﻿146 
  THE 
  EXTINCT 
  BATRACHIA, 
  REPTILIA 
  

  

  rnand 
  record. 
  Its 
  form 
  suggests 
  the 
  same 
  portion 
  of 
  the 
  Thalassochelys 
  planimentum 
  and 
  Th. 
  crassicostatus 
  of 
  

   Owen 
  (Chelone 
  Ow.) 
  from 
  the 
  Eocene 
  of 
  England; 
  but 
  it 
  is 
  much 
  more 
  obtuse, 
  and 
  broader, 
  in 
  relation 
  to 
  its 
  length, 
  

   than 
  either 
  of 
  these. 
  As 
  the 
  extent 
  of 
  the 
  symphysis 
  among 
  Testudinata 
  bears 
  some 
  relation 
  to 
  the 
  position 
  of 
  the 
  

   posterior 
  opening 
  of 
  the 
  nares, 
  the 
  pertinence 
  of 
  this 
  jaw 
  to 
  the 
  Euclastes 
  platyops 
  suggests 
  itself. 
  Its 
  flatness 
  and 
  

   shallowness, 
  and 
  want 
  of 
  recurved 
  alveolar 
  margins, 
  are 
  appropriate 
  to 
  the 
  shallowness 
  and 
  small 
  alveolar 
  margin 
  of 
  

   the 
  maxillo-palatine 
  face. 
  There 
  is, 
  however, 
  no 
  trace 
  of 
  that 
  elevation 
  and 
  acumination 
  of 
  the 
  extremity 
  of 
  the 
  

   symphysis, 
  associated 
  with 
  the 
  premaxillary 
  concavity 
  and 
  foramen 
  to 
  the 
  nasal 
  meatus, 
  which 
  is 
  to 
  be 
  looked 
  for, 
  

   and 
  which 
  occurs 
  to 
  some 
  extent 
  even 
  where 
  the 
  foramen 
  is 
  wanting, 
  e. 
  g., 
  in 
  the 
  Thalassochelys 
  caouana. 
  In 
  its 
  spe- 
  

   cific 
  features, 
  it 
  is 
  different 
  from 
  the 
  E. 
  platyops 
  in 
  its 
  greater 
  abbreviation. 
  In 
  the 
  former, 
  the 
  width 
  at 
  

   the 
  anterior 
  margins 
  of 
  the 
  coronoid 
  process 
  is 
  to 
  the 
  median 
  length 
  anterior 
  to 
  the 
  line 
  between 
  these 
  points, 
  as 
  

   2:4-5; 
  in 
  the 
  latter, 
  measuring 
  on 
  the 
  cranium 
  below, 
  as 
  2:1 
  3-5. 
  

  

  In 
  this 
  species 
  the 
  posterior 
  margin 
  of 
  the 
  symphysis 
  is 
  opposite 
  the 
  anterior 
  part 
  of 
  the 
  coronoid 
  bone 
  ; 
  tha 
  an- 
  

   terior 
  margin 
  of 
  the 
  coronoid 
  elevation 
  of 
  the 
  dentale 
  msasures 
  the 
  posterior 
  or 
  third 
  of 
  the 
  symphysis. 
  The 
  sutures 
  of 
  

   the 
  dentale 
  with 
  other 
  elements 
  nowhere 
  consolidated. 
  The 
  internal 
  groove 
  passes 
  round 
  the 
  hinder 
  face 
  of 
  the 
  arch, 
  

   situated 
  deeply 
  between 
  the 
  prolongations 
  of 
  the 
  superior 
  and 
  inferior 
  plates. 
  Mandible 
  beneath, 
  flat, 
  abruptly 
  ris- 
  

   ing 
  to 
  the 
  alveolar 
  ridge. 
  This 
  is 
  broken 
  away, 
  but 
  from 
  fragments 
  of 
  surface 
  remaining, 
  has 
  been 
  but 
  little 
  elevated. 
  

   Superior 
  alveolar 
  faces, 
  nearly 
  plane, 
  slightly 
  elevated 
  longitudinally 
  on 
  the 
  median 
  line, 
  where 
  the 
  surface 
  is 
  slightly 
  

   striate. 
  Portions 
  of 
  the 
  superficial 
  plate 
  remaining 
  offer 
  no 
  evidence 
  of 
  an 
  upward 
  curvature, 
  though 
  a 
  small 
  portion 
  

   of 
  the 
  extremity 
  has 
  been 
  worn 
  off. 
  

  

  A 
  striking 
  feature 
  in 
  this 
  species 
  is 
  the 
  size 
  and 
  depth 
  of 
  the 
  fossa 
  for 
  the 
  insertion 
  of 
  the 
  masseter 
  muscle. 
  It 
  

   is 
  relatively 
  greater 
  than 
  in 
  any 
  of 
  the 
  recent 
  Chelonidce 
  which 
  I 
  have 
  seen, 
  and 
  indicates 
  great 
  muscular 
  power. 
  

   This 
  necessitates 
  the 
  shortness 
  of 
  the 
  mandible, 
  as 
  it 
  is 
  less 
  strengthened 
  in 
  the 
  vertical 
  direction 
  than 
  the 
  modem 
  

   species. 
  The 
  mental 
  foramen 
  enters 
  in 
  the 
  anterior 
  portion 
  of 
  this 
  fossa. 
  The 
  dental 
  foramen, 
  of 
  equal 
  size, 
  enters 
  

   below 
  the 
  middle 
  of 
  the 
  coronoid 
  bone. 
  The 
  wall 
  of 
  the 
  fossa 
  is 
  the 
  inferior 
  plate 
  of 
  the 
  mentum 
  prolonged 
  into 
  a 
  

   strong 
  ridge. 
  

  

  Measurements. 
  Lines. 
  

  

  Length 
  of 
  symphyseal 
  line, 
  25 
  

  

  "Width 
  at 
  anterior 
  margins, 
  coronoid 
  processes, 
  42.7 
  

  

  " 
  apices 
  coronoid 
  bones, 
  42.7 
  

  

  Elevation 
  apices 
  coronoid 
  bones, 
  19 
  

  

  Depth 
  at 
  symphysis 
  behind, 
  8 
  

  

  Two 
  portions 
  of 
  peculiar 
  marginal 
  bones, 
  from 
  the 
  left 
  side 
  of 
  the 
  carapace 
  of 
  one 
  of 
  the 
  Cheloniidae, 
  found 
  at 
  

   the 
  same 
  time 
  and 
  place 
  as 
  preceding, 
  have 
  much 
  the 
  same 
  mineral 
  character, 
  and 
  probably 
  belong 
  to 
  it. 
  The 
  piece 
  

   from 
  the 
  median 
  margin 
  is 
  quite 
  thick 
  on 
  the 
  inner 
  face, 
  which, 
  with 
  the 
  upper 
  face, 
  is 
  concave; 
  lower, 
  slightly 
  

   convex. 
  

  

  Lines. 
  

   Depth 
  within, 
  10.5 
  

  

  Width 
  below, 
  15.5 
  

  

  Width 
  above, 
  12.5 
  

  

  Fossa 
  for 
  costal 
  extremity, 
  open 
  conic. 
  

  

  A 
  portion 
  of 
  what 
  is 
  perhaps 
  a 
  fourth 
  left 
  marginal, 
  is 
  triangular 
  in 
  section, 
  each 
  side 
  concave, 
  the 
  inner 
  face 
  

   most 
  extensive. 
  The 
  margin 
  is 
  obtuse, 
  and 
  presents 
  an 
  open 
  concavity, 
  thus 
  connecting 
  the 
  forms 
  of 
  the 
  second 
  and 
  

   fifth 
  bones 
  here 
  described. 
  

  

  Width 
  of 
  inferior 
  margin, 
  9.5 
  lines. 
  

  

  Second 
  marginal 
  very 
  shallow, 
  vertically 
  ; 
  a 
  very 
  open 
  emargination 
  between 
  dermal 
  shields, 
  which 
  have 
  left 
  a 
  

   shallow 
  sutural 
  groove. 
  It 
  presents 
  a 
  narrow 
  truncate 
  inner 
  margin, 
  and 
  there 
  is 
  no 
  rib-pit 
  in 
  it. 
  

  

  