456 FISHES. 



and long, and can be completely concealed in a fold of the 

 abdomen. 



G. melampus, from the coast of E"ew Zealand ; scarce. 



IS'OMEUS. — Cleft of the mouth narrow. No finlets. The 

 ventral fin is long and broad, attached to the abdomen by a 

 membrane, and can be received in a fissure of the abdomen. 



N. gronovii is a comraon pelagic fish in the Atlantic and 

 Indian Oceans ; of small size. 



Other genera belonging to this family are Psenes and 

 OuMceps. 



Seventh Family — Scombkid^. 



Bodi/ oblong, scarcely compressed, naked or covered with small 



scales ; eye lateral. Dentition well developed. No hony stay 



for the prceoperculum. Two dorsal fins ; generally finlets. 



Ventrals thoracic, with one spine and five rays. More than ten 



abdominal, and more than fourteen caudal vertebrcB. 



The fishes of the "Mackerel" family are pelagic forms, 

 abundant in all the seas of the tropical and temperate zones. 

 They are one of the four families of fishes which are the most 

 useful to man, the others being the Gadoids, Clupeoids, and 

 Salmonoids. They are fishes of prey, and unceasingly active, 

 their power of endurance in swimming being equal to the 

 rapidity of their motions. Their muscles receive a greater 

 supply of blood-vessels and nerves than in other fishes, and 

 are of a red colour, and more like those of birds or mammals. 

 This energy of muscular action causes the temperature of 

 their blood to be several degrees higher than in other fishes. 

 They wander about in shoals, spawn in the open sea, but 

 periodically approach the shore, probably in the pursuit of 

 other fishes on which they feed.^ 



■^ Mackerel, like other marine fishes, birds, and mammals of prey, follow 

 the shoals of young and adult Clupeoids in their periodical migrations ; on 

 the British coasts it is principally the fry of the Pilchard and Sprat which 

 wanders fi-om the open sea towards the coast, and guides the movements of 

 the Mackerel. 



