142 GIANT FISHES 



smooth and are not provided with spines. The spinous part 

 of the dorsal fin is separated from the soft portion, and is 

 supported by slender spines that can be folded back into a 

 groove in the back ; this part is always shorter than the soft 

 dorsal. The anal fin has from i to 3 feeble spines. Both the 

 soft dorsal and the anal fins are made up of short, pointed 

 front portions, with the fin-rays all crowded together, followed 

 by a series of detached and much-branched rays or finlets. 

 The slender fleshy peduncle of the tail is keeled on either side. 

 The pectoral fins are placed high up on the sides. The pelvic 

 fins are well-developed, each having a spine and 5 branched 

 rays. A lateral line is present, and often follows a somewhat 

 wavy course along the side of the body. The air-bladder is 

 either small or absent altogether. 



These fishes form an important family, and are all rapid 

 swimmers, living at or near the surface of the sea. Most of 

 them have a wide distribution, some being nearly cosmo- 

 politan. The Mackerels and Tunnies are well distinguished 

 by their general shape and metallic coloration, as well as by 

 the characteristic finlets behind the dorsal and anal fins. 

 Most of them are valued as food, the flesh being firm, oily, 

 and usually of a red colour. Fossil remains of fishes of this 

 type abound in rocks of tne Eocene and Miocene periods. 



TUNNIES. 



(Genus Thunnus.) Fig. 48. 



The body is oblong and robust, and the slender peduncle 

 of the caudal fin has a single keel on each side, in addition to 

 the pair of keels at the base of the fin. The whole of the body 

 is covered with small scales, and those of the " shoulder " 

 region are larger, thicker, and form a kind of corselet. Each 

 of the jaws has a single row of pointed teeth, and there are 

 bands of very small, pointed teeth on the roof of the mouth. 

 The first dorsal fin has 13 or 14 spines, and there are 8 to 10 

 finlets behind the soft dorsal and anal fins. The pectoral 

 fins are of moderate length. The coloration is a dark metallic 

 blue on the back, becoming greyish on the sides, with or without 

 silvery spots, and silvery-white on the belly. The caudal fin 



