﻿180 
  PALEONTOLOGY 
  OF 
  BLLINOH 
  

  

  where 
  the 
  punctre 
  are 
  best 
  seeti. 
  they 
  show 
  only 
  obscure 
  indications 
  

   of 
  transverse 
  disposition 
  in 
  more 
  or 
  less 
  irregular 
  parallel 
  roi 
  

   Length 
  of 
  a 
  medium-size 
  tooth 
  at 
  antero-lateral 
  border 
  about 
  9 
  mm 
  ; 
  

   breadth 
  across 
  innei 
  margin 
  nearly 
  6 
  mm. 
  

   'The 
  above 
  description 
  is 
  based 
  upon 
  a 
  few 
  imperfect 
  specie 
  

   which 
  are 
  supposed 
  to 
  represent 
  the 
  posterior 
  teeth 
  of 
  the 
  op] 
  

   jaw. 
  In 
  general 
  outline 
  and 
  coronal 
  contour 
  they 
  conform 
  to 
  the 
  

   characteristics 
  of 
  the 
  genu-. 
  as 
  already 
  remarked, 
  the 
  puncto 
  of 
  

   the 
  triturating 
  surface 
  show 
  an 
  indistinct 
  disposition 
  in 
  tnu 
  

   rows, 
  in 
  which 
  respect 
  the 
  teeth 
  differ 
  most 
  from 
  typical 
  Bpeciea 
  of 
  

   the 
  genus, 
  though 
  to 
  not 
  much 
  greater 
  extent 
  than 
  does 
  the 
  St. 
  Louis 
  

   species, 
  Xystrodus 
  imitates. 
  It 
  differs, 
  however, 
  from 
  either 
  the 
  

   St. 
  Louis 
  or 
  Chester 
  species, 
  A", 
  vents, 
  in 
  the 
  relatively 
  greater 
  

   breadth 
  of 
  the 
  inner 
  margin 
  and 
  consequent 
  greater 
  transvi 
  

   pansion 
  of 
  the 
  posterior 
  alation. 
  From 
  the 
  Upper 
  Burlington 
  

   X. 
  simplex 
  it 
  is 
  distinguished 
  by 
  the 
  greater 
  lateral 
  breadth 
  and 
  

   convexity 
  of 
  the 
  anterior 
  coronal 
  prominence. 
  

  

  The 
  collections 
  have 
  thus 
  far 
  afforded 
  no 
  recognizable 
  examples 
  

   identifiable 
  with 
  the 
  broad 
  posterior 
  teeth 
  of 
  the 
  mandibli 
  

   Geological 
  position 
  and 
  localities: 
  Keokuk 
  limestone. 
  Hamilton 
  and 
  

  

  Warsaw. 
  111., 
  Keokuk 
  and 
  Bentonsport, 
  Iowa. 
  

  

  Xystrodus 
  imitahs, 
  St. 
  .1. 
  and 
  W. 
  

   PL 
  VIII. 
  l'k 
  j. 
  

   Maxillary 
  posterior 
  teeth 
  small, 
  triangular 
  or 
  Bub-OUneate 
  in 
  out- 
  

   line, 
  gently 
  arched 
  longitudinally. 
  Antero-lateral 
  border 
  alightly 
  

   curved 
  sigmoidally, 
  forming 
  above 
  a 
  sharp 
  angle 
  with 
  the 
  coronal 
  

   prominence, 
  a 
  narrow 
  enamel 
  belt 
  folding 
  over 
  the 
  upper 
  

   tinctly 
  defined 
  from 
  the 
  hasal 
  portion, 
  which 
  is 
  nearly 
  vertical 
  or 
  

   projecting 
  slightly 
  outward, 
  terminating 
  in 
  the 
  attenuated 
  inferior 
  

  

  edge, 
  which 
  apparently 
  extends 
  nearly 
  the 
  entire 
  length 
  of 
  this 
  - 
  

  

  of 
  the 
  tooth; 
  inner 
  margin 
  sharply 
  rounded 
  from 
  the 
  anterior 
  an 
  

  

  with 
  a 
  slight 
  concavity 
  in 
  its 
  course 
  to 
  the 
  slightly 
  produce. 
  1 
  | 
  

   tenor 
  angle, 
  and 
  forming 
  nearly 
  a 
  right-angle 
  With 
  the 
  antero-lateral 
  

  

  border; 
  postero-lateral 
  border 
  gradually 
  di\ 
  from 
  th< 
  

  

  tremity 
  at 
  an 
  angle 
  of 
  aboul 
  80 
  with 
  opposite 
  border, 
  \ 
  

  

  Qtly 
  OUTVed, 
  the 
  appet 
  QVeloped 
  in 
  a 
  narrow 
  fold 
  of 
  • 
  

  

  ironal 
  enamel, 
  occupying 
  aboul 
  half 
  the 
  vertical 
  heigh! 
  of 
  the 
  

   border. 
  Coronal 
  surface 
  slightly 
  convex 
  in 
  the 
  inner 
  unworn 
  p 
  

  

  n 
  of 
  the 
  principal 
  prominenoe, 
  with 
  a 
  moderately 
  nto 
  

  

  the 
  media/] 
  depression, 
  from 
  which 
  the 
  surface 
  moi 
  

  

  