2738 



THE BONY FISHES AND GANOIDS 



AND MACKERELS Families NOM^EID^E AND SCOMBERID^S, 



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 compara- 

 tively 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, JVomceus, with 

 two species from the tropical Atlantic and Indian Oceans, lacks finlets, and has a 

 narrow mouth cleft. 



Mackerels 



NEW ZEALAND GASTROCHISMA. 



The second of the two families is typically represented by. the true 

 mackerels {Scomber}, and is characterized 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. Characterized 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, asso- 

 ciating in shoals, which may be of immense size, and frequenting all tropical and 



