﻿VEKTEBEATES. 
  • 
  97 
  

  

  der 
  rapidly 
  converging 
  toward 
  the 
  outer 
  extremity. 
  Median 
  ridge 
  of 
  

   crown 
  prominent, 
  occupying 
  a 
  nearly 
  central 
  position 
  and 
  well 
  de- 
  

   fined 
  from 
  the 
  relatively 
  wide 
  anterior 
  belt, 
  which 
  latter 
  presents 
  

   the 
  characteristic 
  angulation 
  and 
  abrupt 
  face 
  enveloped 
  for 
  the 
  

   greater 
  part 
  of 
  its 
  depth 
  in 
  the 
  coronal 
  enamel; 
  posteriorly 
  the 
  

   slope 
  of 
  the 
  median 
  ridge 
  descends 
  into 
  the 
  broad 
  depression 
  on 
  

   that 
  side, 
  from 
  which 
  rises 
  the 
  relatively 
  wide 
  posterior 
  expansion 
  

   or 
  alation. 
  Crown 
  surface 
  densely 
  punctate. 
  A 
  specimen 
  below 
  

   medium 
  size 
  measures 
  in 
  greatest 
  length 
  from 
  posterior 
  angle 
  to 
  

   outer 
  extremity 
  about 
  11.5 
  m 
  m. 
  ; 
  antero-lateral 
  border 
  about 
  6.5 
  

   m 
  m. 
  ; 
  breadth 
  at 
  inner 
  margin 
  8 
  mm. 
  

  

  Posterior 
  tooth 
  of 
  upper 
  jaw 
  of 
  the 
  usual 
  spatulate 
  outline, 
  antero- 
  

   lateral 
  border 
  obliquely 
  truncated 
  from 
  inner 
  angle 
  forward 
  to 
  outer 
  

   angle, 
  posterior 
  extremity 
  somewhat 
  produced 
  from 
  which 
  the 
  postero- 
  

   lateral 
  border 
  somewhat 
  rapidly 
  converges 
  toward 
  point 
  of 
  inroll- 
  

   ment. 
  Posterior 
  prominences 
  occupy 
  half, 
  or 
  a 
  little 
  more, 
  of 
  

   the 
  coronal 
  area, 
  secondary 
  lobe 
  about 
  one-third 
  the 
  dimensions 
  

   of 
  the 
  principal 
  ridge, 
  from 
  which 
  it 
  is 
  separated 
  by 
  a 
  deep 
  furrow, 
  

   and 
  well 
  defined 
  in 
  front 
  from 
  the 
  apparently 
  smooth 
  anterior 
  area 
  

   which 
  gradually 
  contracts 
  towards 
  the 
  anterior 
  border. 
  Superficial 
  

   punctation 
  agreeing 
  with 
  that 
  described 
  above. 
  A 
  mature 
  specimen 
  

   measures 
  in 
  greatest 
  diameter 
  across 
  the 
  inner 
  margin 
  17 
  m 
  m. 
  ; 
  

   greatest 
  breadth 
  across 
  posterior 
  prominence 
  7mm.; 
  length 
  along 
  

   antero-lateral 
  border 
  4.5 
  m 
  m. 
  

  

  The 
  present 
  species 
  is 
  made 
  known 
  from 
  a 
  single 
  representative 
  

   each 
  of 
  the 
  posterior 
  form 
  pertaining 
  respectively 
  to 
  the 
  upper 
  and 
  

   lower 
  jaws. 
  Neither 
  of 
  these 
  examples 
  is 
  entire, 
  although 
  they 
  

   are 
  sufficiently 
  so 
  to 
  permit 
  of 
  a 
  not 
  unsatisfactory 
  comparison 
  with 
  

   other 
  generically 
  allied 
  forms. 
  The 
  species 
  is 
  most 
  intimately 
  allied 
  

   to 
  that 
  occurring 
  in 
  the 
  St. 
  Louis 
  formation, 
  Deltoptychius 
  expansus; 
  

   especially 
  is 
  this 
  relationship 
  apparent 
  in 
  the 
  close 
  resemblance 
  that 
  

   exists 
  between 
  the 
  maxillary 
  posterior 
  forms 
  of 
  the 
  two 
  species. 
  It 
  

   differs, 
  however, 
  from 
  the 
  latter 
  species 
  in 
  a 
  marked 
  degree 
  in 
  re- 
  

   spect 
  to 
  the 
  coronal 
  contour 
  of 
  the 
  mandibular 
  posterior 
  teeth, 
  

   which 
  shows 
  the 
  median 
  ridge 
  well 
  developed 
  and 
  defined 
  from 
  the 
  

   narrow 
  belt 
  in 
  front 
  and 
  the 
  much 
  greater 
  obliquity 
  of 
  the 
  inner 
  

   margin 
  of 
  the 
  tooth. 
  

  

  Geological 
  position 
  and 
  localities 
  : 
  From 
  characteristic 
  strata 
  of 
  the 
  

   Warsaw 
  formation; 
  Clifton, 
  above 
  Alton, 
  and 
  Golden 
  Bluffs 
  near 
  

   Warsaw, 
  Illinois. 
  

  

  -7 
  

  

  