﻿4 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  A 
  special 
  form 
  of 
  stem 
  development 
  which 
  I 
  wish 
  to 
  illustrate 
  

   is 
  that 
  in 
  which 
  the 
  usually 
  cylindrical 
  or 
  pentagonal 
  straight 
  stem 
  

   loses 
  its 
  characteristic 
  shape, 
  becomes 
  coiled, 
  and 
  takes 
  on 
  a 
  bilateral 
  

   symmetry, 
  by 
  which 
  for 
  the 
  greater 
  part 
  of 
  its 
  length 
  it 
  is 
  flattened 
  

   or 
  concave 
  at 
  the 
  inner 
  side, 
  with 
  the 
  columnals 
  elliptic 
  or 
  crescentic 
  

   in 
  cross 
  section 
  ; 
  and 
  the 
  cirri, 
  instead 
  of 
  occurring 
  in 
  whorls 
  around 
  

   the 
  column, 
  are 
  borne 
  only 
  in 
  two 
  rows 
  at 
  or 
  near 
  the 
  margins 
  of 
  the 
  

   flattened 
  or 
  concave 
  side, 
  or 
  sometimes 
  at 
  the 
  back. 
  This 
  structure 
  

   is 
  correlated 
  — 
  either 
  as 
  a 
  cause 
  or 
  an 
  effect 
  — 
  with 
  a 
  tendency 
  of 
  the 
  

   crown 
  to 
  bend 
  back 
  upon 
  the 
  stem, 
  and 
  of 
  the 
  stem 
  to 
  coil 
  around 
  it 
  

   in 
  the 
  opposite 
  direction 
  in 
  such 
  a 
  way 
  that 
  the 
  crown 
  may 
  be 
  tightly 
  

   enclosed 
  within 
  the 
  coil 
  and 
  completely 
  enveloped 
  by 
  the 
  cirri. 
  The 
  

   part 
  of 
  the 
  stem 
  proximal 
  to 
  the 
  calyx 
  is 
  circular 
  in 
  section, 
  much 
  re- 
  

   duced 
  in 
  diameter, 
  relatively 
  short 
  as 
  a 
  rule, 
  but 
  variable 
  in 
  length; 
  

   and 
  it 
  bears 
  no 
  cirri. 
  The 
  reversed 
  curve 
  is 
  similar 
  to 
  that 
  of 
  a 
  

   swan's 
  neck, 
  and 
  for 
  convenience 
  the 
  term 
  " 
  neck 
  " 
  may 
  be 
  used 
  for 
  it 
  

   in 
  the 
  discussions. 
  

  

  This 
  character 
  was 
  evidently 
  protective 
  in 
  origin, 
  as 
  the 
  crown 
  is 
  

   often 
  very 
  small 
  in 
  comparison 
  with 
  the 
  stem; 
  and 
  in 
  some 
  forms, 
  

   where 
  the 
  cirri 
  are 
  short 
  and 
  closely 
  packed, 
  the 
  crown 
  is 
  so 
  sur- 
  

   rounded 
  by 
  the 
  stem 
  structures 
  that 
  it 
  can 
  rarely 
  be 
  seen 
  in 
  the 
  fos- 
  

   sils 
  ; 
  while 
  in 
  others, 
  in 
  which 
  the 
  cirri 
  are 
  more 
  scattered 
  but 
  strong 
  

   and 
  branching, 
  the 
  neck 
  upon 
  which 
  the 
  crown 
  was 
  borne 
  is 
  long, 
  

   slender, 
  and 
  exceedingly 
  brittle, 
  not 
  tightly 
  rolled, 
  but 
  evidently 
  

   loosely 
  enveloped 
  in 
  a 
  fringe 
  formed 
  by 
  the 
  strong 
  cirri. 
  Here 
  it 
  

   must 
  have 
  been 
  very 
  sensitive 
  to 
  disturbance, 
  for 
  in 
  the 
  fossil 
  the 
  

   stem 
  is 
  almost 
  invariably 
  broken 
  off 
  at 
  the 
  slender 
  neck. 
  In 
  those 
  

   forms 
  in 
  which 
  the 
  stem 
  was 
  tightly 
  coiled 
  it 
  could 
  be 
  uncoiled 
  and 
  

   the 
  crown 
  exposed. 
  

  

  This 
  type 
  of 
  stem 
  is 
  found 
  in 
  otherwise 
  unrelated 
  forms 
  from 
  the 
  

   Silurian 
  to 
  the 
  latest 
  member 
  of 
  the 
  Lower 
  Carboniferous. 
  It 
  occurs 
  

   irregularly, 
  and 
  so 
  far 
  as 
  yet 
  known, 
  without 
  continuity, 
  and 
  without 
  

   any 
  definite 
  or 
  exclusive 
  correlation 
  with 
  other 
  characters. 
  After 
  

   appearing 
  in 
  several 
  Inadunate 
  species 
  in 
  the 
  Niagaran 
  of 
  America, 
  

   and 
  the 
  Wenlockian 
  of 
  England 
  and 
  Sweden, 
  closely 
  followed 
  by 
  

   three 
  in 
  the 
  Lower 
  Devonian 
  and 
  one 
  of 
  uncertain 
  relations 
  in 
  the 
  

   Middle 
  Devonian, 
  the 
  coiled 
  stem 
  structure 
  reappears 
  after 
  a 
  con- 
  

   siderable 
  interval 
  in 
  the 
  Burlington 
  limestone 
  of 
  the 
  Lower 
  Car- 
  

   boniferous, 
  but 
  in 
  a 
  different 
  suborder 
  of 
  the 
  crinoids, 
  the 
  Camerata, 
  

   in 
  one 
  family 
  of 
  which 
  it 
  continues 
  to 
  the 
  end 
  in 
  the 
  upper 
  part 
  of 
  

   the 
  Chester. 
  Generic 
  names 
  have 
  been 
  given 
  based 
  upon 
  these 
  occur- 
  

   rences; 
  but 
  in 
  the 
  Silurian 
  forms, 
  owing 
  to 
  the 
  closely 
  inrolled 
  con- 
  

   dition 
  in 
  which 
  the 
  stems 
  are 
  usually 
  found, 
  the 
  crown 
  is 
  very 
  sel- 
  

   dom 
  seen 
  in 
  a 
  state 
  from 
  which 
  the 
  elements 
  of 
  the 
  calyx 
  can 
  be 
  

   ascertained 
  sufficiently 
  for 
  a 
  proper 
  diagnosis. 
  While 
  there 
  are 
  

  

  