﻿art 
  9 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  67 
  

  

  later 
  stage, 
  involving 
  not 
  only 
  the 
  gut 
  but 
  also 
  its 
  tubular 
  sheath 
  of 
  

   calcareous 
  plates, 
  and 
  that 
  instead 
  of 
  following 
  a 
  simple 
  curvature 
  

   continuing 
  along 
  a 
  convex 
  surface, 
  the 
  direction 
  of 
  the 
  tube 
  is 
  more 
  

   or 
  less 
  suddenly 
  or 
  abruptly 
  reversed. 
  With 
  its 
  upward 
  growth 
  

   thus 
  arrested, 
  the 
  activity 
  of 
  the 
  organ 
  finds 
  an 
  outlet 
  in 
  different 
  

   forms 
  of 
  expansion, 
  or 
  abnormal 
  structures, 
  at 
  or 
  near 
  the 
  point 
  

   where 
  the 
  reversal 
  occurs. 
  As 
  the 
  tube 
  in 
  forms 
  of 
  this 
  group 
  is 
  

   usually 
  built 
  up 
  of 
  plates 
  arranged 
  in 
  longitudinal 
  columns, 
  it 
  is 
  

   not 
  difficult 
  to 
  trace 
  the 
  course 
  of 
  these 
  changes. 
  

  

  The 
  simplest 
  case 
  is 
  seen 
  in 
  species 
  of 
  Pachylocrinus, 
  such 
  as 
  P 
  

   arboreus 
  or 
  P. 
  scojmrius 
  (pi. 
  16, 
  figs. 
  3-7; 
  2), 
  where 
  the 
  tube 
  is 
  

   greatly 
  curved 
  downward 
  toward 
  the 
  anterior 
  to 
  an 
  opening 
  near 
  

   or 
  above 
  midway; 
  the 
  walls 
  along 
  the 
  line 
  of 
  contact 
  are 
  coalesced* 
  

   and 
  the 
  curved 
  portion 
  considerably 
  swollen, 
  but 
  not 
  rising 
  beyond 
  

   the 
  limit 
  of 
  the 
  arms. 
  The 
  longitudinal 
  lines 
  of 
  plates 
  forming 
  the 
  

   sac 
  are 
  distinctly 
  seen 
  in 
  the 
  swollen 
  part. 
  

  

  In 
  P. 
  florealis 
  (pi. 
  16, 
  figs. 
  8, 
  9) 
  the 
  opening 
  lies 
  just 
  below 
  the 
  

   distal 
  end, 
  and 
  the 
  tube 
  is 
  terminated 
  by 
  four 
  spiniferous 
  plates 
  

   barely 
  surmounting 
  the 
  arms. 
  

  

  In 
  Coeliocrinus 
  ventricosus^ 
  where 
  the 
  inflation 
  of 
  the 
  sac 
  is 
  at 
  

   the 
  distal 
  end 
  and 
  takes 
  the 
  form 
  of 
  a 
  narrow-necked 
  balloon, 
  the 
  

   longitudinal 
  columns 
  of 
  plates 
  which 
  appear 
  in 
  several 
  of 
  the 
  speci- 
  

   mens 
  testify 
  that 
  this 
  is 
  only 
  the 
  hypertrophied 
  part 
  of 
  the 
  tube 
  

   incident 
  to 
  its 
  reversal 
  of 
  direction 
  (pi. 
  24, 
  figs. 
  1-8). 
  The 
  anus 
  

   has 
  not 
  been 
  observed 
  in 
  this 
  genus, 
  but 
  we 
  know 
  it 
  must 
  have 
  been 
  

   somewhere 
  in 
  the 
  narrow 
  neck 
  below 
  the 
  inflated 
  part. 
  

  

  Aulocrinus, 
  which 
  wiih 
  its 
  lateral 
  spout 
  appears 
  to 
  be 
  the 
  most 
  

   aberrant 
  form 
  of 
  all, 
  really 
  tells 
  the 
  story 
  the 
  best. 
  This 
  may 
  be 
  

   understood 
  from 
  the 
  figures 
  upon 
  plate 
  19, 
  made 
  from 
  a 
  remarkable 
  

   series 
  of 
  specimens 
  in 
  which 
  the 
  spout-like 
  tube 
  is 
  shown 
  in 
  various 
  

   positions. 
  Here 
  the 
  longitudinal 
  columns 
  of 
  plates 
  are 
  ver}?- 
  con- 
  

   spicuous, 
  being 
  marked 
  by 
  sharp 
  ridges, 
  and 
  it 
  will 
  be 
  observed 
  

   that 
  the 
  number 
  of 
  these 
  columns 
  when 
  seen 
  in 
  a 
  lateral 
  view 
  is 
  

   considerably 
  greater 
  above 
  the 
  level 
  of 
  the 
  spout 
  than 
  it 
  is 
  below. 
  

   This 
  results 
  from 
  the 
  doubling 
  of 
  the 
  tube 
  upon 
  itself, 
  and 
  the 
  

   fusion 
  of 
  the 
  apposed 
  walls 
  of 
  the 
  parts 
  thus 
  brought 
  into 
  contact 
  ;: 
  

   the 
  process 
  is 
  completely 
  shown 
  by 
  the 
  two 
  specimens 
  in 
  which 
  the 
  

   tube 
  is 
  exposed 
  laterally 
  (figs. 
  2 
  and 
  3). 
  In 
  figure 
  2 
  the 
  ridged 
  

   rows 
  of 
  plates 
  can 
  be 
  traced 
  continuously 
  from 
  the 
  original 
  tube 
  into 
  

   the 
  reversed 
  part. 
  

  

  From 
  these 
  it 
  will 
  be 
  seen 
  that 
  the 
  tube 
  of 
  Aulocrinus, 
  instead 
  of 
  

   being 
  curved 
  and 
  inflated 
  as 
  in 
  the 
  preceding 
  examples, 
  is 
  abruptly 
  

   reversed, 
  as 
  if 
  it 
  might 
  have 
  been 
  bent, 
  almost 
  to 
  the 
  point 
  of 
  frac- 
  

   ture, 
  and 
  the 
  pieces 
  bound 
  together 
  so 
  that 
  the 
  distal 
  end 
  could' 
  

   continue 
  to 
  grow 
  in 
  the 
  opposite 
  direction 
  from 
  before. 
  At 
  the 
  line 
  

  

  