﻿INVEKTEBEATES. 
  305 
  

  

  Genus 
  RHODOCRINUS, 
  Miller. 
  

   Ehodocrinus 
  Coxanus, 
  Worthen. 
  

  

  PI. 
  XXVIII, 
  Fig. 
  7. 
  

   Bhodocrinus 
  Coxanus, 
  Woethen, 
  Feb. 
  1882. 
  

   Bulletin 
  No. 
  1, 
  of 
  the 
  Illinois 
  State 
  Museum 
  of 
  Natural 
  History, 
  p. 
  30. 
  

  

  Body 
  of 
  medium 
  size, 
  subglobose, 
  base 
  slightly 
  depressed, 
  the 
  basal 
  

   plates 
  concealed 
  by 
  the 
  first 
  columnar 
  joints. 
  Subradials 
  a 
  little 
  

   wider 
  than 
  long, 
  their 
  lower 
  angles 
  curved, 
  in 
  to 
  form 
  a 
  part 
  of 
  the 
  

   basal 
  concavity. 
  

  

  ■ 
  The 
  first 
  raclials 
  much 
  larger 
  than 
  the 
  succeeding 
  ones, 
  heptagonal 
  

   in 
  form 
  ; 
  second 
  radials 
  nearly 
  quadrangular, 
  and 
  the 
  third 
  hexag- 
  

   onal, 
  supporting 
  above 
  the 
  secondary 
  radial 
  plates, 
  of 
  which 
  there 
  

   is 
  but 
  one 
  to 
  each 
  division 
  of 
  the 
  ray. 
  

  

  Brachials, 
  four 
  to 
  five, 
  short, 
  widening 
  above, 
  the 
  upper 
  one 
  with 
  

   a 
  slightly-projecting 
  angle 
  in 
  the 
  middle, 
  separating 
  the 
  first 
  divisions 
  

   of 
  the 
  arms. 
  From 
  two 
  to 
  five 
  single, 
  wedge-formed 
  pieces 
  succeed 
  

   the 
  brachials, 
  above 
  which 
  the 
  arms 
  are 
  composed 
  of 
  a 
  double 
  series 
  

   of 
  short, 
  interlocking 
  pieces, 
  each 
  one 
  of 
  which 
  gives 
  off 
  a 
  moder- 
  

   ately-strong 
  pinnule. 
  In 
  one 
  of 
  the 
  specimens 
  under 
  examination 
  

   the 
  arms 
  on 
  the 
  two 
  rays 
  visible 
  continue 
  single 
  after 
  the 
  first 
  bi- 
  

   furcation, 
  making 
  four 
  arms 
  to 
  each 
  ray; 
  but 
  in 
  another 
  specimen, 
  

   apparently 
  of 
  the 
  same 
  species, 
  a 
  third 
  branch 
  is 
  given 
  off 
  from 
  the 
  

   third 
  plate 
  above 
  the 
  first 
  division, 
  making 
  six 
  arms 
  to 
  these 
  two 
  

   rays. 
  

  

  From 
  four 
  to 
  six 
  inter-radials 
  can 
  be 
  seen, 
  the 
  first 
  of 
  which 
  is 
  

   larger 
  than 
  the 
  others, 
  but 
  owing 
  to 
  the 
  crushed 
  condition 
  of 
  the 
  

   specimens, 
  the 
  exact 
  form 
  and 
  number 
  of 
  these 
  plates 
  cannot 
  be 
  

   determined. 
  

  

  Column 
  round, 
  rather 
  stout, 
  and 
  composed 
  of 
  alternately 
  thin 
  and 
  

   thicker 
  joints. 
  

  

  The 
  specimen 
  showing 
  six 
  arms 
  to 
  the 
  ray 
  also 
  shows 
  a 
  marked 
  

   prominence 
  in 
  the 
  central 
  portion 
  of 
  the 
  body-plates, 
  which 
  is 
  not 
  

   seen 
  in 
  the 
  other, 
  and 
  this 
  we 
  take 
  as 
  the 
  type 
  of 
  R. 
  Coxanus, 
  and 
  

   if 
  these 
  differences 
  should 
  be 
  regarded 
  as 
  of 
  specific 
  importance,, 
  

   the 
  name 
  R. 
  polydactylus 
  might 
  be 
  used 
  to 
  designate 
  the 
  other 
  va- 
  

   riety. 
  

  

  Geological 
  position 
  and 
  locality: 
  Upper 
  part 
  of 
  the 
  geode 
  bed, 
  one 
  

   mile 
  below 
  Keokuk. 
  

  

  Nos. 
  197 
  and 
  223 
  of 
  Mr. 
  L. 
  A. 
  Cox's 
  collection. 
  

  

  —20 
  

  

  