ACAXTHOPTERYGII 



675 



DIVISION II. SCOMBRIFORMES. 



Xo bony stay for the praeopercle. Spinous dorsal, if distinct, 

 formed of short or feeble, slender spines. Epipleurals usually 

 attached to the centra when ribs are sessile, or to the para- 

 pophyses of the vertebrae, rarely to the ribs. Pectoral arch 

 similar to that of the Perciformes, but pterygials sometimes more 

 abbreviated. Ventral fins thoracic, Caudal fin, if well developed, 

 with very numerous rays deeply forked at the base. 



Although bound by natural ties, the series of families that 

 cluster round the Mackerel offer so many modifications of 

 structure that it is almost impossible to draw up a diagnosis 

 differentiating every one of its members from the Perciformes, 

 with which they are closely connected, and from which they 



FIG. 414. Caudal fin of Sarda orientalis. h.s, Hypural spine. 



hardly deserve to be separated. Even after removing many 

 genera which have been united with them by my predecessors, 

 and which will now be found scattered among various groups of 

 the system, no good definition of the Scombriformes can be 

 given. The Mackerel and Horse -Mackerel are taken as the 

 pattern -forms around which more or less aberrant types are 

 located, types yet not so aberrant as to be traced back to these 

 familiar forms through a number of intermediate grades. As 



