﻿CHELONIA 
  AND 
  A 
  TOOTH 
  OF 
  (?) 
  ORNITHOPSIS. 
  237 
  

  

  the 
  shell 
  of 
  a 
  Chelonian 
  from 
  the 
  Wealden 
  preserved 
  in 
  the 
  Natural 
  

   History 
  Museum, 
  which 
  indicates 
  a 
  species 
  of 
  the 
  genus 
  Plesiochelys 
  

   so 
  nearly 
  allied 
  to 
  P. 
  sanctce-verence, 
  Eiitimeyer, 
  of 
  the 
  Kimeridgian 
  

   of 
  Switzerland, 
  that 
  we 
  were 
  provisionally 
  inclined 
  to 
  refer 
  it 
  to 
  the 
  

   same 
  species. 
  

  

  I 
  have 
  lately 
  received 
  the 
  loan 
  of 
  another 
  Chelonian 
  shell, 
  belong- 
  

   ing 
  to 
  the 
  Rev. 
  P. 
  B. 
  Brodie, 
  from 
  the 
  Wealden 
  of 
  Atherfield, 
  in 
  

   the 
  Isle 
  of 
  Wight, 
  which 
  indicates 
  the 
  occurrence 
  of 
  a 
  second 
  

   English 
  species 
  of 
  Plesiochelys, 
  also 
  allied 
  to 
  a 
  species 
  from 
  the 
  Swiss 
  

   Kimeridgian. 
  

  

  Of 
  this 
  specimen 
  a 
  restored 
  view 
  of 
  the 
  carapace 
  and 
  plastron 
  are 
  

   given 
  in 
  figs. 
  4, 
  5. 
  Unluckily 
  the 
  neural 
  and 
  costal 
  bones 
  of 
  the 
  

   carapace 
  have 
  all 
  been 
  dislocated, 
  and 
  in 
  some 
  cases 
  overlap 
  one 
  

   another 
  to 
  a 
  certain 
  extent 
  ; 
  while 
  several 
  of 
  the 
  neurals 
  and 
  nearly 
  

   all 
  the 
  marginals 
  are 
  missing. 
  Fortunately, 
  however, 
  the 
  sulci 
  

   formed 
  by 
  the 
  boundaries 
  of 
  the 
  vertebral 
  and 
  costal 
  epidermal 
  shields 
  

   are 
  very 
  clearly 
  marked, 
  and 
  are 
  sufficient 
  to 
  show 
  the 
  entire 
  con- 
  

   tour 
  of 
  the 
  vertebral 
  shields. 
  The 
  plastron 
  is 
  nearly 
  entire, 
  and 
  

   shows 
  the 
  absence 
  of 
  a 
  mesoplastral, 
  by 
  which 
  the 
  specimen 
  is 
  at 
  

   once 
  distinguished 
  from 
  Pleurostemum 
  ; 
  the 
  epi- 
  and 
  entoplastrals 
  

   have 
  been 
  dislocated, 
  and 
  thrust 
  in 
  between 
  parts 
  of 
  the 
  broken 
  

   nuchal 
  of 
  the 
  carapace. 
  

  

  The 
  general 
  contour 
  of 
  the 
  specimen, 
  and 
  especially 
  the 
  sinuous 
  

   outline 
  of 
  the 
  borders 
  of 
  the 
  vertebral 
  shields, 
  and 
  the 
  distinct, 
  oblique, 
  

   longitudinal 
  striation 
  of 
  the 
  neural 
  and 
  adjacent 
  portions 
  of 
  the 
  

   costal 
  bones, 
  together 
  with 
  the 
  four 
  long 
  and 
  narrow 
  infra-marginal 
  

   shields 
  on 
  the 
  plastral 
  surface, 
  indicate 
  without 
  doubt 
  that 
  the 
  

   specimen 
  belongs 
  to 
  the 
  genus 
  Plesiochelys. 
  

  

  In 
  the 
  complete 
  ossification 
  of 
  the 
  plastron 
  it 
  agrees 
  with 
  the 
  

   Kimeridgian 
  species 
  P. 
  soloclurensis, 
  Eiitimeyer*, 
  and 
  probably 
  with 
  

   P. 
  sanctce-verence, 
  Eiitimeyer 
  f 
  , 
  and 
  differs 
  from 
  P. 
  Etalloni 
  of 
  the 
  

   same 
  writer, 
  in 
  which 
  there 
  is 
  a 
  persistent 
  plastral 
  vacuity. 
  It 
  

   further 
  differs 
  from 
  P. 
  sanctce-verence, 
  and 
  the 
  above-mentioned 
  

   Wealden 
  shell, 
  by 
  the 
  much 
  less 
  strongly 
  marked 
  striations 
  on 
  the 
  

   neurals 
  and 
  costals, 
  which 
  are 
  mainly 
  confined 
  to 
  the 
  median 
  

   region 
  of 
  the 
  carapace 
  ; 
  the 
  vertebral 
  shields 
  are 
  also 
  relatively 
  

   narrower. 
  The 
  plastron 
  of 
  P. 
  sanctce-verence 
  is 
  unknown 
  ; 
  but 
  that 
  

   of 
  the 
  allied 
  Wealden 
  form 
  is 
  relatively 
  shorter 
  and 
  wider, 
  and 
  con- 
  

   nected 
  by 
  a 
  longer 
  bridge 
  with 
  the 
  plastron. 
  

  

  Compared 
  with 
  Eiitimeyer's 
  figures 
  of 
  the 
  upper 
  and 
  under 
  sur- 
  

   face 
  of 
  the 
  male 
  shell 
  of 
  P. 
  solodvrensis 
  already 
  cited, 
  the 
  resem- 
  

   blance 
  presented 
  by 
  the 
  present 
  specimen 
  is 
  so 
  exceedingly 
  close 
  as 
  

   to 
  leave 
  no 
  doubt 
  of 
  the 
  near 
  relationship 
  of 
  the 
  two 
  forms. 
  In 
  the 
  

   English 
  specimen 
  the 
  pectoral 
  shield 
  of 
  the 
  plastron 
  is 
  nearly 
  as 
  long 
  

   as 
  the 
  abdominal, 
  instead 
  of 
  being 
  very 
  much 
  shorter 
  ; 
  while 
  the 
  

   posterior 
  border 
  of 
  the 
  abdominal 
  is 
  much 
  less 
  oblique. 
  The 
  infra- 
  

   marginals 
  are, 
  moreover, 
  relatively 
  wider 
  in 
  the 
  English 
  form. 
  On 
  

   the 
  carapace 
  the 
  chief 
  difference 
  that 
  can 
  be 
  detected 
  between 
  the 
  

  

  * 
  Foss. 
  Schildkroten 
  von 
  Solothurn, 
  pi. 
  xii. 
  

   t 
  Ibid. 
  pi. 
  xiii. 
  

  

  