﻿art 
  9 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CPJNOIDS 
  SPRINGER 
  23 
  

  

  vonian 
  of 
  the 
  Eifel, 
  which 
  have 
  been 
  in 
  my 
  possession 
  for 
  many 
  

   years, 
  but 
  hitherto 
  undescribed 
  because 
  I 
  was 
  uncertain 
  of 
  their 
  

   affinities. 
  With 
  the 
  present 
  study 
  of 
  this 
  group 
  it 
  seemed 
  probable 
  

   that 
  these 
  curious 
  fossils 
  belonged 
  here, 
  although 
  they 
  resemble 
  

   nothing 
  in 
  the 
  crinoid 
  line 
  that 
  has 
  ever 
  been 
  seen 
  before. 
  Their 
  

   superficial 
  appearance 
  is 
  that 
  of 
  a 
  coiled 
  shell; 
  but 
  that 
  idea 
  was 
  

   excluded 
  by 
  the 
  fact 
  that 
  they 
  have 
  a 
  jointed 
  structure, 
  and 
  are 
  

   built 
  up 
  of 
  movable 
  segments, 
  coordinated 
  by 
  an 
  axial 
  nerve 
  cord 
  

   lodged 
  in 
  a 
  canal 
  which 
  perforates 
  the 
  coil 
  longitudinally, 
  thus 
  en- 
  

   abling 
  it 
  to 
  open 
  and 
  close. 
  Their 
  systematic 
  relation 
  with 
  the 
  group 
  

   now 
  under 
  consideration 
  was 
  definitely 
  established 
  when 
  upon 
  re- 
  

   moving 
  the 
  projecting 
  processes 
  from 
  the 
  segments 
  on 
  one 
  side 
  there 
  

   was 
  disclosed 
  the 
  calyx 
  of 
  a 
  crinoid 
  tightly 
  enveloped 
  within 
  the 
  coil. 
  

  

  The 
  extreme 
  width 
  of 
  the 
  segments 
  forming 
  the 
  enclosing 
  struc- 
  

   ture, 
  in 
  proportion 
  to 
  the 
  diameter 
  of 
  the 
  coil, 
  seemed 
  to 
  preclude 
  

   any 
  analogy 
  with 
  the 
  stem 
  of 
  a 
  crinoid; 
  but 
  the 
  facts 
  as 
  brought 
  

   forth 
  by 
  the 
  investigation 
  show 
  conclusively 
  that 
  it 
  can 
  not 
  be 
  any- 
  

   thing 
  else. 
  They 
  disclose 
  a 
  specialization 
  which 
  amounts 
  almost 
  to 
  

   a 
  freak, 
  furnishing 
  a 
  fresh 
  exemplification 
  of 
  the 
  truth 
  that 
  in 
  na- 
  

   ture 
  any 
  modification 
  of 
  an 
  organism 
  may 
  be 
  expected 
  which 
  is 
  not 
  

   a 
  mechanical 
  impossibility. 
  

  

  A 
  few 
  measurements 
  will 
  show 
  to 
  what 
  an 
  extreme 
  the 
  modifica- 
  

   tion 
  in 
  this 
  form 
  has 
  gone. 
  The 
  coil 
  is 
  tightly 
  closed 
  in 
  both 
  speci- 
  

   mens, 
  with 
  the 
  distal 
  end 
  closely 
  adherent 
  and 
  tapering 
  rapidly 
  to 
  

   a 
  point. 
  It 
  is 
  more 
  or 
  less 
  elliptic 
  in 
  both, 
  with 
  long 
  and 
  short 
  diam- 
  

   eters, 
  respectively, 
  of 
  18-22 
  and 
  15-16 
  mm. 
  It 
  is 
  composed 
  of 
  rela- 
  

   tively 
  few 
  segments, 
  or 
  columnals, 
  which 
  are 
  of 
  great 
  width 
  and 
  

   thickness, 
  and 
  project 
  on 
  the 
  perimeter 
  of 
  the 
  curve 
  in 
  strong 
  ridges, 
  

   like 
  cogs 
  upon 
  a 
  wheel. 
  In 
  the 
  smaller 
  specimen 
  there 
  are 
  20 
  colum- 
  

   nals 
  on 
  the 
  exposed 
  surface, 
  a 
  distance 
  of 
  about 
  50 
  mm., 
  and 
  in 
  

   the 
  larger 
  one 
  24 
  columnals 
  in 
  a 
  distance 
  of 
  62 
  mm. 
  Thus 
  the 
  colum- 
  

   nals 
  are 
  about 
  2.5 
  mm. 
  in 
  thickness, 
  or 
  length 
  longitudinal 
  to 
  the 
  

   curve, 
  at 
  the 
  exterior. 
  In 
  coils 
  of 
  Myelodactylus 
  ammonis 
  of 
  like 
  

   diameter 
  there 
  would 
  be 
  about 
  70 
  and 
  85 
  columnals 
  for 
  correspond- 
  

   ing 
  lengths 
  of 
  curve. 
  

  

  The 
  width 
  of 
  the 
  columnals 
  is 
  still 
  more 
  extraordinary 
  as 
  com- 
  

   pared 
  with 
  those 
  of 
  any 
  similar 
  form. 
  In 
  the 
  region 
  of 
  greatest 
  

   width 
  in 
  the 
  two 
  specimens 
  they 
  are 
  respectively 
  10 
  and 
  12 
  mm. 
  

   wide. 
  That 
  is 
  to 
  say, 
  this 
  over-developed 
  or 
  hypertrophied 
  coiled 
  

   stem 
  has 
  a 
  width 
  exceeding 
  half 
  the 
  diameter 
  of 
  the 
  coil. 
  We 
  are 
  

   accustomed 
  to 
  think 
  of 
  the 
  stem 
  of 
  a 
  crinoid 
  as 
  a 
  much 
  elongated 
  

   structure, 
  but 
  here 
  we 
  have 
  a 
  stem 
  of 
  which 
  the 
  width 
  is 
  about 
  one 
  

   sixth 
  of 
  its 
  possible 
  length. 
  

  

  The 
  most 
  remarkable 
  thing 
  about 
  the 
  organism, 
  however, 
  is 
  the 
  

   marginal 
  appendages, 
  which 
  occupy 
  at 
  either 
  end 
  of 
  the 
  segments 
  

  

  