﻿CHONDROSTEID^. 
  

  

  25 
  

  

  the 
  anterior 
  rays 
  of 
  each 
  fin 
  gradually 
  increasing 
  in 
  length 
  to 
  an 
  

   acumination. 
  Pelvic 
  fins 
  remote, 
  the 
  dorsal 
  opposed 
  to 
  this 
  pair 
  ; 
  

   caudal 
  fin 
  forked, 
  nearly 
  equilobate. 
  Scales 
  absent, 
  except 
  on 
  the 
  

   upper 
  caudal 
  lobe 
  where 
  they 
  are 
  thick 
  and 
  rhombic, 
  invested 
  with 
  

   ganoine 
  ; 
  caudal 
  Moral 
  scales 
  large, 
  with 
  ganoine. 
  

  

  Nothing 
  is 
  known 
  of 
  the 
  ossifications 
  in 
  the 
  chondrocranium 
  of 
  

   Chondrosteus, 
  but 
  many 
  specimens 
  exhibit 
  the 
  chief 
  membrane- 
  

   bones. 
  The 
  parietals 
  (figs. 
  3, 
  4, 
  jp.) 
  are 
  longer 
  than 
  broad 
  and 
  

   comparatively 
  small 
  ; 
  both 
  these 
  and 
  the 
  large 
  frontals 
  (/.) 
  meeting 
  

   at 
  the 
  middle 
  line 
  in 
  a 
  slightly 
  wavy 
  suture, 
  without 
  any 
  inter- 
  

   posed 
  elements 
  or 
  vacuities. 
  The 
  squamosals 
  (sq.) 
  are 
  larger 
  than 
  

   the 
  parietals, 
  extending 
  as 
  far 
  forwards 
  as 
  the 
  latter 
  ; 
  the 
  post- 
  

   frontals 
  (p.f.) 
  are 
  relatively 
  very 
  small. 
  ISTo 
  cranial 
  bones 
  have 
  

   been 
  recognized 
  in 
  advance 
  of 
  the 
  frontals, 
  and 
  the 
  extent 
  of 
  the 
  

   rostrum 
  is 
  thus 
  undetermined. 
  Cheek-plates 
  are 
  also 
  almost 
  

   wanting, 
  only 
  one 
  suborbital 
  (figs. 
  3, 
  5, 
  so.) 
  being 
  observed, 
  bearing 
  

   an 
  upward 
  process 
  ascending 
  towards 
  the 
  postfrontal. 
  A 
  series 
  

   of 
  five 
  supratemporal 
  plates 
  (fig. 
  4, 
  s.t.), 
  of 
  which 
  the 
  three 
  inner- 
  

   most 
  are 
  relatively 
  small, 
  occurs 
  along 
  the 
  occipital 
  border. 
  The 
  

   hyomandibular 
  (figs. 
  3, 
  6, 
  hm.) 
  is 
  shaped 
  as 
  in 
  modern 
  Sturgeons, 
  

   but 
  apparently 
  ossified 
  as 
  far 
  as 
  its 
  lower 
  extremity 
  ; 
  and 
  a 
  sym- 
  

   plectic 
  must 
  have 
  been 
  present, 
  although 
  it 
  is 
  doubtful 
  whether 
  

   this 
  was 
  ossified 
  in 
  any 
  part. 
  The 
  pterygo-quadrate 
  arcade 
  exhibits 
  

   only 
  two 
  ossifications 
  on 
  each 
  side, 
  one 
  being 
  a 
  large 
  expanded 
  

  

  Fig. 
  3. 
  

  

  Profile 
  of 
  head 
  of 
  Chondrosteus 
  acipenseroides, 
  restored 
  (after 
  Traquair). 
  

   j., 
  jugal. 
  Other 
  letters 
  as 
  in 
  figs. 
  4, 
  5. 
  

  

  element 
  (PI. 
  I. 
  fig. 
  3, 
  jot.) 
  of 
  pterygoid 
  nature, 
  and 
  the 
  other 
  a 
  

   small 
  V- 
  S 
  haped 
  bone 
  (pi.) 
  articulated 
  with 
  the 
  maxilla, 
  which 
  

  

  Sheathing 
  the 
  arcade 
  is 
  

  

  may 
  be 
  either 
  palatine 
  or 
  ectopterygoid. 
  

  

  