﻿100 
  PAL 
  1 
  <»\TOLOGY 
  OF 
  ILLINOIS. 
  

  

  teeth, 
  which 
  prohahly 
  helonged 
  to 
  the 
  same 
  species. 
  The 
  latter, 
  

   however, 
  are 
  in 
  so 
  worn 
  and 
  mutilafa 
  1 
  >f 
  preservation 
  as 
  

  

  not 
  to 
  exhibit 
  details 
  heyond 
  mere 
  outline, 
  by 
  which 
  they 
  may 
  be 
  

   satisfactorily 
  compared 
  with 
  other 
  specimens 
  of 
  the 
  same 
  form. 
  

  

  The 
  loan 
  of 
  the 
  type 
  was 
  kindly 
  procured 
  us 
  by 
  Dr. 
  Leidy, 
  a 
  

   careful 
  comparison 
  of 
  which 
  with 
  the 
  material 
  before 
  us 
  leaves 
  not 
  

   the 
  least 
  doubt 
  as 
  to 
  their 
  specific 
  identity. 
  The 
  sp 
  repre- 
  

  

  sented 
  by 
  the 
  posterior 
  teeth 
  of 
  the 
  mandible, 
  is 
  intimately 
  allied 
  to 
  

   D. 
  exparuiu, 
  of 
  the 
  St. 
  Louis 
  limestone, 
  being 
  chiefly 
  d 
  i 
  st 
  ing 
  n 
  i 
  sl 
  

   by 
  its 
  more 
  robust 
  figure. 
  jer 
  inrollment. 
  and 
  narrower 
  pos- 
  

  

  terior 
  alation. 
  The 
  majority 
  of 
  the 
  examples 
  of 
  this 
  form 
  exhibit 
  

   traces 
  of 
  excessive 
  coronal 
  abrasion, 
  which 
  in 
  some 
  instances 
  has 
  

   leveled 
  the 
  median 
  prominence, 
  destroying 
  its 
  definition 
  from 
  the 
  

   plane 
  anterior 
  belt, 
  in 
  which 
  latter 
  condition 
  the 
  individuals 
  bear 
  

   deceptive 
  resemblance 
  to 
  the 
  homologous 
  teeth 
  of 
  Orthoplewrodus. 
  

  

  Geological 
  i">s'ith»i 
  and 
  locality: 
  Chester 
  limeston. 
  ler, 
  111. 
  

  

  Genus 
  STKXOPTERODrs. 
  1 
  Bt.J. 
  and 
  W. 
  

  

  Teeth, 
  probably 
  occupying 
  a 
  posterior 
  position 
  on 
  the 
  upper 
  jaw, 
  

   distinguished 
  by 
  their 
  long-elliptic 
  outline, 
  Btrongly 
  arched 
  and 
  spiral 
  

   inrollment 
  of 
  the 
  outer 
  extremity. 
  Crown 
  traversed 
  by 
  a 
  posterior 
  

   prominence 
  or 
  lobe 
  in 
  the 
  direction 
  of 
  inrollment, 
  more 
  or 
  h 
  >s 
  well- 
  

   defined 
  from 
  the 
  anterior 
  area, 
  which 
  presents 
  a 
  plane 
  surface, 
  

   without 
  prominent 
  revolving 
  or 
  longitudinal 
  folds; 
  posteriorly, 
  the 
  

   crown 
  is 
  well 
  defined 
  from 
  the 
  base 
  by 
  the 
  inbeveled 
  enamel 
  fold. 
  

   beyond 
  which 
  the 
  basal 
  rim 
  usually 
  more 
  or 
  less 
  projects, 
  often 
  

   terminating 
  in 
  a 
  strong 
  posterior 
  process, 
  and 
  forming, 
  in 
  well- 
  

   preserved 
  specimens, 
  a 
  deep 
  border 
  toward 
  the 
  inner 
  margin, 
  becoming 
  

   less 
  oonspiououa 
  outwardly, 
  anteriorly 
  truncate, 
  usually 
  more 
  or 
  less 
  

   obliquely 
  bo 
  from 
  the 
  inner 
  angle 
  outward 
  and 
  backward 
  to 
  point 
  of 
  

  

  iurollnieiit 
  (though 
  sometimes 
  outward 
  and 
  forward 
  from 
  an 
  obi 
  

  

  inner 
  angle), 
  the 
  shallow 
  enamel 
  fold 
  inbeveled 
  and 
  defined 
  l 
  j 
  

  

  narrow 
  sulcus 
  from 
  the 
  base. 
  Surface 
  of 
  crown 
  in 
  pi 
  

  

  I 
  u 
  b 
  dense 
  enamel-like, 
  glossy 
  coating, 
  through 
  which 
  the 
  

   tubular 
  structure 
  presents 
  a 
  delicate 
  papillose 
  appearance; 
  worn 
  

   surfaces 
  minutely 
  and 
  densely 
  pitted 
  by 
  the 
  I 
  extremities 
  of 
  

  

  the 
  medullary 
  tube- 
  ; 
  raso-dentim 
  of 
  base 
  inferior 
  Burl 
  

  

  of 
  the 
  dense 
  inferior 
  lay< 
  daily 
  atriated 
  in 
  the 
  direction 
  of 
  

  

  inrollmi 
  nt. 
  

  

  a. 
  In 
  iii: 
  

   1 
  id.- 
  mttncllbulii 
  'li 
  

  

  