﻿VEKTEBEATES. 
  195 
  

  

  Orthopleurodus 
  Novo 
  Mexicanus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XIII, 
  Fig. 
  1-3. 
  

  

  Teeth 
  below 
  medium 
  size, 
  represented 
  by 
  forms 
  occupying 
  the 
  

   posterior 
  position 
  on 
  the 
  lower 
  and 
  upper 
  jaws. 
  

  

  Mandibular 
  posterior 
  teeth 
  trigonal 
  in 
  outline, 
  moderately 
  arched 
  

   in 
  the 
  direction 
  of 
  inrollment. 
  Antero-lateral 
  border 
  slightly 
  curved 
  

   sigmoidally, 
  enamel 
  belt 
  abrupt 
  and 
  well 
  defined 
  from 
  the 
  down- 
  

   ward 
  and 
  slightly 
  outward 
  produced 
  basal-rim 
  ; 
  postero-lateral 
  border 
  

   making 
  an 
  angle 
  of 
  about 
  55° 
  with 
  the 
  opposite 
  side 
  ; 
  inner 
  margin 
  

   slightly 
  obliquely 
  produced 
  backward 
  from 
  the 
  anterior 
  angle 
  and 
  

   gently 
  curved 
  sigmoidally, 
  worn 
  specimen 
  inbeveled 
  interiorly. 
  Cor- 
  

   onal 
  prominence 
  usually 
  well 
  defined, 
  rather 
  widely 
  expanded 
  toward 
  

   the 
  inner 
  margin, 
  posterior 
  slope 
  merging 
  into 
  the 
  regularly 
  trans- 
  

   versely 
  concave 
  posterior 
  depression, 
  from 
  which 
  the 
  alate 
  expansion 
  

   steeply 
  rises 
  into 
  the 
  prominent 
  postero-lateral 
  border. 
  Surface 
  

   punctation 
  exceedingly 
  minute 
  and 
  widely 
  spaced. 
  Breadth 
  of 
  a 
  

   large 
  specimen 
  between 
  the 
  angles 
  of 
  the 
  inner 
  margin 
  13.5 
  mm. 
  ; 
  

   length 
  along 
  antero-lateral 
  border 
  to 
  point 
  of 
  inrollment 
  about 
  

   12 
  mm. 
  

  

  Posterior 
  teeth 
  of 
  upper 
  jaw 
  subspatulate 
  in 
  outline 
  ; 
  antero-lateral 
  

   border 
  unknown, 
  that 
  extremity 
  of 
  the 
  teeth 
  being 
  extremely 
  atten- 
  

   uated 
  and 
  in 
  consequence 
  mutilated; 
  postero-lateral 
  border 
  exhibit- 
  

   ing 
  the 
  characteristic 
  straight 
  outline, 
  basal 
  border 
  slightly 
  chan- 
  

   neled, 
  and 
  probably 
  continued 
  into 
  a 
  spur-point 
  at 
  the 
  posterior 
  angle 
  ; 
  

   inner 
  margin 
  broadly 
  arched 
  backward 
  round 
  the 
  coronal 
  promi- 
  

   nence 
  and 
  thence 
  more 
  gently 
  curved 
  toward 
  the 
  broken 
  anterior 
  

   angle. 
  Coronal 
  ridge 
  prominent, 
  rounded 
  along 
  the 
  crest 
  which 
  

   culminates 
  close 
  upon 
  the 
  postero-lateral 
  border 
  to 
  which 
  the 
  sur- 
  

   face 
  steeply 
  descends, 
  the 
  broad 
  anterior 
  slope 
  slightly 
  depressed 
  

   before 
  reaching 
  the 
  margin 
  of 
  the 
  tooth, 
  the 
  ridge 
  more 
  or 
  less 
  

   rapidly 
  declining 
  immediately 
  behind 
  the 
  greatest 
  prominence. 
  

   Punctate 
  structure 
  the 
  same 
  as 
  observed 
  in 
  the 
  mandibular 
  teeth. 
  

   An 
  ordinary 
  size 
  specimen 
  measures 
  along 
  the 
  postero-lateral 
  border 
  

   about 
  15 
  mm., 
  greatest 
  breadth 
  of 
  tooth 
  at 
  right 
  angles 
  to 
  the 
  

   straight 
  border 
  7 
  mm. 
  

  

  The 
  present 
  species 
  is 
  determined 
  from 
  a 
  few 
  specimens 
  of 
  the 
  

   maxillary 
  posterior 
  form 
  and 
  a 
  single 
  example 
  of 
  the 
  mandibular 
  

   posterior 
  tooth, 
  which 
  were 
  discovered 
  by 
  Mr. 
  Springer, 
  in 
  the 
  fish- 
  

  

  