﻿130 
  THE 
  EXTINCT 
  BATRACHIA, 
  REPTILIA 
  

  

  bone. 
  The 
  hyosternals 
  are 
  prolonged 
  'forwards, 
  extensively 
  embracing 
  the 
  mesosternnm; 
  

   the 
  latter 
  piece 
  is 
  subcircular, 
  and 
  truncate 
  behind. 
  The 
  episternals 
  and 
  mesosternal 
  

   are 
  lost. 
  The 
  extreme 
  anterior 
  lip 
  of 
  the 
  hyosternals 
  is 
  crossed 
  by 
  a 
  groove, 
  apparently 
  

   the 
  suture 
  of 
  the 
  gular 
  plate; 
  it 
  has 
  reached 
  the 
  external 
  margin 
  a 
  half 
  inch 
  in 
  front 
  of 
  

   the 
  posterior 
  margin 
  of 
  the 
  episternal. 
  This 
  would 
  leave 
  sufficient 
  width 
  for 
  an 
  intergular 
  

   plate, 
  which 
  would 
  refer 
  the 
  genus 
  to 
  the 
  Hydraspididae. 
  As 
  however 
  the 
  other 
  pieces 
  

   of 
  the 
  sternum 
  have 
  been 
  found 
  in 
  England, 
  it 
  is 
  certain 
  that 
  the 
  genus 
  is 
  Cryptodire. 
  

  

  PLEUROSTERNTJM 
  PECTORALE, 
  Cope 
  sp. 
  nov. 
  

  

  The 
  plastron 
  of 
  this 
  species 
  is 
  massive, 
  and 
  three 
  times 
  as 
  thick 
  in 
  the 
  middle 
  as 
  at 
  the 
  sides. 
  The 
  posterior 
  

   hyosternal 
  suture 
  has 
  been 
  immoveable, 
  and 
  its 
  rugae 
  are 
  minute. 
  The 
  anterior 
  or 
  axillary 
  buttresses 
  have 
  risen 
  

   higher 
  on 
  the 
  costal 
  plates, 
  and 
  are 
  directed 
  obliquely 
  forwards. 
  The 
  axillary 
  outline 
  is 
  deeply 
  concave. 
  The 
  

   external 
  surface 
  is 
  without 
  sculpture. 
  Behind 
  the 
  truncate 
  axillary 
  plate 
  is 
  one 
  long 
  hexagonal 
  inner 
  marginal, 
  

   while 
  the 
  anterior 
  third 
  of 
  a 
  second 
  is 
  truncated 
  by 
  the 
  posterior 
  suture. 
  The 
  posterior 
  humeral 
  dermal 
  suture, 
  

   approaches 
  the 
  hyosternal 
  suture 
  towards 
  the 
  median 
  line 
  but 
  slightly. 
  

  

  • 
  In. 
  Lin. 
  

  

  Width 
  of 
  a 
  hyosternal, 
  3 
  

  

  Depth 
  at 
  middle, 
  on 
  hyost. 
  suture, 
  10. 
  

  

  " 
  outer 
  end 
  " 
  " 
  2.8 
  

  

  Length 
  median 
  suture, 
  1 
  6.4 
  

  

  From 
  posterior 
  suture 
  to 
  axilla, 
  1 
  4. 
  6 
  

  

  Antero-posterior 
  extent 
  hyosternal 
  (exclus. 
  sutural 
  process), 
  2 
  2.5 
  

  

  Width 
  inguinal 
  scute 
  interiorly, 
  4. 
  

  

  " 
  " 
  " 
  externally, 
  8.5 
  

  

  The 
  inferior 
  surface 
  of 
  the 
  plastron 
  is 
  convex, 
  the 
  interior 
  nearly 
  plane. 
  

  

  The 
  species 
  was 
  about 
  the 
  size 
  of 
  the 
  Ptychemys 
  rugosa 
  Ag. 
  of 
  the 
  Delaware. 
  It 
  is 
  distinguished 
  from 
  the 
  

   Emys 
  pravu 
  s 
  of 
  Leidy 
  by 
  the 
  transverse 
  hyosternal 
  suture, 
  the 
  greater 
  transverse 
  extent, 
  and 
  thickness 
  of 
  hyos- 
  

   ternals. 
  In 
  A. 
  firm 
  us 
  Leidy 
  the 
  humero-r.ectoral 
  dermal 
  suture 
  is 
  anterior, 
  and 
  the 
  mesosternal 
  is 
  transversely 
  

   truncate 
  behind. 
  

  

  CHELYDRINAE. 
  

  

  The 
  extinct 
  species 
  of 
  this 
  group 
  indicate 
  a 
  successional 
  relation 
  of 
  forms 
  such 
  as 
  the 
  

   theory 
  of 
  evolution 
  would 
  anticipate. 
  

  

  Those 
  of 
  the 
  Miocene 
  and 
  Eocene 
  periods 
  in 
  America 
  are 
  not 
  known, 
  but 
  so 
  far 
  as 
  

   they 
  are 
  in 
  Europe, 
  they 
  resemble 
  those 
  of 
  the 
  present. 
  In 
  the 
  cretaceous, 
  the 
  genus 
  

   Propleura 
  appears, 
  which 
  approximates 
  the 
  genus 
  Chelone 
  in 
  the 
  probable 
  more 
  natatory 
  

   character 
  of 
  the 
  Jbre 
  limb 
  than 
  in 
  Chelydra; 
  the 
  humerus 
  has 
  a 
  more 
  flattened 
  shaft, 
  

   and 
  is 
  not 
  quite 
  so 
  much 
  curved 
  as 
  in 
  the 
  latter; 
  its 
  proximal 
  condyle 
  and 
  crests 
  are 
  

   those 
  of 
  Chelydra, 
  and 
  this 
  point 
  has 
  chiefly 
  decided 
  me 
  in 
  referring 
  the 
  genus 
  to 
  the 
  

   neighborhood 
  of 
  the 
  latter, 
  rather 
  than 
  to 
  the 
  Cheloniidae. 
  The 
  independence 
  of 
  the 
  

   Cheloniidae 
  rests 
  entirely 
  on 
  the 
  structure 
  of 
  the 
  fore 
  limb, 
  for 
  its 
  other 
  peculiarities 
  are 
  

   repeated 
  by 
  genera 
  in 
  various 
  other 
  families. 
  The 
  natatory 
  character 
  has 
  a 
  strong 
  ex- 
  

  

  