caudal series (as well as, in Oxymonticanthiu and 

 Pseudaluteres, by one in the abdominal series), as ex- 

 emplified by Alutera, whose four species have normal 

 vertebral counts ranging from 20 to 23 but all of which re- 

 tain 7 abdominal vertebrae. The greatest increase in 

 number of vertebrae is in the extremely elongate body of 

 Psilocephalus barbatus, the increase again being con- 

 fined to additions in the caudal series. Four of the five 

 specimens of P. barbatus cleared and stained or radio- 

 graphed have 7 abdominal and 22 or 23 caudal verte- 

 brae, while one has 8 abdominal and 22 caudal verte- 

 brae. 



The neural spines of the abdominal vertebrae anterior 

 to the first basal pterygiophore of the soft dorsal fin vary 

 from relatively narrow long slender shafts (e.g., 

 Brachaluteres) to short slender shafts (e.g., Chaeto- 

 derma) to broadly anteroposteriorly expanded plates 

 (e.g., Pseudaluteres), with intermediate conditions 

 found in other genera. As in balistids, which always have 

 five vertebrae anterior to the first basal pterygiophore of 

 the soft dorsal fin, the great majority of monacanthids 

 also have five so placed. The only exceptions are the two 

 Atlantic species of Monacanthus (ciliatus and tuckeri), 

 the single species of Acanthaluteres examined, nd one 

 of the two species of Rudarius (minutus), all of which 

 have only four vertebrae anterior to the first soft dorsal 



Figure 124.— Dorsal viewi of skull* of: 



A, Pnudalutereg nasicomis, 108 mm SL, 



Philippines, highly specialized; 



B, Paraluteres prionurue, 46.4 mm SL, 



Seychelles, moderately specialized; 



C, Chaetoderma spinosiasimus, 33.0 mm SL, 



Malaya, relatively generalized. 



fin basal pterygiophore, and Pseudaluteres nasicornis 

 with six and Psilocephalus barbatus with eight. 



As in balistids, the lateral line system in most mona- 

 canthids is inconspicuous, and can usually only be fol- 

 lowed in cleared and stained specimens examined under 

 a microscope. However, it can be relatively easily seen 

 with the unaided eye even in alcohol preserved speci- 

 mens of a few species of Monacanthus (especially chinen- 

 sis), Paramonacanthus, and Paraluteres prionurus, and, 

 to a lesser extent, in Psilocephalus barbatus. 



The scales of the lateral line in monacanthids typically 

 have a foramen in the basal plate with an upright spiny 

 process like that of the other scales bordering the 

 foramen above and below. The only species examined in 

 which such lateral line scales could not be found was 

 Pseudaluteres nasicornis. 



In all species except Paraluteres prionurus the head 

 and body are more or less fully covered with scales whose 

 upright spinulations usually give a shagreenlike quality 



