﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  

  

  155 
  

  

  the 
  free 
  rib 
  of 
  the 
  corresponding 
  costal 
  bone 
  is 
  directed 
  obliquely 
  backwards 
  to 
  the 
  posterior 
  part 
  of 
  the 
  marginal 
  

   and 
  somewhat 
  in 
  the 
  line 
  of 
  the 
  outer 
  extremity 
  of 
  the 
  costal, 
  instead 
  of 
  parallel 
  to 
  its 
  lateral 
  sutures, 
  as 
  in 
  the 
  

   others, 
  which 
  brings 
  the 
  rib 
  to 
  the 
  middle 
  of 
  the 
  marginal 
  bone. 
  That 
  this 
  is 
  the 
  case, 
  is 
  proven 
  by 
  the 
  extremity 
  

   of 
  the 
  corresponding 
  costal 
  bone. 
  The 
  direction 
  or 
  the 
  free 
  portion 
  of 
  the 
  rib, 
  instead 
  of 
  being 
  parallel 
  to 
  the 
  

   inter-costal 
  suture, 
  makes 
  with 
  it 
  an 
  angle 
  of 
  about 
  35°. 
  This 
  is 
  a 
  marked 
  character, 
  and 
  not 
  present, 
  so 
  far 
  as 
  I 
  

   am 
  aware, 
  in 
  any 
  of 
  the 
  recent 
  species. 
  

  

  A 
  more 
  median 
  marginal 
  is 
  thick, 
  and 
  quite 
  trigonal 
  in 
  section, 
  and 
  narrower 
  than 
  in 
  the 
  Propleuras: 
  widtli 
  

   below, 
  28.5 
  lines; 
  depth 
  of 
  inner 
  (concave) 
  face, 
  21.5 
  lines; 
  the 
  measurements 
  are 
  approximate, 
  as 
  the 
  margins 
  are 
  

   worn. 
  The 
  margin 
  has 
  a 
  strong 
  emargination 
  near 
  the 
  middle. 
  Two 
  more 
  posterior 
  marginals 
  exhibit 
  a 
  pro- 
  

   nounced, 
  but 
  more 
  open 
  notch. 
  Length 
  of 
  one 
  of 
  these 
  3 
  inches, 
  10.5 
  lines 
  (median); 
  width 
  at 
  notch, 
  30 
  lines; 
  

   greatest 
  width, 
  34 
  lines; 
  depth, 
  12 
  lines. 
  Inferior 
  face 
  transversely 
  convex, 
  margin 
  not 
  revolute. 
  In 
  all, 
  the 
  dermal 
  

   intermarginal 
  suture 
  is 
  distinct, 
  crossing 
  a 
  little 
  behind 
  the 
  middle. 
  

  

  The 
  portion 
  of 
  hyosternal 
  is 
  that 
  of 
  a 
  Chelone, 
  and 
  not 
  Chelydriform. 
  

  

  Another 
  species 
  probably 
  occurs 
  in 
  the 
  same 
  bed, 
  but 
  being 
  indicated 
  by 
  the 
  marginal 
  of 
  the 
  young, 
  it 
  is 
  not 
  

   ready 
  for 
  description. 
  

  

  CHELOXE 
  PAHVITECTA, 
  Cope. 
  

  

  Chelone 
  Cope, 
  Sp. 
  Proceed. 
  Acad. 
  Nat. 
  Sci., 
  Phila., 
  18G7, 
  143. 
  

  

  This 
  species 
  is 
  indicated 
  by 
  a 
  costal 
  bone 
  from 
  Squan- 
  

   kum, 
  N. 
  J., 
  and 
  by 
  a 
  part 
  of 
  another 
  from 
  Charles 
  County, 
  

   Maryland. 
  It 
  is 
  characterized 
  by 
  its 
  lightness, 
  and 
  by 
  the 
  

   breadth 
  of 
  the 
  dorsal 
  dermal 
  scutum, 
  as 
  compared 
  with 
  the 
  

   length 
  of 
  the 
  bone, 
  which 
  indicates 
  an 
  abbreviation 
  of 
  the 
  

   latter, 
  and 
  relatively 
  small 
  size 
  of 
  the 
  carapace. 
  The 
  char- 
  

   acter 
  of 
  the 
  broad 
  scute 
  and 
  short 
  costa 
  is 
  one 
  of 
  immatu- 
  

   rity; 
  but 
  the 
  margins 
  of 
  the 
  former 
  are 
  curved, 
  indicating 
  

   length, 
  and 
  an 
  adult 
  outline; 
  and 
  the 
  surface 
  of 
  the 
  bone 
  

   has 
  a 
  peculiar 
  sculpture, 
  not 
  found 
  in 
  the 
  C. 
  grandaeva 
  

   Leidy, 
  the 
  other 
  species 
  from 
  the 
  same 
  beds. 
  The 
  latter 
  is 
  

   larger, 
  and 
  with 
  smooth 
  costal 
  bones 
  of 
  regular 
  thickness 
  

   in 
  specimens 
  of 
  the 
  same 
  size 
  as 
  the 
  present. 
  

  

  The 
  costal 
  of 
  C. 
  parvitecta 
  is 
  light. 
  Its 
  surface 
  is 
  

   marked 
  by 
  longitudinal 
  impressed 
  grooves, 
  which 
  are 
  more 
  

   or 
  less 
  confluent; 
  the 
  surface 
  is 
  thus 
  more 
  or 
  less 
  tubercular. 
  

   On 
  one 
  of 
  the 
  sutures 
  the 
  grooves 
  run 
  transversely 
  to 
  the 
  

   bone 
  for 
  about 
  half 
  its 
  length. 
  "Within 
  the 
  suture 
  of 
  the 
  

   vertebral 
  scutum 
  the 
  surface 
  is 
  strongly 
  punctate; 
  exter- 
  

   nal 
  angle 
  of 
  vertebral 
  scutum 
  less 
  than 
  right; 
  sutures 
  well 
  

   marked. 
  

  

  Fig. 
  42. 
  

  

  CHELONE 
  MIDAS 
  LINN. 
  

  

  Length 
  costal 
  bone 
  without 
  rib, 
  

  

  " 
  " 
  to 
  angle 
  vertebral 
  suture, 
  

  

  Median 
  width 
  costal 
  bone, 
  

   Thickness 
  " 
  at 
  rib, 
  

  

  " 
  " 
  at 
  margin, 
  

  

  In. 
  

  

  Lin. 
  

  

  5 
  

  

  

  1 
  

  

  10.5 
  

  

  1 
  

  

  9. 
  

  

  

  4.2 
  

  

  

  2.5 
  

  

  Position 
  — 
  Probably 
  the 
  Miocene. 
  The 
  rib 
  above 
  described 
  is 
  in 
  the 
  collection 
  of 
  O. 
  

  

  