﻿CHELONIA 
  AND 
  A 
  TOOTH 
  OF 
  (?) 
  OKNITnOPSIS. 
  233 
  

  

  Greensand 
  are 
  not 
  specifically 
  separable 
  from 
  those 
  of 
  the 
  Chalk 
  ; 
  

   and 
  there 
  is 
  ac/cordingly 
  a 
  probability 
  that 
  the 
  specimens 
  under 
  con- 
  

   sideration 
  may 
  be 
  referable 
  to 
  Clielone 
  Benstedi 
  of 
  the 
  last-named 
  

   deposit. 
  That 
  species 
  is, 
  unfortunately, 
  known 
  to 
  us 
  only 
  by 
  the 
  

   young 
  shell, 
  and 
  doubts 
  have 
  been 
  raised 
  whether 
  it 
  is 
  really 
  

   referable 
  to 
  the 
  Chelonidne. 
  I 
  have, 
  however, 
  no 
  doubt 
  that 
  this 
  

   reference 
  is 
  correct, 
  and 
  I 
  may 
  add 
  that 
  in 
  this 
  view 
  I 
  have 
  the 
  

   support 
  of 
  my 
  friend 
  Mr. 
  Boulenger 
  : 
  while 
  the 
  contour 
  of 
  the 
  

   carapace 
  is 
  unlike 
  that 
  of 
  Lytoloma. 
  That 
  form 
  differs, 
  however, 
  

   from 
  existing 
  species 
  of 
  Clielone 
  in 
  its 
  carapace 
  being 
  pointed 
  at 
  both 
  

   extremities, 
  in 
  which 
  respect 
  it 
  agrees 
  with 
  C. 
  Eoffimanni 
  *, 
  I 
  do 
  

   not, 
  however, 
  regard 
  this 
  difference 
  as 
  necessarily 
  of 
  more 
  than 
  

   specific 
  value, 
  and 
  do 
  not 
  therefore 
  propose 
  at 
  present 
  to 
  adopt 
  Sir 
  

   R. 
  Owen's 
  name 
  of 
  Cimo\lio]clielys 
  for 
  the 
  species 
  in 
  question. 
  

  

  It 
  is, 
  of 
  course, 
  impossible 
  to 
  say 
  whether 
  the 
  specimens 
  under 
  

   consideration 
  are 
  or 
  are 
  not 
  specifically 
  identical 
  with 
  O. 
  Benstedi 
  ; 
  

   but 
  in 
  the 
  absence 
  of 
  any 
  evidence 
  of 
  this 
  identity, 
  although 
  bearing 
  

   in 
  mind 
  how 
  extremely 
  undesirable 
  it 
  is 
  to 
  take 
  different 
  parts 
  of 
  

   the 
  skeleton 
  as 
  specific 
  types, 
  I 
  propose 
  to 
  refer 
  them 
  provisionally 
  

   to 
  a 
  new 
  species, 
  as 
  C. 
  Jessoni. 
  

  

  Lytoloma 
  cantabrigiense, 
  n. 
  sp. 
  

  

  The 
  specimens 
  which 
  I 
  have 
  now 
  to 
  describe 
  are 
  in 
  the 
  British 
  

   Museum 
  and 
  comprise 
  an 
  imperfect 
  mandible 
  (No. 
  35178) 
  and 
  

   a 
  humerus 
  (TSTo. 
  35175). 
  Both 
  were 
  purchased 
  at 
  the 
  same 
  time, 
  

   and 
  were 
  very 
  probably 
  associated 
  ; 
  but 
  I 
  take 
  the 
  mandible 
  as 
  the 
  

   type. 
  The 
  latter 
  (fig. 
  2) 
  comprises 
  the 
  entire 
  symphysis 
  and 
  por- 
  

   tions 
  of 
  the 
  two 
  rami. 
  The 
  symphysis 
  is 
  relatively 
  long 
  and 
  wide, 
  

   and 
  is 
  devoid 
  of 
  ridges 
  superiorly, 
  while 
  interiorly 
  it 
  is 
  distinctly 
  

   convex. 
  The 
  general 
  contour 
  of 
  the 
  specimen 
  is 
  essentially 
  that 
  of 
  

   the 
  Chelonidse, 
  and 
  it 
  is 
  quite 
  impossible 
  that 
  this 
  type 
  of 
  mandible, 
  

   which 
  is 
  common 
  in 
  the 
  Cambridge 
  Greensand, 
  can 
  have 
  belonged 
  

   to 
  Rhinochelys, 
  of 
  w 
  7 
  hich 
  the 
  mandible 
  is 
  quite 
  different. 
  

  

  Taking 
  it, 
  then, 
  as 
  certain 
  that 
  this 
  mandible 
  is 
  referable 
  to 
  the 
  

   Chelonidse 
  (in 
  which 
  I 
  include 
  the 
  Propleuridae 
  of 
  Messrs. 
  Dollo 
  and 
  

   Cope), 
  it 
  is 
  clear 
  that 
  it 
  cannot 
  belong 
  to 
  Clielone 
  or 
  to 
  the 
  London- 
  

   Clay 
  Turtles 
  mentioned 
  below 
  under 
  a 
  new 
  generic 
  name, 
  since 
  in 
  

   these 
  forms 
  the 
  mandible 
  is 
  ridged. 
  Of 
  genera 
  with 
  smooth 
  oval 
  

   surfaces 
  to 
  the 
  palate 
  and 
  mandible 
  we 
  have 
  two, 
  namely, 
  the 
  one 
  

   which 
  M. 
  Dollo 
  terms 
  Euclastes, 
  and 
  the 
  existing 
  Thalassochelys. 
  

   Before 
  proceeding 
  further 
  it 
  is, 
  however, 
  necessary 
  to 
  mention 
  that 
  

   the 
  name 
  Euclastes, 
  Cope 
  (1867), 
  is 
  preoccupied 
  by 
  the 
  name 
  

   Euclasta, 
  Led.f 
  , 
  and 
  must 
  therefore 
  be 
  discarded. 
  M. 
  Dollo 
  t 
  has 
  

   recently 
  given 
  what 
  he 
  considers 
  to 
  be 
  the 
  synonymy 
  of 
  this 
  genus, 
  

   and 
  he 
  employs 
  the 
  term 
  Euclastes 
  in 
  place 
  of 
  the 
  earlier 
  Osteopyyis 
  

   as 
  having 
  been 
  founded 
  on 
  the 
  skull 
  instead 
  of 
  the 
  shell, 
  considering 
  

  

  * 
  Dr. 
  Baur 
  has 
  proposed 
  the 
  generic 
  term 
  Allopleuron 
  for 
  this 
  species. 
  

  

  t 
  Yerh. 
  zool.-bot. 
  Ver. 
  Wien, 
  1855, 
  p. 
  252. 
  

  

  \ 
  Geol. 
  Mag. 
  dec. 
  3, 
  vol. 
  v. 
  p. 
  261 
  ; 
  and 
  Ann. 
  Sci. 
  Geol. 
  Nord, 
  vol. 
  xv. 
  p. 
  114 
  

  

  (1888). 
  

  

  