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  ACTINOPTERYGII. 
  

  

  are 
  perhaps 
  rare 
  traces 
  of 
  slight 
  ossifications 
  in 
  its 
  sheath 
  both 
  in 
  

   the 
  abdominal 
  and 
  caudal 
  regions. 
  The 
  neural 
  and 
  hoemal 
  arches, 
  

   however, 
  are 
  all 
  well 
  ossified, 
  numerous, 
  slender, 
  and 
  very 
  closely 
  

   arranged 
  ; 
  while 
  the 
  lamina 
  of 
  each 
  arch 
  is 
  remarkably 
  deep 
  aud 
  

   narrow, 
  and 
  might 
  readily 
  be 
  mistaken 
  for 
  a 
  vertebral 
  element. 
  The 
  

   ribs 
  are 
  especially 
  slender, 
  not 
  extending 
  to 
  the 
  ventral 
  border 
  of 
  the 
  

   abdomen 
  ; 
  and 
  the 
  sigmoidally-bent 
  neural 
  spines 
  in 
  the 
  abdominal 
  

   region 
  remain 
  separate 
  from 
  their 
  supporting 
  arches, 
  fusion 
  not 
  

   taking 
  place 
  until 
  a 
  point 
  considerably 
  behind 
  the 
  origin 
  of 
  the 
  

   dorsal 
  fin. 
  In 
  the 
  caudal 
  region 
  all 
  the 
  spines 
  are 
  firmly 
  fused 
  

   both 
  with 
  the 
  neural 
  and 
  haemal 
  arches, 
  while 
  in 
  its 
  hinder 
  half 
  

   they 
  increase 
  in 
  robustness 
  and 
  in 
  backward 
  inclination. 
  It 
  is 
  also 
  

   noteworthy 
  that 
  one 
  haemal 
  arch 
  develops 
  into 
  a 
  great 
  fan-shaped 
  

   expansion, 
  for 
  the 
  more 
  adequate 
  support 
  of 
  the 
  powerful 
  caudal 
  

   fin. 
  There 
  are 
  no 
  intermuscular 
  bones. 
  

  

  The 
  clavicle 
  is 
  large 
  and 
  extends 
  far 
  forwards 
  in 
  the 
  gular 
  region 
  

   to 
  meet 
  its 
  fellow 
  of 
  the 
  opposite 
  side. 
  There 
  are 
  also 
  large 
  post- 
  

   clavicular 
  plates. 
  The 
  rays 
  of 
  the 
  pectoral 
  fin 
  are 
  very 
  closely 
  

   apposed, 
  and 
  only 
  divided 
  quite 
  at 
  the 
  distal 
  extremity 
  ; 
  its 
  anterior 
  

   margin 
  sometimes 
  exhibits 
  a 
  fringe 
  of 
  relatively 
  minute 
  fulcra. 
  No 
  

   pelvic 
  fins 
  have 
  been 
  observed 
  in 
  any 
  species. 
  The 
  rays 
  of 
  the 
  

   median 
  fins 
  are 
  very 
  slender 
  and 
  exhibit 
  distant 
  articulations, 
  

   which 
  sometimes 
  appear 
  as 
  if 
  incomplete 
  or 
  secondarily 
  fused. 
  At 
  

   the 
  anterior 
  margin 
  of 
  each 
  fin 
  the 
  rays 
  gradually 
  increase 
  in 
  length 
  

   to 
  its 
  apex; 
  but 
  there 
  are 
  very 
  rarely 
  traces 
  of 
  minute 
  fulcra 
  

   between 
  their 
  successive 
  points. 
  A 
  few 
  free 
  fin-supports 
  occur 
  

   above 
  the 
  neural 
  spines 
  in 
  advance 
  of 
  the 
  dorsal 
  fin. 
  

  

  The 
  scales 
  are 
  all 
  thin 
  and 
  very 
  deeply 
  overlapping, 
  not 
  strength- 
  

   ened 
  by 
  ribbings 
  within 
  or 
  united 
  by 
  peg-and 
  -socket. 
  On 
  the 
  flank 
  

   the 
  rhombic 
  exposed 
  areas 
  are 
  about 
  as 
  deep 
  as 
  broad, 
  while 
  towards 
  

   the 
  ventral 
  border 
  a 
  few 
  are 
  broader 
  than 
  deep. 
  There 
  is 
  one 
  

   greatly 
  enlarged 
  scale 
  near 
  the 
  origin 
  of 
  the 
  anal 
  fin. 
  The 
  lateral 
  

   line 
  is 
  distinctly 
  traceable 
  on 
  the 
  flank, 
  and 
  in 
  a 
  few 
  specimens 
  it 
  is 
  

   shown 
  to 
  bifurcate 
  irregularly 
  on 
  some 
  of 
  the 
  scales 
  in 
  the 
  abdo- 
  

   minal 
  region. 
  

  

  The 
  form 
  of 
  the 
  trunk 
  in 
  Pachycormus 
  is 
  such 
  that 
  it 
  assumes 
  

   very 
  varied 
  outlines 
  when 
  crushed. 
  Moreover, 
  the 
  apparent 
  size 
  of 
  

   the 
  scales 
  differs 
  greatly 
  according 
  to 
  the 
  degree 
  and 
  manner 
  in 
  

   which 
  they 
  are 
  displaced. 
  The 
  determination 
  of 
  the 
  species 
  is 
  thus 
  

   very 
  difficult 
  and 
  uncertain, 
  and 
  many 
  more 
  forms 
  have 
  been 
  named 
  

   than 
  it 
  is 
  possible 
  to 
  define. 
  In 
  the 
  following 
  provisional 
  arrange- 
  

   ment 
  the 
  relative 
  depth 
  of 
  the 
  trunk 
  is 
  thus 
  ignored 
  in 
  the 
  diagnoses, 
  

  

  