﻿INVEKTEBKATES. 
  277 
  

  

  PoTERIOCRINUS 
  TENTACULATUS, 
  Worthen. 
  

   PI. 
  XXVIII, 
  Fig. 
  11. 
  

  

  Peteriocrinus 
  tentacvlatus, 
  Wokthen, 
  February, 
  1882. 
  

  

  Bulletin 
  No. 
  1, 
  of 
  the 
  Illinois 
  State 
  Museum 
  of 
  Natural 
  History, 
  p. 
  10. 
  

  

  Body 
  of 
  medium 
  size, 
  depressed 
  cup-shaped, 
  more 
  than 
  twice 
  as 
  

   wide 
  as 
  high. 
  Base 
  depressed, 
  basal 
  plates 
  small 
  and 
  concealed 
  in 
  

   the 
  basal 
  cavity. 
  Subradials 
  as 
  long 
  or 
  longer 
  than 
  wide, 
  three 
  

   hexagonal 
  and 
  two 
  on 
  the 
  anal 
  side 
  heptagonal. 
  

  

  Kadials 
  about 
  twice 
  as 
  wide 
  as 
  long 
  ; 
  heptagonal, 
  and 
  truncated 
  

   squarely 
  across 
  their 
  upper 
  margins 
  for 
  the 
  reception 
  of 
  the 
  brachial 
  

   series. 
  

  

  Brachials 
  two, 
  the 
  first 
  quadrangular, 
  and 
  the 
  second 
  pentangular, 
  

   both 
  as 
  wide 
  or 
  a 
  little 
  wider 
  than 
  the 
  radials 
  ; 
  the 
  second 
  support- 
  

   ing 
  on 
  its 
  upper 
  angles 
  the 
  first 
  divisions 
  of 
  the 
  arms. 
  The 
  arms 
  

   are 
  composed 
  of 
  wide, 
  short, 
  quadrangular 
  joints, 
  and 
  bifurcate 
  the 
  

   second 
  time 
  on 
  the 
  fourth 
  and 
  sixth 
  plates 
  above 
  the 
  brachials, 
  be- 
  

   yond 
  which 
  they 
  are 
  all 
  simple 
  to 
  their 
  extremities, 
  making 
  four 
  

   arms 
  to 
  each 
  ray. 
  Above 
  the 
  second 
  bifurcation 
  the 
  plates 
  of 
  the 
  

   arms 
  gradually 
  diminish 
  in 
  width, 
  and 
  become 
  slightly 
  wedge-formed, 
  

   giving 
  off 
  strong 
  pinnules 
  from 
  their 
  longest 
  sides. 
  

  

  Anal 
  area 
  proportionately 
  large, 
  with 
  nine 
  small 
  anal 
  plates 
  visi- 
  

   ble. 
  The 
  first 
  is 
  pentagonal, 
  and 
  rests 
  between 
  two 
  of 
  the 
  subra- 
  

   dials 
  and 
  partly 
  under 
  one 
  side 
  of 
  the 
  right 
  posterior 
  radial. 
  The 
  

   two 
  succeeding 
  anals 
  are 
  larger, 
  placed 
  side 
  by 
  side, 
  their 
  lower 
  mar- 
  

   gins 
  resting, 
  the 
  left 
  one 
  on 
  the 
  truncated 
  margin 
  of 
  one 
  of 
  the 
  

   subradials, 
  and 
  the 
  other 
  between 
  the 
  upper 
  angle 
  of 
  the 
  first 
  anal 
  

   and 
  the 
  left 
  margin 
  of 
  the 
  first 
  radial 
  to 
  the 
  right. 
  The 
  next 
  series 
  

   of 
  anals 
  consists 
  of 
  three 
  smaller 
  plates 
  placed 
  side 
  by 
  side, 
  and 
  

   these 
  are 
  succeeded 
  by 
  three 
  more 
  that 
  are 
  not 
  fully 
  exposed. 
  

  

  Column 
  unknown. 
  

  

  Position 
  and 
  locality: 
  Upper 
  shales 
  of 
  the 
  geode 
  bed, 
  one 
  mile 
  

   below 
  Keokuk, 
  Iowa. 
  

   No. 
  403 
  of 
  Mr. 
  L. 
  A. 
  Cox's 
  collection. 
  

  

  