﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  217 
  

  

  The 
  teeth 
  are 
  numerous, 
  they 
  are 
  miniatures 
  of 
  those 
  of 
  the 
  Mosasaurus, 
  in 
  most 
  

   respects. 
  Those 
  of 
  the 
  pterygoids 
  appear 
  to 
  be 
  less 
  compressed 
  than 
  the 
  maxillaries; 
  all 
  

   have 
  large 
  pulp 
  cavities, 
  though 
  they 
  are 
  restricted 
  by 
  peripheral 
  ossification, 
  as 
  in 
  other 
  

   genera. 
  

  

  The 
  palatines 
  have 
  not 
  united 
  on 
  the 
  median 
  line, 
  and 
  it 
  would 
  appear 
  that 
  they 
  were 
  

   not 
  in 
  contact. 
  They 
  have 
  a 
  broad 
  longitudinal 
  groove 
  anteriorly. 
  They 
  have 
  no 
  teeth. 
  

   The 
  pterygoids 
  are 
  largely 
  developed. 
  They 
  are 
  widest 
  anteriorly; 
  they 
  present 
  a 
  thin 
  

   free 
  edge 
  externally 
  and 
  a 
  thick 
  reverted 
  margin 
  interiorly 
  ; 
  the 
  tooth 
  series 
  is 
  nearer 
  the 
  

   outer 
  than 
  the 
  inner 
  margin. 
  The 
  ectopterygoid 
  rises 
  from 
  a 
  strong 
  lateral 
  process 
  of 
  the 
  

   pterygoid. 
  It 
  represents 
  an 
  obtuse 
  process 
  downwards 
  and 
  a 
  thin 
  process 
  anteriorly. 
  Its 
  

   position 
  is 
  below 
  the 
  middle 
  of 
  the 
  postfrontal. 
  It 
  is 
  very 
  doubtful 
  whether 
  it 
  had 
  other 
  

   than 
  ligamentous 
  connection 
  with 
  the 
  maxilliary, 
  as 
  it 
  is 
  far 
  removed 
  from 
  its 
  extremity. 
  

  

  The 
  vertebrae 
  in 
  this 
  genus 
  are 
  more 
  numerous 
  than 
  in 
  Mosasaurus, 
  while 
  the 
  number 
  

   of 
  cervicals 
  bearing 
  hypapophyses 
  is 
  less. 
  The 
  caudal 
  diapophyses 
  are 
  reduced 
  to 
  small 
  

   knobs, 
  and 
  disappear 
  on 
  some 
  of 
  the 
  anterior 
  of 
  those 
  that 
  bear 
  chevron 
  bones. 
  The 
  

   neural 
  spines 
  of 
  the 
  caudals 
  are 
  much 
  compressed, 
  and 
  have 
  anterior 
  and 
  posterior 
  ala?. 
  

   On 
  the 
  distal 
  caudals 
  they 
  become 
  cylindric 
  and 
  fish-like. 
  The 
  zygapophyses 
  become 
  ob- 
  

   scure, 
  and 
  finally 
  disappear 
  ; 
  before 
  doing 
  so 
  the 
  posterior 
  acquire 
  an 
  up 
  rather 
  than 
  a 
  

   down-looking 
  face. 
  

  

  The 
  centrum 
  of 
  the 
  atlas 
  is 
  entirely 
  below 
  the 
  very 
  large 
  processus 
  odontoideus. 
  It 
  

   is 
  keeled 
  below, 
  and 
  has 
  less 
  contact 
  with 
  the 
  condyle 
  than 
  has 
  the 
  processus 
  ; 
  the 
  latter 
  

   is 
  free 
  from 
  the 
  axis, 
  which 
  resembles 
  other 
  cervicals. 
  The 
  odontoid 
  ring 
  is 
  not 
  closed 
  

   above. 
  The 
  neurapophyses 
  of 
  the 
  atlas 
  are 
  continuous 
  with 
  the 
  lateral 
  segment 
  of 
  the 
  

   centrum 
  which 
  furnishes 
  articular 
  faces 
  to 
  the 
  basal 
  segment, 
  the 
  odontoid, 
  and 
  to 
  the 
  occi- 
  

   pital 
  condyle, 
  and 
  sends 
  a 
  process 
  back 
  alongside 
  the 
  axis. 
  The 
  neurapophyses 
  are 
  slen- 
  

   der 
  ; 
  if 
  they 
  have 
  a 
  neural 
  spine, 
  it 
  is 
  lost. 
  They 
  are, 
  on 
  the 
  whole, 
  much 
  as 
  in 
  Mosasau- 
  

   rus, 
  and 
  in 
  Varanus. 
  

  

  The 
  ribs 
  commence 
  immediately 
  behind 
  the 
  atlas, 
  if 
  the 
  forms 
  of 
  the 
  diapophyses 
  and 
  

   their 
  articular 
  surfaces 
  are 
  to 
  be 
  relied 
  on. 
  The 
  diapophysis 
  of 
  the 
  axis 
  is 
  nearly 
  horizon- 
  

   tal, 
  descending 
  a 
  little 
  anteriorly 
  ; 
  the 
  posterior 
  portion 
  of 
  its 
  extremity 
  is 
  subtruncate 
  

   for 
  articulation 
  to 
  a 
  small 
  rib. 
  The 
  same 
  part 
  of 
  the 
  diapophysis 
  of 
  the 
  third 
  is 
  more 
  

   prominent, 
  is 
  ovate, 
  and 
  continuous 
  with 
  a 
  subhorizontal 
  ridge 
  with 
  articular-like 
  surface, 
  

   which 
  extends 
  to 
  the 
  rim 
  of 
  the 
  cup. 
  The 
  fourth 
  is 
  similar, 
  but 
  the 
  articular 
  faces 
  are 
  

   more 
  similar 
  in 
  widths 
  and 
  lengths. 
  The 
  inferior 
  limb 
  becomes 
  regularly 
  shorter 
  and 
  less 
  

   horizontal 
  posteriorly. 
  From 
  the 
  eighteenth 
  to 
  the 
  twenty-third 
  the 
  surfaces 
  are 
  a 
  little 
  

   smaller, 
  and 
  without 
  apparent 
  difference 
  in 
  size 
  and 
  form. 
  The 
  rib-bearing 
  surfaces 
  pos- 
  

   terior 
  to 
  this 
  point 
  are 
  lost. 
  

  

  AMERICA. 
  PHILO. 
  SOC. 
  — 
  VOL. 
  XIV. 
  55. 
  

  

  