﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  35 
  

  

  The 
  caudal 
  vertebrae 
  are 
  anteriorly 
  quite 
  as 
  large 
  as 
  the 
  dorsals. 
  Two 
  anterior 
  caudals 
  

   present 
  on 
  the 
  latero-inferior 
  part 
  of 
  the 
  posterior 
  margin, 
  a 
  pair 
  of 
  widely 
  separated 
  artic- 
  

   ular 
  surfaces 
  for 
  chevron 
  bones. 
  A 
  portion 
  of 
  one 
  of 
  the 
  latter 
  remains 
  ; 
  it 
  is 
  narrow 
  and 
  

   sub-cylindric 
  at 
  the 
  base. 
  The 
  diapophyses 
  are 
  situated 
  on 
  the 
  upper 
  part 
  of 
  the 
  centrum, 
  

   and 
  are 
  continuous 
  with 
  it, 
  and 
  without 
  trace 
  of 
  suture. 
  There 
  are 
  two 
  distal 
  cervicals, 
  

   which 
  are 
  much 
  smaller 
  than 
  the 
  preceding. 
  They 
  are 
  solidly 
  co 
  ossified 
  and 
  have 
  been 
  

   broken 
  from 
  one 
  anterior 
  to 
  them, 
  with 
  which 
  they 
  have 
  been 
  also 
  anchylosed. 
  Processes 
  

   in 
  the 
  position 
  of 
  diapophyses 
  have 
  disappeared, 
  while 
  a 
  strong 
  infero-lateral 
  process 
  

   projects 
  from 
  the 
  middle 
  of 
  each, 
  similar 
  in 
  position 
  to 
  the 
  parapophyses 
  (or 
  whatever 
  

   they 
  may 
  be) 
  of 
  the 
  Elasmosaurus. 
  These 
  processes 
  are 
  decurved 
  and 
  much 
  thickened 
  

   and 
  rugose 
  ; 
  they 
  may 
  be 
  described 
  as 
  more 
  or 
  less 
  elongate 
  conic. 
  The 
  neural 
  canal 
  of 
  

   these 
  vertebra? 
  is 
  well 
  marked, 
  though 
  small. 
  The 
  coossification 
  of 
  cervical 
  vertebrae 
  is 
  a 
  

   remarkable 
  character, 
  and 
  very 
  unusual. 
  It 
  does 
  not 
  seem 
  probable 
  that 
  these 
  specimens 
  

   represent 
  a 
  diseased 
  condition, 
  since 
  they 
  are 
  symmetrical, 
  and 
  the 
  inferior 
  surface 
  and 
  for- 
  

   amina 
  are 
  unaffected. 
  The 
  rugosity 
  is 
  much 
  that 
  of 
  a 
  ligamentous 
  articulation. 
  Their 
  

   size 
  indicates 
  a 
  remarkably 
  slender 
  neck 
  as 
  in 
  Plesiosaurus, 
  but 
  even 
  more 
  so, 
  and 
  perhaps 
  

   as 
  elongate 
  as 
  in 
  Elasmosaurus. 
  

  

  That 
  the 
  portions 
  of 
  an 
  extremity 
  alluded 
  to, 
  belong 
  to 
  the 
  posterior, 
  is 
  rendered 
  prob- 
  

   able 
  by 
  the 
  presence 
  of 
  part 
  of 
  an 
  ilium, 
  and 
  by 
  the 
  fact 
  that 
  the 
  portions 
  of 
  the 
  vertebral 
  

   column 
  secured, 
  are 
  chiefly 
  median 
  and 
  posterior. 
  The 
  fragments 
  consist 
  of 
  the 
  extremity 
  

   of 
  the 
  femur, 
  the 
  tibia, 
  several 
  tarsal 
  bones, 
  and 
  numerous 
  phalanges. 
  The 
  whole 
  limb 
  is 
  

   of 
  great 
  size 
  compared 
  with 
  that 
  of 
  the 
  vertebral 
  column, 
  and 
  indicates 
  powerful 
  natatory 
  

   capacity 
  in 
  its 
  possessor. 
  What 
  the 
  relative 
  length 
  of 
  the 
  femur 
  may 
  be, 
  cannot 
  be 
  ascer- 
  

   tained, 
  as 
  the 
  proximal 
  portion 
  is 
  wanting, 
  but 
  if 
  it 
  were 
  like 
  the 
  tibia, 
  it 
  was 
  characterized 
  

   by 
  stoutness 
  rather 
  than 
  by 
  length. 
  The 
  portion 
  remaining 
  is 
  flattened, 
  and 
  presents 
  

   distally 
  two 
  distinct 
  articular 
  faces 
  for 
  ulna 
  and 
  radius, 
  instead 
  of 
  the 
  uniformly 
  convex 
  

   outline 
  characteristic 
  of 
  most 
  of 
  the 
  species 
  of 
  Plesiosaurus. 
  The 
  tibia 
  is 
  broader 
  than 
  

   long, 
  and 
  not 
  emarginate 
  externally. 
  The 
  fibula 
  is 
  wanting. 
  One 
  of 
  the 
  tarsal 
  bones 
  is 
  a 
  

   flat 
  unequally 
  hexagonal 
  disc, 
  of 
  less 
  thickness 
  than 
  the 
  tibia 
  and 
  the 
  tarsals 
  which 
  appear 
  

   to 
  connect 
  with 
  it. 
  One 
  of 
  the 
  latter 
  is 
  transverse 
  parallelogrammic, 
  with 
  three 
  faces 
  of 
  

   broad 
  plane 
  articulations 
  and 
  the 
  outer 
  rounded 
  in 
  section. 
  Another 
  tarsal 
  or 
  metatarsal 
  

   is 
  a 
  parallelopipedon, 
  except 
  that 
  one 
  extremity 
  presents 
  two 
  faces 
  meeting 
  at 
  a 
  right 
  

   angle. 
  Another 
  is 
  similar, 
  but 
  oblique, 
  i. 
  e., 
  rhombic 
  in 
  section 
  ; 
  one 
  of 
  the 
  longitudinal 
  

   angles 
  is 
  also 
  prolonged. 
  

  

  Of 
  the 
  phalanges 
  there 
  are 
  individuals 
  from 
  three 
  series. 
  Portions 
  of 
  flat 
  bones, 
  

   perhaps, 
  belonging 
  to 
  the 
  pelvic 
  arch, 
  indicate, 
  as 
  do 
  all 
  the 
  other 
  pieces, 
  that 
  the 
  bony 
  

   structure 
  in 
  Polycotylus 
  is 
  more 
  massive 
  than 
  in 
  Elasmosaurus, 
  if 
  the 
  only 
  known 
  species 
  

  

  