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  PAL^SONTOLOGI 
  OF 
  tLLINOH 
  

  

  curved; 
  the 
  outer 
  border 
  broadly 
  arched, 
  the 
  basal 
  portion 
  pr 
  

   in» 
  in 
  a 
  prominent, 
  thick 
  rim 
  beyond 
  the 
  coronal 
  limits, 
  slightly 
  

   prod; 
  teriorly, 
  andinbeveled 
  to 
  the 
  inferior 
  surfa 
  inner 
  

  

  border 
  presents 
  precisely 
  the 
  conformation 
  observed 
  in 
  typical 
  ( 
  

  

  eept 
  that 
  the 
  angulation 
  is 
  placed 
  forwards 
  a 
  little 
  less 
  than 
  

   one-fifth 
  the 
  distance 
  from 
  the 
  anterior 
  angle, 
  distinctly 
  defining 
  

   the 
  anterior 
  articular 
  facet 
  from 
  the 
  loii^r 
  posterior 
  articular 
  surface. 
  

   coronal 
  surface 
  is 
  longitudinally 
  moderately 
  arched, 
  and 
  trans- 
  

   Ly 
  depressed, 
  limits 
  of 
  the 
  crown 
  well 
  defined 
  at 
  the 
  sides, 
  the 
  

   inner 
  ridge 
  presenting 
  the 
  abrupt 
  fact 
  I 
  in 
  the 
  above 
  men- 
  

  

  tioned 
  example 
  from 
  I'ella 
  ; 
  the 
  outer 
  ridge 
  also 
  ris< 
  B 
  low 
  

  

  acoumination 
  nearest 
  the 
  anterior 
  angle. 
  The 
  worn 
  Borfaci 
  

   the 
  usual 
  minute 
  punctate 
  structure, 
  hut 
  in 
  the 
  more 
  llepn 
  

   portions 
  which 
  have 
  escaped 
  abrasion, 
  the 
  transven 
  are 
  dis- 
  

  

  cernible, 
  the 
  same 
  as 
  noted 
  in 
  one 
  of 
  the 
  Alton 
  specimens 
  of 
  a 
  very 
  

   elongate 
  tooth. 
  

  

  The 
  present 
  species 
  differs 
  equally 
  from 
  that 
  noticed 
  from 
  the 
  

   Qpper 
  Burlington 
  lime-tone, 
  and 
  Psammodus 
  canaUculatus, 
  M 
  

   of 
  the 
  Irish 
  Mountain 
  limestone: 
  Relatively 
  Bhorter 
  than 
  the 
  i 
  

   from 
  the 
  former 
  it 
  may 
  be 
  distinguished 
  by 
  tin 
  less 
  prominenl 
  

  

  rounded 
  contour 
  of 
  the 
  coronal 
  ridge 
  along 
  the 
  outer 
  holder. 
  

  

  Geological 
  position 
  mid 
  localities: 
  St. 
  Louis 
  formation 
  ; 
  Alton. 
  111. 
  : 
  

   I'ella. 
  Iowa. 
  

  

  Psammodus 
  .is. 
  N. 
  and 
  \V. 
  

  

  PL 
  . 
  !.'-'. 
  

  

  PL 
  XI' 
  

  

  r.a, 
  j«. 
  ti'. 
  

  

  il>.. 
  i'. 
  107, 
  PL 
  XI. 
  f. 
  ' 
  

  

  above 
  designated 
  speci 
  sribed 
  from 
  a 
  nearly 
  perfect 
  

  

  iple 
  beloi 
  ■ 
  the 
  form 
  pi 
  ally 
  n 
  f. 
  i 
  the 
  mandible. 
  

  

  In 
  order 
  to 
  facilitate 
  comparison 
  with 
  the 
  I 
  in 
  pre* 
  

  

  oedin 
  • 
  ventm 
  pplement 
  the 
  brief 
  desoripti 
  

  

  im< 
  what 
  «1< 
  tailed 
  n< 
  apon 
  the 
  

  

  original 
  example 
  and 
  tie 
  wqut 
  nth 
  

  

  covered 
  in 
  the 
  same 
  horizon 
  winner 
  the 
  type 
  was 
  deri 
  

   The 
  supposed 
  mandibular 
  teeth 
  attain 
  medium 
  

  

  lutline. 
  The 
  corona 
  ilarly 
  

  

  arched 
  from 
  behind 
  forwai 
  with, 
  

  

  however, 
  a 
  fullness 
  in 
  the 
  :!t 
  or 
  more 
  of 
  the 
  area, 
  which 
  

  

  

  