3 6 4 
SPINY-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 backwardly-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 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 
