﻿96 
  PALAEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  of 
  their 
  possessors. 
  In 
  some 
  specimens, 
  as 
  that 
  discovered 
  by 
  Mr. 
  

   Wachsinuth, 
  the 
  abraded 
  anterior 
  coronal 
  region 
  presents 
  a 
  coarse, 
  

   irregular 
  punctate 
  structure, 
  characteristic 
  of 
  the 
  vaso-dentine 
  com- 
  

   posing 
  the 
  body 
  of 
  the 
  teeth. 
  In 
  mature 
  and 
  much-worn 
  teeth— 
  

   where 
  the 
  enamel 
  and 
  outer 
  subjacent 
  layers 
  have 
  been 
  removed 
  by 
  

   the 
  process 
  of 
  attrition 
  — 
  a 
  similar 
  exposition 
  of 
  the 
  coarse, 
  tubular 
  

   structure 
  is 
  laid 
  bare 
  all 
  round 
  the 
  inner 
  and 
  outer 
  margins 
  of 
  the 
  

   tooth; 
  in 
  other 
  examples 
  the 
  abrasion 
  has 
  been 
  carried 
  so 
  far 
  ae 
  to 
  

   produce 
  a 
  deep 
  channeling 
  of 
  the 
  surface 
  of 
  the 
  posterior 
  prominence 
  

   in 
  the 
  direction 
  of 
  the 
  long, 
  or 
  transverse 
  diameter 
  of 
  the 
  tooth: 
  

   and 
  in 
  those 
  that 
  preserve 
  the 
  crown 
  surface 
  in 
  a 
  perfect 
  state, 
  the 
  

   enamel 
  along 
  the 
  inner 
  margin, 
  through 
  which 
  the 
  minute, 
  pris- 
  

   matic 
  structure 
  is 
  visible, 
  shows 
  distinct 
  parallel 
  incremental 
  lines, 
  

   more 
  or 
  less 
  sharply 
  impressed, 
  and 
  even 
  reaching 
  well 
  up 
  over 
  the 
  

   crown, 
  producing 
  an 
  irregular, 
  undulated 
  surface, 
  extending 
  alike 
  our 
  

   the 
  posterior 
  prominence 
  and 
  the 
  anterior 
  neck. 
  In 
  well-preserved 
  

   specimens 
  the 
  secondary 
  lobe 
  in 
  front 
  of 
  the 
  principal 
  coronal 
  prom- 
  

   inence 
  is 
  defined 
  with 
  absolute 
  distinctness. 
  The 
  posterior 
  angle 
  

   probably 
  terminated 
  in 
  a 
  more 
  or 
  less 
  produced 
  spur, 
  the 
  enamel 
  

   apparently 
  forming 
  a 
  narrow 
  fold 
  enveloping 
  the 
  superior 
  ed( 
  

   the 
  anterolateral 
  border, 
  similar 
  to 
  what 
  obtains 
  in 
  corresponding 
  

   teeth 
  of 
  CocMiodtis; 
  however, 
  in 
  some 
  specimens 
  this 
  border 
  is 
  slightly 
  

   <\ 
  into 
  a 
  low, 
  obscurely-defined 
  marginal 
  ridge. 
  

   The 
  mandibular 
  posterior 
  teeth, 
  also, 
  exhibit 
  much 
  the 
  same 
  

   superficial 
  features 
  due 
  to 
  the 
  various 
  conditions 
  of 
  usage 
  and 
  pre- 
  

   servation 
  as 
  enumerated 
  in 
  connection 
  with 
  the 
  teeth 
  of 
  the 
  opposite 
  

  

  jaw. 
  The 
  anterior 
  plane-belt 
  is 
  usually 
  merged 
  into 
  the 
  median 
  

  

  prominence 
  toward 
  the 
  outer 
  margin, 
  the 
  result 
  of 
  wearing 
  down 
  

   of 
  the 
  crown 
  surface; 
  but 
  toward 
  the 
  inner 
  margin 
  the 
  coronal 
  

   contour 
  is 
  Well, 
  even 
  sharply 
  defined, 
  the 
  surface 
  enveloped 
  in 
  I 
  

  

  lavt 
  r 
  of 
  polished 
  enamel. 
  

  

  bgical 
  position 
  and 
  localities: 
  Keokuk 
  limestone: 
  Warsaw, 
  Ham- 
  

   ilton, 
  NaUVOO, 
  and 
  lbndei-on 
  county, 
  | 
  Illinois) 
  ;• 
  Keokuk. 
  Danville, 
  

  

  Bentonsport, 
  (Iowa); 
  BoonevuTe, 
  (Missouri). 
  

  

  DbLTOWVOHIUH 
  Yai.-.uhn 
  J. 
  and 
  YY. 
  

  

  PL 
  V 
  Rig. 
  14, 
  i.v 
  

  

  Mandibular 
  posterior 
  teetb 
  trigonal 
  is 
  outline, 
  apparently 
  

  

  inrolled 
  at 
  the 
  outer 
  extremity, 
  inner 
  margin 
  \ery 
  oblique 
  and 
  

   broad!] 
  rounded 
  with 
  alighl 
  Bigmoidal 
  curvature, 
  postero-lateral 
  bor- 
  

  

  