﻿184 
  THE 
  EXTINCT 
  BATRACHIA, 
  REPTILIA 
  

  

  genus, 
  but 
  one 
  is 
  probably 
  figured 
  by 
  Camper 
  (Tab. 
  248, 
  fig. 
  21 
  of 
  Cuvier 
  Ossem. 
  Fossiles), 
  

   which 
  Cuvier 
  says 
  is 
  perhaps 
  an 
  ungueal 
  phalange. 
  The 
  dorsals 
  have 
  no 
  hypapophysis, 
  

   and 
  the 
  diapophyses 
  decrease 
  in 
  vertical 
  extent 
  towards 
  the 
  posterior 
  part 
  of 
  the 
  series. 
  

   The 
  greatest 
  variation 
  is 
  presented 
  by 
  the 
  different 
  species 
  in 
  the 
  long 
  series 
  preceding 
  

   the 
  caudals, 
  which 
  do 
  not 
  present 
  zygapophyses. 
  The 
  posterior 
  of 
  this 
  series 
  are 
  much 
  

   shorter 
  than 
  the 
  anterior, 
  the 
  former 
  having 
  the 
  form 
  of 
  the 
  dorsals, 
  the 
  latter 
  of 
  the 
  cau- 
  

   dals. 
  In 
  the 
  M. 
  clekayi, 
  M. 
  gracilis 
  and 
  M. 
  giganteus, 
  none 
  of 
  these 
  are 
  depressed 
  ; 
  the 
  

   shorter 
  are 
  sub-pentagonal 
  in 
  section 
  ; 
  in 
  M. 
  depressus 
  and 
  M. 
  missuriensis 
  the 
  longer 
  are 
  

   depressed, 
  while 
  the 
  depression 
  of 
  the 
  shorter 
  diminishes 
  regularly 
  to 
  the 
  distal 
  cau- 
  

   dal 
  series. 
  In 
  M. 
  brumbyi 
  the 
  long 
  vertebra? 
  are 
  flattened 
  to 
  a 
  still 
  greater 
  degree. 
  

   (See 
  Gibbes' 
  Mongr.) 
  

  

  The 
  caudals 
  are 
  divided 
  into 
  three 
  series 
  by 
  Cuvier, 
  viz 
  : 
  those 
  with 
  separate 
  chevron 
  

   bones, 
  those 
  where 
  the 
  latter 
  are 
  united 
  to 
  the 
  centrum, 
  and 
  those 
  without 
  them. 
  Pass- 
  

   ing 
  posteriorly 
  these 
  vertebra? 
  become 
  gradually 
  shorter 
  and 
  more 
  vertically 
  ovate 
  in 
  form. 
  

   The 
  more 
  posterior 
  are 
  less 
  narrowed 
  in 
  the 
  M. 
  maximus, 
  M. 
  oarthrus 
  and 
  M. 
  missuriensis 
  

   (vide 
  Leidy's 
  work), 
  while 
  in 
  M. 
  dekayi 
  and 
  the 
  Liodons 
  they 
  are 
  rather 
  more 
  narrowed 
  

   vertically. 
  

  

  The 
  characters 
  of 
  the 
  diapophyses 
  are 
  marked 
  in 
  different 
  parts 
  of 
  the 
  column. 
  In 
  

   all 
  the 
  species 
  of 
  the 
  family 
  they 
  descend 
  from 
  an 
  elevated 
  position 
  on 
  the 
  cervicals 
  and 
  

   anterior 
  dorsals 
  to 
  an 
  inferior 
  one 
  on 
  the 
  lumbars. 
  They 
  nevertheless 
  never 
  spring 
  from 
  

   the 
  neural 
  arch, 
  as 
  in 
  the 
  Archosauria, 
  but 
  always 
  from 
  the 
  base 
  of 
  it. 
  On 
  the 
  median 
  

   dorsals 
  it 
  originates 
  from 
  the 
  middle 
  of 
  the 
  side 
  of 
  the 
  centrum, 
  and 
  on 
  the 
  lumbo-sacrals 
  

   from 
  the 
  plane 
  of 
  the 
  inferior 
  surface. 
  It 
  diminishes 
  in 
  size, 
  and 
  as 
  soon 
  as 
  the 
  articula- 
  

   tions 
  of 
  the 
  chevron 
  bones 
  appear, 
  begins 
  to 
  ascend 
  again. 
  On 
  the 
  anterior 
  caudals 
  it 
  

   rises 
  to 
  near 
  the 
  middle 
  of 
  the 
  centrum 
  and 
  gradually 
  disappears, 
  at 
  different 
  points 
  in 
  the 
  

   different 
  species. 
  

  

  The 
  chevron 
  bones 
  are 
  free 
  throughout 
  the 
  anterior 
  part 
  of 
  the 
  caudal 
  series 
  in 
  the 
  M. 
  

   giganteus, 
  and 
  confluent 
  with 
  the 
  centrum 
  in 
  the 
  posterior 
  portions. 
  This 
  is 
  probably 
  the 
  

   case 
  with 
  many 
  species 
  of 
  the 
  genus. 
  During 
  immaturity 
  they 
  may 
  be 
  all 
  distinct 
  in 
  Mo- 
  

   sasaurns, 
  and 
  in 
  the 
  genus 
  Liodon 
  (vel 
  Macrosaurus) 
  this 
  condition 
  is 
  permanent 
  through- 
  

   out 
  life, 
  and 
  so 
  characteristic. 
  This 
  is 
  indicated 
  by 
  the 
  very 
  large 
  individual 
  typical 
  of 
  

   L. 
  proriger, 
  and 
  is 
  visible 
  in 
  two 
  other 
  species 
  of 
  the 
  genus. 
  

  

  Genera. 
  The 
  four 
  genera 
  below 
  enumerated 
  appear 
  to 
  differ 
  in 
  tangible 
  characters 
  

   These 
  are 
  found 
  in 
  the 
  relations 
  of 
  the 
  pterygoid 
  bones 
  and 
  teeth, 
  and 
  characters 
  of 
  verte- 
  

   brae 
  A 
  number 
  of 
  genera 
  have 
  been 
  proposed 
  on 
  minor 
  modifications 
  in 
  the 
  forms 
  of 
  the 
  

   teeth. 
  These 
  are 
  Liodon, 
  Owen, 
  Holcodus, 
  Gibbes, 
  and 
  Polygonodon 
  and 
  PMogonodon 
  

   of 
  Leidv. 
  The 
  verv 
  close 
  similarity 
  in 
  dental 
  characters 
  among 
  the 
  members 
  of 
  this 
  

  

  