SCOMBROIDS. 
89 
plates as well as their number also varies in individual 
cases. Thus the development of form in accordance 
with the changes due to age, has become most advanced, 
both in the Atlantic and in the Pacific, in the warmer 
parts of the ocean, where this species without doubt 
has its original home. 
Fam SCOMBRI I) M. 
Body fusiform , more or less elongated. Head underneath (i towards the lower jaw and the isthmus) so compressed 
that as a whole it more or less closely resembles a three-sided pyramid. Eyes middle-sized or small. Of the ex- 
ternal bones of the head the preopercula during youth are dentated at the margin or furnished with spines , in 
adult specimens smooth ( like the other bones). Scales small or completely wanting , but in the region of the pectoral 
fins most often large and forming a ‘ corslet Spinous part of the whole dorsal fin-system shorter than the soft- 
rayed; but there being two dorsal fins , the anterior ( spinous ) is longer than the continuous part of the posterior, 
ivlien the latter, as well as the anal, has a number of finlets behind it a . No free spinous ray , or only one , in 
front of the anal fin. Simple, pointed, conical or compressed ( cutting ) teeth, at least in youth, on the jaws and 
generally on the palate as well. Jaws of equal length, or the lower somewhat longer than the upper. Upper lon- 
gitudinal ridges of the skull comparatively little developed: supra- occipital ridge not continued (at least not without 
a break) on the frontal bones. Ventral fins thoracic, generally with one spinous ray and five soft. Gill-openings 
large, and branchiostegal membranes separate. Branchiostegal rays 7. Branched rays in the caudal fin at least 
15 h . Vertebrae more than 25 c , more than 10 of which are abdominal. 
It is the Mackerel family, next to those of the 
Herring, Cod and Salmon, that is the most important 
to man from an economical point of view. Their so- 
ciable life makes these fishes comparatively easy to 
catch, and their good flavour and fatness give them a 
place of honour in the kitchen. This is also true, 
though in a less degree, of the preceding family, which 
the Scombroids, as we have already said, resemble 
so closely that the family-character is restricted to a 
higher or lower degree of development of certain pe- 
culiarities. In the Mackerel family, however, we never 
find the body so high and compressed as it sometimes 
is in the Carangidae. Further, in the former family, 
the eyes are not so large as in some species of the 
latter, the bony ridges on the skull are not so high 
or so long, nor is the reduction of the ventral fins or 
of the first dorsal so great. But the spinous rays of 
the anal fin to a great extent vanish, and in the fusi- 
form body, which is more or less elongated, we may 
sometimes find the number of vertebrae to be as high 
as 45. 
The system of the lateral line is much less de- 
veloped, externally at least, than in certain of the Ca- 
rangidce. The distinct dorsal canal is either entirely 
wanting or, as in Scomberomorus ( Cybium ), only ex- 
tends as far as the beginning of the first dorsal fin'*. 
In the Scombroids the articulation of the mouth is 
peculiarly arranged. On the outside of the lower jaw 
is a well-defined groove, which really corresponds to 
the fold beneath the underlip when it is laid down, 
in other fishes. This groove is continued in a down- 
ward direction back from the corners of the mouth. 
There is a corresponding groove in the upper jaw; but 
this is formed under the inferior margin of the pre- 
“ In the genus Elacate, which, it appears to me, should hardly be separated from the Scombroid family — Gill, however (Cat. Fish. 
East. Coast N. Amer., 1873, Smiths. Misc. Coll., No. 283, p. 29), has made it a distinct family, after having previously (Proc. Acad. Nat. 
Sc. Philad. 1862, p. 126) referred it to the Carangiclce ■ — - the whole of the soft-rayed part of the second dorsal fin (as well as of the anal) is con- 
tinuous, and in this case the spinous-rayed part of the dorsal — here broken up into free spines — is shorter than the soft-rayed. This is 
also the case in some species of Echeneis, which genus may still lay claim to a place among the Scombridai, though the family-diagnosis 
can scarcely notice all such variations. 
b According to Lilljeborg, Auxis thazard has only 14 of these rays. 
c According to Gunther, there are only 25 vertebras in Elacate. 
d On the other hand a ventral branch of the lateral line occurs in Orcynus (Thynnus) bilineatus , a Tunny from the Red Sea which 
has been described by Ruppell. 
Scandinavian Fishes. 
12 
