﻿146 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  and 
  I>. 
  UTtdulatw, 
  ample 
  and 
  variable 
  mi 
  their 
  bounds 
  as 
  they 
  are, 
  w*/Ac, 
  

   do 
  not 
  make 
  it 
  clear 
  that 
  the 
  present 
  form 
  is 
  bat 
  a 
  varietal 
  phasis 
  

   of 
  one 
  or 
  other 
  of 
  the 
  last 
  mentioned 
  species. 
  

  

  Geological 
  position 
  and 
  localities: 
  Keokuk 
  limestone, 
  near 
  Warsaw 
  

   and 
  Hamilton, 
  111. 
  ; 
  Keokuk, 
  Iowa. 
  

  

  Deltodus 
  cinctulis. 
  St. 
  J. 
  and 
  W. 
  

  

  PL 
  IX, 
  Fig. 
  C. 
  7. 
  

  

  Teeth 
  below 
  medium 
  size. 
  Mandibular 
  posterior 
  tooth 
  triangular 
  

   in 
  outline, 
  lateral 
  diameter 
  relatively 
  broad 
  compared 
  to 
  the 
  length, 
  

   and 
  somewhat 
  strongly 
  inrolled 
  at 
  the 
  outer 
  extremity. 
  Antero- 
  

   lateral 
  border 
  nearly 
  at 
  right 
  angles 
  with 
  a 
  line 
  connecting 
  the 
  

   inner 
  angles 
  of 
  the 
  tooth. 
  The 
  upper 
  half 
  or 
  more 
  of 
  its 
  height 
  

   enveloped 
  in 
  the 
  strong, 
  inbeveled 
  enamel 
  fold, 
  beneath 
  which 
  the 
  

   basal 
  portion 
  forms 
  a 
  narrow 
  rim 
  showing 
  a 
  coarse 
  vascular 
  struc- 
  

   ture 
  ; 
  inner 
  margin 
  with 
  a 
  slight 
  sigmoidal 
  curvature, 
  broadly 
  

   arched 
  round 
  the 
  base 
  of 
  the 
  coronal 
  ridge, 
  with 
  a 
  moderate 
  con- 
  

   cavity 
  in 
  passing 
  the 
  posterior 
  depression 
  into 
  the 
  posterior 
  angle; 
  

   postero-lateral 
  border 
  gradually 
  converging 
  toward 
  the 
  outer 
  margin, 
  

   occupied 
  by 
  a 
  well-defined 
  enamel 
  fold 
  extending 
  nearly 
  half 
  the 
  

   depth, 
  basal 
  portion 
  slightly 
  channeled 
  and 
  terminating 
  in 
  a 
  nar 
  

   row 
  rim 
  inferiorly. 
  Coronal 
  ridge 
  relatively 
  broad, 
  strongly 
  arched 
  

   laterally, 
  culminating 
  a 
  little 
  anterior 
  of 
  the 
  median 
  line, 
  with 
  a 
  

   gradual 
  slope 
  into 
  the 
  posterior 
  depression 
  from 
  which 
  rises 
  the 
  rel- 
  

   atively 
  narrow, 
  slightly 
  upraised 
  alate 
  lobe 
  which 
  terminates 
  in 
  the 
  

   sub-acute 
  posterior 
  angle; 
  in 
  mature 
  or 
  somewhat 
  worn 
  Bpecim< 
  

   where 
  the 
  surface 
  has 
  been 
  deprived 
  of 
  the 
  original 
  enamel 
  LnvestllH 
  lit. 
  

   the 
  crown 
  is 
  undulated 
  by 
  BUD-equal 
  transverse 
  Colds 
  and 
  intervening 
  

   narrow 
  Buloi 
  conforming 
  to 
  tlie 
  bands 
  of 
  elongate 
  punota 
  that 
  mark 
  

   the 
  order 
  of 
  increment 
  of 
  the 
  tooth 
  Bubstanoe. 
  Breadth 
  of 
  an 
  ordi- 
  

   nary-sized 
  Bpeoimeu 
  at 
  the 
  inner 
  margin, 
  L1.5mm; 
  length 
  of 
  antero- 
  

   lateral 
  border 
  to 
  point 
  of 
  inrollment, 
  about 
  '.' 
  nun. 
  

  

  Posterior 
  tooth 
  of 
  the 
  upper 
  jaw 
  trigonal 
  in 
  outline, 
  moderately 
  

  

  arched 
  in 
  the 
  longitudinal 
  direction. 
  Inner 
  margin 
  making 
  a 
  sig- 
  

   moidal 
  curvature 
  from 
  the 
  posterior 
  sub-aoute 
  angle, 
  broadly 
  rounded 
  

   into 
  tin 
  anterolateral 
  border 
  with 
  which 
  it 
  is 
  more 
  or 
  leas 
  oblique; 
  

   anterior 
  artioular 
  edge 
  unknown; 
  postero-lateral 
  border 
  gradually 
  

   converging 
  toward 
  the 
  outer 
  extremity 
  A 
  enamel 
  fold 
  well 
  defined 
  

   and 
  separated 
  from 
  the 
  basal 
  portion 
  bj 
  a 
  narrow 
  channel. 
  Coronal 
  

  

  