﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  143 
  

  

  CATAPLEURA, 
  Cope. 
  

  

  In 
  this 
  genus, 
  as 
  in 
  the 
  two 
  preceding, 
  the 
  carapacial 
  disc 
  is 
  united 
  by 
  suture 
  to 
  two 
  

   marginal 
  bones, 
  on 
  each 
  side 
  of 
  the 
  nuchal 
  bone, 
  forming 
  a 
  solid 
  arch. 
  What 
  the 
  mode 
  

   of 
  attachment 
  between 
  the 
  two 
  may 
  be 
  posteriorly, 
  material 
  is 
  not 
  sufficient 
  to 
  deter- 
  

   mine 
  ; 
  but 
  from 
  the 
  form 
  of 
  some 
  tenth 
  and 
  ninth 
  marginals, 
  I 
  suspect 
  that 
  this 
  union 
  is 
  

   not 
  so 
  great 
  as 
  in 
  Osteopygis, 
  but 
  rather 
  as 
  in 
  Propleura, 
  by 
  the 
  caudal 
  marginal 
  only. 
  

   There 
  is 
  a 
  nuchal 
  scutum, 
  as 
  in 
  the 
  last 
  genus. 
  What 
  distinguishes 
  it 
  from 
  that 
  genus, 
  as 
  

   "well 
  as 
  from 
  Osteopygis, 
  is 
  the 
  entire 
  absence 
  of 
  the 
  rib 
  and 
  pit 
  articulation 
  between 
  the 
  

   second 
  marginal 
  and 
  the 
  corresponding 
  costal 
  bones. 
  It 
  is 
  in 
  this 
  respect 
  similar 
  to 
  C'hc- 
  

   lydra, 
  and 
  to 
  Chelone, 
  counting 
  one 
  rib 
  less 
  than 
  in 
  Propleura. 
  From 
  the 
  similarity 
  in 
  

   thickness 
  and 
  form 
  of 
  the 
  first 
  marginal, 
  I 
  suppose 
  the 
  genus 
  Lytoloma 
  to 
  have 
  been 
  simi- 
  

   lar 
  to 
  the 
  present, 
  in 
  this 
  respect, 
  and 
  a 
  supposed 
  second 
  marginal 
  confirms 
  the 
  view. 
  

  

  The 
  only 
  species 
  of 
  this 
  genus 
  yet 
  known 
  is 
  peculiar 
  in 
  the 
  form 
  of 
  the 
  nuchal 
  margi- 
  

   nal. 
  It 
  is 
  not 
  wider 
  than 
  the 
  first 
  and 
  second 
  marginals, 
  and 
  does 
  not, 
  therefore, 
  extend 
  

   over 
  the 
  front 
  of 
  the 
  carapace, 
  as 
  in 
  Osteopygis, 
  Chelydra 
  and 
  Chelone. 
  It 
  is 
  intermedi- 
  

   ate 
  in 
  extent 
  in 
  Propleura 
  sopita, 
  while 
  it 
  is 
  identical 
  in 
  form 
  in 
  the 
  Lytoloma 
  jeanesii. 
  

   The 
  natural 
  position 
  of 
  the 
  type 
  species 
  is, 
  therefore, 
  plain 
  enough. 
  In 
  the 
  present 
  genus 
  

   and 
  Propleura 
  the 
  form 
  of 
  this 
  piece 
  is 
  perhaps 
  of 
  not 
  more 
  than 
  specific 
  value. 
  

  

  I. 
  The 
  margins 
  of 
  the 
  posterior 
  marginal 
  plates 
  repand 
  or 
  concave. 
  

  

  Posterior 
  lateral 
  bones, 
  with 
  upper 
  margin 
  produced 
  within, 
  narrow 
  ; 
  width 
  6-7ths 
  

   length, 
  margin 
  openly 
  repand; 
  anterior 
  marginal 
  scuta 
  22| 
  long 
  as 
  wide, 
  many 
  of 
  these 
  

   bones 
  confluent 
  with 
  disc, 
  none 
  concave 
  on 
  outer 
  surface. 
  

  

  C. 
  REPANDA. 
  

  

  CATAPLEURA 
  REPANDA, 
  Cope. 
  

  

  Osteopygis 
  repandus, 
  Cope, 
  Proc. 
  A. 
  N. 
  Sci., 
  Pliila., 
  18G3, 
  p. 
  1-47. 
  

  

  This 
  species 
  is 
  based 
  on 
  remains 
  of 
  one 
  individual, 
  which 
  is 
  represented 
  by 
  parts 
  or 
  wholes 
  of 
  ten 
  marginal 
  and 
  

   of 
  many 
  costal 
  plates. 
  Its 
  size 
  is 
  smaller 
  than 
  the 
  preceding 
  species, 
  and 
  it 
  is 
  further 
  characterized 
  by 
  the 
  repand 
  

   outline 
  of 
  the 
  posterior 
  marginals 
  with 
  obtuse 
  points 
  at 
  the 
  dermal 
  sutures. 
  The 
  middle 
  marginals 
  are 
  concave 
  in- 
  

   stead 
  of 
  convex 
  below, 
  as 
  in 
  0. 
  emarginatus. 
  The 
  narrow 
  anterior 
  marginals 
  are 
  convex 
  on 
  the 
  outer 
  surface, 
  and 
  

   bear 
  very 
  elongate 
  scutes, 
  which 
  are 
  narrower 
  than 
  in 
  any 
  other 
  species. 
  Five 
  of 
  these 
  marginal 
  bones 
  have 
  been 
  

   united 
  above 
  by 
  suture 
  to 
  vertebral 
  or 
  costal 
  plates, 
  indicating 
  the 
  same 
  degree 
  of 
  ossification 
  as 
  in 
  0. 
  emargina- 
  

   tus. 
  The 
  dermal 
  sutures 
  are 
  less 
  marked 
  than 
  in 
  that 
  species, 
  but 
  are 
  indistinct, 
  as 
  in 
  P. 
  sopita. 
  On 
  two 
  costal 
  

   plates, 
  the 
  margins 
  of 
  these 
  are 
  distinct. 
  They 
  are 
  straight, 
  make 
  open 
  angles 
  with 
  the 
  transverse 
  grooves, 
  and 
  with 
  

   each 
  other, 
  and 
  indicate 
  scutes 
  longer 
  than 
  broad. 
  The 
  costal 
  bones 
  are 
  plane, 
  longitudinally, 
  but 
  considerably 
  dc- 
  

   curved 
  from 
  and 
  below 
  the 
  middle. 
  The 
  costal 
  ridge 
  is 
  distinct 
  throughout, 
  and 
  narrow, 
  and 
  extends 
  obliquely 
  to 
  

   the 
  posterior 
  suture, 
  and 
  then 
  projects 
  shortly 
  for 
  attachment 
  to 
  the 
  marginal 
  bone. 
  The 
  costal 
  heads 
  present 
  at 
  their 
  

   posterior 
  bases 
  an 
  acute 
  ridge, 
  which 
  diverges 
  posteriori 
  y, 
  embracing 
  a 
  strong 
  groove 
  between 
  it 
  and 
  the 
  body 
  of 
  the 
  rib: 
  

   both 
  extend 
  but 
  a 
  short 
  distance 
  posteriorly. 
  I 
  have 
  not 
  seen 
  this 
  feature 
  in 
  the 
  ribs 
  of 
  the 
  0. 
  emarginatus, 
  and 
  0- 
  

   platyloinus. 
  

  

  