﻿tor 
  

  

  126 
  PALEONTOLOGY 
  OF 
  ILLINOIS 
  

  

  lections 
  afford 
  examples 
  of 
  teeth 
  corresponding 
  to 
  the 
  anterior 
  form 
  

   described 
  by 
  Professor 
  Owen. 
  

  

  In 
  relative 
  frequency 
  of 
  occurrence 
  it 
  would, 
  of 
  course, 
  be 
  expected 
  

   that 
  the 
  larger 
  and 
  more 
  massive 
  teeth 
  appear 
  most 
  abundant 
  in 
  

   the 
  collections. 
  The 
  posterior 
  teeth 
  of 
  the 
  mandibles 
  and 
  auxil- 
  

   iaries 
  are 
  represented 
  about 
  equally 
  in 
  numbers, 
  while 
  the 
  narrow 
  

   median 
  teeth 
  of 
  the 
  lower 
  jaw, 
  and 
  the 
  Helodus-tike 
  forms 
  presum- 
  

   ably 
  pertaining 
  to 
  the 
  anterior 
  portion 
  of 
  the 
  upper 
  jaw, 
  are 
  

   frequently 
  met 
  with. 
  This 
  is 
  also 
  true 
  of 
  other 
  species 
  of 
  the 
  same 
  

   and 
  allied 
  genera 
  occurring 
  in 
  the 
  Lower 
  Carboniferous 
  formal 
  

   and 
  the 
  absence 
  of 
  certain 
  forms 
  ought 
  not 
  to 
  militate 
  against 
  the 
  

   conviction 
  of 
  their 
  existence. 
  

  

  Geological 
  pontion 
  and 
  localities: 
  St. 
  Louis 
  limestone; 
  Alton, 
  and 
  

   Monroe 
  county, 
  Illinois; 
  St. 
  Louis, 
  Missouri: 
  Telia. 
  Iowa. 
  

  

  Cochliodcs 
  obliqui 
  >, 
  St. 
  J. 
  and 
  W. 
  

   PL 
  VII. 
  Elg-. 
  IT. 
  

  

  Tooth 
  resembling 
  in 
  coronal 
  contour 
  the 
  form 
  assigned 
  to 
  the 
  

   posterior 
  position 
  on 
  the 
  upper 
  jaw. 
  wry 
  small, 
  obliquely 
  trapezoidal 
  

   in 
  outline, 
  moderately 
  arched 
  in 
  the 
  direction 
  of 
  inrollment. 
  Antero- 
  

   lateral 
  border 
  nearly 
  straight, 
  obliquely 
  produced 
  forward 
  from 
  the 
  

   inner 
  angle, 
  making 
  an 
  angle 
  of 
  about 
  l(> 
  with 
  a 
  right 
  line 
  con- 
  

   necting 
  the 
  anterior 
  and 
  posterior 
  angles 
  of 
  the 
  inner 
  margin, 
  low 
  

   basal 
  portion 
  forming 
  a 
  shallow, 
  channeled 
  rim. 
  defined 
  above 
  by 
  

   the 
  narrow, 
  rounded, 
  inbev. 
  'led 
  enamel 
  fold 
  : 
  postero-lah 
  ral 
  or 
  oblique 
  

  

  border 
  converging 
  from 
  the 
  rounded 
  posterior 
  extremity 
  to 
  point 
  of 
  

   Inrollment, 
  at 
  an 
  angle 
  of 
  20 
  . 
  more 
  or 
  Less, 
  with 
  the 
  opposite 
  bor- 
  

   tier, 
  basal 
  portion 
  relatively 
  deep, 
  moderately 
  Lnbeveled 
  and 
  slightly 
  

   ohanneled, 
  the 
  coronal 
  enamel 
  forming 
  a 
  delicate 
  fold 
  defining 
  the 
  

   upper 
  edge-; 
  inner 
  margin 
  broadly 
  arched 
  round 
  ti 
  of 
  the 
  

  

  r* 
  posterlcoronal 
  Lobe, 
  thence 
  to 
  the 
  obtuse 
  anterior 
  angle 
  nearly 
  

  

  i 
  and 
  closely 
  conforming 
  to 
  a 
  line 
  connecting 
  the 
  inner 
  ai)| 
  

   of 
  ,i„. 
  tooth. 
  Coronal 
  region 
  presenting 
  a 
  strong 
  | 
  promi- 
  

  

  ,„.,„.,.. 
  ti„ 
  i, 
  ,oad 
  outer 
  dope 
  rounding 
  into 
  the 
  border, 
  from 
  which 
  

   ,t 
  i> 
  denned 
  by 
  a 
  alight 
  depressed 
  belt, 
  anterior 
  Blope 
  more 
  abrupt 
  

   ;m 
  ,l 
  m 
  akii] 
  [ht 
  angulation 
  where 
  it 
  joins 
  the 
  anterior 
  d< 
  

  

  portion 
  of 
  wn\ 
  the 
  Latter 
  | 
  :"» 
  sxet 
  "f 
  about 
  the 
  same 
  

  

  breadth 
  m 
  that 
  occupied 
  by 
  the 
  posterior 
  Lobe, 
  depressed, 
  and 
  

   marked 
  by 
  two 
  faint, 
  revolving 
  folds, 
  with 
  a 
  third 
  

  

  