﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  29 
  

  

  PYTHONOMORPHA. 
  

  

  Characters 
  of 
  skeleton 
  as 
  the 
  preceding, 
  except 
  : 
  opisthotic 
  distinct, 
  prolonged 
  from 
  the 
  

  

  cranial 
  walls 
  as 
  suspensoriinn 
  of 
  the 
  qnadratum. 
  

   No 
  symphysis 
  mandibnli. 
  

   Squamosal 
  present 
  ; 
  premaxilliary 
  single. 
  

  

  Cranium 
  with 
  alisphenoid 
  and 
  parietal 
  developed 
  in 
  front 
  of 
  prootic. 
  

   Limbs 
  inflexible, 
  natatory 
  ; 
  sacrum 
  none 
  ; 
  chevron 
  bones. 
  

   Neural 
  arches 
  not 
  attached 
  to 
  centrum 
  by 
  suture. 
  

   Pubes 
  and 
  ischia 
  wanting. 
  (?) 
  

  

  OPHIDIA. 
  

  

  Characters 
  of 
  Lacertilia 
  except 
  : 
  opisthotic 
  free, 
  distinct 
  from 
  the 
  cranium 
  except 
  proxi- 
  

   mally, 
  supporting 
  qnadratum 
  ; 
  no 
  squamosal. 
  

  

  Cranial 
  cavity 
  largely 
  ossified 
  anteriorly. 
  

  

  Palatine 
  bones 
  free 
  from 
  other 
  elements 
  except 
  pterygoids. 
  

  

  No 
  symphysis 
  mandibuli. 
  

  

  Sternal 
  and 
  pelvic 
  arches 
  wanting 
  ; 
  no 
  limbs 
  except 
  rarely 
  rudiments 
  posteriorly 
  ; 
  no 
  

   sacrum. 
  

  

  Vertebrae 
  united 
  by 
  double 
  articulation 
  ; 
  neural 
  arches 
  continuous 
  with 
  centra 
  ; 
  no 
  chev- 
  

   ron 
  bones. 
  

  

  Circulatory 
  and 
  Nervous 
  Systems, 
  in 
  important 
  features 
  as 
  Lacertilia. 
  

  

  ICHTHYOPTER1GIA. 
  

  

  ICHTHYOSAURUS, 
  Conybeare. 
  

  

  Leidy 
  says 
  with 
  reference 
  to 
  the 
  species 
  here 
  described, 
  "They 
  have 
  an 
  affinity 
  to 
  

   Ichthyosaurus 
  and 
  Eosaurus, 
  nor 
  am 
  I 
  prepared 
  to 
  prove 
  that 
  they 
  do 
  not 
  belong 
  to 
  one 
  

   of 
  these." 
  

  

  ICHTHYOSAURUS 
  GRANDIS, 
  Leidy. 
  

  

  Chonespondylus 
  yrandia, 
  Leidy. 
  Proc. 
  Acad. 
  Nat. 
  Sci., 
  Philada., 
  18G8 
  — 
  178. 
  

  

  Humboldt 
  Co., 
  Nevada. 
  

  

  AMERI. 
  PHILOSO. 
  SOC. 
  — 
  VOL. 
  XIV. 
  8 
  

  

  