PERCIFORMES 



439 



Flo. 450. 

 Monacanthus chaeroccphalus, Blkr. (After Day, Fishes of India.) 



Family OSTRACIONTIDAE. ' 

 narrow teeth. The carapace 

 has an almost vertical front edge, 

 angular sides, and often large 

 frontal and anal horns. 



Ostracion, L. ; tropical seas ; 

 Eocene, Europe. Aracana, Gr. ; 

 Lactophrys, Sw. tropical seas. 



BRANCH 2. TRIODONTES. 

 Family TRIODONTIDAE. A family 

 intermediate between the first 

 and third sub-groups, whose exact 

 position it is difficult to deter- 

 mine. The teeth coalesce into a 

 beak, single below but paired 

 above. The spinous dorsal and 

 the pelvic fins have disappeared, 

 there is a dilatable oesophageal 

 sac. Yet a movable pelvis is 

 present as in the Balistidae, which 

 they resemble in many characters 

 of the skeleton. There are twenty 

 vertebrae, and the body is covered 

 with small spiny plates. 



Triodon, Keinw. ; E. Indies. 



BRANCH 3. GYMNODONTES. 

 There are no normal scales, no 

 dorsal spinous fin, no pelvic fin 



Trunk'- or 'Coffer -Fish,' with long 



ac. 



sot:. 



\iot. 



ac. 



Fio. 451. 



ChUomycterus reticulatus, L. Porcupine fish ; 

 from specimens in British Museum. Vertical 

 median section of both jaws, a.c, alveolar cavity 

 in which young teeth develop ; i.o.t, grinding 

 surface formed by inner set of old tooth-plates ; 

 s.o.t, grinding surface formed by outer set of old 

 tooth-plates ; y.t, young tooth-plates. 



