CHAPTER XI 

 ACANTHOPTERYGII ; SYNENTOGNATHI 



RDER Acanthopterygii, the Spiny-rayed Fishes. The 

 most of the remaining bony fishes constitute a natural 

 group for which the name Acanthopterygii (a^artfa, 

 spine; mepvB,, nrepov, fin or wing) may be used. This name 

 is often written Actinopteri, a form equally correct and more 

 euphonious and convenient. These fishes are characterized, 

 with numerous exceptions, by the presence of fin spines, by 

 the connection of the ventral fins with the shoulder-girdle, 

 by the presence in general of more than one spine in the an- 

 terior part of dorsal and anal fins, and as a rule of one spine and 

 five rays in the ventral fins, and by the absence in the adult 

 of a duct to the air-bladder. Minor characters are these: 

 the pectoral fins are inserted high on the shoulder-girdle, the 

 scales are often ctenoid, and the edge of the upper jaw is formed 

 by the premaxillary alone, the maxillary being always toothless. 



But it is impossible to define or limit the group by any 

 single character or group of characters. It is connected with 

 the Malacopterygii through the Haplomi on the one hand by 

 transitional groups of genera which may lack any one of these 

 characters. On the other hand, in the extreme forms, each 

 of these distinctive characters may be lost through degenera- 

 tion. Thus fin spines, ctenoid scales, and the homocercal tail 

 are lost in the codfishes, the connection of ventrals with shoulder- 

 girdle fails in the Percesoces, etc., and the development of the 

 air-duct is subject to all sorts of variations. In one family 

 even the adipose fin remains through all the changes and 

 modifications the species have undergone. 



The various transitional forms between the Haplomi and 

 the perch-like fishes have been from time to time regarded as 



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