﻿AXD 
  REPTILIA 
  OF 
  NORTH 
  AMERICA. 
  O 
  

  

  The 
  present 
  genns 
  resembles 
  Lepterpeton, 
  Huxl., 
  of 
  the 
  Irish 
  coal-measures, 
  in 
  

   the 
  form 
  of 
  the 
  cranium 
  and 
  in 
  proportions 
  of 
  body, 
  but 
  that 
  exhibits 
  divided 
  abdomi- 
  

   nal 
  rods, 
  or 
  " 
  oat-shaped 
  scales 
  " 
  and 
  the 
  caudal 
  vertebras 
  have 
  not 
  the 
  fan-like 
  

   processes. 
  In 
  the 
  last 
  point 
  the} 
  7 
  agree 
  with 
  Urocordylus, 
  Huxl., 
  but 
  this 
  genus 
  is 
  

   not 
  represented 
  as 
  possessing 
  ribs, 
  and 
  the 
  abdominal 
  rods 
  are 
  also 
  divided, 
  forming 
  the 
  

   " 
  oat-shaped 
  scales." 
  I 
  formerly 
  referred 
  the 
  species 
  of 
  Ptyonius 
  to 
  O'estoceplialus, 
  

   but 
  in 
  that 
  genus 
  no 
  pectoral 
  shields 
  have 
  been 
  observed. 
  The 
  vertebras 
  in 
  remex 
  

   are 
  of 
  rather 
  more 
  elongate 
  form 
  than 
  in 
  the 
  species 
  of 
  Ptyonius. 
  Should, 
  however, 
  

   the 
  pectoral 
  plates 
  be 
  found 
  in 
  O. 
  remex, 
  this 
  genus 
  must 
  be 
  united 
  with 
  that 
  one. 
  

   Four 
  species 
  have 
  been 
  detected 
  by 
  the 
  geological 
  survey 
  of 
  Ohio. 
  

   I. 
  Vertebras 
  shorter 
  ; 
  fan-like 
  processes 
  of 
  caudal 
  vertebras 
  broad, 
  equilateral. 
  

   a 
  Abdominals 
  rods 
  coarser, 
  not 
  more 
  than 
  ten 
  in 
  .005 
  m. 
  

  

  P 
  Median 
  pectoral 
  plate 
  broad, 
  radiate 
  ridged. 
  P. 
  marshii. 
  

  

  an. 
  Abdominals 
  rods 
  hair-like, 
  fifteen 
  or 
  more 
  in 
  .005 
  m. 
  

  

  P 
  Middle 
  pectoral 
  shield 
  with 
  radii 
  from 
  the 
  centre, 
  the 
  principal 
  forming 
  a 
  

  

  cross 
  ; 
  form 
  wider. 
  P. 
  vixchelliaxus. 
  

  

  P 
  Middle 
  pectoral 
  with 
  pits 
  at 
  the 
  centre 
  and 
  few 
  or 
  no 
  radii 
  ; 
  form 
  narrow. 
  

  

  P. 
  PECTLXATUS. 
  

  

  P 
  Middle 
  pectoral 
  shield 
  narrow, 
  closely 
  reticulate 
  medially, 
  and 
  radiate 
  

   towards 
  the 
  circumference 
  ; 
  size 
  half 
  that 
  of 
  the 
  last. 
  P. 
  serrula. 
  

  

  PTYONIUS 
  MARSHII, 
  Cope. 
  

  

  Colosteus 
  marshii, 
  Cope, 
  Transac. 
  Amer. 
  Philos. 
  Soc, 
  XIV., 
  1869, 
  p. 
  24; 
  Oestocephalus 
  marshii, 
  Cope, 
  Proceed. 
  

   Amer. 
  Pliilcs. 
  Soc. 
  1871, 
  p. 
  177. 
  

  

  PTYONIUS 
  VINCHELLIANUS, 
  Cope. 
  

  

  Oestocephalus 
  vinchellianus, 
  Proceed. 
  Amer. 
  Philos. 
  Soc. 
  1871, 
  177. 
  

  

  Represented 
  by 
  the 
  opposite 
  halves 
  of 
  a 
  single 
  specimen, 
  which 
  includes 
  only 
  the 
  cranium 
  and 
  anterior 
  half 
  of 
  

   the 
  body. 
  The 
  fan-shaped 
  neural 
  spines 
  commence 
  but 
  a 
  short 
  distance 
  behind 
  the 
  line 
  of 
  the 
  pectoral 
  shields 
  ; 
  they 
  

   are 
  low, 
  and 
  with 
  a 
  few 
  coarse 
  ridges 
  ; 
  the 
  margin 
  entire. 
  The 
  abdominal 
  rods 
  are 
  delicate 
  and 
  hair-like. 
  The 
  

   pectoral 
  shield 
  is 
  an 
  oval, 
  with 
  a 
  few 
  radiating 
  crests 
  which 
  originate 
  at 
  the 
  centre 
  ; 
  in 
  the 
  areas 
  between 
  these 
  there 
  

   are 
  a 
  few 
  scattered 
  tubercles. 
  The 
  lateral 
  shields 
  are 
  ridged 
  near 
  the 
  margin. 
  

  

  The 
  cranium 
  is 
  lanceolate 
  in 
  form, 
  and 
  the 
  bones 
  of 
  the 
  superior 
  walls 
  are 
  marked 
  with 
  a 
  few 
  raised 
  points 
  and 
  

   ridges. 
  There 
  is 
  a 
  thin 
  bone 
  which 
  I 
  have 
  already 
  alluded 
  to 
  as 
  the 
  squamosal 
  or 
  preoperculum, 
  shaped 
  like 
  a 
  right- 
  

   angled 
  triangle 
  separated 
  from 
  the 
  outer 
  posterior 
  angle 
  of 
  the 
  head, 
  which 
  exhibits 
  a 
  few 
  similar 
  marks. 
  

  

  M. 
  

  

  Length 
  of 
  cranium, 
  0.020 
  

  

  Width 
  " 
  " 
  -008 
  

  

  Length 
  median 
  pectoral 
  plate, 
  .0042 
  

  

  This 
  small 
  species 
  is 
  about 
  the 
  size 
  of 
  P. 
  pectinatus, 
  and 
  should 
  be 
  especially 
  compared 
  with 
  it. 
  In 
  specimens 
  

  

  