﻿180 
  PROF. 
  OWEN 
  ON 
  AN 
  EXTINCT 
  CHELONIAN 
  

  

  neural 
  (s 
  2). 
  In 
  this 
  character 
  Notochelys 
  differs 
  from 
  Chelone 
  

   longiceps 
  *, 
  and 
  agrees 
  with 
  Chelone 
  breviceps 
  f 
  . 
  

  

  Only 
  the 
  mesial 
  expanded 
  portion 
  of 
  the 
  first 
  costal 
  (jpl 
  1), 
  which 
  

   articulates 
  also 
  with 
  the 
  nuchal 
  (ch) 
  and 
  second 
  costal 
  plates, 
  is 
  pre- 
  

   served 
  ; 
  its 
  fore 
  border 
  joins 
  the 
  second 
  marginal 
  plate 
  (m 
  2) 
  ; 
  the 
  lateral 
  

   anterior 
  angle 
  also 
  articulates 
  with 
  the 
  first 
  marginal 
  plate 
  (m 
  1). 
  

   Fractured 
  parts 
  of 
  the 
  narrower 
  rib-like 
  outward 
  extension 
  of 
  the 
  

   first 
  costal 
  (pi 
  1) 
  are 
  preserved, 
  indicating 
  a 
  length 
  of 
  the 
  entire 
  plate 
  

   of 
  5 
  inches. 
  The 
  breadth 
  of 
  the 
  expanded 
  portion 
  exceeds 
  that 
  of 
  

   the 
  same 
  part 
  in 
  the 
  succeeding 
  costal 
  plates. 
  

  

  The 
  second 
  neural 
  plate 
  (ib. 
  s 
  2), 
  of 
  greater 
  breadth 
  than 
  the 
  

   first, 
  has 
  the 
  anterior 
  costal 
  plate 
  (pi 
  x 
  ) 
  articulated 
  with 
  the 
  an- 
  

   terior 
  truncated 
  angle. 
  The 
  posterior 
  angles 
  of 
  the 
  second 
  neural 
  

   are 
  also 
  truncated, 
  but 
  in 
  a 
  minor 
  degree, 
  for 
  articulation 
  with 
  the 
  

   third 
  costal 
  plate 
  (pi 
  3), 
  in 
  which 
  character 
  it 
  differs 
  from 
  the 
  

   Eocene 
  Chelonians 
  figured 
  in 
  the 
  under-cited 
  work, 
  some 
  of 
  which, 
  

   e. 
  g. 
  Chelone 
  longiceps, 
  Ch. 
  subcristata, 
  Ch. 
  convexa, 
  show 
  the 
  second 
  

   vertebral 
  plate 
  (s 
  2) 
  articulating 
  with 
  the 
  second 
  costal 
  exclusively 
  ; 
  

   others 
  (e.g. 
  Chelone 
  breviceps 
  and 
  Ch. 
  subcarinata) 
  articulate, 
  as 
  in 
  

   the 
  existing 
  Chelone 
  my 
  das, 
  with 
  a 
  portion 
  of 
  the 
  second 
  costal, 
  

   but 
  not 
  with 
  any 
  part 
  of 
  the 
  third 
  costal 
  plate. 
  

  

  The 
  third 
  neural 
  plate 
  (ib. 
  s 
  3) 
  has 
  marginal 
  articulations 
  

   exclusively 
  with 
  the 
  third 
  costal 
  plate 
  (jpl 
  3), 
  and 
  neither 
  the 
  fore 
  

   nor 
  the 
  hind 
  angles 
  are 
  truncated. 
  In 
  Chelone 
  subcarinata% 
  the 
  third 
  

   neural 
  plate 
  articulates 
  with 
  both 
  the 
  second 
  and 
  third 
  costal 
  plates 
  ; 
  

   and 
  in 
  Ch. 
  breviceps, 
  in 
  a 
  larger 
  proportion 
  with 
  the 
  second 
  costal 
  — 
  the 
  

   third 
  vertebral 
  plate 
  here 
  presenting 
  a 
  hexagonal 
  figure, 
  while 
  in 
  

   the 
  present 
  species 
  it 
  is 
  a 
  parallelogram. 
  Its 
  length, 
  in 
  Notochelys, 
  is 
  

   1 
  inch 
  8 
  lines, 
  its 
  breadth 
  9 
  lines 
  ; 
  it 
  is 
  crossed 
  transversely 
  a 
  little 
  

   in 
  advance 
  of 
  its 
  mid 
  length 
  by 
  the 
  line 
  of 
  junction 
  of 
  the 
  second 
  

   to 
  the 
  third 
  vertebral 
  scutes 
  (v 
  2, 
  v 
  3). 
  

  

  The 
  fourth 
  neural 
  plate 
  (ib. 
  s 
  4), 
  with 
  a 
  broader 
  anterior 
  border 
  

   than 
  the 
  third 
  (s 
  3), 
  shows 
  the 
  anterior 
  truncated 
  angles 
  of 
  that 
  bor- 
  

   der 
  articulating 
  with 
  the 
  third 
  costal 
  plate 
  ; 
  the 
  long 
  lateral 
  borders 
  

   articulate 
  exclusively 
  with 
  the 
  fourth 
  costal 
  (pi 
  4). 
  But 
  a 
  small 
  

   portion 
  only 
  of 
  the 
  fifth 
  neural 
  plate 
  (s 
  5) 
  is 
  preserved. 
  

  

  The 
  second 
  costal 
  plate 
  (pi 
  2) 
  is 
  larger, 
  but 
  antero-posteriorly 
  

   narrower 
  than 
  the 
  first. 
  The 
  extent 
  of 
  the 
  posterior 
  suture 
  with 
  

   the 
  third 
  costal, 
  2 
  inches 
  9 
  lines, 
  gives 
  that 
  of 
  the 
  expanded 
  part 
  of 
  

   the 
  plate 
  : 
  beyond 
  the 
  suture 
  it 
  begins 
  to 
  contract 
  to 
  the 
  ordinary 
  

   rib-like 
  proportions, 
  the 
  preserved 
  extent 
  of 
  which 
  free 
  part 
  is 
  3 
  

   inches. 
  The 
  expanded 
  part 
  is 
  impressed 
  with 
  the 
  lateral 
  angle 
  of 
  

   the 
  second 
  vertebral 
  scute, 
  from 
  which 
  is 
  extended 
  the 
  impression 
  

   of 
  part 
  of 
  the 
  junction 
  of 
  the 
  first 
  costal 
  (c 
  ]), 
  with 
  the 
  second 
  

   costal 
  (c 
  2) 
  scutes. 
  

  

  The 
  third 
  costal 
  plate 
  (pi 
  3) 
  has 
  similar 
  proportions 
  of 
  the 
  ex- 
  

   panded 
  and 
  rib-like 
  parts 
  to 
  those 
  of 
  the 
  second 
  costal. 
  It 
  articulates 
  

   mesially 
  with 
  the 
  third 
  neural 
  and 
  the 
  anterior 
  angle 
  of 
  the 
  broader 
  

  

  * 
  Hist, 
  of 
  British 
  Fossil 
  Reptiles 
  (4to, 
  1849), 
  plate 
  13. 
  fig. 
  1. 
  

   t 
  Ib. 
  plate 
  10. 
  J 
  lb. 
  plate 
  10. 
  

  

  