Adaptations of Fishes 205 



most species, the common anchovy of Europe (Engraulis enchra- 

 sicolus), has 46 vertebrae. A tropical species (Anchovia browni) 

 has 41. 



There are, however, a few soft-rayed fishes confined to the 

 tropical seas in which the numbers of vertebrae are still large, 

 an exception to the general rule. Among these are Albula vulpes, 

 the bonefish, with 70 vertebras, Elops saurus, the ten-pounder, 

 with 72, the tarpon (Tarpon atlanticus), with about 50, and the 

 milkfish, Chanos chanos, with 72. 



In a fossil Eocene herring from the Green River shales (Dip- 

 lomystus) I count 40 vertebrae; in a bass- like fish (Mioplosus) 

 from the same locality 24 these being the usual numbers in 

 the present tropical members of these groups. 



The great family of Silurida, or catfishes, is represented in all 

 the fresh waters of temperate and tropical America, as well as in 

 the warmer parts of the Old World. One division of the family, 

 containing numerous species, abounds on the sandy shores of 

 the tropical seas. The others are all fresh-water fishes. So 

 far as the vertebrae in the Silurida have been examined, no 

 conclusions can be drawn. The vertebrae in the marine species 

 range from 35 to 50 ; in the North American forms, from 37 to 45 ; 

 and in the South American fresh-water species, where there is 

 almost every imaginable variation in form and structure, the 

 numbers range from 28 to 50 or more. The Cyprinidoz (carp 

 and minnows!, confined to the fresh waters of the northern hemi- 

 sphere, and their analogues, the Characinidcs of the rivers of 

 South America and Africa, have also numerous vertebrae, 36 to 

 50 in most cases. 



In general we may say of the soft-rayed fishes that very 

 few of them are inhabitants of tropical shores. Of these few, 

 some which are closely related to northern forms have fewer 

 vertebrae than their cold-water analogues. In the northern 

 species, the fresh-water species, and the species found in the deep 

 sea the number of vertebrae is always large, but the same is 

 true of some of the tropical species also. 



The Flounders. In the flounders, the halibut and its rela- 

 tives, arctic genera (Hippoglossus and Atheresthes] , have from 

 49 to 50 vertebrae. The northern genera (Hippoglossoides, 

 Lyopsetta, and Eopsetta) have from 43 to 45 ; the members of 



