﻿art 
  9 
  UNUSUAL. 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  15 
  

  

  after 
  several 
  failures 
  succeeded 
  in 
  getting 
  a 
  polished 
  section 
  giving 
  

   the 
  outline 
  of 
  the 
  crown. 
  All 
  that 
  it 
  shows 
  is 
  that 
  the 
  arms 
  are 
  

   long 
  and 
  extremely 
  slender, 
  with 
  calyx 
  evidently 
  of 
  the 
  heterocrinid 
  

   type 
  (pi. 
  3, 
  fig. 
  7). 
  To 
  judge 
  by 
  the 
  space 
  it 
  occupies 
  this 
  crown 
  

   may 
  have 
  only 
  four 
  rays. 
  

  

  On 
  plate 
  9, 
  figure 
  10, 
  there 
  is 
  a 
  picture 
  of 
  a 
  round 
  stem 
  spirally 
  

   coiled 
  and 
  tightly 
  wound 
  about 
  another 
  crinoid 
  stem, 
  without 
  any 
  

   trace 
  of 
  bilateralism. 
  It 
  is 
  shown 
  here 
  in 
  order 
  to 
  caution 
  observers 
  

   against 
  being 
  misled 
  by 
  a 
  superficial 
  resemblance, 
  in 
  view 
  of 
  the 
  fact 
  

   that 
  coiled 
  stem 
  fragments 
  like 
  this, 
  attached 
  to 
  other 
  objects, 
  are 
  not 
  

   uncommon 
  in 
  the 
  same 
  Silurian 
  formation 
  of 
  Tennessee 
  which 
  con- 
  

   tains 
  species 
  of 
  Myelodactylus 
  herein 
  described. 
  Such 
  a 
  piece 
  was 
  

   figured 
  by 
  Eoemer 
  in 
  Silurian 
  Fauna 
  des 
  Westlichen 
  Tennessee, 
  1860 
  

   (pi. 
  4, 
  figs. 
  11a, 
  b, 
  c) 
  and 
  discussed 
  on 
  page 
  57. 
  These 
  spiral 
  stems 
  

   have 
  not 
  been 
  found 
  in 
  connection 
  with 
  the 
  corresponding 
  crown 
  or 
  

   calyx. 
  But 
  this 
  form 
  has 
  nothing 
  whatever 
  to 
  do 
  with 
  the 
  bilateral 
  

   stem 
  of 
  Myelodactylus, 
  and 
  belongs 
  to 
  some 
  entirely 
  different 
  group. 
  

  

  These 
  two 
  kinds 
  of 
  stem 
  .have 
  formed 
  the 
  subject 
  of 
  an 
  elaborate 
  

   paper 
  by 
  Dr. 
  K. 
  Ehrenberg 
  upon 
  Coiled 
  Stems 
  in 
  the 
  Pelmatozoa 
  

   and 
  their 
  relation 
  to 
  Sessility, 
  10 
  which 
  only 
  came 
  to 
  my 
  attention 
  

   after 
  the 
  present 
  memoir 
  was 
  nearly 
  completed. 
  In 
  it 
  he 
  refers 
  to 
  

   another 
  paper 
  devoted 
  especially 
  to 
  Herpetocrinus 
  soon 
  to 
  appear, 
  

   but 
  which 
  I 
  have 
  not 
  seen. 
  

  

  Doctor 
  Ehrenberg 
  divides 
  the 
  crinoids 
  with 
  coiled 
  stem 
  into 
  two 
  

   general 
  types, 
  the 
  first 
  with 
  nonbilateral 
  stem 
  in 
  which 
  the 
  coiling 
  

   is 
  more 
  or 
  less 
  limited 
  to 
  the 
  distal 
  part 
  — 
  which 
  would 
  be 
  like 
  the 
  

   specimens 
  above 
  mentioned; 
  and 
  the 
  second 
  in 
  which 
  the 
  stem 
  is 
  

   bilateral, 
  and 
  coiled 
  throughout 
  its 
  entire 
  length, 
  such 
  as 
  Myelodac- 
  

   tylus 
  {Herpetocrinus 
  as 
  he 
  prefers 
  to 
  call 
  it) 
  and 
  similar 
  forms. 
  

   The 
  first 
  type, 
  being 
  capable 
  of 
  attachment 
  by 
  its 
  coiled 
  distal 
  end 
  to 
  

   other 
  objects, 
  he 
  considers 
  to 
  be 
  adapted 
  to 
  a 
  sessile 
  mode 
  of 
  life. 
  

   In 
  the 
  second, 
  where 
  the 
  coiling 
  involves 
  the 
  entire 
  stem, 
  and 
  the 
  

   crown 
  is 
  enveloped 
  within 
  it, 
  there 
  is 
  no 
  indication 
  of 
  sessility, 
  but 
  

   it 
  had 
  a 
  vagrant, 
  pelagic 
  habitus, 
  somewhat 
  like 
  that 
  of 
  the 
  Ammon- 
  

   ites. 
  In 
  each 
  type 
  the 
  coiling 
  must 
  be 
  viewed 
  as 
  an 
  adaptation 
  to 
  its 
  

   particular 
  mode 
  of 
  life. 
  

  

  I 
  do 
  not 
  here 
  attempt 
  to 
  follow 
  the 
  author's 
  discussion 
  of 
  the 
  

   origin 
  of 
  the 
  coiled 
  stem, 
  and 
  its 
  bearing 
  upon 
  the 
  phylogeny 
  of 
  the 
  

   Pelmatozoa, 
  but 
  I 
  hope 
  the 
  new 
  facts 
  now 
  being 
  brought 
  out 
  may 
  

   throw 
  further 
  light 
  upon 
  that 
  phase 
  of 
  the 
  subject. 
  

  

  Horizon 
  and 
  locality. 
  — 
  Silurian, 
  Brownsport 
  formation 
  of 
  the 
  late 
  

   Niagaran; 
  Decatur 
  County, 
  Tennessee. 
  

  

  10 
  Acta 
  Zoologica. 
  Vienna, 
  1022, 
  vol. 
  3, 
  p. 
  271. 
  and 
  following. 
  

  

  