﻿CHELOJNTA, 
  AND 
  A 
  TOOTH 
  OF 
  (?) 
  ORNITHOPSIS. 
  

  

  239 
  

  

  propose 
  to 
  regard 
  it 
  as 
  the 
  type 
  of 
  a 
  second 
  Weald 
  en 
  species, 
  under 
  

   the 
  name 
  of 
  P. 
  valdensis. 
  

  

  ■ 
  Pig. 
  5. 
  — 
  The 
  Plastron 
  of 
  Plesiochelys 
  Brodiei. 
  (\ 
  nat. 
  size.) 
  

  

  1, 
  intergular 
  shield 
  ; 
  2, 
  gular 
  ditto 
  ; 
  3, 
  humeral 
  ditto 
  ; 
  4, 
  pectoral 
  ditto 
  : 
  

   5, 
  abdominal 
  ditto 
  ; 
  6, 
  femoral 
  ditto 
  ; 
  7, 
  anal 
  ditto. 
  

  

  Both 
  P. 
  Brodiei 
  and 
  P. 
  valdensis 
  may, 
  in 
  all 
  probability, 
  be 
  re- 
  

   garded 
  as 
  the 
  direct 
  descendants 
  of 
  the 
  two 
  Kimeridgian 
  species 
  to 
  

   which 
  they 
  are 
  respectively 
  allied, 
  and 
  it 
  is 
  interesting 
  to 
  note 
  the 
  

   long 
  continuance 
  of 
  the 
  two 
  types, 
  each 
  represented 
  by 
  a 
  Kime- 
  

   ridgian 
  and 
  a 
  Wealden 
  species. 
  It 
  is 
  further 
  somewhat 
  remarkable 
  

   that 
  in 
  both 
  types 
  the 
  Wealden 
  form 
  differs 
  from 
  the 
  Kimeridgian 
  

   in 
  the 
  same 
  characters. 
  

  

  5. 
  Chelone 
  gigas, 
  Owen, 
  from 
  the 
  London 
  Clay. 
  

  

  In 
  his 
  ' 
  History 
  of 
  British 
  Fossil 
  Eeptilia,' 
  vol. 
  iii. 
  p. 
  188, 
  and 
  

   vol. 
  iv. 
  pis. 
  xxx., 
  xxxi., 
  and 
  also 
  in 
  his 
  ' 
  Reptilia 
  of 
  the 
  London 
  

   Clay,' 
  vol. 
  ii. 
  pis. 
  i., 
  ii. 
  (1880), 
  Sir 
  R. 
  Owen 
  described 
  a 
  large 
  Che- 
  

   Ionian 
  skull 
  from 
  the 
  London 
  Clay, 
  under 
  the 
  name 
  of 
  Chelone 
  gigas. 
  

   Having 
  had 
  occasion 
  recently 
  to 
  examine 
  this 
  specimen 
  (which 
  is 
  in 
  

   the 
  Natural 
  History 
  Museum), 
  I 
  find 
  that 
  it 
  differs 
  in 
  toto 
  from 
  the 
  

   Chelonidse, 
  and 
  agrees 
  in 
  all 
  essential 
  characters 
  with 
  Dermatochelys 
  

   (Sphargis), 
  this 
  being 
  at 
  once 
  shown 
  by 
  the 
  absence 
  of 
  a 
  floor 
  to 
  

   the 
  nasal 
  passage, 
  and 
  the 
  consequent 
  forward 
  position 
  of 
  the 
  poste- 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  178. 
  t 
  

  

  