﻿PALEONTOLOGY 
  OF 
  ILLINmi- 
  

  

  jagged 
  srest; 
  their 
  worn 
  apices 
  sh< 
  fcinet 
  punctate 
  structure, 
  

  

  intimately 
  resembling 
  the 
  eroded 
  coronal 
  surfaces 
  of 
  Orwhu 
  and 
  

   oth< 
  t 
  teeth 
  oeonrring 
  in 
  these 
  deposits, 
  the 
  intertuberoular 
  spi 
  

   showing 
  the 
  ordinary 
  Btriato-pnnetate 
  markings 
  of 
  ichthyodorolil 
  

   The 
  fragment 
  does 
  not 
  reveal 
  the 
  thickness 
  of 
  the 
  trails 
  nor 
  any 
  

   part 
  of 
  the 
  pulp 
  cavity; 
  it 
  evidently 
  belonged 
  to 
  a 
  medium-- 
  

   spine. 
  

  

  Compared 
  with 
  Oraeanthus 
  obliqutu 
  of 
  the 
  Keokuk 
  limestone, 
  the 
  

   present 
  form 
  is 
  distinguished 
  by 
  its 
  more 
  rigid 
  outline 
  and 
  ti 
  

   regular 
  distribution 
  of 
  the 
  tubercles. 
  In 
  both 
  forms 
  the 
  oblique 
  

   transversely 
  elongate 
  tubercles 
  are 
  asymmetrical; 
  in 
  other 
  wordsi 
  

   the 
  crest 
  culminates 
  in 
  a 
  suhmedian 
  apex 
  along 
  the 
  angularly 
  rounded 
  

   border, 
  from 
  which 
  the 
  Longer 
  lateral 
  crest 
  declines 
  obliquely 
  up- 
  

   ward 
  and 
  backward 
  in 
  the 
  K- 
  ol.uk 
  spine 
  on 
  the 
  right 
  >i<lt 
  <.f 
  the 
  

   anterior 
  angle, 
  and 
  in 
  the 
  present 
  form 
  on 
  the 
  left 
  side 
  "f 
  the 
  

   angularly 
  rounded 
  anterior 
  border. 
  We 
  are, 
  h< 
  inclined 
  to 
  

  

  regard 
  the 
  unique 
  example 
  of 
  the 
  Keokuk 
  speci 
  

   the 
  anterior 
  edge 
  of 
  the 
  spine, 
  and 
  the 
  Chester 
  form 
  here 
  alluded 
  

   to 
  as 
  possibly 
  belonging 
  to 
  the 
  opposite 
  or 
  posterior 
  edge. 
  I 
  

   amined 
  in 
  the 
  relative 
  positions 
  thus 
  indicated, 
  the 
  direction 
  of 
  the 
  

   obliquity 
  of 
  the 
  transverse 
  rows 
  of 
  tubercles 
  in 
  tin- 
  unique 
  n 
  

   tativea 
  of 
  the 
  species 
  mentioned, 
  merely 
  indicate 
  the 
  opposed 
  1 
  

   of 
  the 
  respective 
  fragments, 
  in 
  both 
  of 
  which 
  the 
  obliqu< 
  .rse 
  

  

  disposition 
  of 
  the 
  tubercles 
  is 
  essentially 
  tin 
  If 
  the 
  n 
  la- 
  

  

  position 
  of 
  the 
  fragment 
  of 
  the 
  present 
  spine 
  is 
  correctly 
  inferred, 
  

   it 
  differs 
  from 
  the 
  form 
  occurring 
  in 
  the 
  St. 
  Louis 
  li; 
  

   vetxuttu, 
  Leidy, 
  in 
  the 
  much 
  less 
  marked 
  obliquity 
  of 
  the 
  trai 
  

   elongate 
  tubercles 
  near 
  the 
  anterior 
  border, 
  in 
  which 
  latter 
  res] 
  

  

  however, 
  the 
  latter 
  species 
  show- 
  variations 
  approaching 
  the 
  con- 
  

   dition 
  observed 
  in 
  the 
  )c 
  pine. 
  But 
  the 
  relations 
  of 
  these 
  

   spun 
  - 
  i 
  an 
  only 
  he 
  determined 
  from 
  the 
  examination 
  of 
  more 
  com- 
  

   plete 
  and 
  better 
  preserved 
  individuals 
  in 
  the 
  

  

  species 
  ami 
  that 
  fiom 
  the 
  Keokuk 
  formation. 
  

  

  'ogical 
  position 
  and 
  l<>c<iHti/. 
  Chester 
  Umestoi 
  

  

  