Figure \23.—Pseudaluteres 

 nasicornis: lateral view of 

 head, 108 mm SL, Philippines, 

 with inset above showing 

 detail of the snout region 



size of the pectoral girdle and of the fin it supports, with 

 the rays reduced in number to eight (usually) or nine, 

 plus the uppermost rudimentary ray. This attests to the 

 far greater reliance in Psilocephalus on the especially 

 long-based and many-rayed soft dorsal (43-52 rays; 

 average of five specimens 49) and anal (53-66 rays, 

 average 58) fins for locomotion. Psilocephalus is the only 

 monacanthid regularly to have far more anal than dorsal 

 fin rays. 



As in balistids, the scapula completely encloses its 

 foramen in most monacanthids, but in Pseudaluteres 

 and Psilocephalus the scapular foramen is incomplete 

 anteriorly, being bounded by the cleithrum. In 

 Psilocephalus this is probably correlated with the reduc- 



ed size of the pectoral girdle and fin, but Pseudaluteres 

 has a well-developed pectoral girdle and a moderate 

 number (11-13) of rays. 



Variation in the monacanthid caudal skeleton mainly 

 concerns the presence or absence of an upper free hy- 

 pural. There is always a single epural and usually a free 

 upper hypural in contrast to the other hypurals which are 

 fused to one another and to the centrum, and a free 

 parhypural. A free upper hypural is absent in the majori- 

 ty of specimens of Monacanthus ciliatus examined and 

 in those of Rudarius ercodes and R. minutus and in the 

 single specimen of Amanses scopas examined (Tyler 

 1970b: 15, erroneously implied that R. ercodes has an up- 

 per free hypural). Of 12 specimens of M. ciliatus examin- 



