are 

 most abundant on the confines of the Arctic seas, and 

 gradually diminish as they approach the southern shores 

 of Europe, where the species, although many, are almost 

 all of the aberrant forms ; and yet not one example of 

 the whole family was observed by us in the Brazilian 

 seas. As we shall occasionally touch upon this subject 

 in the succeeding pages, further instances need not be 

 mentioned in support of our opinion. The fact, we 

 have no doubt, will ultimately be established, that fishes 

 are nearly as much limited in their geographic distri- 

 bution as birds ; and that temperature alone has very 

 little to do in regulating this distribution. 



B 3 



