﻿110 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  deemed 
  sufficient 
  to 
  justify 
  the 
  separation 
  of 
  these 
  individuals 
  from 
  

   the 
  more 
  characteristic 
  representatives 
  of 
  the 
  species 
  with 
  which 
  

   they 
  are 
  associated. 
  

  

  Compared 
  with 
  heretofore 
  described 
  species, 
  the 
  present 
  one 
  is 
  

   allied 
  to 
  that 
  occurring 
  in 
  the 
  Keokuk 
  formation 
  described 
  by 
  M. 
  m 
  

   Newberry 
  and 
  Worthen, 
  under 
  the 
  names 
  PcecUodus 
  rugosiu 
  and 
  /'. 
  

   amatois. 
  'The 
  species 
  differ, 
  however, 
  in 
  several 
  marked 
  peculiarities. 
  

   The 
  closest 
  resemblance 
  between 
  them 
  is 
  noted 
  in 
  connection 
  with 
  

   the 
  proportions 
  and 
  coronal 
  contour 
  of 
  the 
  mandibular 
  posterior 
  

   teeth, 
  the 
  Upper 
  Burlington 
  form 
  being 
  mainly 
  distinguishable 
  by 
  

   the 
  more 
  delicate 
  and 
  close 
  arrangement 
  of 
  the 
  tram 
  

   tions. 
  The 
  median 
  teeth 
  of 
  the 
  mandibles 
  of 
  the 
  two 
  species 
  differ 
  

   to 
  a 
  greater 
  extent 
  one 
  from 
  the 
  other, 
  the 
  coronal 
  prominence 
  in 
  

   the 
  present 
  species 
  possessing 
  greater 
  elevation 
  and 
  more 
  pro- 
  

   nounced 
  differentiation 
  of 
  the 
  culminating 
  ridge. 
  In 
  the 
  posterior 
  

   teeth 
  of 
  the 
  upper 
  jaw 
  the 
  divergence 
  in 
  the 
  contrast- 
  between 
  the 
  

   species 
  is 
  even 
  more 
  emphasized, 
  the 
  Upper 
  Burlington 
  exam] 
  

   being 
  destitute 
  of 
  the 
  supplementary 
  rugosities 
  thai 
  surmount 
  the 
  

   crest 
  of 
  the 
  posterior 
  lobe 
  in 
  the 
  Keokuk 
  species. 
  

  

  It 
  seems 
  not, 
  therefore, 
  improbable 
  thai 
  the 
  examination 
  i 
  

   larger 
  suite 
  of 
  specimens 
  may 
  reveal 
  the 
  exifi 
  a 
  contempora- 
  

  

  neous 
  species 
  during 
  the 
  Opper 
  Burlington 
  epoch, 
  which 
  the 
  present 
  

   material 
  rather 
  BUggebts 
  than 
  demonstrates, 
  much 
  less 
  affords 
  the 
  

   necessary 
  data 
  for 
  the 
  satisfactory 
  discrimination 
  of 
  its 
  distinctive 
  

   characteristics. 
  The 
  illustrations 
  convey 
  a 
  fair 
  impression 
  of 
  I 
  

   species 
  as 
  determined 
  from 
  such 
  remains 
  as 
  are 
  at 
  hand, 
  while 
  at 
  

  

  the 
  same 
  time 
  they 
  Eerve 
  to 
  show 
  the 
  variable 
  appearance 
  individual 
  

   specimens 
  present, 
  the 
  limits 
  of 
  which 
  are 
  difficult 
  to 
  define. 
  

  

  logical 
  position 
  and 
  localities: 
  Upper 
  Burlington 
  limestone: 
  Bur- 
  

   lington, 
  Buffington 
  oreek, 
  Louisa 
  county. 
  Pleasant 
  Grove, 
  augui 
  

   Iowa 
  : 
  Quinoy, 
  111. 
  

  

  ChTTONODUS 
  kS 
  J. 
  and 
  \Y. 
  

  

  Pi 
  \l.i 
  . 
  

  

  Mandibular 
  posterior 
  tooth 
  less 
  than 
  medium 
  sue, 
  fa 
  d 
  in 
  

  

  general 
  outline, 
  Btrongly 
  inrolled 
  and 
  correspondingly 
  arched 
  l< 
  

   tudinally. 
  Am. 
  i 
  i 
  making 
  nearlj 
  with 
  

  

  ■ 
  

  

  