﻿OSTEOLOGY 
  OF 
  TESTIDO 
  PHAKKXTANS 
  — 
  GILMORE 
  297 
  

  

  before 
  me 
  in 
  hav^ing 
  shorter 
  prefontals, 
  smaller 
  frontals, 
  and 
  longi- 
  

   tudinal 
  channels 
  on 
  the 
  masticatory 
  surfaces 
  unequal 
  in 
  width. 
  

   Wlii'ihcr 
  those 
  diU'eronces 
  constitute 
  stable 
  characters 
  that 
  can 
  be 
  

   relied 
  upon 
  for 
  their 
  specific 
  separation 
  cannot 
  be 
  determined 
  until 
  

   more 
  skulls 
  ai-e 
  available. 
  

  

  The 
  roof 
  of 
  the 
  mouth 
  is 
  moderately 
  vaulted 
  and 
  traversed 
  along 
  

   the 
  midline 
  by 
  a 
  sharp 
  ridge 
  (fig. 
  22), 
  the 
  anterior 
  end 
  of 
  which 
  abrupt- 
  

   ly 
  widens 
  where 
  the 
  vomer 
  articulates 
  with 
  tiie 
  premaxillaries 
  and 
  

  

  SQ 
  

  

  Figure 
  23. 
  — 
  Lower 
  jaw 
  of 
  Testudo 
  praeextans 
  Lainbe 
  (U.S.N.M. 
  No. 
  15874), 
  superior 
  view: 
  

   ar, 
  articular; 
  c, 
  coronoid; 
  d, 
  dentary; 
  prar, 
  prearticular; 
  sa, 
  surangular. 
  Natural 
  size. 
  

  

  maxillary 
  bones. 
  Posteriorly 
  this 
  vomerine 
  ridge 
  underlaps 
  the 
  

   pterj-goid 
  part 
  of 
  the 
  ridge, 
  which 
  merges 
  into 
  the 
  palatal 
  surfaces 
  

   of 
  the 
  pterygoid 
  slightly 
  in 
  advance 
  of 
  their 
  median 
  union 
  with 
  the 
  

   basisphenoid. 
  

  

  The 
  masticatory 
  surface 
  of 
  the 
  ma.xillary 
  is 
  divided 
  by 
  a 
  low 
  metlian 
  

   ridge 
  that 
  is 
  received 
  in 
  a 
  groove 
  of 
  the 
  mandible. 
  This 
  ridge 
  is 
  

   bordered 
  on 
  each 
  side 
  by 
  longitudinal 
  grooves 
  of 
  about 
  equal 
  width. 
  

   In 
  this 
  respect 
  this 
  specimen 
  differs 
  markedly 
  from 
  Testudo 
  thomsoni, 
  

   w 
  liich 
  has 
  a 
  very 
  narrow 
  inner 
  groove 
  and 
  a 
  widened 
  out(^r 
  groove. 
  

   The 
  imier 
  ridge 
  is 
  unusually 
  low, 
  and 
  it 
  meets 
  its 
  fellow 
  of 
  the 
  opposite 
  

   side 
  on 
  the 
  posterior 
  border 
  of 
  the 
  premaxillary. 
  At 
  the 
  midline 
  

   along 
  th(! 
  symphysis 
  of 
  the 
  premaxillae 
  there 
  is 
  a 
  prominent 
  longi- 
  

   tudinal 
  ridge, 
  as 
  in 
  Oopherus 
  and 
  in 
  some 
  living 
  species 
  of 
  Testudo. 
  

   This 
  ridge 
  is 
  absent 
  in 
  the 
  skulls 
  of 
  other 
  American 
  fossil 
  Testudo 
  

   now 
  known. 
  It 
  was 
  the 
  sup[)osed 
  absence 
  of 
  this 
  ridge 
  in 
  front 
  of 
  the 
  

   choanae 
  that 
  led 
  Hay 
  to 
  use 
  it 
  as 
  one 
  of 
  the 
  important 
  characters 
  for 
  

   distinguishing 
  Testudo 
  from 
  Stylemys} 
  

  

  ' 
  Hay. 
  O. 
  ['., 
  Fossil 
  turtUs 
  of 
  .North 
  Amcrlcn. 
  rarncRlc 
  trust. 
  Washington 
  Publ. 
  75. 
  p. 
  307, 
  \W». 
  

  

  