Families of Teleostean Fishes. 181 



Division II. SCOMBKIFOEMES. 



No bony stay for the praeopercle. Spinous dorsal, if 

 distinct, formed of short or feeble, slender spines. Epi- 

 pleurals usually attached to the centra when ribs are sessile, 

 or to the parapophyses of the vertebroe, rarely to the ribs. 

 Pectoral arch similar to that of the Perciformes, but ptery- 

 gials 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 

 hardly deserve to be separated. Even after removing many 

 genera which have been united with them by my pre- 

 decessors, and which will now be found scattered among 

 various groups of the system, no better definition of the 

 Scombriformes can be given than that 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 regards external 

 features, it may be stated that the dorsal and anal spines, 

 if present, are weak and slender, or, if strong, short and 

 detached, the caudal peduncle is constricted, and the caudal 

 fin, if well developed, is usually deeply forked and with the 

 forked bases of the very numerous rays much longer than 

 in most of the Perciformes, embracing at least a considerable 

 portion of the expanded ural bones, a character by which the 

 Chaetodontida?, Acanthuridse, and several extinct types which 

 have been placed with the Carangida3 are at once excluded. 

 All are marine and many are palagic and of very wide distri- 

 bution. No prastertiary members of this division, as here 

 defined, have yet been found. 



Nine families : — 



I. Praemaxillaries more or less protractile, not beak-like ; scales small 

 or absent, sometimes with enlarged lateral scutes ; spinous dorsal 

 short or replaced by a series of isolated spines ; aual usually with 

 one or two spines detached from the rest of the tin. 



Praeeaudal vertebrfe with transverse processes, behind 



which the ribs are attached 1. Carangidce. 



Praeeaudal vertebrae without well-developed para- 

 pophyses ; ribs and epipleurals inserted close 

 together on the centra 2. 2thachicentrid&. 



