3 6 4 



SPIiVY-FINNED GROUP. 



head, which disappears in the adult. Carnivorous in their diet, the horse-mackerels 

 are distributed at the present day over all temperate and tropical seas ; and were 

 also abundant during the Tertiary period, and likewise represented by extinct 

 genera in the antecedent Cretaceous epoch. Remains of these fishes are found in 

 extraordinary profusion in the middle Eocene strata of Monte Bolca, one of the 

 most remarkable types from that formation being the extinct Semiophorus, in 

 which the dorsal fin is so elevated as to exceed the total length of the head and 

 body, while the pectorals formed a pair of back wardly- directed tapering spines. 

 True Horse- In the typical genus Caranx the body is generally more or less 



Mackerels, compressed, although sometimes almost cylindrical ; the hard dorsal 



COMMON MACKEREL AND HORSE-MACKEREL (J nat. size). 



fin, which may be rudimentary, is continuous, with about eight weak spines ; while 

 in a few species the soft portion of both this and the anal is broken up into finlets. 

 The scales are very small ; and while in the British horse-mackerel (C. trachurus), 

 represented in the lower figure of our illustration, the lateral line is protected by 

 bony plates throughout its entire extent, in many other species these plates are 

 restricted to its hinder moiety. Several of these plates may be traversed by a keel 

 terminating in a spine. The genus is represented by nearly a hundred species, 

 some of which have teeth on the palate, while in others these are wanting. Rang- 

 ing over almost all temperate and tropical seas, many of them swim out to 

 considerable distances from the shore, and thus acquire a very large distributional 

 area. The larger forms may measure fully a yard in length ; and the flesh of all 



