﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  

  

  133 
  

  

  Fijr. 
  38. 
  

  

  osteoptgis 
  plattlomtjs 
  carapace. 
  

  

  The 
  xiphisternal 
  is 
  united 
  with 
  the 
  hypo-sternal 
  precisely 
  as 
  in 
  Chelydra, 
  that 
  is, 
  

   by 
  a 
  mutual 
  marginal 
  gomphosis 
  at 
  the 
  anterior 
  extremity 
  of 
  the 
  former, 
  its 
  peg 
  being 
  

   the 
  external; 
  and 
  by 
  a 
  deep 
  groove 
  in 
  the 
  inner 
  margin 
  of 
  the 
  xiphisternal, 
  which 
  

   receives 
  the 
  adapted 
  margin 
  of 
  the 
  hyposternal. 
  The 
  xiphisternal 
  lobe 
  is 
  wider 
  than 
  in 
  

   Chelydra, 
  while 
  the 
  bridge 
  is 
  very 
  much 
  wider, 
  being 
  about 
  as 
  in 
  Trionyx, 
  and 
  much 
  

   narrower 
  than 
  in 
  Chelone. 
  This 
  constitutes 
  a 
  point 
  of 
  separation 
  from 
  the 
  first 
  named 
  

   genus. 
  There 
  is 
  a 
  median 
  fontanelle, 
  larger 
  than 
  in 
  Chelydra 
  serpentina 
  at 
  the 
  junc- 
  

   tion 
  of 
  the 
  four 
  sternal 
  elements. 
  The 
  external 
  margin 
  of 
  the 
  hyosternal, 
  is 
  free 
  and 
  

   serrate 
  as 
  in 
  Chelydra. 
  The 
  mesosternal 
  has 
  not 
  been 
  identified, 
  but 
  the 
  episterna 
  are 
  

   narrower 
  and 
  greatly 
  incurved, 
  more 
  as 
  in 
  Chelydra 
  and 
  Chelone 
  than 
  as 
  in 
  Trionyx. 
  

   In 
  the 
  accompanying 
  restoration, 
  the 
  shaded 
  portions 
  are 
  those 
  which 
  have 
  not 
  been 
  pre- 
  

  

  AMERI. 
  PHILOSO. 
  SOC. 
  VOL. 
  XIV. 
  34 
  

  

  