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  THE 
  EXTINCT 
  BATRACHIA, 
  REPTILIA 
  

  

  has 
  not 
  attained 
  such 
  huge 
  dimensions 
  as 
  some 
  of 
  the 
  latter. 
  These 
  fragments 
  do 
  not 
  

   throw 
  much 
  light 
  on 
  the 
  structure 
  of 
  the 
  pelvic 
  arch. 
  *- 
  

  

  The 
  structure 
  of 
  the 
  bones 
  is, 
  like 
  that 
  in 
  the 
  order 
  generally, 
  of 
  the 
  coarsest 
  descrip- 
  

   tion. 
  There 
  are 
  no 
  medullary 
  cavities, 
  but 
  the 
  medullary 
  cells 
  are 
  large, 
  and 
  extended 
  

   everywhere 
  in 
  the 
  direction 
  of 
  the 
  axis 
  of 
  each 
  bone. 
  

  

  The 
  characters 
  which 
  separate 
  this 
  genus 
  from 
  Plesiosaurus 
  may 
  be 
  derived 
  from 
  the 
  

   preceding 
  as 
  follows 
  : 
  

  

  First 
  ; 
  the 
  deeply 
  biconcave, 
  and 
  very 
  short 
  vertebral 
  centra. 
  

  

  Second 
  ; 
  the 
  tibia 
  broader 
  than 
  long, 
  resembling 
  those 
  of 
  Ichthyosaurus. 
  

  

  Third; 
  the 
  coalescence 
  and 
  depression 
  of 
  some 
  of 
  the 
  cervicals. 
  

  

  Fourth 
  ; 
  the 
  continuity 
  of 
  the 
  neural 
  arches. 
  

  

  Fifth 
  ; 
  the 
  continuity 
  of 
  the 
  diapophyses 
  of 
  the 
  caudals. 
  

  

  The 
  only 
  genus 
  with 
  which 
  this 
  genus 
  compares 
  nearly, 
  is 
  the 
  Thaumatosaurus 
  of 
  

   Meyer. 
  This 
  is 
  known 
  but 
  by 
  a 
  few 
  fragments, 
  and 
  of 
  these, 
  but 
  few 
  are 
  present 
  in 
  the 
  

   Kansas 
  animal. 
  The 
  character 
  on 
  which 
  I 
  rely 
  at 
  present 
  to 
  distinguish 
  them, 
  is 
  the 
  

   much 
  less 
  concavity 
  of 
  the 
  dorsal 
  vertebra? 
  in 
  Thaumatosaurus. 
  This 
  is 
  however, 
  not 
  

   entirely 
  satisfactory. 
  Thaumatosaurus 
  oolithicus 
  Meyer 
  is 
  from 
  the 
  lower 
  oolite 
  of 
  South 
  

   Germany. 
  

  

  The 
  bones 
  are 
  thoroughly 
  mineralized, 
  and 
  the 
  adherent 
  matrix 
  is 
  a 
  light 
  yellow 
  

   chalky 
  limestone, 
  similar 
  to 
  that 
  which 
  yielded 
  the 
  fine 
  fragments 
  of 
  the 
  Macrosaurus 
  

   proriger. 
  This, 
  Dr. 
  Leconte 
  informs 
  me, 
  is 
  probably 
  Meek 
  and 
  Hayden's 
  upper 
  Cretaceous 
  

   No. 
  3, 
  and 
  is 
  a 
  higher 
  horizon 
  than 
  that 
  near 
  Fort 
  Wallace 
  from 
  which 
  Dr. 
  Turner 
  

   procured 
  the 
  Elasmosaurus 
  platyurus. 
  The 
  specimens 
  were 
  all 
  taken 
  out 
  under 
  the 
  

   direction 
  of 
  W. 
  E. 
  Webb, 
  of 
  Topeka, 
  from 
  the 
  same 
  spot 
  ; 
  from 
  every 
  point 
  of 
  view 
  there 
  

   is 
  reason 
  to 
  believe 
  that 
  they 
  belong 
  to 
  the 
  same 
  animal. 
  

  

  V 
  

  

  POLYCOTYLUS 
  LATIPINNIS, 
  Cope. 
  

  

  The 
  anterior 
  dorsal 
  vertebrae 
  have 
  the 
  centra 
  slightly 
  compressed 
  or 
  vertically 
  oval, 
  while 
  the 
  posterior 
  are 
  more 
  

   rounded. 
  The 
  anterior 
  caudals 
  appear 
  to 
  have 
  been 
  round 
  or 
  nearly 
  so; 
  they 
  are 
  somewhat 
  distorted 
  by 
  pressure. 
  

   The 
  sides 
  of 
  the 
  centrum 
  are 
  slighly 
  concave 
  in 
  the 
  longitudinal 
  direction; 
  below, 
  there 
  is 
  no 
  carina, 
  but 
  at 
  least 
  two 
  

   venous 
  foramina. 
  There 
  is 
  another 
  large 
  foramen 
  on 
  the 
  side 
  of 
  the 
  centrum, 
  usually 
  not 
  far 
  from 
  the 
  neural 
  arch 
  ; 
  

   there 
  are 
  usually 
  other 
  smaller 
  foramina 
  below 
  this. 
  The 
  bases 
  of 
  the 
  diapophyses 
  are 
  longitudinally 
  grooved 
  

   behind, 
  and 
  separate 
  a 
  concavity 
  of 
  the 
  arch 
  in 
  front 
  of 
  them 
  from 
  one 
  behind. 
  In 
  the 
  must 
  median, 
  the 
  most 
  

   elevated 
  diapophysis 
  stands 
  about 
  equally 
  on 
  the 
  neurapophysis 
  and 
  the 
  neural 
  spine 
  above 
  it. 
  The 
  diapophysis 
  

   are 
  vertically 
  compressed, 
  and 
  the 
  costal 
  articulation 
  of 
  the 
  only 
  one 
  preserved, 
  is 
  in 
  the 
  same 
  plane. 
  The 
  margins 
  

   of 
  the 
  external 
  surfaces 
  are 
  not 
  coarsely 
  striate 
  as 
  in 
  many 
  Sauropterygia. 
  The 
  venous 
  foramina 
  of 
  the 
  distal 
  

   coi'issified 
  cervicals 
  are 
  in 
  pairs, 
  and 
  of 
  a 
  large 
  size. 
  In 
  the 
  proximal 
  caudals 
  the 
  diapophyses 
  are 
  above 
  the 
  middle 
  of 
  

   the 
  sides 
  of 
  the 
  centra. 
  In 
  one 
  the 
  basis 
  of 
  a 
  chevron 
  is 
  preserved. 
  It 
  is 
  cylindric 
  and 
  striate. 
  The 
  zygapophysis 
  

  

  