MOUPHOLOGY OF TELEOSTEAN HEAD SKKLETON. 579 



the face of these considerations would savour too much of 

 unnecessary conservatism. 



On the other hand, when put together they form a com- 

 pact and natural group, clearly marked off from the Acan- 

 thopterygii by the reduced condition of the metapterygoid, 

 the shape of the ethmoid, and the abdominal position of the 

 pelvic fins; and furtlier from the Percesoces and Haplomi by 

 the acrartete condition, the elongated symplectic, the strong 

 tendency to the reduction of the branchial apparatus, and the 

 possession in the trunk of so-called interclavicles and of bony 

 scutes, which may either form a more or less complete arma- 

 ture, or be developed merely along dorsal, ventral, and lateral 

 lines. 



There is some difficulty in determining what degree of im- 

 portance must be attached to this last feature. Sagemehl 

 (85, p. 3) has brought forward a number of valid arguments 

 against its reliability ; but when, in a natural group of fishes 

 such as this, all the members, including even the scaled 

 forms, possess bony scutes, generally arranged in definite 

 order, it can only be regarded as something more than a 

 superficial similarity. That a group of Teleosts should have 

 arisen in which the ganoid plates along some lines were re- 

 tained, instead of being converted into scales, is a possibility 

 which receives an air of probability from the fact that in 

 Gasterosteus the plates of the lateral series are provided 

 with that peg-and-socket arrangement (Parker, 68, p. 41) so 

 characteristic of ganoid plates. 



Other features there are— such as the sculpturing of the 

 roofing bones in the less specialised members ; the simple 

 post-tempoi'al ; the absence of opisthotic ; the general ab- 

 sence of maxillary process and the teeth in the palatine ; the 

 single pterygoid bone; the complete withdrawal of the 

 cranial cavity fi'om the orbit, even in the lowest members ; 

 the general shape of the body ; the elevated pectorals ; the 

 position of dorsal and ventral median fins relative to one 

 another — to which much importance cannot be attached 

 singly, but which, when taken together, help substantially to 



