Percomorphi 259 



orous and predaceous. But among the multitude of forms are 

 many variations, and some of these will seem to be exceptions 

 to any definition of mackerel-like fishes which could possibly 

 be framed. 



The mackerels, or Scombroidea, have usually the tail very 

 slender, composed of very strong bones, with widely forked 

 fin. In the perch and bass the tail is stout, composed largely 

 of flesh, the supporting vertebrae relatively small and spread out 

 fan-fashion behind. Neither mackerels nor perch nor any of 

 their near allies ever have more than five soft rays in the ventral 

 fins, and the persistence of this number throughout the Per- 

 comorphi, Squamipinnes, Pharyngognathi, and spiny fishes 

 generally must be attributed to inheritance from the primitive 

 perch-like or mackerel-like forms. In almost all the groups 

 to be considered in this work, after the Berycoidea the ventral 

 rays are I, 5, or else fewer through degeneration, never more. 

 In the central or primitive members of most of these groups 

 there are twenty-four vertebras, the number increased in cer- 

 tain forms, probably through repetitive degeneration. 



The True Mackerels: Scombridae. We may first consider 

 the great central family of Scombridce, or true mackerels, 

 distinguished among related families by their swift forms, 

 smooth scales, metallic coloration, and technically by the 

 presence of a number of detached finlets behind the dorsal 

 and anal fins. The cut of the mouth is peculiar, the spines 

 in the fins are feeble, the muscular system is extremely strong, 

 the flesh oily, and the air-bladder reduced in size or altogether 

 wanting. As in most swift-swimming fishes and fishes of 

 pelagic habit, the vertebras are numerous and relatively small, 

 an arrangement which promotes flexibility of body. It is 

 not likely that this group is the most primitive of the scombroid 

 fishes. In some respects the Stromateidce stand nearer the 

 primitive stock. The true mackerels, however, furnish the 

 most convenient point of departure in reviewing the great 

 group. 



In the genus of true mackerels, Scomber, the dorsal fins 

 are well separated, the first being rather short, and the scales 

 of the shoulders are not modified to form a corselet. There 

 are numerous species, two of them of general interest. The 



