NOMALIDS AND MACKERELS 369 



point, and the pelvic fins are composed of numerous rays. This fish, which attains 

 to the length of 4 feet, is remarkable for the beauty of its coloration, the body 

 being bluish, with round silvery spots, and the fins brilliant scarlet. Its flesh is 

 reported to be of good flavour. In the allied Mene, also represented by a single 

 species (M. maculata), inhabiting the Indian and Malayan seas, and attaining a 

 length of 8 or 9 inches, the jaws are toothed, the mouth is very protractile, and 

 the first rays of the pelvic fins are greatly elongated. This genus is found in a 

 fossil state in the middle Eocene of Monte Bolca ; while in the London Clay we 

 have the extinct Goniognathus. 



NOM^IDS AND MACKERELS, Families NOM^ID^E and SCOMBERID^:. 



Both these families agree in having two dorsal fins, and in the number of 

 trunk-vertebrae exceeding ten, and the caudal fourteen. In the first small and 

 comparatively unimportant group there may be finlets behind the dorsal and anal 

 fins ; the dorsal has a distinct spinous portion, the caudal is forked, and the body 

 covered with cycloid scales of moderate size. All these fishes are marine, and, in 

 the young state at least, pelagic. Of the better-known genera, Gastrochisma, with 

 a broad cleft to the mouth, finlets on the back and abdomen, and enormous pelvic 

 fins, capable of being folded into a cleft in the body, and of which the position is 

 thoracic, is known by a single New Zealand species (G. melampus). On the other 

 hand, Nomce-us, with two species from the Tropical Atlantic and Indian Ocean, 

 lacks finlets, and has a narrow mouth-cleft. 



The second of the two families is typically represented by the 

 true mackerels (Scomber), and is characterised by the oblong or 

 slightly elongated form of the body which is but very slightly compressed, and 

 covered either with very minute scales, or naked and the structure of the dorsal 

 fins. The first of these may be either modified into free spines, or an adhesive disc, 

 or the posterior dorsal, together with the anal, is split up into finlets. There may or 

 may not be an air-bladder. Characterised by their beautiful protective coloration, 

 which is some shade of bluish green, mottled or barred with black above, and 

 iridescent silver beneath, the members of this family are all pelagic and 

 carnivorous fish, associating in shoals, which may be of immense size, and 

 frequenting all tropical and temperate seas. To enable them to keep up their 

 constant rapid movements, their muscles, which are consequently red in colour, 

 receive a much more abundant supply of blood than is the case with other 

 members of the class, and their temperature is thereby raised several degrees 

 higher. Although spawning in the open sea, at certain times of the year they make 

 periodical migrations towards the shore in pursuit of the shoals of herrings and 

 their fry on which they so largely subsist. In time, the family dates from the 

 lower Eocene deposits of Switzerland, where it is represented by several extinct 

 genera, and likewise by a species of sucking-fish ; while many of the other existing 

 genera occur in the latter deposits. 



The true mackerels are characterised by the first dorsal fin being continuous, 

 with feeble spines ; the presence of five or six finlets behind the dorsal and anal ; 

 the very small scales, which are evenly distributed over the body ; the small size of 



VOL. V. 24 



