﻿OF 
  FIVE 
  GENERA 
  OF 
  MESOZOIC 
  REPTILES. 
  45 
  

  

  dilian 
  and 
  Dinosaurian 
  feature 
  of 
  carrying 
  the 
  upper 
  costal 
  articu- 
  

   lation 
  on 
  the 
  arch, 
  and 
  the 
  lower 
  on 
  the 
  centrum. 
  Its 
  Dinosaurian 
  

   nature 
  is 
  proved 
  by 
  the 
  opisthoccelous 
  centrum 
  ; 
  and 
  I 
  shall 
  show 
  

   below 
  that 
  there 
  is 
  a 
  considerable 
  probability 
  that 
  it 
  belonged 
  to 
  the 
  

   Theropodous 
  group 
  of 
  that 
  order. 
  

  

  The 
  most 
  peculiar 
  feature 
  of 
  this 
  specimen 
  consists 
  in 
  the 
  presence 
  

   of 
  a 
  distinct 
  intercentrum 
  (hypapophysis) 
  on 
  its 
  anterior 
  border, 
  

   which 
  I 
  have 
  not 
  seen 
  described 
  in 
  any 
  member 
  of 
  the 
  order. 
  The 
  

   flattened 
  kidney-shaped 
  surface, 
  marked 
  d 
  in 
  the 
  figure, 
  is 
  evidently 
  

   for 
  the 
  articulation 
  of 
  the 
  odontoid 
  process, 
  or 
  centrum 
  of 
  the 
  atlas 
  ; 
  

   while 
  the 
  marginal 
  receding 
  surfaces 
  (e) 
  are 
  for 
  the 
  inferior 
  ring 
  of 
  

   the 
  atlas, 
  which 
  is 
  now 
  generally 
  regarded 
  as 
  representing 
  the 
  first 
  

   intercentrum 
  *, 
  or 
  that 
  between 
  the 
  cranium 
  and 
  the 
  atlas. 
  

  

  Compared 
  with 
  the 
  very 
  small 
  figure 
  of 
  the 
  axis 
  of 
  Oeratosaurus 
  

   given 
  by 
  Prof. 
  Marsh 
  in 
  the 
  ' 
  Amer. 
  Journ.' 
  ser. 
  3, 
  vol. 
  xxvii. 
  pi. 
  x. 
  

   (1884), 
  the 
  general 
  resemblance 
  is 
  so 
  close 
  as 
  to 
  indicate 
  the 
  strong 
  

   probability 
  that 
  the 
  present 
  specimen 
  belongs 
  to 
  the 
  same 
  suborder 
  ; 
  

   and 
  it 
  therefore 
  seems 
  highly 
  likely 
  that 
  it 
  may 
  be 
  referable 
  to 
  

   the 
  Wealden 
  species 
  of 
  Megalosaurus, 
  or 
  to 
  a 
  nearly 
  allied 
  form. 
  

   In 
  the 
  American 
  genus, 
  however, 
  the 
  centrum 
  of 
  the 
  atlas 
  is 
  anchy- 
  

   losed 
  to 
  that 
  of 
  the 
  axis 
  to 
  form 
  an 
  odontoid 
  process 
  • 
  and 
  from 
  the 
  

   forward 
  projection 
  of 
  the 
  inferior 
  border 
  of 
  the 
  anterior 
  part 
  of 
  the 
  

   centrum 
  of 
  the 
  axis 
  it 
  would 
  appear 
  that 
  the 
  second 
  intercentrum, 
  

   or 
  that 
  between 
  the 
  atlas 
  and 
  axis, 
  is 
  likewise 
  anchylosed 
  to 
  the 
  

   centrum 
  of 
  the 
  latter. 
  This 
  appears 
  to 
  be 
  the 
  view 
  adopted 
  by 
  

   Dr. 
  Baur, 
  who, 
  on 
  page 
  289 
  of 
  the 
  memoir 
  cited, 
  observes 
  that 
  in 
  

   Crocodiles 
  " 
  the 
  hypapophysis 
  (intercentrum) 
  between 
  the 
  axis 
  and 
  

   atlas 
  is 
  probably 
  coossified 
  with 
  the 
  anterior 
  and 
  lower 
  part 
  of 
  the 
  

   axis-centrum, 
  as 
  in 
  Birds 
  and 
  some 
  Dinosaurs." 
  

  

  The 
  present 
  instance 
  of 
  the 
  persistence 
  of 
  this 
  second 
  inter- 
  

   centrum 
  as 
  a 
  separate 
  ossification 
  in 
  a 
  Wealden 
  Dinosaur 
  is 
  a 
  

   circumstance 
  of 
  considerable 
  interest, 
  apparently 
  pointing 
  to 
  the 
  

   derivation 
  of 
  the 
  order 
  from 
  Reptiles 
  in 
  which 
  this 
  was 
  always 
  the 
  

   case. 
  Whether 
  any 
  of 
  the 
  earlier 
  Crocodiles 
  exhibit 
  a 
  similar 
  

   feature 
  will 
  be 
  a 
  matter 
  for 
  future 
  investigation. 
  

  

  III. 
  Femur 
  of 
  an 
  Iguanodont 
  Dinosaur 
  from 
  the 
  Oxford 
  

   Clay 
  near 
  Peterborough. 
  

  

  The 
  only 
  evidence 
  hitherto 
  recorded 
  of 
  the 
  existence 
  of 
  Iguano- 
  

   dont 
  Dinosaurs 
  in 
  England 
  during 
  the 
  period 
  of 
  the 
  Oxford 
  Clay 
  is 
  

   based 
  upon 
  a 
  right 
  femur 
  described 
  and 
  figured 
  by 
  Prof. 
  Seeley 
  in 
  

   vol. 
  xxxi. 
  p. 
  149, 
  pi. 
  vi. 
  of 
  the 
  Society's 
  ' 
  Journal 
  ' 
  for 
  1875, 
  under 
  

   the 
  name 
  of 
  Cryptosaurus 
  eumerus. 
  That 
  specimen, 
  of 
  which 
  the 
  

   precise 
  locality 
  seems 
  to 
  be 
  unknown, 
  is 
  preserved 
  in 
  the 
  Woodwardian 
  

   Museum 
  at 
  Cambridge, 
  and 
  indicates 
  a 
  comparatively 
  small 
  species, 
  

   its 
  total 
  length 
  being 
  12*25 
  inches. 
  The 
  grounds 
  on 
  which 
  that 
  

   specimen 
  was 
  made 
  the 
  type 
  of 
  a 
  distinct 
  genus 
  are 
  stated 
  to 
  be 
  

  

  * 
  See 
  Baur, 
  Amer. 
  Nat. 
  vol. 
  xx. 
  pp. 
  288-293 
  (1886). 
  

  

  