﻿546 
  Mr. 
  R. 
  W. 
  Hooley 
  oti 
  the 
  

  

  Group 
  B. 
  

  

  J. 
  a. 
  6, 
  35. 
  Tliis 
  example 
  was 
  figured 
  by 
  Owen* 
  and 
  also 
  

   hy 
  Seeley 
  f- 
  It 
  difiers 
  from 
  Orn'ithodesmus 
  latldens 
  in 
  the 
  

   circular 
  pit 
  on 
  the 
  articular 
  surface 
  being 
  postaxial. 
  while 
  in 
  

   the 
  Atherfield 
  specimen 
  it 
  is 
  nearer 
  the 
  ])reaxial. 
  The 
  pre- 
  

   axial 
  or 
  radial 
  area 
  of 
  the 
  Cambridge 
  specimens, 
  as 
  described 
  

   by 
  Owen 
  J, 
  " 
  shows 
  a 
  slightly 
  convex 
  surface 
  occujijing 
  its 
  

   major 
  part, 
  and 
  a 
  small 
  well-defined 
  flat 
  surface 
  placed 
  

   obliquely 
  .^^ 
  The 
  " 
  slightly 
  convex 
  surface'^ 
  becomes 
  more 
  

   convex 
  ventrally 
  as 
  it 
  uears 
  the 
  flat 
  oblique 
  surface. 
  Witb 
  

   a 
  i)art 
  of 
  the 
  former 
  aud 
  the 
  whole 
  of 
  the 
  latter 
  the 
  radius 
  

   articulated 
  ; 
  but 
  the 
  dorsal 
  moiety 
  of 
  the 
  "slightly 
  convex 
  

   surface" 
  was 
  a 
  portion 
  of 
  the 
  ulnar 
  articulation, 
  which 
  is 
  

   continued 
  round 
  the 
  dorsal 
  margin 
  to 
  the 
  postaxial 
  edge 
  

   (ulnar 
  side), 
  where 
  it 
  becomes 
  an 
  oval 
  concave 
  suiface. 
  The 
  

   ulnar 
  tubercle 
  is 
  placed 
  on 
  the 
  ventral 
  border 
  only, 
  and 
  not 
  

   on 
  the 
  postaxial, 
  as 
  in 
  Ornithodesmvs 
  latidens. 
  By 
  nos. 
  20, 
  

   20, 
  33, 
  and 
  34 
  it 
  is 
  seen 
  that 
  in 
  this 
  group 
  there 
  is 
  no 
  trans- 
  

   verse 
  valley, 
  but 
  that 
  the 
  ulna 
  ai)parently 
  occupied 
  the 
  whole 
  

   of 
  the 
  transveise 
  diameter 
  of 
  the 
  articular 
  end. 
  

  

  Group 
  C. 
  

  

  The 
  most 
  perfect 
  distal 
  end 
  of 
  this 
  group 
  is 
  J. 
  a. 
  6, 
  36. 
  

   It 
  is 
  crescentic, 
  with 
  the 
  convexity 
  on 
  the 
  dorsal 
  side. 
  The 
  

   articulation 
  exhibits 
  a 
  radial 
  and 
  median 
  convexity, 
  with 
  a 
  

   depression 
  between 
  them, 
  forming 
  a 
  trochlea. 
  On 
  the 
  

   ventral 
  margin 
  of 
  the 
  postaxial 
  side 
  there 
  is 
  a 
  tubercle 
  

   directed 
  distally, 
  and 
  dorsal 
  to 
  this 
  an 
  oval 
  concave 
  facet, 
  

   obliquely 
  placed 
  aud 
  looking 
  outwards. 
  On 
  the 
  ventral 
  

   surface, 
  between 
  the 
  horns 
  of 
  the 
  crescent, 
  there 
  is 
  a 
  deep 
  

   concavity, 
  and, 
  as 
  the 
  radial 
  and 
  ulnar 
  condyle 
  both 
  have 
  a 
  

   flat 
  facet 
  looking 
  inwards, 
  it 
  is 
  probable 
  that 
  the 
  radius 
  

   articulated 
  with 
  both 
  these. 
  

  

  The 
  type 
  of 
  ulna 
  shown 
  on 
  tablet 
  J. 
  a. 
  9, 
  no. 
  1, 
  we 
  believe 
  

   to 
  belong 
  to 
  this 
  group, 
  because 
  of 
  its 
  similar 
  articular 
  

   surfaces. 
  

  

  It 
  is 
  highly 
  probable 
  that 
  the 
  proximal 
  ends 
  of 
  Groups 
  A, 
  

  

  * 
  R. 
  Owen, 
  Rep. 
  Cret. 
  Form. 
  (Mon. 
  Pal. 
  .Soc. 
  1851), 
  Suppl. 
  i. 
  pi. 
  iv. 
  

   figs. 
  1-3. 
  

  

  t 
  H. 
  G. 
  Seeley, 
  ' 
  Ornitliosauria,' 
  1870, 
  pi. 
  iv. 
  fig. 
  14. 
  

   \ 
  R. 
  Owen, 
  loc. 
  cit. 
  p. 
  1(3. 
  

  

  