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  190 
  PALEONTOLOGY 
  OF 
  ILLIXO! 
  

  

  other 
  in 
  outline 
  and 
  coronal 
  contour 
  exactly 
  after 
  the 
  manner 
  

   noticed 
  in 
  the 
  Keokuk 
  and 
  Burlington 
  sp- 
  Che 
  tooth 
  subse- 
  

  

  quently 
  described, 
  under 
  the 
  designation 
  <S\/ 
  ndalodua 
  . 
  X. 
  and 
  

  

  W., 
  from 
  the 
  same 
  formation, 
  is 
  identical 
  with 
  the 
  former 
  described 
  

   form, 
  the 
  original 
  account 
  of 
  8. 
  epatulattu 
  being 
  founded 
  upon 
  an 
  imper- 
  

   fect, 
  excessively 
  worn 
  tooth. 
  The 
  collection 
  of 
  Mr. 
  Van 
  Home 
  contains 
  

   a 
  splendid 
  suite 
  of 
  the 
  latter 
  forms, 
  in 
  all 
  stages 
  of 
  growth 
  and 
  con- 
  

   ditions 
  of 
  preservation, 
  permitting 
  of 
  the 
  most 
  satisfactory 
  study 
  of 
  

   their 
  normal 
  peculiarities 
  and 
  variations, 
  so 
  far 
  as 
  this 
  may 
  be 
  

   made 
  from 
  detached 
  and 
  scattered 
  teeth. 
  

  

  Geological 
  position 
  and 
  localities: 
  St. 
  Louis 
  limestone; 
  Alton, 
  and 
  

   Monroe 
  county, 
  111., 
  St. 
  Louis, 
  Mo. 
  

  

  Genus 
  ORTHOPLEURODUS, 
  1 
  st. 
  J. 
  and 
  W. 
  

  

  Posterior 
  teeth 
  of 
  the 
  upper 
  jaw 
  subspatulate 
  in 
  general 
  outline: 
  

   postero-lateral 
  border 
  straight 
  or 
  nearly 
  so, 
  and 
  probably 
  gently 
  

   curved 
  downward 
  and 
  inward 
  at 
  the 
  outer 
  extremity 
  and 
  gently 
  

   arched 
  in 
  the 
  same 
  direction, 
  terminating 
  posteriorly 
  in 
  an 
  acul 
  

   angle 
  or 
  spur, 
  whence 
  the 
  inner 
  margin, 
  which 
  is 
  greatly 
  thickened 
  

   or 
  massive, 
  is 
  broadly 
  rounded 
  into 
  and 
  merging 
  with 
  the 
  thin 
  

   anterolateral 
  border 
  towards 
  the 
  extremity. 
  Coronal 
  Buri 
  on- 
  

  

  pied 
  by 
  a 
  prominent 
  principal 
  fold 
  or 
  ridgi 
  rising 
  nearest 
  the 
  

   straight 
  border, 
  and 
  flanked 
  on 
  the 
  anterior 
  slope 
  by 
  an 
  obscure 
  

   secondary 
  ridge; 
  the 
  punctate 
  enamel 
  forms 
  a 
  distind 
  narrow 
  Cold 
  

   along 
  the 
  thickened 
  straight 
  border, 
  where 
  it 
  is 
  distinctly 
  defii 
  

   from 
  the 
  basal 
  portion 
  by 
  a 
  alight 
  

  

  Teeth 
  supposed 
  to 
  have 
  ooonpied 
  a 
  similar 
  position 
  on 
  the 
  man- 
  

   dibles, 
  distinguished 
  by 
  their 
  trigonal 
  outline, 
  somewhat 
  md 
  

   spiral 
  inrolhneiit 
  of 
  tin 
  extremity, 
  toward 
  whioh 
  Che 
  antero-and 
  -J 
  

   postero-lateral 
  bord 
  darly 
  converge, 
  inner 
  margin 
  m 
  

   obliquely 
  rounded 
  and 
  sigmoidally 
  curved 
  from 
  front 
  towai 
  

   p 
  isterior 
  angle. 
  Coronal 
  surface 
  presenting 
  a 
  more 
  or 
  leas 
  well-de- 
  

   fined 
  plane 
  anterior 
  fold, 
  abruptly 
  broken 
  down 
  on 
  tfa 
  

   the 
  ooronal 
  enamel 
  forms 
  a 
  wide 
  belt 
  sharply 
  denned 
  from 
  the 
  d< 
  

  

  il 
  rim, 
  and 
  limited 
  behind 
  by 
  the 
  mon 
  deep 
  longitudinal 
  

  

  d( 
  preaaion 
  from 
  which 
  rises 
  the 
  al 
  b 
  rior 
  lobe, 
  which 
  i- 
  limit 
  

  

  l> 
  by 
  a 
  na 
  now 
  fold 
  of 
  < 
  nam. 
  1 
  separating 
  the 
  crown 
  from 
  the 
  

  

  I 
  portion 
  of 
  the 
  tooth. 
  

  

  rnl 
  i 
  

  

  

  

  