﻿218 
  PALEONTOLOGY 
  OP 
  ILLINOIS. 
  

  

  *ply 
  rounded 
  anterior 
  an^le 
  is 
  about 
  11.6 
  mm., 
  the 
  basal 
  rim 
  

   Bomewha, 
  expanded 
  laterally 
  and 
  produo, 
  ,1 
  posteriorly, 
  increasing 
  the 
  

   length 
  of 
  foe 
  border 
  to 
  abont 
  18 
  nun. 
  The 
  transverse 
  diameter 
  

  

  rose 
  the 
  posterior 
  margin 
  exceeded 
  Li 
  millimetres 
  ; 
  in 
  consequ< 
  

  

  the 
  tooth 
  is 
  no 
  shown. 
  The 
  posterior 
  margin 
  is 
  somewhat 
  deeply 
  

   concave 
  m 
  outiine, 
  the 
  anterior 
  extremity 
  was 
  apparently 
  gently 
  

   arched 
  or 
  nearly 
  straight, 
  but 
  ii 
  hears 
  evidences 
  of 
  wear 
  by 
  which 
  

   its 
  outhne 
  is 
  made 
  to 
  appear 
  slightly 
  concave, 
  the 
  coronal 
  margins 
  

   ;' 
  * 
  efined 
  ' 
  n,m 
  ""' 
  base, 
  making 
  a 
  aught 
  angulation 
  in 
  front 
  and 
  

   behind 
  sharply 
  defining 
  the 
  inbeveled 
  inferior 
  basal 
  face 
  

  

  The 
  above 
  described 
  tooth 
  is 
  peculiar 
  in 
  outline, 
  hut 
  the 
  coronal 
  

   sculpturing 
  resembles 
  that 
  of 
  Psammodus 
  ghptm, 
  also 
  P. 
  retmdatu* 
  

   N. 
  and 
  W 
  of 
  the 
  Chester 
  limestone, 
  although 
  it 
  cannot 
  be 
  con' 
  

   founded 
  with 
  either 
  of 
  those 
  species. 
  The 
  rug* 
  show 
  irregular 
  dis- 
  

   position, 
  m 
  which 
  particular 
  the 
  tooth 
  contrasts 
  with 
  the 
  superficial 
  

   ornamentation 
  observed 
  in 
  individuals 
  of 
  the 
  form 
  referred 
  to 
  /< 
  

   crasaidens, 
  while 
  it 
  represents 
  a 
  different 
  form 
  from 
  that 
  upon 
  which 
  

   the 
  latter 
  species 
  was 
  based. 
  

  

  'ogical 
  pogitwn 
  and 
  locality: 
  St. 
  Louis 
  formation. 
  Pella, 
  Iowa. 
  

  

  PSAMMODCS 
  CRASSHH 
  Ns. 
  St. 
  J. 
  and 
  W. 
  

   PI. 
  XVIII. 
  Ii 
  k 
  .. 
  M, 
  

  

  ■«d 
  WoBXBMr.i866.minol6GeoL8arv. 
  ir 
  ,. 
  m 
  P) 
  v, 
  

   Co, 
  Sa. 
  Not 
  P. 
  ruaoaus, 
  kgat 
  ' 
  ' 
  

  

  Teeth 
  attain 
  large 
  size, 
  Bubrhomboidal 
  in 
  outline. 
  Coronal 
  am 
  

   moderately 
  arched 
  from 
  behind 
  forwards, 
  somewhat 
  steeply 
  sloped 
  

   '» 
  tbe 
  region 
  of 
  the 
  anterior 
  margin, 
  with 
  a 
  distinct 
  longitudinal 
  

  

  Uan 
  depression, 
  bordered 
  on 
  either 
  side 
  by 
  a 
  moderately 
  promi- 
  

   nent 
  fold 
  rounded 
  to 
  the 
  lateral 
  borders, 
  where 
  lb., 
  coronal 
  enamel 
  

  

  more 
  or 
  less 
  distinctly 
  defined 
  from 
  the 
  basal 
  portion 
  of 
  the 
  

   , 
  "" 
  t 
  "- 
  '""• 
  outer 
  border 
  is 
  gently 
  arched, 
  rather 
  sharply 
  rounded 
  

   into 
  the 
  anterior 
  margin, 
  terminating 
  posteriorly 
  in 
  an 
  acute 
  angle- 
  

  

  ..-Kin 
  also 
  broadly 
  arched 
  from 
  the 
  rounded 
  outer 
  an 
  

   ( 
  " 
  ■ 
  inner 
  angle, 
  presenting 
  in 
  unworn 
  individuals 
  

  

  B?eled 
  With 
  the 
  basal 
  portion: 
  

  

  lurvnture 
  of 
  the 
  opposite 
  extremity 
  

  

  by 
  undulations, 
  and 
  terminating 
  m 
  sharp' 
  

  

  t,,< 
  ' 
  " 
  m,r 
  : 
  general 
  way 
  to 
  the 
  oun 
  

  

  ,,1,v 
  " 
  f 
  tl 
  " 
  "!' 
  ' 
  .Ward 
  the 
  antr, 
  .; 
  10 
  

  

  