SCOMBROIDS. 



89 



plates as well as their iuiml)ev also vai-ies in individual I both in the Atlnntie and in the Pacific, in the warmer 

 cases. Thus the de\'(!lopnient of iorni in accordance parts of the ocean, where this species without doubt 

 with the clianges due to age, has become most advanced, has its original home. 



Fam SCOMBRIl)^. 



Bodij fusiform^ more or less elongated. Head underneath {towards the loiver jaw and the isthmus) so compressed 

 that as a tvhole it more or less closely resembles a three-sided pyramid. Eyes middle-sized or small. Of the ex- 

 tenud hones of the head the preoperctda durinr/ youth are dentated at the margin or furnished tvith spines, in 

 adult specimens smooth (like the other hones). Scales small or completely wanting, hut in the region of the pectoral 

 fns most often large and forming a 'corslet! Spinous part of the whole dorsal fin-system shorter than the soft- 

 rayed ; but there being tiro dorsal fins, the anterior {spinous) is longer than the continuous piart of the posterior, 

 wlien the latter, as u-ell as the anal, has a number of finlets behind it". No free spinotis ray, or only one, in 

 front of the anal fin. Simple, pointed, conical or compressed {cutting) teeth, at least in youth, on the jatcs 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 tcithout 

 a break) on the frontal bones. Ventral fins thoracic, generally tvith 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''. Vertehrce more than 25% 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 Carangidce. 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 vertebra? 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- 

 rangidfc. The distinct dorsal canal is either entirely 

 wanting or, as in Scomheromorus {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 tlie genus Elacate, whicli, it appears to me, should hardly he separated from the Scombroid family — Gill, however (Cat. Fisli. 

 East. Coast N. Amei:, 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 Carangklce — 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 spimnis-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 Echeiieis, which genus may still lay claim to a place among the Scombrida, though the family-diagnosis 

 can scarcely notice all such variations. 



* According to Lilljeborg, Axixis thazard has only 14 of these rays. 



"^ According to GCxtiier, there are only 25 vertebra; in Elacate. 



'' On the other hand a ventral branch of the lateral line occurs in Orcijmis (Thynmis) Mlineatus, a Tunny from the Red Sea which 

 has been described by RtppELL. 



12 



Scandinavian Fishes. 



