1/:^:^ 



Figure 294. —Ventral viewsof upper jaws to 



show trituration tooth plates: A, Chilomycterus 



orbicularis, 77.0 mm SL, Somalia, and 158 mm SL, 



Philippines: B, C. schoepfi, 62..'j mm SL, Texas, and 168 mm SL, 



Florida, the latter species with trituration 



plates more or less typical of all 



diodontids except C. orbicularis. 



Figure 29.5. — Chilomycterus schoepfi: upper 

 left, lateral view of upper jaw, with inset 

 showing detail of lateral edge of crushing 

 beak with its individual dental units 

 incorporated into but distinct from the 

 bony matrix of the premaxillary; lower 

 left, cross section through middle of one 



of the individual flattened disklike 



trituration teeth; right, outline of about 



one-half of a trituration tooth, with the 



detail showing the irregular surface; 



ie8 mm SL, Florida. 



The dentition of the pharyngobranchials is also slight- 

 ly variable in diodontids. The pharyngobranchials of the 

 first and second arches always bear small to minute 

 teeth, while the pharyngobranchial of the third arch, 

 when present, is always smaller than those preceding it 

 and is nearly always toothless. The pharyngobranchial of 

 the third arch is absent in Chilomycterus affinis, atinga, 

 reticulatus, and tigrinus, and it is especially small and 

 toothless in C. antillarum, mauretanicus, orbicularis, 

 spinosus, and Dicotylichthys nicthemerus . In C. schoepfi 

 this pharyngobranchial is as small as in the preceding 

 species, but it sometimes bears minute teeth even though 

 usually it is toothless. In D. punctulatus this pharyngo- 

 branchial is toothless but of moderate size. In Diodon 

 this pharyngobranchial is toothless and of moderate 

 (hystrix, jaculiferus) to relatively large (holocanthus) 

 size. 



Gill rakers along the anterior edge of the fourth cer- 

 atobranchial are present in Chilomycterus affinis, 

 atinga, reticulatus, tigrinus, orbicularis, Diodon holo- 

 canthus, hystrix, jaculiferus, and in Dicotylichthys nic- 

 themerus and punctulatus, while they are absent in C. 

 antennatus, antillarum, mauretanicus, schoepfi, and 

 spinosus. The loss of gill rakers along the anterior edge of 

 the fourth arch must be considered a specialization, since 

 in the only other family without a fourth gill, the tetrao- 

 dontids, rakers are always present here. 



Both the dorsal and ventral hypohyals are present in 

 all of the diodontids examined except for Chilomycterus 

 atinga, reticulatus, and tigrinus, which lack (in the 

 single specimen examined of each species) the dorsal ele- 

 ment. 



The trituration teeth internal to the biting edge of the 

 upper and lower jaws always form a large plate divided 

 into right and left halves, each half formed by a single 

 series of large wide flattened tooth plates whose medial 



