﻿330 
  ACTINOPTEEYGII. 
  

  

  of 
  the 
  jaws, 
  smaller 
  on 
  the 
  palatine 
  and 
  on 
  the 
  splenial, 
  where 
  they 
  

   are 
  in 
  single 
  series 
  anteriorly, 
  minute 
  and 
  almost 
  granular 
  on 
  the 
  

   other 
  inner 
  bones 
  ; 
  preoperculum 
  nearly 
  smooth 
  and 
  narrow 
  ; 
  oper- 
  

   culum 
  deep, 
  much 
  broader 
  below 
  than 
  above, 
  and 
  suboperculum 
  of 
  

   moderate 
  size. 
  Ossifications 
  in 
  the 
  sheath 
  of 
  the 
  notochord 
  insigni- 
  

   ficant 
  or 
  absent 
  in 
  the 
  smaller 
  species, 
  consisting 
  only 
  of 
  separate 
  

   hypocentra 
  and 
  pleurocentra 
  in 
  the 
  largest 
  species 
  ; 
  ossified 
  ribs 
  

   slender, 
  not 
  reaching 
  the 
  ventral 
  border 
  of 
  the 
  abdomen. 
  Fulcra 
  

   biserial, 
  well-developed 
  on 
  all 
  the. 
  fins,, 
  those 
  of 
  the 
  pectoral 
  being 
  

   especially 
  elongated 
  and 
  sometimes 
  in 
  part 
  fused 
  together. 
  Pectoral 
  

   much 
  exceeding 
  the 
  pelvic 
  fins 
  in 
  size, 
  but 
  the 
  latter 
  well-developed 
  ; 
  

   dorsal 
  and 
  anal 
  fins 
  triangular 
  in 
  shape, 
  the 
  former 
  arising 
  opposite 
  

   or 
  immediately 
  behind 
  the 
  pelvic 
  fins; 
  caudal 
  fin 
  deeply 
  forked. 
  

   Scales 
  delicate, 
  smooth, 
  feebly 
  crimped 
  or 
  in 
  part 
  tuberculated, 
  

   deeply 
  overlapping, 
  and 
  none 
  much 
  deeper 
  than 
  broad 
  ; 
  a 
  few 
  series 
  

   anteriorly 
  quadrangular 
  and 
  possibly 
  sometimes 
  united 
  with 
  peg-and- 
  

   socket, 
  the 
  others 
  more 
  or 
  less 
  cycloidal, 
  and 
  very 
  few 
  narrowed 
  on 
  

   the 
  ventral 
  aspect 
  of 
  the 
  fish. 
  Lateral 
  line 
  inconspicuous. 
  

  

  The 
  osteology 
  of 
  Caturus 
  as 
  exhibited 
  partly 
  in 
  specimens 
  from 
  

   the 
  French 
  and 
  German 
  Lithographic 
  Stone, 
  but 
  especially 
  in 
  those 
  

   from 
  the 
  English 
  Oxford 
  Clay, 
  is 
  proved 
  to 
  be 
  essentially 
  similar 
  

   to 
  that 
  of 
  Eugnathus 
  already 
  described 
  (p. 
  287). 
  The 
  state 
  of 
  pre- 
  

   servation 
  of 
  the 
  Oxfordian 
  fossils 
  in 
  the 
  Leeds 
  Collection, 
  however, 
  

   permits 
  the 
  determination 
  of 
  a 
  few 
  additional 
  features. 
  In 
  advance 
  

   of 
  the 
  basipterygoid 
  process 
  of 
  the 
  parasphenoid 
  there 
  is 
  a 
  very 
  

   large 
  alisphenoidal 
  ossification, 
  much 
  exceeding 
  in 
  size 
  either 
  of 
  the 
  

   otics 
  behind. 
  The 
  prootic 
  is 
  equally 
  well 
  ossified, 
  and 
  the 
  opisthotic 
  

   is 
  still 
  more 
  robust 
  ; 
  but 
  no 
  undoubted 
  traces 
  of 
  pterotic 
  and 
  epiotic 
  

   ossifications 
  have 
  hitherto 
  been 
  observed. 
  As 
  in 
  Eugnathus, 
  the 
  

   mesethmoid 
  appears 
  to 
  have 
  been 
  little 
  ossified, 
  and 
  it 
  was 
  probably 
  

   small. 
  In 
  front 
  of 
  the 
  parasphenoid 
  there 
  is 
  a 
  pair 
  of 
  large 
  vomers, 
  

   bearing 
  a 
  few 
  teeth 
  only 
  at 
  their 
  anterior 
  end. 
  The 
  nasals 
  are 
  

   proved 
  to 
  resemble 
  those 
  of 
  Amia. 
  The 
  supraorbitals 
  are 
  irregular 
  

   and 
  much 
  subdivided 
  at 
  their 
  outer 
  margin, 
  the 
  tessera? 
  extending 
  

   somewhat 
  upon 
  the 
  cheek. 
  The 
  symplectic 
  in 
  Caturus 
  still 
  remains 
  

   unknown 
  ; 
  but 
  the 
  palatine 
  has 
  been 
  well 
  observed 
  in 
  this 
  genus, 
  

   forming 
  a 
  small 
  laterally 
  compressed 
  plate 
  of 
  bone 
  with 
  a 
  row 
  of 
  

   teeth 
  on 
  its 
  oral 
  margin. 
  The 
  ceratohyal 
  does 
  not 
  exhibit 
  so 
  much 
  

   evidence 
  of 
  twisting 
  as 
  in 
  Eugnathus. 
  The 
  gill-filaments 
  have 
  

   calcified 
  supports, 
  and 
  there 
  are 
  small 
  tooth-like 
  gill-rakers, 
  some 
  

   arranged 
  on 
  the 
  edge 
  of 
  little 
  triangular 
  flakes 
  of 
  bone 
  like 
  those 
  

   observed 
  in 
  Amia. 
  

  

  \ 
  

  

  \ 
  

  

  