﻿124 
  PALEONTOLOGY 
  OF 
  ILLINOb 
  

  

  a 
  triturating 
  surface 
  interrupted 
  by 
  prominent 
  transverse 
  ridges 
  and 
  

   intervening 
  deep 
  furrows, 
  corresponding 
  to 
  the 
  coronal 
  crests 
  of 
  the 
  

   individuals 
  of 
  the 
  series; 
  in 
  some 
  instances 
  the 
  individual 
  teeth 
  are 
  

   so 
  intimately 
  united 
  along 
  the 
  impingement 
  of 
  their 
  basts 
  as 
  to 
  

   obliterate 
  all 
  trace 
  of 
  suture; 
  again, 
  in 
  other 
  examples 
  the 
  original 
  

   or 
  occasional 
  individuality 
  of 
  the 
  teeth 
  is 
  indicated 
  by 
  a 
  faint 
  

   suture, 
  extending 
  in 
  from 
  the 
  borders 
  of 
  the 
  series, 
  while 
  oth> 
  

   again 
  show 
  the 
  complete 
  series 
  in 
  natural 
  Bueeessional 
  order, 
  but 
  

   with 
  their 
  bases 
  free. 
  The 
  individuals 
  of 
  the 
  series 
  regularly 
  

   diminish 
  in 
  size 
  from 
  within 
  outward, 
  although 
  the 
  tooth 
  of 
  the 
  

   inner 
  margin 
  sometimes 
  presents 
  an 
  immature 
  coronal 
  crest, 
  adher- 
  

   ing 
  to 
  the 
  inner 
  basal 
  declivity 
  of 
  the 
  immediately 
  preceding 
  fully 
  

   developed 
  tooth, 
  a 
  feature 
  known 
  to 
  obtain 
  in 
  the 
  Helodus-Hka 
  teeth 
  

   associated 
  with 
  uhitonodus 
  lotus, 
  e. 
  g. 
  Helodus 
  coruolidatus, 
  N. 
  and 
  

   W. 
  The 
  independent 
  teeth 
  are 
  distinguished 
  by 
  their 
  long-elliptical 
  

   transverse 
  outline 
  seen 
  from 
  above, 
  slightly 
  arched 
  backward 
  along 
  

   the 
  inner 
  margin 
  of 
  the 
  crown, 
  the 
  opposite 
  side 
  being 
  protuberant 
  

   in 
  the 
  middle, 
  with 
  concave 
  curvature 
  towards 
  the 
  extremities. 
  The 
  

   crown 
  rises 
  into 
  a 
  tumid 
  eccentric 
  apt 
  \ 
  Dearer 
  the 
  posterolateral 
  

   extremity, 
  outer 
  face 
  slightly 
  concave, 
  opposite 
  side 
  nuub 
  lately 
  con- 
  

   vex, 
  sharply 
  inbeveled 
  and 
  denned 
  from 
  the 
  base, 
  the 
  extremil 
  

   marked 
  by 
  a 
  sort 
  of 
  enamel 
  fold, 
  which 
  also 
  faintly 
  Appears 
  all 
  

   the 
  outer 
  margin, 
  but 
  destitute 
  of 
  imbrications, 
  such 
  as 
  appear 
  in 
  

   the 
  coronal 
  belt 
  of 
  Chomatodus. 
  The 
  base 
  is 
  relatively 
  shall 
  

   inbeveled 
  in 
  front, 
  more 
  or 
  less 
  channeled 
  and 
  irregularly 
  eoare 
  

  

  pitted, 
  inner 
  margin 
  much 
  produced 
  outward 
  and 
  downward 
  to 
  the 
  

  

  dull 
  inferior 
  edge, 
  vertically 
  coarsely 
  rugose 
  ; 
  inferior 
  surface 
  faintly 
  

   depressed, 
  smooth. 
  The 
  large 
  tooth 
  of 
  a 
  medium 
  of 
  

  

  three 
  firmly 
  ooalescent 
  individuals 
  measures 
  in 
  lateral 
  diameter 
  of 
  

   ciown 
  ti 
  mm., 
  diameter 
  at 
  the 
  middle 
  2 
  mm.: 
  greatest 
  height 
  

   crown 
  1 
  mm. 
  Crown 
  originally 
  enveloped 
  in 
  a 
  dense 
  semi-opaque 
  

   enamel, 
  the 
  worn 
  surface 
  Bhowing 
  rather 
  widely 
  Bpaoed 
  pun. 
  

   varying, 
  however, 
  considerably 
  in 
  the 
  latter 
  respect. 
  Th< 
  ited 
  

  

  teeth 
  clearly 
  homologous 
  with 
  the 
  p 
  form, 
  present 
  rather 
  • 
  

  

  wii 
  in 
  sanation, 
  particularly 
  in 
  r«-; 
  the 
  oontou] 
  

  

  the 
  coronal 
  region. 
  In 
  Borne 
  of 
  tin 
  teeth 
  the 
  crown 
  is 
  muob 
  de- 
  

   pressed; 
  in 
  otl 
  am. 
  the 
  outer 
  face 
  presents 
  a 
  wide, 
  plain, 
  

   elliptic 
  ai.a. 
  th.- 
  hum 
  r 
  dope 
  wy 
  low. 
  mid 
  the 
  rowded 
  I 
  

   past 
  th,. 
  basal 
  border, 
  in 
  which 
  condition 
  it 
  resembles 
  certain 
  forms 
  

   of 
  Tanaodu*, 
  although 
  th. 
  i 
  ntirely 
  different 
  from 
  that 
  of 
  the 
  

   lattt 
  t 
  genus. 
  

  

  