﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  135 
  

  

  I. 
  The 
  margins 
  of 
  the 
  posterior 
  marginal 
  plates 
  continuous, 
  cither 
  notched 
  or 
  even 
  

   medially. 
  

  

  a 
  The 
  rib-fossae 
  of 
  the 
  marginals 
  flat 
  ; 
  \ 
  no 
  nuchal 
  scute. 
  

  

  Upper 
  margin 
  of 
  inner 
  face 
  of 
  (7th 
  and 
  8th) 
  posterior 
  marginals 
  much 
  produced; 
  

   lower 
  margin 
  not 
  prolonged. 
  Lower 
  margin 
  of 
  5th 
  and 
  6th 
  marginals 
  not 
  projecting, 
  

   their 
  inner 
  face 
  vertical. 
  Outer 
  face 
  of 
  narrow 
  marginals 
  convex 
  or 
  little 
  concave, 
  their 
  

   scuta 
  l.§ 
  long 
  as 
  wide. 
  Eighth 
  marginal 
  g 
  wide 
  as 
  long. 
  platylomus. 
  

  

  aa 
  The 
  rib-fossae 
  of 
  the 
  lateral 
  marginals 
  cylindric 
  ; 
  a 
  nuchal 
  scute. 
  

  

  Upper 
  and 
  lower 
  margins 
  7th 
  marginal 
  both 
  prolonged 
  ; 
  lower 
  margin 
  5th 
  very 
  much 
  

   produced 
  inwards 
  giving 
  a 
  horizontal 
  inner, 
  as 
  well 
  as 
  outer 
  face 
  ; 
  outer 
  face 
  of 
  narrow 
  

   marginals 
  concave 
  except 
  the 
  anterior; 
  scuta 
  of 
  latter 
  \\ 
  long 
  as 
  wide; 
  9th 
  marginal 
  7 
  6 
  ° 
  

   wide 
  as 
  long; 
  5th 
  marginal 
  nearly 
  .75 
  wide 
  as 
  long. 
  emarginatus. 
  

  

  II. 
  Margins 
  of 
  the 
  posterior 
  marginal 
  plates 
  acuminate 
  medially. 
  

  

  Posterior 
  lateral 
  bones 
  short, 
  wide, 
  width 
  greater 
  and 
  length, 
  pit 
  round, 
  margin 
  

   strongly 
  repand; 
  anterior 
  laterals 
  less 
  confluent 
  with 
  disc, 
  strongly 
  concave 
  on 
  outer 
  face. 
  

  

  CHELYDRLNUS. 
  

   OSTEOPYGIS 
  PLATYLOMUS, 
  Cope 
  Sp. 
  Nov. 
  

  

  This 
  species 
  is 
  represented 
  by 
  portions 
  of 
  two 
  individuals, 
  first 
  perhaps 
  half 
  the 
  carapace 
  and 
  plastron 
  with 
  all 
  

   the 
  marginal 
  bones 
  of 
  one 
  side, 
  and 
  many 
  of 
  those 
  of 
  the 
  other, 
  of 
  a 
  large 
  individual 
  from 
  the 
  Pemberton 
  Marl 
  Com- 
  

   pany's 
  Pits, 
  Burlington 
  Co., 
  N. 
  Jersey, 
  presented 
  to 
  the 
  Academy 
  by 
  Dr. 
  Samuel 
  Ashhurst; 
  the 
  second, 
  a 
  few 
  por- 
  

   tions 
  from 
  the 
  pits 
  of 
  David 
  Haines, 
  near 
  Medford, 
  Camden 
  Co., 
  N. 
  J. 
  

  

  The 
  carapace 
  is 
  fiat, 
  as 
  indicated 
  by 
  the 
  slight 
  curvature 
  of 
  numerous 
  costal 
  bones, 
  and 
  without 
  keels, 
  as 
  indi- 
  

   cated 
  by 
  an 
  anterior 
  and 
  two 
  posterior 
  vertebral 
  bones. 
  The 
  posterior 
  and 
  adjacent 
  margin 
  is 
  flat 
  and 
  wide, 
  extend- 
  

   ing 
  to 
  a 
  thin 
  edge. 
  The 
  anterior 
  vertebral, 
  has 
  the 
  anterior 
  margin 
  entirely 
  forming 
  a 
  deep 
  notch, 
  extending 
  to 
  

   nearly 
  opposite 
  the 
  lateral 
  angles 
  of 
  the 
  bone 
  a 
  feature 
  not 
  seen 
  in 
  the 
  genus 
  Chelone. 
  It 
  is 
  crossed 
  not 
  far 
  from 
  

   its 
  middle 
  (it 
  is 
  broken 
  behind) 
  by 
  the 
  dermal 
  suture. 
  The 
  posterior 
  vertebral 
  is 
  transverse, 
  occupies 
  a 
  concavity 
  

   formed 
  by 
  the 
  three 
  posterior 
  marginals, 
  extending 
  to 
  beyond 
  the 
  middle 
  of 
  the 
  penultimates 
  on 
  each 
  side. 
  The 
  

   posterior 
  vertebral 
  dermal 
  scute 
  is 
  of 
  great 
  width, 
  its 
  outer 
  suture 
  not 
  reaching 
  the 
  marginals 
  on 
  any 
  of 
  the 
  bones 
  

   just 
  mentioned. 
  The 
  anterior 
  vertebral 
  scuta 
  as 
  seen 
  on 
  numerous 
  costal 
  bones, 
  were 
  of 
  peculiar 
  form. 
  Their 
  

   borders 
  diverged 
  very 
  little 
  at 
  their 
  anterior 
  and 
  posterior 
  portions, 
  but 
  curved 
  outwards 
  abruptly 
  to 
  meet 
  the 
  costal 
  

   dermal 
  suture, 
  forming 
  an 
  acute 
  angle. 
  

  

  Marginal 
  bones 
  heavy 
  at 
  the 
  sides 
  and 
  in 
  front, 
  the 
  former 
  concave 
  on 
  the 
  upper 
  face, 
  the 
  lower 
  face 
  plane 
  but 
  

   upturned 
  at 
  the 
  edge. 
  Front 
  laterals 
  convex 
  below 
  with 
  broad 
  rounded 
  margin; 
  none 
  of 
  these 
  projecting 
  above 
  the 
  

   marginal 
  dermal 
  suture 
  except 
  to 
  foim 
  suture 
  with 
  costal 
  plate 
  as 
  in 
  C. 
  repanda. 
  This 
  suture 
  first 
  appears 
  on 
  the 
  

   middle 
  of 
  the 
  tenth 
  marginal 
  bone 
  counting 
  the 
  lateral 
  caudal 
  as 
  first 
  : 
  marginal 
  bones 
  eleven 
  on 
  each 
  side, 
  all 
  with 
  

   equal 
  lengths, 
  as 
  in 
  Cheloniidae. 
  

  

  The 
  rib 
  pits 
  are 
  fiat, 
  very 
  much 
  so 
  medially, 
  the 
  anterior 
  one 
  more 
  nearly 
  cylindric. 
  

  

  The 
  width 
  of 
  the 
  marginal 
  scute 
  on 
  the 
  ninth 
  and 
  tenth 
  marginal 
  bones, 
  is 
  1.G6 
  its 
  length, 
  measuring 
  from 
  the 
  

   obtuse 
  margin. 
  The 
  width 
  of 
  the 
  first 
  (posterior) 
  scute 
  is 
  nearly 
  equal 
  to 
  its 
  length. 
  

  

  The 
  surface 
  of 
  the 
  bone 
  generally 
  is 
  marked 
  by 
  small 
  irregular 
  straight 
  grooves. 
  

  

  Portions 
  of 
  the 
  sternum 
  are 
  parts 
  of 
  two 
  hypo, 
  a 
  hyo-, 
  and 
  xiphisternal. 
  The 
  hyposternal 
  of 
  the 
  left 
  side 
  lias 
  a 
  

  

  