﻿28 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  TOL. 
  67 
  

  

  of 
  the 
  curve 
  only 
  in 
  the 
  last 
  5 
  cm., 
  where 
  the 
  columnals, 
  which 
  are 
  

   of 
  about 
  equal 
  length 
  throughout, 
  become 
  slightly 
  elliptic; 
  they 
  are 
  

   small, 
  not 
  very 
  regularly 
  placed, 
  but 
  mostly 
  on 
  alternate 
  columnals. 
  

   The 
  alternation 
  of 
  paired 
  nodals 
  with 
  one 
  or 
  more 
  large 
  internodals, 
  

   which 
  is 
  so 
  marked 
  a 
  character 
  in 
  the 
  later 
  species, 
  has 
  not 
  appeared 
  

   in 
  this 
  one. 
  

  

  This 
  form 
  is 
  exceedingly 
  rare, 
  not 
  having 
  been 
  observed 
  by 
  any 
  of 
  

   the 
  early 
  collectors 
  at 
  Burlington 
  — 
  the 
  fine 
  specimen 
  here 
  illustrated 
  

   and 
  another 
  imperfect 
  one 
  being 
  the 
  only 
  examples 
  among 
  the 
  

   numerous 
  collections 
  covering 
  a 
  period 
  of 
  over 
  fifty 
  years 
  at 
  that 
  

   prolific 
  locality. 
  

  

  Horizon 
  and 
  locality.— 
  Mississippian, 
  Upper 
  Burlington 
  lime- 
  

   stone; 
  Burlington, 
  Iowa. 
  

  

  CAMPTOCRINUS 
  MYELODACTYLUS 
  Wachsmuth 
  and 
  Springer 
  

  

  Plate 
  7, 
  figs. 
  2-5& 
  

  

  Camptocrinus 
  myelodactylus 
  Wachsmuth 
  and 
  Springer, 
  North 
  American 
  

   Crinoidea 
  Camerata, 
  1897, 
  p. 
  779, 
  pi. 
  75, 
  figs. 
  2a 
  and 
  2b 
  (not 
  fig. 
  1). 
  

  

  Coil 
  close 
  in 
  proximal 
  region. 
  Stem 
  long, 
  extending 
  in 
  the 
  middle 
  

   and 
  distal 
  portions 
  into 
  a 
  broad 
  curve, 
  tapering 
  to 
  near 
  the 
  end; 
  

   below 
  the 
  proximal 
  neck, 
  which 
  is 
  relatively 
  short, 
  it 
  is 
  composed 
  of 
  

   pairs 
  of 
  short 
  columnals 
  (nodals) 
  bearing 
  the 
  cirri 
  in 
  marginal 
  

   rows 
  at 
  each 
  end, 
  with 
  a 
  longer 
  one 
  (internodal) 
  interposed 
  between 
  

   them 
  equal 
  in 
  length 
  to 
  the 
  two 
  combined 
  nodals. 
  Cirri 
  strong, 
  

   rounded, 
  rather 
  long; 
  composed 
  of 
  15 
  to 
  20 
  diminishing 
  cirrals, 
  

   and 
  tapering 
  rapidly 
  from 
  their 
  origin; 
  they 
  are 
  doubled 
  (or 
  

   trebled) 
  from 
  each 
  side 
  of 
  the 
  paired 
  nodals, 
  springing 
  from 
  a 
  large 
  

   facet 
  midway 
  of 
  the 
  pair, 
  with 
  an 
  additional 
  facet 
  or 
  bifurcation 
  

   following 
  behind 
  it. 
  Thus 
  there 
  are 
  along 
  each 
  margin 
  at 
  the 
  con- 
  

   cave 
  side 
  of 
  the 
  stem 
  what 
  appear 
  to 
  be 
  duplicate 
  cirri, 
  separated 
  by 
  

   the 
  interval 
  of 
  the 
  longer 
  internodal 
  columnal. 
  This 
  is 
  the 
  way 
  

   they 
  usually 
  appear 
  in 
  well 
  preserved 
  specimens; 
  but 
  actually 
  there 
  

   is 
  frequently 
  a 
  third 
  cirrus, 
  and 
  perhaps 
  a 
  fourth, 
  each 
  smaller 
  than 
  

   the 
  one 
  preceding, 
  forming 
  a 
  cluster 
  diminishing 
  in 
  size 
  inward. 
  

   The 
  innermost 
  cirri 
  beyond 
  the 
  second 
  are 
  only 
  to 
  be 
  seen 
  after 
  

   most 
  careful 
  preparation 
  under 
  a 
  strong 
  magnifier, 
  being 
  crowded 
  

   inward 
  and 
  covered 
  by 
  the 
  outer 
  ones 
  overlapping 
  owing 
  to 
  the 
  

   curvature 
  of 
  the 
  stem. 
  It 
  was 
  only 
  after 
  patient 
  work, 
  under 
  ex- 
  

   ceptionally 
  favorable 
  conditions 
  of 
  preservation, 
  that 
  the 
  facts 
  were 
  

   ascertained 
  from 
  which 
  the 
  sketches 
  were 
  composed 
  by 
  Mr. 
  Chap- 
  

   man, 
  showing 
  the 
  details 
  of 
  these 
  structures 
  in 
  this 
  and 
  other 
  

   species. 
  

  

  