﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  137 
  

  

  The 
  third 
  and 
  fourth 
  marginal 
  bones, 
  while 
  of 
  the 
  same 
  length 
  as 
  those 
  of 
  0. 
  emarginatus, 
  are 
  half 
  as 
  wide 
  

   again, 
  a 
  form 
  produced 
  by 
  the 
  projection 
  inwards 
  of 
  the 
  lower 
  face. 
  The 
  fifth 
  presents 
  the 
  same 
  peculiarity 
  in 
  a 
  

   more 
  marked 
  degree, 
  and 
  has 
  a 
  thicker 
  outer 
  margin 
  or 
  is 
  more 
  rounded 
  from 
  below. 
  The 
  fossa 
  for 
  the 
  rib 
  is 
  less 
  

   than 
  .2 
  the 
  length 
  of 
  the 
  bone, 
  while 
  the 
  same 
  in 
  0. 
  emarginatus 
  is 
  .33 
  the 
  length. 
  The 
  seventh 
  marginal 
  has 
  the 
  

   prominent 
  inner 
  lower 
  edge, 
  but 
  is 
  more 
  elevated 
  than 
  the 
  same 
  in 
  the 
  species 
  last 
  described. 
  Its 
  superior 
  surface 
  

   is 
  therefore 
  considerably 
  more 
  concave. 
  The 
  most 
  posterior 
  marginals, 
  as 
  characteristic 
  of 
  the 
  genus, 
  are 
  prolonged 
  

   considerably 
  within 
  the 
  inner 
  suture 
  of 
  the 
  marginal 
  scuta. 
  They 
  are 
  quite 
  flat, 
  plane 
  above, 
  and 
  with 
  a 
  rounded 
  

   concavity 
  beneath 
  within 
  the 
  margin; 
  the 
  rib 
  pit 
  is 
  flattened 
  in 
  these. 
  The 
  dermal 
  suture 
  crosses 
  the 
  marginal 
  bones 
  

   in 
  all 
  the 
  marginals 
  from 
  the 
  fifth 
  backwards 
  inclusive 
  just 
  in 
  front 
  of 
  the 
  costal 
  pit. 
  A 
  hyosternal, 
  a 
  hyposternal, 
  

   and 
  two 
  xiphisternal 
  bones 
  are 
  all 
  that 
  remain 
  of 
  the 
  sternum. 
  They 
  are 
  of 
  much 
  the 
  same 
  form 
  as 
  those 
  of 
  0. 
  

   emarginatus. 
  The 
  hyposternal 
  has 
  the 
  external 
  groove 
  posteriorly 
  to 
  receive 
  the 
  xiphisternal, 
  while 
  the 
  episternals 
  

   have 
  a 
  groove 
  internally 
  to 
  receive 
  the 
  hyosternals. 
  The 
  xiphisternals 
  are 
  toothed 
  on 
  their 
  inner 
  margin 
  for 
  common 
  

   suture 
  which 
  is 
  not 
  so 
  long 
  as 
  in 
  O. 
  emarginatus. 
  The 
  xiphisternals 
  have 
  evidently 
  been 
  shorter 
  and 
  more 
  broadly 
  

   rounded 
  behind 
  than 
  in 
  that 
  species. 
  They 
  have 
  not 
  the 
  same 
  thin 
  acute 
  external 
  margin 
  proximally 
  nor 
  strong 
  

   intermarginal 
  thickening 
  distally 
  seen 
  in 
  the 
  same, 
  but 
  are 
  of 
  more 
  uniform 
  proportions. 
  The 
  hyosternal 
  preserved 
  

   is 
  the 
  distal 
  portion, 
  while 
  that 
  of 
  0. 
  emarginatus 
  is 
  chiefly 
  proximal. 
  It 
  is 
  however 
  obviously 
  a 
  thinner 
  plate 
  than 
  in 
  

   the 
  latter, 
  and 
  more 
  as 
  in 
  Propleura 
  sopita. 
  The 
  anterior 
  margin 
  preserved 
  is 
  that 
  between 
  the 
  episternal 
  and 
  

   axillary 
  portions; 
  it 
  is 
  regularly 
  thinned 
  out; 
  the 
  distal 
  part 
  of 
  the 
  bone 
  is 
  flat, 
  and 
  the 
  median 
  suture 
  toothed. 
  A 
  

   short 
  free 
  margin 
  indicates 
  a 
  mesosternal 
  fontanelle. 
  Median 
  and 
  posterior 
  fontanelles 
  also 
  present. 
  

  

  Measurements. 
  

   Length 
  second 
  marginal, 
  

   Width 
  " 
  " 
  (external) 
  

  

  Length 
  fifth 
  " 
  

  

  Width 
  " 
  " 
  (below) 
  

  

  Length 
  seventh 
  " 
  

   Width 
  " 
  " 
  (below) 
  

  

  Length 
  tenth 
  " 
  

  

  Width 
  " 
  " 
  (external) 
  

  

  Length 
  of 
  a 
  vertebral 
  bone, 
  

   Width 
  " 
  " 
  " 
  

  

  From 
  end 
  of 
  xiphisternal 
  notch 
  to 
  anterior 
  margin 
  of 
  hyposternal, 
  

   Greatest 
  width 
  episternal, 
  

  

  Portions 
  of 
  another 
  individual 
  from 
  Barnesboro, 
  confirm 
  the 
  characters 
  already 
  given, 
  and 
  indicate 
  the 
  largest 
  

   of 
  the 
  group 
  known 
  by 
  the 
  shell 
  alone. 
  

  

  The 
  remains 
  are 
  the 
  first 
  and 
  eleventh 
  marginal 
  bones 
  of 
  the 
  right 
  side, 
  and 
  the 
  fifth 
  of 
  the 
  left, 
  with 
  the 
  nuchal 
  

   and 
  numerous 
  costals, 
  including 
  the 
  humeral 
  or 
  first 
  costal. 
  Also 
  several 
  vertebral 
  bones, 
  with 
  parts 
  of 
  the 
  sternum, 
  

   the 
  scapula, 
  coracoid, 
  femora, 
  etc. 
  

  

  The 
  marginals 
  exhibit 
  the 
  characters 
  of 
  the 
  genus, 
  the 
  eleventh 
  particularly, 
  which 
  is 
  wanting 
  in 
  the 
  first 
  

   specimen, 
  exhibiting 
  a 
  suture 
  for 
  union 
  with 
  pygal 
  bone. 
  It 
  is 
  therefore 
  produced 
  much 
  beyond 
  the 
  suture 
  of 
  the 
  

   marginal 
  scuta, 
  a 
  peculiarity 
  not 
  existing 
  in 
  any 
  species 
  of 
  Propleura. 
  The 
  same 
  bone 
  is 
  relatively 
  considerably 
  

   stouter 
  than 
  in 
  P. 
  sopita. 
  The 
  first 
  marginal 
  is 
  deeper 
  and 
  shorter 
  than 
  in 
  the 
  same, 
  and 
  the 
  fifth 
  differs 
  in 
  the 
  same 
  

   way, 
  and 
  is 
  much 
  wider 
  as 
  well. 
  The 
  nuchal 
  is 
  concave 
  and 
  arched 
  medially, 
  and 
  bears 
  a 
  well 
  marked 
  marginal 
  

   scutum. 
  The 
  adjacent 
  scutum 
  on 
  each 
  side 
  is 
  relatively 
  shorter 
  than 
  any 
  of 
  the 
  others, 
  and 
  has 
  an 
  oblique 
  inner 
  

   suture. 
  

  

  The 
  vertebral 
  bones 
  are 
  narrower 
  than 
  in 
  the 
  O. 
  platylomus 
  and 
  are 
  elongate 
  oval 
  in 
  outline 
  behind. 
  Tliey 
  

   present 
  superiorly 
  a 
  shallow 
  longitudinal 
  groove 
  interrupted 
  at 
  the 
  middle 
  of 
  the 
  length. 
  

  

  The 
  scapula 
  presents 
  a 
  short 
  coracoid 
  articular 
  surface. 
  The 
  procoracoid 
  is 
  flattened 
  in 
  the 
  plane 
  of 
  the 
  scapula. 
  

   AMERT. 
  nilLOSO. 
  SOC. 
  VOL. 
  XIV. 
  35 
  

  

  In. 
  

  

  Lin. 
  

  

  3 
  

  

  0.75 
  

  

  2 
  

  

  4. 
  

  

  2 
  

  

  11. 
  

  

  2 
  

  

  

  3 
  

  

  2. 
  

  

  2 
  

  

  8. 
  

  

  3 
  

  

  3. 
  

  

  3 
  

  

  10.5 
  

  

  2 
  

  

  5. 
  

  

  1 
  

  

  9.5 
  

  

  2 
  

  

  C. 
  

  

  2 
  

  

  4.5 
  

  

  