supraoccipito 



reduced but functionally similar version of that of 

 balistids, but the other monacanthids have further 

 reduced the apparatus variously to the point of the total 

 absence of a fin -ray element, encasing scales and dorsal 

 pelvic lobe. It is clear, however, that it was a balistid 

 group with a flexible series of encasing scales that gave 

 rise to the monacanthids, the most generalized of which 

 also have a flexible series of scales. 



Probably associated with a greater body flexibility in 

 monacanthids, the constant 7 + 11 = 18 vertebral for- 

 mula of balistids is changed in monacanthids by an in- 

 crease of at least one vertebra in the caudal series, and 

 often more. In balistids the basal pterygiophores of the 

 soft dorsal and anal fins bear a flange for muscle attach- 

 ment along their lengths. This is true also of 

 monacanthids, but in the latter family the crest is fur- 

 ther elaborated, particularly distally, where it is es- 

 pecially expanded laterally into a more or less hooklike 

 process partially separating the inclinator, erector, and 

 depressor muscles of each fin ray from those of the 

 preceding and succeeding rays. The distal pterygio- 

 phores are much less different between the two groups. 

 Those of most balistids, like their triacanthid ancestral 

 group, have the right and left halves fused into a single 

 piece, although far posteriorly in the soft dorsal and anal 

 fins the right and left halves may remain separate. The 

 distal pterygiophores of balistids may also be expected to 

 be in separate halves in very young specimens. Of the 



Figure 75.— Lateral view of most specialized 



balistid skull and suspensorium: 



OdonuB niger, 173 mm SL, New Guinea. 



balistids examined, only Balistes polylepis, B. ca- 

 priscus, B. ueluta, and Sufflamen verres have most of 

 the distal pterygiophores as separate halves, but the 

 specimens of these are all relatively small, and the distal 

 pterygiophores can be expected to be fused into a single 

 piece in adult specimens of these species. Only in 

 Canthidermis maculatus do the distal pterygiophores re- 

 main as separate halves even in large specimens. In an 

 80.1 mm specimen nearly all the distal pterygiophores 

 have separate halves, while in a large 217 mm adult 

 those in approximately the anterior one-third of the soft 

 dorsal and anal fins have the two halves fused into a 

 single piece while more posteriorly they remain separate. 

 The retention of mostly separate halves in the distal 

 pterygiophores of Canthidermis is probably related in 

 some way both to its oceanic existence and late develop- 

 ment of full ossification. 



In the derived monacanthids, nearly all of the distal 

 pterygiophores are single pieces even in small specimens, 

 and always so in large specimens. 



