﻿INVEETEBRATES. 
  283 
  

  

  Poteriocrinus 
  Otterensis, 
  Worthen. 
  

  

  PI. 
  XXVIII, 
  Fig. 
  4. 
  

  

  Poteriocrinus 
  Otterensis, 
  Wobthen, 
  February, 
  1882. 
  

  

  Bulletin 
  No. 
  1, 
  of 
  the 
  Illinois 
  State 
  Museum 
  of 
  Natural 
  History, 
  p. 
  14. 
  

  

  Body 
  above 
  the 
  medium 
  size, 
  basin-shaped, 
  about 
  once 
  and 
  a 
  

   half 
  as 
  wide 
  as 
  high, 
  base 
  depressed 
  and 
  the 
  basal 
  plates 
  hidden 
  

   by 
  the 
  column, 
  which 
  is 
  quite 
  stout 
  and 
  pentalobate 
  where 
  it 
  joins 
  

   the 
  body. 
  

  

  Subradials 
  about 
  one-fourth 
  wider 
  than 
  long, 
  the 
  lower 
  angle 
  

   curving 
  inward 
  to 
  form 
  a 
  part 
  of 
  the 
  basal 
  concavity. 
  The 
  center 
  

   of 
  these 
  plates 
  is 
  smooth 
  and 
  a 
  little 
  protuberant, 
  with 
  four 
  deep 
  

   indentations 
  on 
  their 
  borders, 
  two 
  of 
  which 
  are 
  lateral, 
  to 
  meet 
  

   those 
  of 
  the 
  adjacent 
  subradials, 
  and 
  two 
  directed 
  obliquely 
  upward 
  

   to 
  meet 
  similar 
  depressions 
  in 
  the 
  radial 
  plates. 
  

  

  Badials 
  wider 
  than 
  long, 
  constricted 
  across 
  the 
  middle, 
  and 
  pro- 
  

   jecting 
  on 
  their 
  upper 
  margins, 
  with 
  two 
  slightly 
  oblique 
  depres- 
  

   sions 
  below, 
  that 
  meet 
  two 
  of 
  those 
  in 
  the 
  subradial 
  plates. 
  They 
  

   are 
  pentagonal 
  in 
  form 
  and 
  support 
  on 
  their 
  upper 
  truncated 
  mar- 
  

   gins 
  the 
  brachial 
  series. 
  

  

  Brachials 
  one 
  to 
  each 
  of 
  the 
  postero-lateral 
  rays, 
  smaller 
  than 
  

   the 
  radials, 
  slightly 
  constricted, 
  and 
  sharply 
  angular 
  above, 
  giving 
  

   support 
  to 
  the 
  first 
  divisions 
  of 
  the 
  rays. 
  Arm 
  structure 
  unknown. 
  

  

  Three 
  anal 
  plates 
  are 
  visible, 
  the 
  first 
  nearly 
  as 
  large 
  as 
  the 
  sub- 
  

   radials, 
  the 
  others 
  a 
  little 
  smaller, 
  and 
  all 
  having 
  from 
  four 
  to 
  six 
  

   depressions 
  around 
  their 
  borders 
  that 
  correspond 
  to 
  similar 
  depres- 
  

   sions 
  on 
  adjacent 
  plates. 
  The 
  anal 
  plates 
  have 
  been 
  shoved 
  out 
  of 
  

   their 
  true 
  position 
  by 
  the 
  crushing 
  of 
  the 
  specimen, 
  so 
  that 
  their 
  

   relation 
  to 
  the 
  adjacent 
  plates 
  cannot 
  be 
  clearly 
  determined. 
  

  

  Position 
  and 
  locality: 
  This 
  unique 
  form 
  was 
  obtained 
  from 
  the 
  

   Keokuk 
  limestone, 
  on 
  Otter 
  Creek, 
  Jersey 
  county, 
  111. 
  

  

  No. 
  2,466, 
  Illinois 
  State 
  collection. 
  

  

  