﻿Plate 
  21 
  

  

  All 
  figures 
  natural 
  size 
  

  

  Page 
  

   ZEACRINUS 
  BURSAEFORMIS 
  White 
  79 
  

  

  Fig. 
  1. 
  Posterior 
  view 
  of 
  complete 
  crown, 
  showing 
  anal 
  area 
  with 
  

   broadly 
  truncate 
  post. 
  B, 
  short 
  RA, 
  short 
  quadrangular 
  bra- 
  

   chials 
  and 
  heterotomous 
  arms, 
  hut 
  having 
  elongate 
  instead 
  

   of 
  depressed 
  calyx, 
  and 
  turbinate 
  base 
  instead 
  of 
  concave. 
  

   Lower 
  Burlington 
  limestone 
  ; 
  Burlington, 
  Iowa. 
  

  

  ZEACRINUS 
  ELEGANS 
  Hall 
  65. 
  SO 
  

  

  Fig. 
  2. 
  Anterior 
  view 
  of 
  a 
  typical 
  specimen, 
  with 
  complete 
  crown, 
  

   showing 
  depressed 
  broadly 
  rounded 
  calyx, 
  and 
  maximum 
  

   number 
  of 
  bifurcations 
  all 
  on 
  the 
  outer 
  arm 
  of 
  the 
  ray 
  toward 
  

   the 
  inner 
  side; 
  anterior 
  ray 
  branches 
  on 
  second 
  brachial 
  above 
  

   primibrach. 
  

   2a. 
  R. 
  post, 
  view 
  of 
  same, 
  showing 
  form 
  of 
  club-shaped 
  sac 
  with 
  

   rounded 
  and 
  expanding 
  distal 
  end. 
  

  

  3. 
  Posterior 
  view 
  of 
  another 
  large 
  specimen 
  having 
  only 
  six 
  arms 
  

  

  to 
  the 
  ray. 
  

   3a. 
  Anterior 
  view 
  of 
  same, 
  with 
  anterior 
  ray 
  bifurcating 
  on 
  third 
  

   brachial, 
  and 
  having 
  only 
  4 
  arms. 
  

  

  4. 
  Posterior 
  view 
  of 
  small 
  specimen, 
  with 
  typical 
  form 
  of 
  anal 
  area 
  

  

  for 
  the 
  earlier 
  species 
  — 
  broadly 
  truncate 
  post. 
  B. 
  and 
  short 
  

   RA. 
  

   Upper 
  Burlington 
  limestone; 
  Burlington, 
  Iowa. 
  

  

  128 
  

  

  