﻿7i 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  Geological 
  position 
  and 
  location: 
  St. 
  Louis 
  limestone; 
  Alton, 
  111., 
  

   St. 
  Louis, 
  M". 
  

  

  PsKPHODUS 
  (TNri.VlTS. 
  St. 
  J. 
  and 
  W. 
  

   PI. 
  II. 
  Fik'. 
  4. 
  

  

  Tooth 
  small, 
  quadrato-lunate 
  in 
  outline, 
  lateral 
  borders 
  nearly 
  

   parallel, 
  posterior 
  margin 
  strongly 
  arched 
  forward, 
  making 
  obtuse 
  

   angles 
  with 
  the 
  lateral 
  borders, 
  anterior 
  margin 
  correspondingly 
  

   concave, 
  terminating 
  in 
  the 
  acute, 
  outward-produced 
  lateral 
  angles. 
  

   Coronal 
  region 
  moderately 
  arched 
  in 
  both 
  directions, 
  with 
  an 
  abrupt 
  

   declivity 
  bordering 
  the 
  anterior 
  side, 
  the 
  surface 
  presenting 
  I 
  boi 
  

   what 
  uneven 
  contour, 
  which 
  is 
  also 
  discoverable 
  in 
  the 
  slightly 
  greater 
  

   prolongation 
  and 
  rounding 
  of 
  one 
  of 
  the 
  e»4** 
  lateral 
  angles, 
  and 
  AX^^r*-/ 
  

   the 
  relatively 
  greater 
  depth 
  of 
  the 
  tooth 
  at 
  that 
  side: 
  the 
  enamel 
  

   makes 
  a 
  distinct 
  narrow 
  belt 
  sharply 
  inbeveled 
  to 
  the 
  basal 
  portion 
  

   all 
  round, 
  lateral 
  borders 
  obscurely 
  undulated, 
  posterior 
  edge 
  plioato- 
  

   denticulate, 
  outer 
  margin 
  occupied 
  by 
  vertical 
  plica 
  terminating 
  below 
  

   in 
  ,1,, 
  p 
  nenulations. 
  The 
  base 
  isrelatively 
  thick: 
  inferior 
  Burfaoe 
  

   slightly 
  depressed 
  and 
  smooth, 
  lateral 
  borders 
  marly 
  vertical 
  and 
  

   faintly 
  channeled, 
  inner 
  margin 
  deeply 
  channeled, 
  together 
  with 
  

   the 
  coronal 
  belt, 
  and 
  terminating 
  below 
  in 
  a 
  thin 
  rim 
  slightly 
  in 
  

   advance 
  of 
  the 
  coronal 
  edge, 
  the 
  edges 
  all 
  round 
  coarsely 
  piti 
  

   Coronal 
  surface 
  presents 
  a 
  somewhat 
  irregular, 
  minute 
  punoti 
  

   structure, 
  Bhowing 
  marked 
  evidences 
  of 
  attrition 
  from 
  use. 
  Breadth 
  

   across 
  outer 
  margin 
  9.5 
  mm.; 
  length 
  along 
  one 
  of 
  the 
  lateral 
  

   borders 
  5mm.: 
  length 
  along 
  median 
  line 
  B 
  m 
  m. 
  

  

  The 
  unique 
  specimen 
  above 
  described 
  represents 
  a 
  marly 
  perfect 
  

   tooth 
  of 
  a 
  form 
  not 
  before 
  met 
  with. 
  Its 
  affinities 
  are 
  unquestion- 
  

   ably 
  with 
  PiephodlU, 
  with 
  whose 
  numerous 
  dental 
  remains 
  it 
  

   SOciated. 
  The 
  narrow 
  forms 
  of 
  V. 
  crcnuhitu* 
  (N. 
  and 
  W., 
  B] 
  

  

  present, 
  in 
  their 
  orenulated 
  margins, 
  striking 
  resemblance 
  with 
  the 
  

  

  |m 
  sent 
  tooth, 
  even 
  as 
  to 
  the 
  details 
  enumerated 
  above, 
  though 
  

  

  perhaps 
  nol 
  so 
  pronounced 
  as 
  observed 
  in 
  the 
  individual 
  described. 
  

   The 
  Bame 
  observation 
  holds 
  as 
  regards 
  the 
  coronal 
  contour, 
  which 
  

   radually 
  doped 
  from 
  the 
  brink 
  of 
  the 
  abrupt 
  outer 
  declivity 
  to 
  

   the 
  inner 
  margin. 
  It 
  is 
  therefore, 
  with 
  some 
  doubt 
  . 
  5c 
  dis- 
  

  

  tinotn< 
  lised; 
  it 
  may 
  pro\e 
  to 
  belong 
  to 
  a 
  posterior 
  i 
  

  

  •I, 
  of 
  one 
  or 
  other 
  jaw, 
  or 
  possibly 
  int. 
  Dear 
  the 
  sym. 
  

  

  JlllN 
  D 
  ti„. 
  tlat. 
  narrow, 
  //,/.,/,/.< 
  like 
  teeth, 
  whoftfi 
  Bpeedfio 
  

  

  identity 
  with 
  the 
  contorted, 
  inroUed 
  median 
  plates 
  of 
  /'. 
  crtnulai 
  

  

  