THE HORSE MACKERELS 2733 



in one genus the number of the latter is increased to sixteen. The gill openings 

 are wide, the eyes lateral, and there is no bony stay connecting the preopercular 

 with the infraorbital ring. The scales, which are usually small, may be altogether 

 wanting, and in many cases the lateral line is wholly or partially armed with shield- 

 like overlapping plates. There is always an air bladder. In the young of some 

 forms there is an armature of the head, which disappears in the adult. Carnivo- 

 rous 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. 



In the typical genus Caranx the body is generally more or less 



True Horse com p resse d, although sometimes almost cylindrical; the hard dorsal 

 Mackerels . . , 



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. 

 Ranging 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 is 

 edible. The genus is represented in the Monte Bolca Eocene. Horse mackerel 

 sometimes make their appearance in enormous shoals on the British coasts and it is 

 stated that on one occasion upward of ten thousand were taken in Cornwall. A 

 correspondent of Yarrell wrote, that in the summer of 1834 vast shoals of these fish 

 were seen on the Glamorganshire coast. " They were first observed in the evening, 

 and the whole sea, as far as we could command it with the eye, seemed in a 

 state of fermentation with their numbers. Those who stood on some projecting 

 rock had only to dip their hands into the water, and with a sudden jerk, they 

 might throw up three or four. The bathers felt them come against their bodies, 

 and the sea, looked on from above, appeared one dark mass of fish. Every net was 

 immediately put in requisition, and those which did not give way from the weight, 

 were drawn on shore laden with spoil. One of the party who had a herring seine 

 with a two-inch mesh was the most successful; every mesh held its fish, and formed 

 a wall that swept on the beach all before it. The quantity is very inadequately 

 expressed by numbers, they were caught by cart loads. As these shoals were pass- 

 ing us for a week, with their heads directed up channel, we had the opportunity of 

 noticing that the feeding time was morning and evening. They were pursuing the 

 fry of the herring, and I found their stomachs constantly full of them." 



