﻿INVERTEBRATES. 
  345 
  

  

  The 
  interradials 
  of 
  the 
  four 
  lateral 
  rays, 
  toward 
  the 
  anterior 
  side, 
  

   consist 
  of 
  seven 
  plates 
  in 
  four 
  series, 
  2, 
  2, 
  2, 
  1 
  ; 
  at 
  the 
  anterior 
  side 
  

   of 
  only 
  six 
  pieces, 
  2, 
  1, 
  2, 
  1. 
  The 
  plates 
  of 
  the 
  first 
  series 
  rest 
  

   with 
  their 
  lower 
  sloping 
  sides 
  against 
  two 
  of 
  the 
  intercalated 
  pieces 
  — 
  

   those 
  composing 
  the 
  second 
  ring 
  around 
  the 
  basals 
  ; 
  they 
  are 
  placed 
  

   with 
  their 
  lateral 
  side 
  against 
  the 
  sides 
  of 
  their 
  fellows 
  of 
  the 
  ad- 
  

   joining 
  interradial 
  area, 
  except 
  toward 
  the 
  anterior 
  and 
  posterior 
  

   side, 
  where 
  they 
  abut, 
  at 
  the 
  former 
  against 
  the 
  first 
  radial, 
  at 
  the 
  

   latter 
  against 
  one 
  of 
  the 
  special 
  anal 
  plates. 
  The 
  plates 
  of 
  the 
  

   succeeding 
  series 
  rest 
  with 
  their 
  outer 
  sides 
  within 
  the 
  angle 
  be- 
  

   tween 
  two 
  radials, 
  with 
  the 
  other 
  side 
  against 
  the 
  adjoining 
  inter- 
  

   radials. 
  The 
  plates 
  of 
  the 
  interradial 
  areas 
  are 
  either 
  hexagonal 
  or 
  

   pentagonal, 
  and 
  their 
  increase 
  in 
  size 
  in 
  an 
  upward 
  direction 
  is 
  

   even 
  greater 
  in 
  that 
  same 
  direction 
  among 
  the 
  radials, 
  the 
  upper 
  

   one 
  being 
  fully 
  three 
  times 
  larger 
  than 
  the 
  two 
  interradials 
  of 
  the 
  

   first 
  series. 
  The 
  same 
  is 
  true 
  with 
  regard 
  to 
  the 
  azygous 
  side. 
  i 
  

  

  The 
  anal 
  side 
  is 
  very 
  wide, 
  and 
  is 
  composed 
  of 
  a 
  median 
  row 
  of 
  

   four 
  hexagonal 
  pieces, 
  longitudinally 
  arranged, 
  and 
  of 
  a 
  series 
  of 
  

   seven 
  plates 
  at 
  each 
  side 
  of 
  it. 
  The 
  latter 
  are 
  arranged 
  like 
  the 
  

   seven 
  plates 
  of 
  the 
  two 
  interradial 
  areas 
  adjoining 
  the 
  anterior 
  ray, 
  

   and 
  as 
  the 
  radials 
  of 
  that 
  side, 
  as 
  already 
  stated, 
  are 
  arranged 
  and 
  

   constructed 
  like 
  the 
  special 
  anal 
  plates, 
  the 
  anterior 
  side, 
  with 
  its 
  

   two 
  interradial 
  series, 
  is 
  almost 
  a 
  perfect 
  counterpart 
  of 
  the 
  anal 
  

   area. 
  The 
  uppermost 
  anal 
  plate 
  is 
  hexagonal 
  or, 
  perhaps, 
  octagonal, 
  

   its 
  upper 
  side 
  truncate 
  ; 
  its 
  size 
  is 
  equal 
  to, 
  if 
  not 
  larger 
  than, 
  that 
  

   of 
  the 
  first 
  radials. 
  

  

  Acrocrinus 
  Wortheni 
  differs 
  from 
  the 
  two 
  previously 
  described 
  species 
  

   of 
  this 
  genus 
  most 
  conspicuously 
  in 
  the 
  form 
  of 
  the 
  basal 
  plates. 
  

   The 
  construction 
  of 
  the 
  other 
  plates 
  is 
  so 
  imperfectly 
  known 
  that 
  a 
  

   comparison 
  of 
  other 
  parts 
  is 
  impossible. 
  There 
  is 
  also 
  a 
  great 
  dif- 
  

   ference 
  in 
  the 
  form 
  of 
  the 
  body. 
  

  

  The 
  specific 
  name 
  is 
  given 
  in 
  honor 
  of 
  Prof. 
  A. 
  H. 
  Worthen, 
  the 
  

   able 
  director 
  of 
  the 
  Illinois 
  geological 
  survey. 
  

  

  Geological 
  position 
  and 
  locality: 
  From 
  the 
  Coal 
  Measures 
  of 
  Peoria 
  

   county, 
  111. 
  

  

  The 
  type 
  is 
  in 
  the 
  Illinois 
  State 
  collection. 
  

  

  I 
  

  

  