146 



PALEONTOLOGY 



Order IV.— ACANTHOPTERI. 

 Char. — Endo-skeleton ossified ; fins with one or more of the 

 first rays unjointed or inflexible spines ; ventrals in most 

 beneath or in advance of the pectorals ; swim-bladder 

 without air-duct, 



Sub-Order 1 .— CTEXOIDEI. 

 Exo-skeleton as ctenoid scales (fig. 58). 



Of this sub-order may be given two genera, both of which 

 are now extinct. 

 One {Semiopho- 

 rus) belongs to ' 

 the chetodont 



Fig. 58. 



Scale of Perca 



(Recent). 



family ; the 

 other (Smerdis) 

 to the Percoids. 

 The genus 

 Semiophorus, 

 Ag. (fig. 59), is 

 represented ex- 

 clusively by ex- 

 tinct species pe- 

 culiar to the 

 tertiary deposits 

 at Monte Bolca. 

 It is character- 

 ized by the ex- 



Fig. 59. 

 Semiophorus velicans (Monte Bolca). 



treme height or prolongation of the anterior part of the dorsal 



