﻿164 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  attachment 
  between 
  Platyceras 
  and 
  the 
  crinoids. 
  With 
  the 
  

   opening 
  of 
  the 
  Devonic 
  the 
  development 
  of 
  Platyceras 
  became 
  

   enormous, 
  so 
  much 
  so 
  that 
  the 
  calcareous 
  phase 
  of 
  the 
  earliest 
  

   Devonic 
  has 
  been 
  termed 
  the 
  Platyceras 
  stage. 
  The 
  crinoids 
  alsc 
  

   were 
  common 
  at 
  this 
  time, 
  but 
  cases 
  of 
  any 
  dependent 
  conjunction 
  

   of 
  the 
  two 
  are 
  extraordinarily 
  rare 
  ; 
  the 
  only 
  instance 
  of 
  this 
  earl}; 
  

   date 
  known 
  to 
  me 
  is 
  that 
  cited 
  by 
  Drevermann 
  from 
  the 
  Cob- 
  

   lentzian. 
  Little 
  by 
  little, 
  however, 
  the 
  habit 
  was 
  assumed 
  and 
  

   becoming 
  more 
  frequent 
  in 
  the 
  Middle 
  Devonic 
  it 
  seems 
  to 
  have 
  

   attained 
  a 
  culmination 
  in 
  the 
  faunas 
  of 
  the 
  earlier 
  Carbonic. 
  

   During 
  all 
  the 
  ages 
  which 
  have 
  intervened 
  between 
  the 
  

  

  Silicified 
  specimens 
  of 
  Platyceras 
  attached 
  to 
  the 
  dome 
  of 
  Megistocrinus 
  farns- 
  

   worthi 
  White, 
  from 
  the 
  Middle 
  Devonic 
  of 
  Iowa. 
  The 
  perfect 
  adjustment 
  of 
  the 
  shell 
  

   to 
  the 
  crinoid 
  is 
  seen 
  in 
  the 
  adaptation 
  of 
  its 
  margin 
  to 
  every 
  irregularity 
  of 
  the 
  surface 
  

   of 
  the 
  dome. 
  Loaned 
  by 
  Prof. 
  Samuel 
  Calvin 
  

  

  Paleozoic 
  and 
  the 
  present 
  there 
  is 
  no 
  record 
  which 
  has 
  come 
  to 
  

   my 
  notice 
  to 
  prove 
  that 
  this 
  ancient 
  habit 
  has 
  had 
  an 
  uninter- 
  

   rupted 
  existence. 
  The 
  crinoids 
  and 
  the 
  limpets 
  have 
  continued 
  

   and 
  certainly 
  the 
  detailed 
  records 
  of 
  Mesozoic 
  and 
  Cenozoic 
  faunas 
  

   should 
  have 
  given 
  some 
  account 
  of 
  this 
  habit 
  had 
  it 
  perdured. 
  

   We 
  have 
  remarked 
  that 
  the 
  consociation 
  was 
  always 
  an 
  easy 
  one 
  

   to 
  which 
  even 
  at 
  its 
  hight 
  not 
  all 
  the 
  members 
  of 
  the 
  genus 
  Platy- 
  

   ceras 
  were 
  compelled. 
  In 
  the 
  absence 
  of 
  demonstration, 
  it 
  may 
  be 
  

   fair 
  to 
  hold 
  it 
  possible 
  that 
  the 
  descendants 
  of 
  these 
  mollusks 
  really 
  

   abandoned 
  this 
  form 
  of 
  attachment 
  and 
  rebounded 
  from 
  the 
  degen- 
  

   erative 
  condition 
  which 
  it 
  involved; 
  this 
  would 
  be 
  a 
  fact 
  of 
  pro- 
  

   found 
  significance 
  if 
  it 
  indicates 
  that 
  an 
  organism 
  once 
  started 
  on 
  

   the 
  downward 
  path 
  can 
  take 
  a 
  new 
  hold 
  of 
  life 
  and 
  regain 
  its 
  inde- 
  

   pendence. 
  Yet 
  we 
  are 
  doubtless 
  not 
  justified 
  in 
  such 
  a 
  conclu- 
  

  

  