﻿200 
  H. 
  G. 
  SEELEY 
  ON 
  MXJRiENOSA.URUS 
  LEEDSII, 
  

  

  downward, 
  superimposed 
  upon 
  the 
  angular 
  bone 
  ; 
  it 
  widens 
  the 
  

   jaw 
  from 
  side 
  to 
  side 
  ; 
  and 
  below 
  the 
  articulation 
  the 
  angular 
  bone 
  

   is 
  compressed 
  from 
  side 
  to 
  side 
  to 
  form 
  a 
  rounded 
  heel. 
  The 
  heel 
  

   behind 
  the 
  articulation 
  is 
  1| 
  inch 
  long 
  ; 
  at 
  first 
  it 
  is 
  triangular 
  in 
  

   section 
  from 
  being 
  flattened 
  above, 
  but 
  tapers 
  posteriorly 
  in 
  all 
  

   ways 
  and 
  terminates 
  in 
  a 
  rounded 
  vertical 
  concavity 
  about 
  \ 
  an 
  

   inch 
  in 
  diameter. 
  The 
  extreme 
  width 
  of 
  the 
  lower 
  jaw 
  over 
  the 
  

   articulations 
  is 
  5| 
  inches 
  ; 
  the 
  heels 
  approximate 
  still 
  more 
  and 
  

   appear 
  to 
  have 
  measured 
  4| 
  inches 
  from 
  side 
  ro 
  side 
  ; 
  but 
  the 
  left 
  

   heel 
  is 
  fractured. 
  

  

  The 
  hindermost 
  teeth 
  look 
  directly 
  upward 
  ; 
  but 
  as 
  they 
  approach 
  

   the 
  front 
  of 
  the 
  jaw 
  they 
  are 
  necessarily 
  directed 
  more 
  and 
  more 
  out- 
  

   ward 
  and 
  forward. 
  

  

  Vertebral 
  Column. 
  

  

  The 
  vertebral 
  column, 
  as 
  preserved, 
  comprises 
  79 
  vertebras, 
  which 
  

   I 
  group 
  as 
  44 
  cervical, 
  3 
  pectoral, 
  20 
  dorsal, 
  4 
  pelvic, 
  and 
  8 
  caudal. 
  

   No 
  vertebras 
  appear 
  to 
  be 
  missing 
  in 
  the 
  series 
  ; 
  and 
  probably 
  these 
  

   numbers, 
  except 
  for 
  the 
  missing 
  tail, 
  give 
  the 
  vertebral 
  formula 
  of 
  

   the 
  species. 
  Arranged 
  end 
  to 
  end, 
  as 
  Mr. 
  Leeds 
  has 
  placed 
  them, 
  

   they 
  measure 
  about 
  13 
  feet 
  ; 
  so 
  that 
  with 
  the 
  missing 
  part 
  of 
  the 
  

   tail 
  the 
  length 
  of 
  the 
  vertebral 
  column 
  may 
  have 
  been 
  something 
  

   under 
  15 
  feet, 
  or 
  nearly 
  as 
  long 
  as 
  in 
  Plesiosaurus 
  meter 
  opt 
  erus 
  from 
  

   the 
  Lias, 
  though 
  the 
  proportion 
  of 
  length 
  of 
  head 
  to 
  length 
  of 
  body 
  

   probably 
  comes 
  nearest 
  to 
  Plesiosaurus 
  dolichodeirus, 
  where 
  it 
  is 
  one 
  

   to 
  thirteen. 
  

  

  Cervical 
  Vertebrae. 
  

  

  The 
  atlas 
  and 
  axis 
  are 
  anchylosed 
  ; 
  and 
  all 
  trace 
  of 
  their 
  union 
  

   with 
  the 
  wedge-bones 
  is 
  obliterated. 
  From 
  front 
  to 
  back 
  these 
  

   vertebras 
  measure 
  rather 
  less 
  than 
  2\ 
  inches. 
  The 
  atlantal 
  cup 
  for 
  the 
  

   basioccipital 
  is 
  imperfectly 
  preserved 
  ; 
  it 
  is 
  lg 
  inch 
  deep, 
  but 
  appears 
  

   to 
  have 
  been 
  narrower. 
  The 
  whole 
  mass 
  widens 
  from 
  side 
  to 
  side 
  

   behind 
  the 
  posterior 
  articular 
  surface 
  of 
  the 
  centrum, 
  being 
  nearly 
  

   circular, 
  \\ 
  inch 
  from 
  above 
  downward 
  and 
  1| 
  inch 
  from 
  side 
  to 
  

   side 
  ; 
  it 
  is 
  flattened, 
  but 
  slightly 
  concave. 
  The 
  neural 
  arches 
  are 
  

   not 
  preserved, 
  but 
  appear 
  to 
  have 
  been 
  distinct 
  from 
  each 
  other 
  ; 
  

   and 
  the 
  arch 
  of 
  the 
  axis 
  was 
  more 
  developed 
  than 
  that 
  of 
  the 
  

   atlas. 
  The 
  neural 
  canal 
  is 
  flat 
  below 
  and 
  smooth, 
  and 
  1| 
  inch 
  long, 
  

   so 
  that, 
  as 
  is 
  usual 
  in 
  Plesiosaurians, 
  the 
  inferior 
  wedge-bones 
  pro- 
  

   long 
  the 
  articulation 
  for 
  the 
  basioccipital 
  bone 
  forward 
  considerably 
  

   on 
  the 
  inferior 
  margin. 
  A 
  hypapophysis 
  is 
  developed 
  in 
  the 
  median 
  

   line 
  of 
  the 
  underside, 
  but 
  does 
  not 
  reach 
  within 
  \ 
  an 
  inch 
  of 
  the 
  

   hindmost 
  articular 
  surface; 
  anteriorly 
  it 
  is 
  broad, 
  strong, 
  and 
  

   rounded, 
  posteriorly 
  sharp 
  and 
  compressed 
  from 
  side 
  to 
  side, 
  but 
  not 
  

   greatly 
  developed. 
  The 
  cervical 
  ribs 
  of 
  these 
  vertebras 
  are 
  broken 
  

   away 
  ; 
  that 
  of 
  the 
  atlas 
  appears 
  to 
  have 
  been 
  very 
  small, 
  while 
  that 
  

   of 
  the 
  axis 
  does 
  not 
  differ 
  in 
  its 
  articular 
  facet 
  from 
  that 
  of 
  an 
  ordinary 
  

   cervical 
  vertebra. 
  

  

  The 
  seventh 
  cervical 
  vertebra 
  (PI. 
  XXL 
  fig. 
  1) 
  has 
  the 
  centrum 
  

  

  