﻿VERTEBRATES. 
  85 
  

  

  from 
  the 
  plain 
  anterior 
  neck. 
  Surface 
  along 
  inner 
  margin 
  often 
  

   preserving 
  the 
  external 
  coating 
  of 
  dense 
  opaque 
  enamel, 
  with 
  more 
  

   or 
  less 
  distinct 
  lines 
  of 
  growth; 
  otherwise 
  the 
  surface 
  exhibits 
  a 
  

   minute 
  pitted 
  structure 
  produced 
  by 
  the 
  relatively 
  widely-spaced 
  

   punctse. 
  A 
  mature 
  tooth 
  measures 
  in 
  greatest 
  width 
  between 
  the 
  

   inner 
  angles 
  10 
  mm.; 
  length 
  of 
  antero-lateral 
  border 
  to 
  point 
  of 
  

   inrollment 
  4.5 
  m 
  m. 
  

  

  Thus 
  far 
  only 
  the 
  posterior 
  teeth 
  of 
  the 
  upper 
  jaw 
  have 
  been 
  

   identified. 
  The 
  fragmentary 
  condition 
  of 
  the 
  majority 
  of 
  the 
  speci- 
  

   mens 
  often 
  renders 
  their 
  identification 
  with 
  one 
  another 
  a 
  difficult 
  

   matter, 
  not 
  to 
  mention 
  the 
  necessary 
  comparisons 
  in 
  order 
  to 
  

   determine 
  their 
  relationship 
  with 
  other 
  similar 
  forms 
  occurring 
  in 
  

   the 
  same 
  strata. 
  In 
  their 
  general 
  aspect 
  these 
  teeth 
  bear 
  a 
  striking 
  

   resemblance 
  to 
  Deltoptychius 
  expansus 
  ; 
  but 
  they 
  may 
  be 
  dis- 
  

   tinguished 
  by 
  the 
  absence 
  of 
  the 
  median 
  sulcus 
  and 
  subordinate 
  

   ridge 
  in 
  front 
  of 
  the 
  posterior 
  coronal 
  prominence, 
  and 
  specifically 
  

   by 
  their 
  narrow 
  transverse 
  diameters. 
  

  

  Associated 
  with 
  the 
  above 
  mentioned 
  teeth, 
  certain 
  forms 
  repre- 
  

   senting 
  the 
  mandibular 
  posterior 
  teeth 
  occur, 
  which 
  might 
  be 
  mis- 
  

   WQ-V'/l 
  taken 
  for 
  jaae^ 
  specimens 
  of 
  the 
  homologous 
  form 
  of 
  Deltoptychius 
  

  

  / 
  expansus. 
  None 
  of 
  the 
  latter 
  specimens 
  are 
  in 
  a 
  state 
  of 
  preserva- 
  

  

  tion 
  to 
  show 
  their 
  distinctive 
  features 
  with 
  sufficient 
  clearness 
  to 
  

   dispel 
  all 
  uncertainty 
  in 
  regard 
  to 
  their 
  generic 
  relations. 
  Their 
  

   coronal 
  region 
  is 
  divested 
  of 
  the 
  superficial 
  enamel 
  coating, 
  expos- 
  

   ing 
  the 
  minute 
  close 
  punctate 
  structure 
  such 
  as 
  appears 
  in 
  worn 
  

   surfaces, 
  and 
  presenting 
  a 
  nearly 
  plain 
  coronal 
  prominence 
  without 
  

   subordinate 
  narrow 
  belt 
  along 
  the 
  antero-lateral 
  border, 
  as 
  occurs 
  

   in 
  typical 
  examples 
  of 
  Deltoptychius 
  ; 
  in 
  the 
  latter 
  respect 
  these 
  

   teeth 
  approach 
  the 
  corresponding 
  form 
  referred 
  to 
  Orthopleurodus, 
  

   and 
  while 
  we 
  are 
  in 
  doubt 
  as 
  to 
  their 
  actual 
  affinities, 
  they 
  are 
  

   provisionally 
  placed 
  in 
  the 
  present 
  specific 
  association, 
  of 
  which 
  

   characteristic 
  examples 
  of 
  both 
  forms 
  are 
  presented 
  in 
  the 
  illustra- 
  

   tions. 
  Compared 
  with 
  the 
  homologous 
  teeth 
  of 
  Deltoptychius 
  expan- 
  

   sus, 
  they 
  are 
  further 
  distinguished 
  by 
  the 
  less 
  oblique 
  backward 
  

   course 
  of 
  the 
  inner 
  margin, 
  which 
  forms 
  nearly 
  a 
  right 
  angle 
  with 
  

   the 
  antero-lateral 
  border, 
  the 
  appreciably 
  narrower 
  and 
  less 
  up- 
  

   raised 
  alation, 
  which 
  is 
  marked 
  near 
  the 
  border 
  by 
  a 
  slight 
  furrow 
  

   or 
  angulation 
  from 
  which 
  rises 
  the 
  narrow 
  marginal 
  belt 
  along 
  that 
  

   side, 
  and 
  which 
  is 
  inbeveled 
  to 
  the 
  channeled 
  basal 
  portion. 
  The 
  

   deep 
  antero-lateral 
  border 
  is 
  abruptly 
  truncated, 
  half 
  its 
  height 
  

   enveloped 
  in 
  the 
  belt 
  of 
  coronal 
  enamel, 
  which 
  is 
  well 
  defined 
  from 
  

  

  