﻿PLATE 
  XXI. 
  

  

  Paob. 
  

  

  CTEN 
  acanthi's 
  0OZAOT8, 
  St. 
  J. 
  and 
  \V 
  233 
  

  

  r 
  Fig. 
  l 
  a. 
  Bide 
  view 
  of 
  spine, 
  outline 
  restored; 
  1 
  b, 
  do., 
  showing 
  anterior 
  edge; 
  l 
  c, 
  do., 
  

   posterior 
  face, 
  the 
  wall 
  broken 
  away 
  expo- 
  ] 
  ,1. 
  Jo., 
  

  

  transverse 
  section 
  near 
  middle. 
  Keokuk; 
  M-ntrose, 
  Iowa. 
  Mr. 
  < 
  

  

  Cten 
  acanthus 
  Tellknsis 
  3S7 
  

  

  r 
  Fig. 
  2 
  a. 
  Fragment 
  of 
  spine, 
  showing 
  the 
  dorsal 
  or 
  anterior 
  edge: 
  2 
  b. 
  do., 
  side 
  view, 
  

   outline 
  partially 
  restored; 
  3 
  o, 
  do. 
  •. 
  showing 
  st- 
  

  

  erol 
  edges 
  and 
  the 
  deep 
  trough 
  of 
  the 
  pulp 
  cavity: 
  2 
  >/. 
  di>.. 
  enbr. 
  

   of 
  surface, 
  showing 
  variable 
  ehanaterof 
  BUpecflOleJ 
  • 
  rDarnontnll 
  | 
  

   do., 
  cross 
  section. 
  St. 
  Louis 
  formation; 
  Pella, 
  Iowa. 
  Mr. 
  Y.i 
  

  

  t'TKNACANTHl- 
  I 
  \ 
  N 
  Ml 
  1 
  It 
  ATI'S. 
  St. 
  J. 
  an<l 
  V? 
  33* 
  

  

  Fig. 
  3d. 
  Bide 
  view 
  of 
  fragment 
  of 
  spine; 
  8 
  6. 
  do., 
  anterior 
  or 
  dorsal 
  f,i 
  k 
  -. 
  pos- 
  

  

  terior 
  faoe; 
  8 
  d, 
  do., 
  transverse 
  aeoi 
  QL 
  Dr. 
  Ham- 
  

  

  bach. 
  

  

  A8TER01 
  ' 
  and 
  w 
  

  

  Fig. 
  < 
  a. 
  Fra+ri- 
  lew 
  of 
  left 
  side: 
  4 
  b, 
  do., 
  enlarg 
  do., 
  

  

  transverse 
  seotlon. 
  Cpper 
  i 
  n. 
  

  

  