﻿208 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  The 
  enamel 
  belt 
  also 
  distinctly 
  defined 
  and 
  delicately 
  Bculptured 
  

   in 
  vertical 
  rugosities, 
  traces 
  of 
  which 
  are 
  also 
  detected 
  in 
  the 
  belt 
  

   of 
  the 
  anterior 
  and 
  posterior 
  margins; 
  outer 
  border 
  gently 
  curv< 
  

   and 
  very 
  gradually 
  diverging 
  from 
  the 
  rounded 
  anterior 
  angle 
  to 
  

   the 
  posterior 
  angle, 
  which 
  terminates 
  in 
  a 
  somewhat 
  prodnc 
  

   spur, 
  the 
  basal 
  portion 
  projecting 
  prominently 
  beyond 
  the 
  border 
  of 
  

   the 
  crown, 
  which 
  is 
  limited 
  by 
  a 
  narrow 
  enamel 
  fold. 
  The 
  coronal 
  

   region 
  presents 
  a 
  remarkably 
  uniform 
  surface, 
  in 
  the 
  main 
  gently 
  

   depressed 
  transversely 
  without 
  well-defined 
  inner 
  prominence, 
  and 
  

   rather 
  abruptly 
  upraised 
  along 
  the 
  outer 
  border, 
  which 
  forms 
  the 
  

   most 
  prominent 
  part 
  of 
  the 
  coronal 
  surface. 
  The 
  worn 
  surface 
  i 
  

   hibits 
  minute 
  punctation, 
  and 
  the 
  less 
  worn 
  portions 
  show 
  a 
  delk 
  

   reticulate 
  structure, 
  produced 
  by 
  the 
  walls 
  of 
  the 
  vertical 
  prisms 
  

   enclosing 
  the 
  medullary 
  tubes. 
  Greatest 
  diameter 
  across 
  the 
  posl 
  

   rior 
  margin, 
  53 
  millimeters; 
  length 
  along 
  the 
  inner 
  margin, 
  about 
  

   mm.; 
  breadth 
  across 
  anterior 
  margin, 
  8& 
  mm. 
  ; 
  thickness 
  of 
  tooth, 
  

   about 
  1") 
  millimetres. 
  

  

  Mandibular 
  form 
  subquadrangular 
  in 
  outline, 
  moderately 
  arched 
  

   in 
  both 
  directions. 
  Inner 
  border 
  marked 
  by 
  a 
  slight 
  angulation 
  de- 
  

   lining 
  the 
  anterior 
  and 
  posterior 
  articular 
  facets 
  which 
  are 
  appar- 
  

   ently 
  nearly 
  equal 
  in 
  extent, 
  coronal 
  enamel 
  well 
  defined 
  along 
  the 
  

   deep, 
  slightly 
  inhevoled 
  basal 
  portion; 
  exterior 
  border 
  gently 
  arch 
  

   very 
  gradually 
  converging 
  toward 
  the 
  obtuse 
  or 
  sharply 
  rounded 
  

   ant. 
  rim- 
  angle, 
  the 
  basal 
  portion 
  projecting 
  more 
  or 
  less 
  beyond, 
  

   and 
  well 
  defined 
  from 
  the 
  rounded 
  coronal 
  border; 
  anterior 
  and 
  i 
  

   terior 
  margins 
  making 
  the 
  same 
  slight 
  rigmoidal 
  curvature, 
  with 
  a 
  

   shallow 
  concavity 
  in 
  front 
  and 
  a 
  corresponding 
  broad 
  convexity 
  

   behind 
  from 
  the 
  inner 
  angles, 
  the 
  basal 
  portion 
  all 
  around 
  more 
  or 
  

   less 
  distinctly 
  marked 
  by 
  vertical 
  rugosities. 
  The 
  ■ 
  

   the 
  ooxonal 
  region 
  is 
  occupied 
  by 
  the 
  broad 
  low 
  convexity 
  of 
  the 
  

  

  inner 
  prominence, 
  Which 
  is 
  rounded 
  to 
  the 
  inner 
  border, 
  and 
  on 
  the 
  

   other 
  hand 
  slopes 
  into 
  the 
  narrow 
  shallow 
  depression 
  holder, 
  d 
  by 
  

   th, 
  narrow 
  fold 
  along 
  the 
  Outer 
  border; 
  in 
  front, 
  the 
  coronal 
  prom- 
  

   inence 
  presents 
  a 
  Lunate, 
  slightly 
  depressed 
  area, 
  extending 
  back 
  

   from 
  the 
  anterior 
  margin 
  a 
  greater 
  or 
  lees 
  distance, 
  evidence 
  of 
  wear 
  

   while 
  m 
  ase. 
  The 
  surface 
  presents, 
  apparently, 
  the 
  same 
  .ham 
  

  

  ,,l 
  punctation 
  observed 
  in 
  the 
  above 
  noticed 
  form. 
  I 
  trans- 
  

  

  ter 
  across 
  the 
  posterior 
  margin, 
  :i"> 
  mm.: 
  length 
  al< 
  

   inner 
  border, 
  86 
  mm.: 
  breadth 
  at 
  the 
  ant. 
  nor 
  margin, 
  98 
  mm. 
  

  

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