6 II. \1 I-ISIIICS iHHTICROSOMAI A) 



with them by means of a hfjament ; (3) in Pscttodvs tlie caudal tin is normally formed, 

 with 17 principal rays, of which 15 are branched, but in the Gadoids the caudal fin is 

 (urnied mainly of dorsal and anal rays, the true homocercal fin being much reduced ; 



14) there is no air-bladder in the adult Psetloiles, but this is present in the Gadoids ; 



15) in Psetlodes there are well-developed pseudobranchia[', whereas in the Gadoids 

 these structures, if present, are reduced and glandular ; and (6) in Pseltodes the 

 oinsthotic bone is Muall, whereas in the Gadoids it is larce, .ind extends downwards 



to the basi-occipital. separating the pro-otic and ex-occipital. As Regan (iqioE. p. 48b) 

 has remarked, " the absence of spinous fin-rays, the large number of rays m the pelvic 

 fins, and the indirect attachment of the pelvic bones to the cleithra may be regarded 

 as primitive features, and it is probable that these fishes [the Gadoids'; have evolved 

 from generalised Iniomi, such as the Aulopida? ". 



In suggestmg a near relationship of the Hetero.somata to the Zeidae. Thilo (1902A. 

 p. 332) emphasised the following points of resemblance : (i) The general form of the 

 body ; (2) the number of abdominal vertebrae ; (3) the structure of the bony supports 

 of the anal fin ; (4) the structure of the pelvic bones ; (5) the form of the pectoral 

 arch ; (0) the connection of pectoral and pelvic fins ; and (7) the form of the urohyal. 



