﻿I58 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Taken 
  as 
  a 
  whole 
  this 
  combination 
  is 
  very 
  complicated 
  commen- 
  

   salism 
  from 
  a 
  date 
  so 
  ancient 
  as 
  the 
  Devonic, 
  more 
  extreme 
  than 
  

   any 
  other 
  yet 
  known 
  from 
  the 
  Paleozoic 
  rocks. 
  But 
  we 
  find 
  a 
  

   somewhat 
  parallel 
  case 
  in 
  the 
  present 
  described 
  by 
  Bouvier 
  as 
  occur- 
  

   ring 
  in 
  the 
  Gulf 
  of 
  Aden 
  — 
  a 
  coral 
  and 
  a 
  worm 
  growing 
  together, 
  

   and 
  hidden 
  in 
  the 
  coral 
  substance 
  a 
  gastropod 
  on 
  which 
  both 
  settled 
  

   down 
  when 
  the 
  partnership 
  began 
  ; 
  furthermore 
  there 
  appears 
  to 
  be 
  

   a 
  small 
  bivalve 
  in 
  association 
  with 
  the 
  worm. 
  Other 
  somewhat 
  

   similar 
  cases 
  might 
  be 
  cited. 
  

  

  The 
  Devonic 
  coral 
  Acervularia 
  and 
  the 
  spiral 
  worm 
  Streptindytes 
  

   acervulariae 
  ; 
  a 
  Siluric 
  Stromatopora 
  with 
  a 
  somewhat 
  similar 
  spiral 
  

   worm, 
  Streptindytes 
  concoenatus; 
  a 
  Devonic 
  Stromatopora 
  with 
  

   the 
  spiral 
  worm, 
  Streptindytes 
  compactus. 
  The 
  first 
  of 
  these 
  occur- 
  

   rences 
  was 
  described 
  some 
  years 
  ago 
  by 
  Prof. 
  Samuel 
  Calvin 
  [On 
  

   a 
  New 
  Genus 
  and 
  Species 
  of 
  Tubicolar 
  Annelida. 
  Am. 
  Geol. 
  1 
  124. 
  

   1888]. 
  It 
  is 
  the 
  case 
  of 
  a 
  large 
  annelid 
  whose 
  tube 
  measures 
  •§- 
  to 
  

   J 
  inch 
  in 
  diameter 
  growing 
  upward 
  in 
  numbers 
  among 
  the 
  cells 
  of 
  

   the 
  compound 
  coral 
  Acervularia 
  davidsoni 
  Edw. 
  & 
  H. 
  from 
  

   the 
  Middle 
  Devonic 
  rocks 
  of 
  Iowa. 
  The 
  species 
  has 
  not 
  before 
  been 
  

   illustrated 
  and 
  I 
  have 
  to 
  thank 
  Dr 
  Calvin 
  for 
  the 
  privilege 
  of 
  

   introducing 
  the 
  accompanying 
  cut 
  of 
  this 
  interesting 
  commensal 
  

   [pi. 
  1, 
  fig. 
  7]. 
  

  

  Another 
  example 
  of 
  these 
  spiral 
  commensal 
  worms 
  (Streptin- 
  

   dytes 
  concoenatus) 
  is 
  afforded 
  by 
  the 
  Stromatopora. 
  reefs 
  

   of 
  the 
  Cobleskill 
  limestone 
  (Upper 
  Siluric). 
  The 
  illustration 
  here 
  

   given 
  [pi. 
  1, 
  fig. 
  5, 
  6], 
  affords 
  some 
  idea 
  of 
  how 
  a 
  small 
  mass 
  of 
  Stro- 
  

   matopora 
  may 
  be 
  quite 
  riddled 
  with 
  these 
  minute 
  corkscrews. 
  

   This 
  is 
  taken 
  from 
  a 
  single 
  section 
  across 
  a 
  small 
  colony 
  in 
  which 
  it 
  

   is 
  apparent 
  that 
  these 
  worms 
  have 
  become 
  sessile 
  at 
  different 
  stages 
  

   of 
  growth 
  in 
  the 
  coral 
  mass 
  as 
  they 
  start 
  at 
  different 
  levels 
  in 
  the 
  

   colony. 
  It 
  is 
  also 
  clear 
  that 
  the 
  worm 
  tube 
  made 
  at 
  least 
  one 
  hor- 
  

   izontal 
  convolution 
  before 
  starting 
  on 
  its 
  upward 
  spiral 
  growth 
  and 
  

   it 
  is 
  more 
  than 
  likely 
  that 
  its 
  elongated 
  spiral 
  is 
  due 
  to 
  the 
  require- 
  

   ment 
  of 
  keeping 
  its 
  tentacular 
  end 
  up 
  at 
  the 
  feeding 
  surface 
  of 
  the 
  

   growing 
  coral. 
  These 
  tubicolous 
  worms 
  have 
  very 
  plastic 
  tubes 
  and 
  

   readily 
  adjust 
  themselves 
  to 
  surroundings. 
  In 
  the 
  worm 
  of 
  Pleu- 
  

   rodictyum 
  (Hicetes 
  innexus) 
  the 
  early 
  spiral 
  form 
  was 
  

   soon 
  lost, 
  perhaps 
  because 
  the 
  corallites 
  are 
  so 
  large 
  and 
  close 
  that 
  

   such 
  growth 
  was 
  effectually 
  obstructed. 
  I 
  have 
  given 
  here 
  some 
  

  

  