﻿G. 
  B. 
  Wieland 
  — 
  Huge 
  Cretaceous 
  Turtles. 
  241 
  

  

  The 
  differences 
  between 
  these 
  two 
  quadrato-jugals 
  are 
  there- 
  

   fore 
  striking. 
  Firstly, 
  the 
  outer 
  area 
  of 
  that 
  of 
  the 
  present 
  

   specimen, 
  which 
  as 
  just 
  stated 
  is 
  broadly 
  crescentic 
  in 
  outline, 
  

   is 
  relatively 
  more 
  than 
  double 
  that 
  of 
  Protostega, 
  which 
  is 
  

   isosceles-triangular 
  in 
  outline 
  with 
  the 
  equal 
  sides 
  slightly 
  

   concave. 
  Secondly, 
  the 
  flat 
  free 
  posterior 
  border 
  just 
  outside 
  

   the 
  articulation 
  with 
  the 
  quadrate 
  as 
  seen 
  in 
  Archelon, 
  is 
  

   represented 
  in 
  Protostega 
  by 
  an 
  oblique 
  surface 
  mostly 
  taken 
  

   up 
  by 
  the 
  quadrate 
  suture. 
  Lastly, 
  the 
  articulations 
  must 
  be 
  

   essentially 
  different. 
  Since 
  the 
  outline 
  in 
  Protostega 
  is 
  dis- 
  

   tinctly 
  triangular, 
  the 
  union 
  with 
  the 
  jugal 
  and 
  post-orbital 
  is 
  

   by 
  two 
  sutural 
  lines 
  making 
  an 
  angle 
  of 
  60° 
  with 
  each 
  other, 
  

   instead 
  of 
  by 
  a 
  long 
  curved 
  sutural 
  boundary 
  as 
  in 
  Archelon. 
  

   Now 
  since 
  the 
  upper 
  of 
  these 
  sutural 
  lines 
  is 
  nearly 
  horizontal, 
  

   and 
  the 
  general 
  outline 
  in 
  Protostega 
  that 
  seen 
  in 
  Dermochelys, 
  

   it 
  is 
  probable 
  that 
  the 
  latter 
  and 
  Protostega 
  agree 
  in 
  squamoso- 
  

   jugal 
  union. 
  On 
  the 
  contrary, 
  in 
  Archelon 
  there 
  is 
  marked 
  

   squamoso-jugal 
  separation. 
  For 
  reasons 
  which 
  I 
  have 
  pointed 
  

   out 
  elsewhere 
  I 
  do 
  not 
  lay 
  great 
  stress 
  upon 
  squamoso-jugal 
  

   union 
  or 
  non-union 
  alone 
  (13). 
  But 
  the 
  more 
  salient 
  fact 
  to 
  

   be 
  borne 
  in 
  mind 
  is 
  that 
  the 
  great 
  differences 
  in 
  general 
  con- 
  

   formation 
  compel 
  accompanying 
  variations 
  in 
  the 
  jugal, 
  

   parietal, 
  and 
  squamosal 
  which 
  are 
  fundamentally 
  generic. 
  

  

  The 
  Squamosal. 
  — 
  This 
  element 
  is 
  also 
  present 
  in 
  both 
  the 
  

   Kansas 
  material 
  and 
  the 
  present 
  specimen. 
  The 
  anterior 
  por- 
  

   tion 
  extends 
  upward 
  to 
  meet 
  the 
  parietal 
  as 
  a 
  long 
  narrow 
  band 
  

   nearly 
  covered 
  by 
  the 
  post-frontal, 
  and 
  does 
  not 
  expand 
  nearly 
  

   so 
  much 
  as 
  in 
  Protostega. 
  The 
  articular 
  surface 
  for 
  the 
  quad- 
  

   rate 
  is 
  placed 
  well 
  up 
  on 
  the 
  interior 
  side, 
  more 
  as 
  in 
  Dermo- 
  

   ehelys 
  than 
  in 
  either 
  Protostega 
  or 
  Thalassochelys. 
  The 
  lower 
  

   border 
  is 
  shallow 
  sigmoidal 
  in 
  outline 
  and 
  the 
  posterior 
  exten- 
  

   sion 
  instead 
  of 
  ending 
  bluntly 
  as 
  in 
  Protostega 
  runs 
  out 
  into 
  a 
  

   heavy 
  rounded 
  point 
  somewhat 
  as 
  in 
  Trionyx 
  spinifer. 
  As 
  in 
  

   Protostega, 
  there 
  is 
  however 
  no 
  posterior 
  inferior 
  grooving 
  of 
  

   this 
  extension. 
  

  

  The 
  Prefrontals. 
  — 
  These 
  are 
  somewhat 
  rhomboidal 
  in 
  out- 
  

   line. 
  The 
  junction 
  with 
  the 
  postfrontal 
  is 
  long 
  and 
  prominent, 
  

   and 
  much 
  as 
  in 
  Dermochelys. 
  Of 
  the 
  four 
  elements 
  bounding 
  

   the 
  orbit 
  the 
  prefrontal 
  takes 
  least 
  part. 
  The 
  prefrontals 
  

   extend 
  much 
  further 
  back 
  from 
  the 
  external 
  nares 
  than 
  in 
  

   Dermochelys, 
  the 
  general 
  resemblances 
  being 
  intermediate 
  to 
  

   the 
  latter 
  and 
  Thalassochelys. 
  

  

  The 
  Frontah. 
  — 
  These 
  bones 
  are 
  narrow 
  and 
  relatively 
  

   elongate. 
  As 
  the 
  cranial 
  roof 
  underwent 
  some 
  crushing, 
  it 
  

   is 
  difficult 
  to 
  discern 
  the 
  precise 
  position 
  of 
  the 
  parietal 
  bound- 
  

   ary. 
  Resemblances 
  Thalassochelan. 
  

  

  The 
  Postfrontal. 
  — 
  The 
  markings 
  and 
  boundaries 
  of 
  this 
  

  

  