﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  131 
  

  

  pression 
  in 
  the 
  form 
  of 
  both 
  humerus 
  and 
  femur, 
  and 
  decided 
  by 
  this 
  test, 
  the 
  genera 
  

   following 
  are 
  all 
  Chelydroid 
  Emydidae. 
  

  

  The 
  metatarsals 
  of 
  the 
  hind 
  foot 
  preserved, 
  indicate 
  a 
  broad 
  natatory 
  member 
  more 
  

   like 
  those 
  of 
  Trionyx 
  than 
  those 
  of 
  Chelydra. 
  

  

  At 
  the 
  same 
  time 
  the 
  vertebral 
  dermal 
  scutes 
  have 
  the 
  most 
  narrowed 
  form 
  character- 
  

   istic 
  of 
  various 
  genera 
  of 
  Emydidae. 
  The 
  femur 
  has 
  a 
  slender 
  curved 
  shaft 
  as 
  in 
  Chely- 
  

   dra 
  and 
  Chelys. 
  The 
  sternum 
  is 
  more 
  that 
  of 
  Chelydra 
  than 
  of 
  the 
  sea 
  turtles. 
  This 
  is 
  

   seen 
  in 
  the 
  narrowness 
  of 
  the 
  sterno-carapacial 
  bridge, 
  which 
  is 
  very 
  wide 
  in 
  Chelone, 
  

   and 
  very 
  narrow 
  in 
  Chelydra. 
  In 
  the 
  cretaceous 
  genera, 
  the 
  width 
  is 
  intermediate, 
  and 
  

   the 
  hyo 
  and 
  hyposternal 
  bones 
  are 
  united 
  medially, 
  and 
  are 
  not 
  merely 
  prolonged 
  ante- 
  

   riorly 
  and 
  posteriorly 
  as 
  in 
  Chelone. 
  The 
  lateral 
  sternal 
  regions 
  were 
  therefore 
  less 
  pro- 
  

   tected 
  than 
  in 
  the 
  sea 
  turtles, 
  while 
  the 
  general 
  small 
  size 
  and 
  form 
  of 
  the 
  sternal 
  bones 
  

   also 
  point 
  to 
  the 
  cross-shaped 
  plastron 
  of 
  Chelydra. 
  

  

  It 
  does 
  not 
  offer 
  any 
  approach 
  to 
  the 
  Pleurodira, 
  since 
  the 
  xiphisternum 
  is 
  free 
  from 
  

   the 
  pelvis. 
  The 
  cranium 
  of 
  the 
  genus 
  Euclastes, 
  which 
  belongs 
  here, 
  shows 
  the 
  techni- 
  

   cal 
  details 
  of 
  the 
  Cheloniidae, 
  with 
  the 
  form 
  of 
  head, 
  physiognomy, 
  and 
  no 
  doubt, 
  the 
  

   carnivorous 
  adaptations 
  of 
  Chelydra. 
  In 
  the 
  genus 
  Osteopygis, 
  also 
  of 
  the 
  cretaceous, 
  

   the 
  characters 
  diverge 
  still 
  more 
  from 
  those 
  of 
  the 
  modern 
  sea 
  turtles. 
  Here 
  five 
  margi- 
  

   nals 
  in 
  front 
  and 
  three 
  behind, 
  are 
  united 
  with 
  the 
  disc. 
  The 
  anterior 
  marginal 
  scutum 
  

   becomes 
  united 
  with 
  the 
  first 
  vertebral. 
  In 
  other 
  respects 
  the 
  characters 
  are 
  those 
  of 
  

   Propleura. 
  In 
  Lytoloma 
  the 
  marginals 
  are 
  free 
  as 
  in 
  Chelone. 
  

  

  Several 
  genera 
  have 
  been 
  discovered 
  in 
  the 
  lithographic 
  slates 
  and 
  other 
  strata 
  of 
  the 
  

   Jurassic 
  period 
  in 
  Germany, 
  Switzerland 
  and 
  France. 
  These 
  have 
  been 
  described 
  by 
  

   Minister, 
  Wagner,* 
  and 
  Von 
  Meyer."f* 
  Some 
  of 
  these 
  are 
  allied 
  to 
  Chelone, 
  but 
  the 
  

   majority 
  of 
  them 
  appear 
  to 
  me 
  to 
  have 
  a 
  near 
  relationship 
  to 
  Chelydra, 
  and 
  to 
  those 
  

   herein 
  described. 
  This 
  has 
  been 
  scarcely 
  alluded 
  to 
  by 
  the 
  learned 
  authors 
  quoted, 
  and 
  

   in 
  general 
  their 
  affinities 
  to 
  existing 
  forms 
  have 
  been 
  but 
  obscurely 
  indicated. 
  Those 
  

   which 
  I 
  would 
  refer 
  to 
  this 
  neighborhood 
  are: 
  

  

  EURYSTERNUM 
  Miinst. 
  

  

  E. 
  wagleri 
  Miinst. 
  

  

  E. 
  crassipes 
  Wagn. 
  (Palaeomedusa 
  

  

  Mey.) 
  

   E. 
  redtenbacheri 
  (Aciclielys 
  Mey.) 
  

  

  Idiochelys 
  Mey. 
  

  

  I. 
  fitzingeri 
  Mey. 
  

   I. 
  wagneri 
  Mey. 
  

   Hydropelta 
  Mey. 
  

  

  H. 
  meyeri 
  Thioll. 
  

  

  Platychelys 
  Wagn. 
  

  

  P. 
  oberndorferi 
  Wagn. 
  

  

  * 
  Abhandl. 
  d. 
  m. 
  ph. 
  cl. 
  K. 
  Bayerisch 
  Acad. 
  Wiss. 
  IX. 
  f 
  Reptilien 
  o. 
  d. 
  Lithograph. 
  Schiefer. 
  

  

  