24 David Starr Jordan 



to the elongation* of their individual vertebrae and not to 

 their increase in number. 



In the great group of blenny-like fishes the facts are equall}' 

 striking. The arctic species are very slender in form as com- 

 pared with the tropical blennies, and this fact, caused by a 

 great increase in the number of their vertebrae, has led to the 

 separation of the group into several families. The tropical forms 

 composing the family of Blemiiidcs f have from 28 to 49 verte- 

 brae, while in the arctic genera the numbers range from 75 to 100. 



The anacanthine fishes in whole or in part seem to have 

 sprung from a blennioid stock. Of these the most specialized 

 group is that of the flounders,! below described. The 

 wide distribution of this family, its members being found on 

 the sandy shores of all zones, renders it especially important 

 in the present discussion. The other anacanthine families are 

 chiefly confined to the cold waters or to the depths of the seas. 



In the cod family § (^Gadidce) the number of vertebrae is 

 usually about 50, and in their deep-sea allies, the grenadiers|| 

 or rat-tails, the numbers range from 65 to 80. 



*Thus the very slender goby, Gobiiis oceaniciis has the same number 

 (25) of vertebrae as its thick-set relative Gobius soporator or the chubby 

 Lophogobuis cyprirwides. 



tOf the true Blenniidcs, which are all tropical or semi-tropical, 

 Blennius has 28 to 35 vertebrae ; Salarias, 35 to 38 ; Labrosojnus, 34 ; 

 Clinus, 49 ; Cristiceps, 40. A fresh water species of Cristiceps found in 

 Australia has 46. Blennioid fishes in the Arctic seas are A?iarrhichas, 

 with 76 vertebrae ; Anarrhichthys, with 100 or more ; Luinpenus, "](); 

 Mures itoides, 85; Ly codes, 112; Gyjunelis, 93. Ly codes and Gyninelis 

 have lost all the dorsal spines and are intermediate between the blennies 

 and the forms called Anacanthine. The gradual degeneration of such 

 northern forms may perhaps be attributed to the influence of " Pan- 

 mixia " or the cessation of selection. XPleuronectida;. 



^ Fifty- one in the codfish {Gadus callarias,) 58 in the Siberian cod 

 {Eteginus navaga) 54 in the haddock {Melanogratnmus csglifinus) 54 

 in the whiting {Merlangus inerlansius\, 54 in the coal-fish i Pollachius 

 virens) 52 in the Alaskan coal-fish {Pollachius chat cogr animus) , 51 in 

 the hake {Mertuccius merluccius). In the burbot {Lota lota) the only 

 fresh water codfish, 59 ; in the deep water ling [3Iolva ntotva), 64 ; in 

 the rocklings {Gaidropsarus) 47 to 49. Those few species found in the 

 Mediterranean and the Gulf of Mexico have fewer fin rays and prob- 

 ably fewer vertebrae than the others, but none of the family enter warm 

 water, the southern species living at greater depths. || Macruridce. 



