﻿148 
  PALAEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  Deltodus 
  tkilobus, 
  St. 
  J. 
  and 
  W« 
  

  

  PI. 
  IX, 
  Fig. 
  8. 
  

  

  Mandibular 
  median 
  tooth 
  of 
  medium 
  size, 
  wedge-shaped 
  in 
  outline, 
  

   moderately 
  arched 
  and 
  rather 
  strongly 
  inrolled. 
  Postero-lateral 
  or 
  

   ohlique 
  border, 
  converging 
  toward 
  the 
  outer 
  extremity 
  at 
  an 
  angle 
  

   of 
  about 
  15° 
  with 
  the 
  opposite 
  border, 
  slightly 
  sigmoidally 
  carved 
  

   from 
  the 
  sub-acute 
  inner 
  angle 
  to 
  point 
  of 
  inrollment, 
  basal 
  portion 
  

   of 
  moderate 
  depth, 
  rather 
  deeply 
  and 
  angularly 
  channeled, 
  tbe 
  in- 
  

   ferior 
  rim 
  produced 
  downward 
  and 
  slightly 
  outward 
  beyond 
  tbe 
  lim- 
  

   its 
  of 
  the 
  enamel 
  fold, 
  which 
  latter 
  forms 
  a 
  wide 
  belt 
  abruptly 
  

   beveled 
  above, 
  with 
  an 
  inbeveled 
  narrow 
  strip 
  below; 
  anterolateral 
  

   border 
  proportionately 
  short, 
  or 
  hardly 
  more 
  than 
  half 
  the 
  length 
  of 
  

   the 
  opposite 
  articular 
  border, 
  the 
  rounded 
  anterior 
  coronal 
  lobe 
  in- 
  

   beveled 
  to 
  the 
  relatively 
  Bhallow-channeled, 
  inbeveled 
  (?) 
  basal 
  rim; 
  

   inner 
  margin 
  very 
  obliquely 
  produced 
  backward 
  from 
  tin 
  very 
  obtuse 
  

   anterior 
  angle 
  to 
  the 
  broadly 
  rounded 
  base 
  of 
  the 
  principal 
  coronal 
  

   ridge, 
  thence 
  to 
  the 
  posterior 
  angle, 
  making 
  nearly 
  a 
  right 
  angle 
  to 
  

   its 
  anterior 
  course, 
  with 
  a 
  slight 
  concavity 
  in 
  tbe 
  region 
  of 
  tbe 
  | 
  

   tciior 
  depression. 
  Tbe 
  principal 
  ridge 
  occupies 
  balf 
  or 
  more 
  of 
  tbe 
  

   transverse 
  diameter 
  of 
  the 
  coronal 
  region, 
  rising 
  into 
  a 
  high, 
  roun< 
  

   crest, 
  the 
  anterior 
  slope 
  steep 
  and 
  terminating 
  in 
  a 
  narrow 
  depi 
  

   sion 
  outwardly 
  defined 
  by 
  tbe 
  rather 
  prominent, 
  rounded 
  lobe 
  trav- 
  

   ersing 
  the 
  anterolateral 
  border; 
  tbe 
  opposite 
  dope 
  is 
  very 
  abrupt, 
  

   with 
  slight 
  transverse 
  concavity, 
  merging 
  into 
  tbe 
  rather 
  deep 
  | 
  

   terior 
  depression, 
  which 
  is 
  bordered 
  by 
  tbe 
  prominent 
  alate 
  lobe 
  of 
  

  

  tbe 
  postero-lateral 
  border. 
  Coronal 
  surface 
  smooth, 
  the 
  inner 
  mar 
  

  

  preserving 
  the 
  thin 
  enamel 
  coating, 
  the 
  worn 
  surfaces 
  exhibiting 
  hue. 
  

   closely 
  arranged 
  punotea. 
  Breadth 
  of 
  tooth 
  at 
  inner 
  margin 
  about 
  

   li» 
  mm; 
  length 
  along 
  the 
  oblique 
  border 
  to 
  point 
  of 
  inrollnunt 
  11 
  

   mm. 
  

  

  The 
  above 
  description 
  is 
  based 
  anon 
  a 
  single 
  marly 
  perfect 
  tooth, 
  

   the 
  antero-lateral 
  border 
  being 
  Blightly 
  distorted 
  by 
  pressure. 
  Com* 
  

   pared 
  with 
  allied 
  Bpeoies, 
  it 
  is 
  readily 
  distinguished 
  from 
  the 
  mandi- 
  

   bular 
  median 
  form 
  of 
  the 
  Keokuk 
  and 
  Upper 
  Burlington 
  

   /(,/,'..,/' 
  Liedy, 
  jp.) 
  and 
  D. 
  tpatuiatui, 
  N.andW., 
  i 
  • 
  > 
  

  

  distinct 
  lobed 
  condition 
  of 
  the 
  anterior 
  boi.h 
  . 
  tin 
  alate 
  

  

  more 
  prominent 
  than 
  in 
  D, 
  sputuhitus, 
  and 
  h 
  >■> 
  expanded 
  than 
  

   in 
  I 
  >. 
  .; 
  cidt 
  Ht,llis. 
  

  

  