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  ACTINOPTEEYGII. 
  

  

  only 
  exposed 
  on 
  the 
  cheek 
  in 
  its 
  lower 
  portion. 
  The 
  subopercnlum 
  

   exhibits 
  a 
  feeble 
  ascending 
  process 
  at 
  its 
  antero-snperior 
  angle; 
  

   and 
  the 
  interopercnlum 
  is 
  relatively 
  large. 
  There 
  are 
  about 
  six 
  

   broad 
  branchiostegal 
  rays; 
  and 
  a 
  large 
  broadly-oval 
  gular 
  plate, 
  

   marked 
  by 
  a 
  V-shaped 
  groove 
  for 
  the 
  sensory 
  canal, 
  occurs 
  in 
  front, 
  

  

  In 
  the 
  axial 
  skeleton 
  of 
  the 
  trunk 
  the 
  notochord 
  must 
  have 
  been 
  

   persistent, 
  and 
  no 
  traces 
  of 
  ossifications 
  in 
  its 
  sheath 
  have 
  been 
  

   detected. 
  The 
  neural 
  and 
  haemal 
  arches, 
  however, 
  are 
  all 
  well 
  

   ossified 
  at 
  least 
  superficially, 
  and 
  only 
  the 
  thickness 
  of 
  the 
  squa- 
  

   mation 
  prevents 
  their 
  being 
  frequently 
  displayed. 
  Throughout 
  the 
  

   trunk 
  as 
  far 
  as 
  the 
  middle 
  of 
  the 
  caudal 
  region, 
  the 
  neural 
  spines 
  

   are 
  not 
  fused 
  with 
  their 
  corresponding 
  arches, 
  this 
  fusion 
  taking 
  

   place 
  only 
  in 
  the 
  hinder 
  half 
  of 
  the 
  tail. 
  The 
  first 
  few 
  neurals 
  are 
  

   especially 
  robust, 
  expanded 
  at 
  their 
  upper 
  end, 
  though 
  not 
  sup- 
  

   porting 
  the 
  stout 
  ridge-scales, 
  and 
  directly 
  apposed 
  to 
  their 
  arches 
  ; 
  

   the 
  remaining 
  neurals 
  are 
  more 
  slender, 
  taper 
  below, 
  and 
  slightly 
  

   overlap 
  their 
  arches. 
  The 
  ribs 
  in 
  the 
  abdominal 
  region 
  form 
  a 
  regular 
  

   series, 
  but 
  do 
  not 
  reach 
  the 
  ventral 
  border; 
  the 
  haemal 
  spines 
  

   in 
  the 
  caudal 
  region 
  are 
  fused 
  with 
  their 
  corresponding 
  arches, 
  are 
  

   sharply 
  bent 
  backwards, 
  and 
  exhibit 
  a 
  small 
  triangular 
  expansion 
  

   anteriorly 
  at 
  their 
  base. 
  There 
  are 
  no 
  intermuscular 
  bones. 
  

  

  All 
  the 
  fins 
  bear 
  uniserial 
  fulcra 
  of 
  moderate 
  size 
  ; 
  but 
  the 
  two 
  

   halves 
  of 
  the 
  fin-rays 
  at 
  least 
  in 
  the 
  median 
  fins 
  seem 
  to 
  be 
  loosely 
  

   apposed. 
  The 
  number 
  of 
  the 
  fin-supports 
  in 
  the 
  dorsal 
  is 
  proved 
  to 
  

   equal 
  exactly 
  that 
  of 
  the 
  rays, 
  and 
  there 
  is 
  no 
  fusion 
  of 
  supports 
  at 
  

   its 
  origin. 
  The 
  paired 
  fins 
  are 
  small 
  and 
  delicate, 
  but 
  nothing 
  

   worthy 
  of 
  note 
  is 
  known 
  in 
  reference 
  to 
  the 
  supports. 
  There 
  is 
  a 
  

   large 
  post-temporal 
  plate 
  on 
  each 
  side 
  articulated 
  with 
  the 
  supra- 
  

   clavicle 
  ; 
  and 
  the 
  long, 
  arched 
  clavicle 
  exhibits 
  its 
  anterior 
  margin 
  

   sharply 
  bent 
  inwards. 
  

  

  The 
  scales 
  in 
  Dapedius 
  have 
  a 
  broad 
  peg-and-socket 
  articulation, 
  

   but 
  no 
  sharply 
  thickened 
  rib 
  on 
  the 
  inner 
  face. 
  The 
  azygous 
  ridge- 
  

   scale 
  are 
  not 
  acuminate, 
  except 
  at 
  the 
  origin 
  of 
  the 
  anal 
  fin, 
  where 
  

   a 
  few 
  are 
  enlarged. 
  

  

  Most 
  of 
  the 
  minor 
  characters 
  of 
  Dapedius 
  are 
  very 
  variable, 
  and 
  

   it 
  is 
  thus 
  difficult 
  to 
  subdivide 
  the 
  genus 
  into 
  well-defined 
  species. 
  

   In 
  the 
  majority 
  of 
  forms, 
  the 
  scales 
  are 
  tuberculated 
  only 
  in 
  the 
  

   anterior 
  dorsal 
  and 
  ventral 
  regions 
  ; 
  rarely 
  the 
  tuberculations 
  extend 
  

   over 
  the 
  flank. 
  One 
  group 
  of 
  species 
  has 
  the 
  marginal 
  teeth 
  bi- 
  

   cuspid, 
  while 
  another 
  group 
  has 
  the 
  same 
  teeth 
  unicuspid 
  ; 
  but 
  in 
  

   observing 
  this 
  character 
  it 
  must 
  be 
  remembered 
  that 
  the 
  former 
  

   teeth 
  when 
  seen 
  in 
  side 
  view 
  may 
  easily 
  be 
  mistaken 
  for 
  the 
  latter. 
  

   There 
  are 
  also 
  tolerably 
  constant 
  differences 
  in 
  the 
  form 
  of 
  the 
  trunk, 
  

  

  