﻿194 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  and 
  obliquely 
  rounded, 
  with 
  slight 
  sigmoidal 
  outline 
  extending 
  into 
  

   the 
  posterior 
  alation, 
  which 
  latter 
  is 
  usually 
  broken 
  away. 
  An- 
  

   terior 
  coronal 
  lobe 
  occupying 
  half 
  or 
  more 
  the 
  breadth 
  of 
  the 
  tooth, 
  

   gently 
  arched 
  transversely, 
  conspicuously 
  so 
  toward 
  the 
  inner 
  mar- 
  

   gin, 
  merging 
  into 
  the 
  postero- 
  lateral 
  depression, 
  from 
  which 
  it 
  is 
  

   defined 
  by 
  the 
  rounded 
  angulation 
  of 
  that 
  side. 
  Surface 
  uniformly 
  

   and 
  minutely 
  punctate. 
  Length 
  of 
  a 
  medium 
  size 
  tooth 
  along 
  an- 
  

   terolateral 
  border, 
  19 
  mm.; 
  breadth 
  across 
  inner 
  margin, 
  about 
  

   14 
  mm. 
  

  

  Maxillary 
  posterior 
  tooth 
  subspatulate 
  in 
  outline, 
  broadly 
  rounded 
  

   at 
  inner 
  margin, 
  postero-lateral 
  border 
  slightly 
  concave, 
  gently 
  arched 
  

   from 
  within 
  outward, 
  extremity 
  not 
  known. 
  Crown 
  surface 
  consult 
  

   ably 
  arched 
  transversely 
  over 
  the 
  principal 
  prominence 
  in 
  the 
  vicinity 
  

   of 
  the 
  inner 
  margin, 
  where 
  the 
  tooth 
  attains 
  comparatively 
  thick, 
  

   massive 
  proportions, 
  the 
  ridge 
  anteriorly 
  rapidly 
  diminishing 
  in 
  prom- 
  

   inence. 
  Surface 
  punctation 
  minute 
  and 
  uniform. 
  Length 
  of 
  a 
  tooth 
  

   below 
  medium 
  size 
  along 
  straight 
  border, 
  probably 
  at 
  hast 
  15 
  mm.; 
  

   breadth, 
  about 
  9 
  mm. 
  

  

  The 
  above 
  descriptions 
  are 
  founded 
  upon 
  a 
  single 
  example 
  of 
  each 
  

   form, 
  respectively, 
  discovered 
  by 
  Prof. 
  -1. 
  J. 
  Btbphbnboh. 
  Both 
  speci- 
  

   mens 
  are 
  in 
  imperfect 
  condition, 
  but 
  such 
  parts 
  as 
  remain 
  present 
  

   certain 
  peculiarities 
  which 
  seem 
  to 
  justify 
  their 
  reference 
  to 
  a 
  dis- 
  

   tinct 
  species. 
  Compared 
  with 
  the 
  species 
  prevalent 
  in 
  the 
  Coal 
  M< 
  

   ores 
  of 
  the 
  western 
  States, 
  Orihoplewrodu* 
  carbonarius, 
  the 
  mandibular 
  

   posterior 
  tooth 
  differs 
  in 
  the 
  marked 
  transverse 
  convexity 
  of 
  the 
  prin- 
  

   cipal 
  lobe 
  along 
  the 
  straight 
  Bide, 
  instead 
  of 
  being 
  tlat, 
  as 
  in 
  that 
  

   form; 
  the 
  opposed 
  teeth 
  of 
  the 
  upper 
  jaw 
  are 
  wry 
  like, 
  in 
  both 
  the 
  

   western 
  and 
  eastern 
  forms,— 
  the 
  latter, 
  perhaps, 
  being 
  distinguished 
  

   b> 
  its 
  mon 
  massive 
  proportions 
  in 
  the 
  region 
  of 
  the 
  inner 
  margin. 
  

   A 
  i 
  ute 
  of 
  materia] 
  from 
  the 
  Allegheny 
  region 
  may 
  Bhow 
  the 
  

  

  above 
  distinctive 
  features 
  to 
  be 
  of 
  subordinate 
  importance, 
  mail 
  

   nun 
  individual 
  variation, 
  but 
  in 
  a 
  direction 
  not 
  apparent 
  in 
  anyol 
  

   the 
  western 
  specimens. 
  

  

  Geological 
  position 
  and 
  locality: 
  Prom 
  Btrata 
  above 
  Mahoning 
  Band* 
  

   -tone. 
  Coal 
  Measures; 
  near 
  Morgantown, 
  West 
  Virginia. 
  

  

  