A CA NTH OP TER YGII 



425 



sub-order is the fact that the pelvic fins are always very far 

 forward. Except in the Salmopercae, the pelvic bones are attached 

 to the cleithra, and the pelvic fins are 'thoracic' or 'jugular,' 

 with usually much less than eighteen dermal rays. Excepting in a 

 few of the lowest genera, the pneumatic duct is closed. Among 

 mere primitive characters may be mentioned a continuous dorsal 

 fm, the presence of a toothed palate, an eye-muscle canal, a scapular 

 foramen, both pleural ribs and epipleurals attached to them, and 

 four complete gills with five branchial slits. All these characters, 

 however, are liable to great modification in the more specialised 

 families, and it is in this sub-order that the Teleostei attain their 

 highest development. 



Extremely numerous and diversified at the present time, the 

 Acanthopterygii make their appearance only in the Cretaceous 

 epoch. They may be classed in two Divisions, to the second of 

 which most of the modern forms seem to belong. 



Division 1. SALMOPERCAE. 



The pelvic fins are, strictly speaking, abdominal, not being 

 closely attached to the cleithral symphysis. 



Family Percopsidae. An interesting intermediate family of dis- 

 tinctly perch-like structure ; but the pelvic fins are not attached to the 



Fig. 430. 

 Columbia transmontana, Eig. (From Jordan and Evermann.) 



pectoral girdle, although close to it, and there is an adipose fin. The 

 scales are strongly ctenoid, and do not cover the head. The air-bladder 

 has an open duct. The hones of the skull have large mucous cavities. 

 The myodome and epipleurals are absent. One radial rests on the 



