﻿INVEKTEBRATES. 
  279 
  

  

  a 
  part 
  of 
  the 
  basal 
  concavity, 
  and 
  the 
  upper 
  angles 
  depressed 
  to 
  

   correspond 
  with 
  similar 
  depressions 
  in 
  the 
  lower 
  margins 
  of 
  the 
  

   radial 
  plates. 
  

  

  Kadials 
  short, 
  about 
  as 
  wide 
  as 
  long, 
  pentagonal, 
  depressed 
  at 
  

   their 
  lower 
  angles, 
  with 
  a 
  gaping 
  suture 
  between 
  them 
  and 
  the 
  suc- 
  

   ceeding 
  brachials. 
  

  

  Brachials 
  two, 
  the 
  first 
  quadrangular, 
  the 
  second 
  sharply 
  angu- 
  

   lar 
  above, 
  and 
  but 
  little 
  narrower 
  than 
  the 
  radial 
  series. 
  A 
  slight 
  

   angular 
  prominence 
  extends 
  lengthwise 
  across 
  the 
  brachial 
  plates, 
  

   and 
  the 
  same 
  may 
  be 
  seen 
  on 
  tbe 
  lower 
  portion 
  of 
  the 
  arms 
  under 
  

   a 
  good 
  glass. 
  

  

  Arms 
  on 
  the 
  anterior 
  ray, 
  after 
  the 
  first 
  division 
  on 
  the 
  second 
  

   brachial, 
  divide 
  again 
  on 
  the 
  fourth 
  and 
  sixth 
  plate, 
  and 
  both 
  the 
  

   outer 
  divisions 
  again 
  on 
  the 
  eighth 
  plate, 
  while 
  the 
  inner 
  one 
  ap- 
  

   pears 
  to 
  be 
  simple 
  after 
  the 
  second 
  division, 
  thus 
  giving 
  six 
  arms 
  

   to 
  this 
  ray. 
  The 
  antero-lateral 
  rays 
  appear 
  to 
  divide 
  once 
  more, 
  

   giving 
  eight 
  arms 
  to 
  those 
  rays. 
  

  

  Arm 
  pieces 
  rounded, 
  moderately 
  wedge-shaped, 
  and 
  diminish 
  

   rather 
  rapidly 
  in 
  width 
  toward 
  their 
  extremities. 
  Delicate 
  pinnules 
  

   are 
  given 
  off 
  from 
  their 
  longest 
  sides. 
  Anal 
  plates 
  and 
  column 
  un- 
  

   known. 
  

  

  The 
  depressions 
  at 
  the 
  angles 
  of 
  the 
  body 
  plates, 
  give 
  a 
  rugged 
  

   appearance 
  to 
  the 
  body 
  of 
  this 
  species, 
  and 
  will 
  serve 
  to 
  distin- 
  

   guish 
  it 
  from 
  the 
  other 
  forms 
  with 
  which 
  it 
  is 
  associated. 
  

  

  Position 
  and 
  locality: 
  Upper 
  part 
  of 
  the 
  geodiferous 
  shales 
  of 
  the 
  

   Keokuk 
  group, 
  one 
  mile 
  below 
  Keokuk. 
  

  

  No. 
  191, 
  Mr. 
  L. 
  A. 
  Cox's 
  collection. 
  

  

  Poteriocrinus 
  BEiiBRius, 
  Worthen. 
  

  

  PI. 
  XXVII, 
  Pig. 
  4. 
  

  

  Poteriocrinus 
  bricerius, 
  Worthen, 
  February, 
  1882. 
  

  

  Bulletin 
  No. 
  1, 
  of 
  the 
  Illinois 
  State 
  Museum 
  of 
  Natural 
  History, 
  p. 
  12. 
  

  

  Body 
  of 
  medium 
  size, 
  cup-shaped, 
  base 
  depressed; 
  the 
  basal 
  

   plates 
  small, 
  not 
  extending 
  beyond 
  the 
  columnar 
  facet. 
  Subradials 
  

   prominent 
  in 
  the 
  center 
  and 
  depressed 
  at 
  the 
  angles, 
  three 
  hexa- 
  

   gonal 
  and 
  two 
  on 
  the 
  posterior 
  side 
  rather 
  larger 
  than 
  the 
  others, 
  

   and 
  heptagonal. 
  

  

  