﻿VEKTEBKATES. 
  127 
  

  

  along 
  anterolateral 
  border 
  to 
  which 
  its 
  anterior 
  slope 
  is 
  steeply 
  

   beveled. 
  Enamel 
  coating 
  along 
  inner 
  margin 
  showing 
  faint 
  lines 
  of 
  

   growth, 
  the 
  worn 
  crown 
  surface 
  exhibiting 
  relatively 
  coarse 
  crowded 
  

   punctae. 
  Length 
  of 
  antero-lateral 
  border 
  to 
  point 
  of 
  inrollment 
  1.5 
  

   mm. 
  ; 
  breadth 
  across 
  inner 
  margin, 
  2.5 
  mm. 
  

  

  The 
  above 
  form 
  is 
  represented 
  by 
  a 
  single 
  example, 
  and 
  notwith- 
  

   standing 
  its 
  minute 
  size, 
  the 
  perfect 
  state 
  of 
  preservation 
  of 
  the 
  

   tooth 
  permits 
  a 
  detailed 
  interpretation 
  of 
  its 
  diagnostic 
  charac- 
  

   teristics 
  and 
  comparison 
  with 
  allied 
  forms. 
  We 
  are, 
  however, 
  in 
  

   some 
  doubt 
  as 
  to 
  its 
  generic 
  identity, 
  although 
  there 
  is 
  strong 
  evi- 
  

   dence 
  of 
  its 
  intimate 
  relationship 
  with 
  Cochliodus, 
  the 
  Strebloifei 
  &U* 
  Z 
  Q'y 
  

   maxillary 
  posterior 
  form 
  of 
  which 
  it 
  closely 
  resembles 
  in 
  coronal 
  

   contour. 
  This 
  unique 
  specimen, 
  however, 
  does 
  not 
  seem 
  to 
  be 
  

   referable 
  to 
  the 
  associated 
  species 
  Coch. 
  VanHornii, 
  unless 
  we 
  are 
  

   to 
  suppose 
  a 
  most 
  extraordinary 
  change 
  takes 
  place, 
  by 
  which 
  young 
  

   and 
  mature 
  teeth 
  are 
  made 
  to 
  assume 
  the 
  most 
  unlike 
  semblance 
  

   to 
  one 
  another. 
  The 
  present 
  tooth, 
  however, 
  compared 
  with 
  the 
  

   streblodoid 
  maxillary 
  form 
  of 
  Coch. 
  Van 
  Hornii, 
  is 
  distinguished 
  by 
  

   the 
  following 
  pronounced 
  contrasts 
  : 
  the 
  general 
  obliquity 
  of 
  outline 
  

   and 
  relatively 
  narrower 
  breadth 
  compared 
  with 
  the 
  length 
  in 
  the 
  

   direction 
  of 
  inrollment 
  (a 
  feature 
  which 
  is 
  necessarily 
  persistent 
  and 
  

   directly 
  dependent 
  on 
  the 
  law 
  of 
  development 
  of 
  the 
  dental 
  plates), 
  

   the 
  extremely 
  prominent 
  posterior 
  lobe, 
  and 
  the 
  depressed 
  median 
  

   portion 
  of 
  the 
  neck 
  defined 
  by 
  the 
  comparatively 
  prominent 
  ridge 
  

   along 
  the 
  antero-lateral 
  border. 
  It 
  is 
  in 
  the 
  latter 
  respects 
  the 
  form 
  

   here 
  especially 
  alluded 
  to 
  offers 
  greatest 
  contrast 
  with 
  the 
  prevailing 
  

   coronal 
  contour 
  of 
  Cochliodus, 
  and 
  suggests 
  a 
  possible 
  relationship 
  

   with 
  Deltoptychius. 
  

  

  Geological 
  position 
  and 
  locality: 
  St. 
  Louis 
  limestone; 
  St. 
  Louis, 
  

   Missouri. 
  

  

  Cochliodus 
  Leidyi, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  VII. 
  Fig. 
  11-16. 
  

  

  Teeth 
  of 
  small 
  size, 
  the 
  collections 
  furnishing 
  representatives 
  of 
  

   the 
  posterior 
  and 
  median 
  teeth 
  of 
  the 
  mandible, 
  and 
  the 
  posterior 
  

   form 
  and 
  Helodus-like 
  series 
  of 
  teeth 
  of 
  the 
  upper 
  jaw. 
  

  

  Mandibular 
  posterior 
  teeth 
  distinguished 
  by 
  their 
  compact 
  build 
  and 
  

   relatively 
  narrow 
  transverse 
  diameter 
  compared 
  with 
  the 
  length 
  in 
  

   the 
  direction 
  of 
  the 
  strong 
  enrollment. 
  Antero-lateral 
  border 
  slightly 
  

   curved 
  between 
  the 
  inner 
  angle 
  and 
  point 
  of 
  inrollment, 
  presenting 
  

  

  