﻿G. 
  P. 
  Wieland 
  — 
  Huge 
  Cretaceous 
  Turtles. 
  249 
  

  

  Case 
  in 
  Lis 
  discussion 
  of 
  the 
  relationships 
  of 
  Protostega 
  (5), 
  

   its 
  exact 
  position 
  may 
  not 
  vet 
  be 
  asserted 
  positively. 
  Bearing 
  

   in 
  mind 
  that 
  the 
  turtles 
  are 
  an 
  ancient 
  highly 
  specialized 
  and 
  

   numerous 
  group 
  of 
  great 
  constancy 
  of 
  form, 
  it 
  becomes 
  both 
  

   convenient 
  and 
  necessary 
  to 
  separate 
  genera 
  and 
  families 
  on 
  

   less 
  distinct 
  anatomical 
  differences 
  than 
  in 
  the 
  case 
  of 
  more 
  

   variant 
  orders. 
  Moreover 
  more 
  exact 
  knowledge 
  of 
  the 
  frag- 
  

   mentary 
  material 
  of 
  the 
  Mesozoic 
  is 
  the 
  first 
  requisite; 
  for 
  

   many 
  forms 
  will 
  be 
  found 
  like 
  the 
  present, 
  disposing 
  of 
  old 
  

   questions 
  only 
  to 
  raise 
  new 
  ones. 
  

  

  In 
  general 
  I 
  am 
  however 
  inclined 
  to 
  accept 
  Cope's 
  Proto- 
  

   stegidce 
  (7) 
  as 
  containing 
  the 
  genera 
  Protostega 
  and 
  Archelon. 
  

   It 
  is 
  scarcely 
  necessary 
  to 
  say, 
  however, 
  that 
  there 
  is 
  a 
  vastly 
  

   greater 
  interval 
  between 
  the 
  Dermochelyidce 
  and 
  Protostegidce 
  

   as 
  thus 
  constituted, 
  than 
  between 
  the 
  latter 
  and 
  the 
  Cheloniidw. 
  

   I 
  would 
  lay 
  especial 
  stress 
  upon 
  the 
  necessity 
  of 
  recognizing 
  

   this 
  general 
  fact. 
  

  

  The 
  position 
  of 
  Protosphargis 
  Veronensis 
  Capellini 
  (3) 
  is 
  

   very 
  doubtful, 
  firstly 
  because 
  its 
  skull, 
  nuchal 
  and 
  fore-arm 
  are 
  

   unknown, 
  and 
  secondly 
  because 
  of 
  the 
  uncertainty 
  concerning 
  

   the 
  validity 
  of 
  the 
  paraplastron, 
  as 
  I 
  have 
  termed 
  what 
  I 
  

   suppose 
  represents 
  the 
  fused 
  anterior 
  plastral 
  elements 
  in 
  Pro- 
  

   tostega 
  and 
  Archelon 
  (15). 
  

  

  While 
  the 
  latter 
  genera 
  appear 
  to 
  be 
  much 
  too 
  strongly 
  

   specialized 
  to 
  represent 
  more 
  than 
  a 
  Cretaceous 
  offshoot 
  from 
  

   the 
  Dermochelan 
  line 
  of 
  descent, 
  Protosphargis 
  may 
  possibly 
  

   be 
  exactly 
  in 
  this 
  line. 
  The 
  form 
  of 
  the 
  plastron 
  especially 
  

   suggests 
  such 
  a 
  position. 
  The 
  center 
  of 
  greatest 
  interest 
  has 
  

   therefore 
  in 
  large 
  measure 
  shifted 
  to 
  Protosphargis. 
  The 
  dis- 
  

   covery 
  of 
  further 
  specimens 
  of 
  this 
  genus 
  will 
  be 
  of 
  the 
  first 
  

   importance. 
  

  

  Attention 
  should 
  here 
  be 
  drawn 
  to 
  the 
  interesting 
  determina- 
  

   tion 
  of 
  the 
  marginal 
  series 
  of 
  Protosphargis 
  by 
  Capellini 
  (4). 
  

   I 
  may 
  mention 
  too 
  that 
  a 
  single 
  marginal 
  w 
  T 
  as 
  figured 
  in 
  the 
  

   first 
  description 
  of 
  A. 
  ischyros 
  (13) 
  which 
  is 
  wholly 
  character- 
  

   istic. 
  The 
  entire 
  marginal 
  series 
  in 
  this 
  form 
  is 
  unusual 
  in 
  the 
  

   spiny 
  development 
  of 
  both 
  the 
  dorsal 
  and 
  ventral 
  interior 
  

   marginal 
  borders, 
  which 
  are 
  strongly 
  spine-set 
  after 
  the 
  man- 
  

   ner 
  of 
  the 
  plastron. 
  Case 
  has 
  figured 
  a 
  portion 
  of 
  the 
  marginal 
  

   series 
  in 
  Protostega 
  (5), 
  but 
  his 
  material 
  did 
  not 
  bring 
  to 
  light 
  

   such 
  a 
  full 
  development 
  of 
  spiniferous 
  marginalia 
  as 
  is 
  seen 
  in 
  

   A. 
  ischyros 
  and 
  Ma/rshii. 
  That 
  these 
  spines 
  represent 
  the 
  

   disappearing 
  remnants 
  of 
  a 
  normally 
  developed 
  carapace 
  is 
  a 
  

   reasonable 
  supposition 
  and 
  nothing 
  more. 
  But 
  whether 
  

   representing 
  advancing 
  or 
  receding 
  ossification 
  the 
  slender 
  and 
  

   untoothed 
  marginals 
  of 
  Protosphargis 
  indicate 
  a 
  sharp 
  interval 
  

   in 
  development 
  between 
  these 
  forms. 
  The 
  latter 
  is 
  undoubt- 
  

   edlv 
  a 
  well 
  marked 
  genus. 
  

  

  