﻿136 
  echinocystis 
  and 
  pal^odiscijs. 
  [Feb. 
  1897. 
  

  

  ago 
  by 
  Dr. 
  Torell 
  in 
  the 
  Cambrian 
  rocks 
  of 
  Sweden, 
  apparently 
  the 
  

   oldest 
  at 
  present 
  known. 
  

  

  The 
  Authok 
  replied 
  that 
  the 
  Spatangopsis 
  of 
  Torell 
  may 
  be 
  an 
  

   echinoderm, 
  but 
  it 
  is 
  not 
  an 
  ally 
  of 
  the 
  Cystocidaroida. 
  In 
  reply 
  

   to 
  Mr. 
  Blake, 
  he 
  said 
  that 
  the 
  development 
  of 
  the 
  echinid 
  ambu- 
  

   lacral 
  plates 
  is 
  from 
  the 
  simple 
  to 
  the 
  complex. 
  He 
  had 
  not 
  said 
  

   that 
  Loven, 
  Carpenter, 
  or 
  Sladen 
  had 
  asserted 
  the 
  development 
  of 
  

   Echinoidea 
  from 
  Crinoidea, 
  but 
  only 
  that 
  their 
  homology 
  of 
  the 
  

   apical 
  plates 
  with 
  the 
  calyx-plates 
  of 
  the 
  Pelmatozoa 
  suggested 
  

   the 
  origin 
  of 
  the 
  Echinoidea 
  from 
  that 
  group 
  of 
  echinoderms 
  of 
  

   which 
  the 
  Crinoidea 
  are 
  the 
  only 
  living 
  representatives. 
  He 
  had 
  not 
  

   stated 
  it 
  as 
  his 
  opinion 
  that 
  a 
  penta 
  radiate 
  water-vascular 
  system 
  

   was 
  an 
  essential 
  character 
  of 
  an 
  echinoderm, 
  but 
  that 
  this 
  view 
  

   was 
  assumed 
  by 
  those 
  who 
  argued 
  that 
  the 
  pentaradiate 
  symmetry 
  of 
  

   echinoderms 
  was 
  due 
  to 
  fixation. 
  He 
  agreed 
  with 
  Mr. 
  Bather 
  that 
  

   this 
  character 
  was 
  not 
  essential. 
  The 
  madreporite 
  of 
  Echinocystis 
  

   is 
  not 
  at 
  the 
  apex, 
  but 
  in 
  the 
  posterior 
  interambulacrum. 
  

  

  