468 WILLIAM K. GREGORY 



forms articulating independently of the premaxillary with the 

 ethmoid (contrast the Ostariophysi) . A symplectic is usually 

 present 1 ; the opercular bones are complete 2 (contrast the 

 Ostariophysi) ;the pharyngeal bones are simple, above and below; 

 the bony supraoccipital, in many forms still separated by the 

 parietals from the frontals, progressively gains contact with the 

 frontals (see page 471). As in Ostariophysi and actinopterous 

 Ganoids, the precoracoid (mesocoracoid) arch is retained and 

 the pectoral arch is suspended from the skull by a bony post- 

 temporal. The simple air bladder (usually present) has a 

 pneumatic duct leading into the digestive tract. The dermal 

 rays of the median fins articulate with an equal number of 

 endoskeletal supports. The dorsal and anal fins are spineless, 3 

 i. e. the fin rays are articulated, the pectorals (when present) 

 are abdominal. Intermuscular bones are present. The caudal 

 hsemapophyses and neurapophyses progressively expand and fuse 

 into hypural and epural bones, the caudal portion of the verte- 

 bral column degenerating and becoming upturned, the tail finally 

 becoming completely homocercal. Ganoidean characters, such 

 as intergulars, interclavicles, fin fulcra, ganoine, splenials, coro- 

 noids, the intestinal spiral valve, and the multivalvular bulbus 

 arterious, are all greatly reduced or absent. 



The ordinal characters of this group are all generalized as 

 compared with those of other Teleosts, which is equivalent to 

 saying that the order is a central one related to the ancestors of 

 the Mesichthyes and Acanthopteroidei. The generalized Lep- 

 tolepididae from the Jurassic and Cretaceous have already been 

 noticed. 



The Elopidae are the most generalized of living Teleosts, with 

 numerous representatives in the Cretaceous (e.g. Spaniodori), 

 and with two surviving genera, Elops and the Tarpon (Me- 

 galops), both of which retain the Ganoidean gular plates. A 

 progressive character is the forward and upward growth of the 

 supraoccipital, which attains such importance in higher orders, 



1 Except in Mormyridas, Phractolasmidas, Cromeriidas. 



2 Except in Pantodontidaa. 



* Compare, however, the non-articulated rays in the dorsal fin of the 



Ctenothrissidae. 



