﻿164 
  ACTINOPTERYGJI. 
  

  

  pterygo-palatine 
  arcade 
  {pi.) 
  bears 
  at 
  least 
  one 
  series 
  of 
  large, 
  well- 
  

   spaced 
  conical 
  or 
  styliform 
  teeth 
  ; 
  and 
  there 
  is 
  a 
  cluster 
  of 
  similar 
  

   teeth 
  on 
  the 
  vomer 
  (vo.). 
  The 
  maxilla 
  (mx.) 
  is 
  elongated, 
  tapering 
  

   in 
  front 
  ; 
  and 
  the 
  premaxilla 
  {pmoc.) 
  is 
  very 
  short, 
  with 
  a 
  slender 
  

   ascending 
  process. 
  The 
  mandible 
  is 
  much 
  deepened 
  in 
  the 
  coronoid 
  

   region, 
  and 
  von 
  Zittel 
  recognizes 
  dentary 
  (d.), 
  splenial 
  (spl.\ 
  and 
  

   angular 
  (ar.) 
  elements. 
  In 
  the 
  hyoid 
  arch, 
  the 
  epihyal, 
  cerato- 
  

   Tiyal, 
  and 
  hypohyal 
  bones 
  are 
  well 
  ossified. 
  The 
  opercular 
  apparatus 
  

   is 
  complete; 
  the 
  suboperculum 
  {s.op.) 
  exhibiting 
  an 
  ascending 
  

   process 
  at 
  its 
  antero-superior 
  angle, 
  and 
  the 
  large 
  inferior 
  limb 
  of 
  

   the 
  preoperculum 
  (p.op.) 
  being 
  much 
  turned 
  forwards. 
  The 
  bran- 
  

   chiostegal 
  rays 
  (br.) 
  are 
  few, 
  well-spaced, 
  constricted 
  at 
  their 
  point 
  

   of 
  attachment 
  and 
  much 
  expanded 
  in 
  their 
  distal 
  portion. 
  A 
  gular 
  

   plate 
  has 
  only 
  been 
  observed 
  in 
  Ophiopsis 
  and 
  Eusernius. 
  

  

  The 
  ossifications 
  in 
  the 
  notochordal 
  sheath 
  do 
  not 
  advance 
  beyond 
  

   the 
  stage 
  of 
  unconstricted 
  rings 
  ; 
  and 
  Yetter 
  1 
  has 
  observed 
  completed 
  

   annular 
  pleurocentra 
  and 
  hypocentra 
  alternating 
  in 
  the 
  caudal 
  

   region 
  of 
  Ophiopsis. 
  The 
  ribs 
  are 
  ossified, 
  though 
  usually 
  delicate 
  

   and 
  not 
  extending 
  quite 
  to 
  the 
  ventral 
  border 
  of 
  the 
  fish 
  ; 
  and 
  the 
  

   neural 
  spines 
  are 
  fused 
  with 
  their 
  supporting 
  arches 
  both 
  in 
  the 
  

   abdominal 
  and 
  caudal 
  regions. 
  

  

  The 
  basals 
  in 
  the 
  pectoral 
  fin 
  of 
  Ophiopsis 
  are 
  not 
  less 
  than 
  nine 
  

   in 
  number 
  (PL 
  III. 
  fig. 
  3); 
  and 
  the 
  pelvic 
  fin-supports 
  are 
  

   irregularly 
  hour-glass 
  shaped, 
  the 
  proximal 
  end 
  exhibiting 
  the 
  

   widest 
  expansion. 
  

  

  There 
  is 
  one 
  series 
  of 
  enlarged 
  postclavicular 
  scales, 
  especially 
  

   well 
  shown 
  in 
  Histionotus; 
  and 
  the 
  dorsal 
  fin-rays 
  in 
  this 
  genus 
  

   seem 
  to 
  be 
  equal 
  in 
  number 
  to 
  bhe 
  vertical 
  series 
  of 
  regular 
  flank- 
  

   scales 
  beneath 
  them 
  2 
  . 
  There 
  are 
  enlarged 
  ridge-scales 
  on 
  the 
  

   caudal 
  pedicle, 
  which 
  attain 
  an 
  extreme 
  development 
  on 
  its 
  ventral 
  

   border 
  in 
  Macrosemius. 
  

  

  Synopsis 
  of 
  Genera. 
  

  

  I. 
  Dorsal 
  fin 
  single. 
  

  

  Back 
  nearly 
  straight 
  and 
  dorsal 
  fin 
  occupy- 
  

   ing 
  from 
  one-half 
  to 
  two-thirds 
  of 
  its 
  

   length 
  ; 
  caudal 
  fin 
  forked 
  ; 
  fulcra 
  on 
  all 
  

   median 
  fins 
  ; 
  squamation 
  complete 
  and 
  

   flank-scales 
  scarcely 
  if 
  at 
  all 
  deepened. 
  . 
  Ophiopsis 
  (p. 
  165). 
  

  

  1 
  Mitth. 
  k. 
  mineral.-geol. 
  Mus. 
  Dresden, 
  pt. 
  iv. 
  (1881), 
  p. 
  56. 
  

  

  2 
  See 
  figure 
  of 
  Histionotus 
  angularis 
  by 
  J. 
  C. 
  Mansel-Pleydell, 
  Geol. 
  Mag. 
  

   13] 
  vol. 
  vi. 
  (1889), 
  pi. 
  vii. 
  

  

  