﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  211 
  

  

  POLYGONODON 
  RECTUS. 
  Emmons. 
  

   Mosasaurus 
  rectus, 
  Emmons, 
  Geological 
  Survey, 
  N. 
  Ca., 
  1858, 
  218. 
  Polygonodon 
  rectus, 
  Emmons, 
  1. 
  c. 
  tab. 
  

  

  Emmons 
  found 
  his 
  specimen 
  in 
  the 
  miocene 
  in 
  North 
  Carolina, 
  but 
  considered 
  it 
  an 
  

   intrusive 
  fossil 
  from 
  the 
  Cretaceous. 
  The 
  present 
  survey 
  under 
  Prof. 
  Kerr 
  has 
  a 
  similar 
  

   specimen 
  also 
  from 
  the 
  Miocene. 
  

  

  Miocene 
  of 
  Bladen 
  and 
  Duplin 
  Counties, 
  North 
  Carolina. 
  

  

  CLIDASTIDJE. 
  

   CLIDASTES, 
  Cope. 
  

   Proceedings 
  Academy 
  Nat. 
  Sci., 
  Phil., 
  1868, 
  p. 
  233. 
  

  

  This 
  genus 
  was 
  originally 
  established 
  on 
  a 
  species 
  represented 
  by 
  a 
  single 
  dorsal 
  ver- 
  

   tebra, 
  but 
  its 
  characters 
  have 
  been 
  chiefly 
  developed 
  from 
  remains 
  of 
  two 
  other 
  species, 
  

   especially 
  the 
  nearly 
  complete 
  skeleton 
  of 
  the 
  C. 
  propython. 
  The 
  vertebra 
  is 
  highly 
  

   characteristic, 
  and 
  resembles 
  considerably 
  that 
  of 
  such 
  genera 
  of 
  Iguanidae 
  as 
  Euphryne 
  

   and 
  Dipsosaurus, 
  and 
  in 
  some 
  degree 
  those 
  of 
  Cyclura 
  and 
  Iguana. 
  It 
  differs 
  from 
  the 
  

   dorsals 
  of 
  known 
  serpents 
  in 
  having 
  the 
  zygosphen 
  on 
  the 
  plane 
  of 
  the 
  anterior 
  zygapo- 
  

   physis, 
  and 
  in 
  having 
  the 
  costal 
  articular 
  surface 
  continuous 
  with 
  and 
  covering 
  the 
  diapo- 
  

   physes. 
  It 
  differs 
  from 
  the 
  genera 
  of 
  Iguanidse 
  mentioned, 
  in 
  the 
  very 
  small 
  amount 
  of 
  

   upward 
  direction 
  which 
  the 
  face 
  of 
  the 
  articular 
  ball 
  of 
  the 
  centrum 
  exhibits. 
  

  

  The 
  zygapophyses 
  are 
  spread 
  apart, 
  and 
  their 
  outer 
  margin 
  continues 
  in 
  a 
  straight 
  

   line 
  from 
  the 
  diapophyses. 
  The 
  diapophyses 
  are 
  directed 
  upwards, 
  and 
  are 
  vertical 
  com- 
  

   pressed 
  in 
  form 
  ; 
  they 
  are 
  opposite 
  to 
  about 
  equal 
  portions 
  of 
  the 
  centrum 
  and 
  neural 
  

   arch. 
  Their 
  posterior 
  face 
  is 
  slightly 
  concave, 
  and 
  the 
  upper 
  face 
  behind 
  forms, 
  with 
  the 
  

   neural 
  arch, 
  a 
  deeply 
  concave 
  line. 
  The 
  convexity 
  of 
  the 
  ball 
  is 
  not 
  so 
  great 
  as 
  in 
  the 
  

   Crocodilia, 
  and 
  with 
  the 
  thin 
  -lipped 
  cup, 
  resembles 
  that 
  of 
  Mosasaurus 
  ; 
  this 
  resemblance 
  is 
  

   heightened 
  by 
  the 
  slightly 
  depressed 
  upper 
  outline 
  of 
  the 
  ball, 
  and 
  the 
  form 
  of 
  the 
  

   diapophyses. 
  

  

  The 
  genus 
  is 
  most 
  nearly 
  allied 
  to 
  Liodon, 
  in 
  some 
  of 
  the 
  vertebrae 
  of 
  which 
  a 
  slight 
  

   groove 
  beside 
  the 
  zygapophysis 
  is 
  the 
  rudiment 
  of 
  the 
  zygantrum. 
  

  

  The 
  premaxillary 
  is 
  a 
  narrow, 
  simple 
  element, 
  one-half 
  of 
  a 
  cone 
  anteriorly, 
  and 
  mucli 
  

   attenuated 
  posteriorly, 
  separating 
  the 
  maxillaries 
  above, 
  by 
  width 
  of 
  its 
  spine 
  only. 
  Its 
  

   extremity 
  projects 
  considerably 
  beyond 
  the 
  latter, 
  and 
  its 
  sides 
  are 
  only 
  bevelled 
  to 
  receive 
  

   them, 
  there 
  being 
  no 
  sutural 
  connection. 
  The 
  spine 
  terminates 
  a 
  short 
  distance 
  beyond 
  

   the 
  anterior 
  margin 
  of 
  the 
  nares. 
  The 
  anterior 
  extremity 
  bears 
  two 
  teeth 
  on 
  each 
  side, 
  

   which 
  are 
  smaller 
  than 
  the 
  larger 
  maxillaries. 
  

  

  The 
  maxillary 
  bones 
  are 
  long 
  and 
  slender, 
  and 
  widely 
  separated 
  on 
  the 
  palatal 
  sur- 
  

  

  