474 Percomorphi 
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 vertebre 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, Pharyngognatht, 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 Berycotdea 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 vertebrz, the number increased in cer- 
tain forms, probably through repetitive degeneration. 
The True Mackerels: Scombride.— We may first consider 
the great central family of Scombride, 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 vertebree 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 Stromateide 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 
