﻿68 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  channeled 
  and 
  undulated 
  as 
  in 
  the 
  opposite 
  horder; 
  inner 
  margin 
  

   hroadly 
  rounded, 
  hase 
  excavated 
  as 
  in 
  the 
  previously 
  described 
  form. 
  

   Crown 
  very 
  slightly 
  arched 
  transversely, 
  well-preserved 
  spt 
  cimens 
  

   showing 
  two 
  obscure 
  longitudinal 
  prominences, 
  one 
  near 
  and 
  rising 
  

   rather 
  abruptly 
  from 
  the 
  posterior 
  border, 
  the 
  other 
  a 
  little 
  anti 
  rior 
  

   of 
  the 
  middle; 
  a 
  third, 
  and 
  perhaps 
  sometimes 
  quite 
  as 
  well 
  marked 
  

   ridge, 
  occurs 
  just 
  back 
  of 
  the 
  anterior 
  border. 
  Coronal 
  surface 
  finely 
  

   and 
  closely 
  punctate. 
  A 
  medium-sized 
  tooth 
  measures 
  across 
  the 
  

   inner 
  margin 
  2u 
  mm; 
  ditto, 
  outer 
  margin 
  16 
  mm; 
  length 
  along 
  

   anterior 
  border 
  21 
  mm; 
  ditto, 
  posterior 
  border 
  32 
  m 
  m 
  ; 
  depth 
  of 
  

   tooth 
  at 
  middle 
  of 
  anterior 
  border 
  3 
  mm; 
  ditto, 
  inner 
  margin 
  about 
  

   5 
  mm. 
  

  

  A 
  very 
  small 
  specimen 
  which 
  is 
  provisionally 
  identified 
  with 
  the 
  

   maxillary 
  form 
  of 
  the 
  present 
  species, 
  shows 
  a 
  proportionately 
  shorter 
  

   tooth 
  of 
  a 
  more 
  rhombic 
  outline, 
  the 
  outer 
  margin, 
  also 
  an; 
  

   and 
  posterior 
  borders, 
  distinctly 
  crenulated. 
  the 
  former 
  strong 
  

   and 
  further 
  distinguished 
  by 
  the 
  gradual 
  convergence 
  of 
  the 
  lateral 
  

   borders, 
  greater 
  and 
  more 
  regular 
  transverse 
  convexity 
  of 
  the 
  coronal 
  

   region, 
  as 
  contrasted 
  with 
  the 
  typical 
  specimens. 
  These 
  featun 
  

   coronal 
  contour 
  are 
  also 
  intimately 
  shared 
  by 
  a 
  more 
  elongate 
  ma- 
  

   ture 
  tooth, 
  but 
  which, 
  though 
  imperfect 
  along 
  the 
  anterior 
  horder. 
  

   and 
  considerably 
  worn 
  towards 
  the 
  outer 
  extremity, 
  evidently 
  closely 
  

   agrees 
  in 
  outline 
  with 
  the 
  typical 
  examples. 
  

  

  Compared 
  with 
  other 
  American 
  Carboniferous 
  forms 
  of 
  Psephodu$, 
  

   the 
  present 
  offers 
  characteristics 
  readily 
  flintiwgniahiTig 
  them 
  specifi- 
  

   cally. 
  From 
  /'. 
  en 
  n 
  ala 
  tun 
  |N. 
  and 
  W.) 
  of 
  the 
  Cluster 
  Formation, 
  

   the 
  species 
  differ 
  in 
  the 
  uniformly 
  larger 
  size 
  of 
  the 
  teeth, 
  repre- 
  

   senting 
  the 
  dentition 
  of 
  different 
  parts 
  or 
  opposite 
  jaws. 
  The 
  large 
  

   median 
  teeth, 
  probably 
  belonging 
  to 
  the 
  lower 
  jaw. 
  differ 
  in 
  being 
  

  

  massive, 
  possessing 
  fewer 
  and 
  less 
  distinct 
  undulations 
  in 
  either 
  

   border 
  supposed 
  to 
  have 
  relation 
  to 
  contiguous 
  series 
  «'t 
  smaller 
  

   teeth, 
  ami 
  the 
  les^ 
  strongly 
  marked 
  crenulations 
  of 
  the 
  narrow 
  

  

  ooronalfold. 
  The 
  depressed 
  trapezoidal 
  teeth 
  included 
  in 
  the 
  second 
  

   form 
  described 
  under 
  the 
  above 
  Bpeoifio 
  caption, 
  and 
  which 
  are 
  sup- 
  

   i 
  to 
  have 
  belonged 
  to 
  the 
  upper 
  jaw. 
  differ 
  from 
  the 
  oorrea* 
  

   ponding 
  teeth 
  of 
  the 
  Chester 
  atially 
  the 
  same 
  respects 
  

  

  above 
  cited, 
  with 
  perhaps 
  less 
  marked 
  obliquity 
  of 
  inner 
  and 
  outer 
  

   margins 
  and 
  less 
  strong 
  spiral 
  inrollment. 
  Kxamples 
  of 
  both 
  of 
  

   the 
  above 
  forms 
  of 
  the 
  Chest 
  -how 
  the 
  entire 
  margins 
  and 
  

  

  borders 
  of 
  the 
  teeth 
  to 
  have 
  been 
  orenulated 
  ; 
  besides 
  they 
  are 
  more 
  

   or 
  less 
  deeply 
  ootohed 
  in 
  one 
  oi 
  other 
  border, 
  Bhowing 
  the 
  manner 
  

  

  