﻿394 
  PROF. 
  H. 
  G. 
  SEELET 
  OX 
  THE 
  PELTIS 
  OF 
  ORNITHOPSIS. 
  

  

  The 
  suture 
  with 
  the 
  ischium, 
  which 
  is 
  nearly 
  straight, 
  may 
  have 
  

   heen 
  nearly 
  vertical 
  ; 
  it 
  is 
  30 
  centim. 
  long. 
  The 
  sutural 
  surface 
  

   becomes 
  narrow 
  as 
  it 
  descends, 
  and 
  the 
  bone 
  becomes 
  thin 
  towards 
  

   the 
  median 
  line. 
  

  

  The 
  ischium 
  is 
  curved 
  in 
  length, 
  with 
  the 
  convexity 
  on 
  the 
  inner 
  

   side, 
  and 
  it 
  is 
  twisted 
  at 
  an 
  angle 
  of 
  45°, 
  so 
  that 
  the 
  superior 
  distal 
  

   surfaces 
  are 
  directed 
  outward 
  and 
  upward, 
  and 
  the 
  inferior 
  margins 
  

   converge 
  and 
  meet 
  in 
  a 
  broad 
  V 
  shape. 
  This 
  union 
  is 
  assisted 
  by 
  

   the 
  internal 
  distal 
  border 
  of 
  the 
  bones 
  being 
  bevelled 
  at 
  an 
  angle 
  of 
  

   45° 
  for 
  a 
  length 
  of 
  30 
  centim., 
  and 
  this 
  surface 
  is 
  marked 
  with 
  coarse 
  

   parallel 
  longitudinal 
  sutural 
  lines. 
  Externally 
  the 
  distal 
  extremity 
  

   of 
  the 
  bone 
  is 
  thickened 
  superiorly 
  for 
  15 
  centim., 
  as 
  though 
  for 
  

   muscular 
  attachment. 
  The 
  bone 
  is 
  imperfectly 
  preserved, 
  so 
  that 
  

   the 
  larger 
  part 
  of 
  the 
  anterior 
  sutural 
  union 
  with 
  the 
  pubis 
  is 
  broken 
  

   away 
  towards 
  the 
  median 
  line 
  of 
  the 
  body. 
  At 
  a 
  distance 
  of 
  43 
  

   centim. 
  from 
  the 
  proximal 
  end 
  there 
  is, 
  on 
  the 
  internal 
  border, 
  a 
  

   small 
  portion 
  of 
  smooth 
  ossified 
  margin 
  which 
  is 
  concave, 
  and 
  this 
  I 
  

   take 
  to 
  indicate 
  the 
  posterior 
  termination 
  of 
  the 
  proximal 
  expansion 
  

   of 
  the 
  bone. 
  Externally 
  the 
  infra-acetabular 
  surface 
  is 
  concavely 
  

   excavated 
  in 
  the 
  usual 
  way. 
  The 
  sutural 
  surface 
  for 
  the 
  ilium 
  is 
  

   15 
  centim. 
  long 
  ; 
  the 
  acetabular 
  interval 
  between 
  the 
  ischium 
  and 
  

   pubis 
  is 
  15 
  centim. 
  wide, 
  and 
  the 
  iliac 
  attachment 
  on 
  the 
  pubis 
  is 
  

   19 
  centim. 
  long, 
  as 
  preserved, 
  and 
  appears 
  originally 
  to 
  have 
  mea- 
  

   sured 
  about 
  33 
  centim. 
  The 
  greatest 
  thickness 
  of 
  the 
  bone 
  where 
  

   it 
  unites 
  with 
  the 
  ilium 
  is 
  5 
  centimetres. 
  I 
  am 
  not 
  aware 
  that 
  this 
  

   type 
  of 
  pelvis 
  has 
  hitherto 
  been 
  observed. 
  The 
  antero-posterior 
  

   arch 
  between 
  the 
  anterior 
  symphysis 
  of 
  the 
  pubic 
  bones 
  and 
  the 
  

   posterior 
  symphysis 
  of 
  the 
  ischia 
  is 
  a 
  well-marked 
  characteristic 
  

   of 
  Saurischian 
  reptiles 
  ; 
  but 
  it 
  remains 
  to 
  be 
  determined 
  to 
  what 
  

   extent 
  the 
  median 
  union 
  of 
  the 
  pubic 
  bones 
  is 
  developed 
  in 
  the 
  

   group. 
  

  

  From 
  the 
  imperfect 
  fragment 
  preserved 
  it 
  is 
  impossible 
  to 
  judge 
  

   of 
  the 
  form 
  of 
  the 
  ilium, 
  but 
  it 
  does 
  not 
  make 
  any 
  recognizable 
  

   approximation 
  to 
  the 
  bone 
  in 
  those 
  American 
  genera 
  which 
  offer 
  

   the 
  closest 
  resemblance 
  of 
  form 
  to 
  the 
  pubis 
  and 
  ischium. 
  

  

  When 
  the 
  bones 
  from 
  the 
  Oxford 
  Clay 
  are 
  compared 
  with 
  those 
  

   from 
  the 
  Wealden 
  of 
  the 
  Isle 
  of 
  Wight 
  there 
  are 
  several 
  minor 
  

   differences 
  of 
  proportion 
  ; 
  but 
  although 
  the 
  internal 
  border 
  of 
  the 
  

   Wealden 
  pubis 
  is 
  badly 
  preserved, 
  its 
  distal 
  inner 
  border 
  shows 
  an 
  

   inclined 
  symphysial 
  suture, 
  and 
  a 
  symphysial 
  suture 
  is 
  present 
  on 
  the 
  

   most 
  convex 
  part 
  of 
  the 
  arch 
  in 
  the 
  middle 
  of 
  the 
  bone, 
  which 
  is 
  

   more 
  prominent 
  than 
  in 
  the 
  relatively 
  wider, 
  thicker 
  bone 
  of 
  

   Ornithopsis 
  Leedsii. 
  In 
  the 
  Wealden 
  specimen 
  the 
  obturator 
  foramen 
  

   in 
  the 
  pubis 
  is 
  relatively 
  nearly 
  twice 
  as 
  large 
  as 
  in 
  the 
  Oxford-clay 
  

   specimen, 
  and 
  is 
  more 
  obliquely 
  placed. 
  The 
  ischium 
  in 
  the 
  

   Wealden 
  specimen 
  is 
  relatively 
  much 
  broader 
  and 
  stronger 
  than 
  in 
  

   the 
  Oxford-clay 
  fossil 
  ; 
  it 
  has 
  a 
  much 
  wider 
  iliac 
  head, 
  defined 
  

   by 
  a 
  deep 
  concave 
  subacetabular 
  notch, 
  which 
  is 
  almost 
  wanting 
  in 
  

   the 
  other 
  type; 
  the 
  distal 
  end 
  is 
  expanded, 
  and 
  though 
  its 
  symphysis 
  

  

  