THE MACKERELS 



Family XXXII. Scombrida 



Body elongate, fusiform, not much compressed, covered with 

 minute, cycloid scales, those anteriorly forming a corselet; lateral 

 line undulate; head subconic, pointed anteriorly; mouth rather 

 large, premaxillaries not protractile; no supplemental maxillary 

 bone; jaws with sharp teeth; preopercle entire; opercle unarmed; 

 gill-openings very wide, the membranes not united, free from the 

 isthmus; pseudobranchise large; branchiostegals 7; dorsal fins 2, 

 the first of rather weak spines, depressible in a groove, the 

 second similar to the anal, the elevated anterior lobe always dis- 

 tinct; anal spines weak; last rays of dorsal and anal detached and 

 separate, forming in each case a series of finlets; caudal peduncle 

 extremely slender, keeled, the caudal lobes abruptly divergent and 

 falcate, the fin adapted for rapid motion; ventral fins I, 5, thoracic 

 and well developed; lower pharyngeals separate; stomach sac- 

 shaped; pyloric cceca numerous; air-bladder small, sometimes ab- 

 sent. Colouration, metallic, often brilliant, the prevailing shade 

 steel-blue. 



Genera about 20, species about 60. Fishes of the high seas, 

 many of them cosmopolitan, and all having a wide range; mosl 

 of them valued as food-fishes, the flesh being firm and oily, but 

 sometimes coarse. Eight genera are represented in our waters 

 by about 15 species. 



a. Caudal peduncle without median keel on each side; 



Scomber, 273 

 aa. Caudal peduncle with a median keel on each side. 



b. Dorsal spines 10 to 16. 



c. Body scaleless, except about the lateral line and corselet. 



d. Dorsals well separated, the interspace more than half head. 



Auxis, 276 

 dd. Dorsals contiguous, the interspace not one-fifth length of 



head ; Gymnosarda, 277 



cc. Body wholly covered with small scales, those on corselet and 



lateral line sometimes enlarged. 



e. Teeth of jaws slender, subconical, little if at all compressed; 



gillrakers numerous; corselet distinct; pectorals inserted low. 

 /. Vomer and palatines with villiform or sand-like teeth; body 

 robust, not compressed. 



272 



