﻿\ki 
  9 
  UNUSUAL, 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  — 
  SPRINGER 
  19 
  

  

  Horizon 
  and 
  locality. 
  — 
  Silurian, 
  Rochester 
  shale; 
  Lockport, 
  Xew 
  

   York, 
  Avhere 
  it 
  is 
  one 
  of 
  the 
  leading 
  crinoid 
  species. 
  No 
  trace 
  of 
  

   it 
  has 
  been 
  seen 
  in 
  other 
  horizons 
  in 
  which 
  the 
  genus 
  occurs. 
  

  

  MYELODACTYLUS 
  KEYSERENSIS, 
  new 
  species 
  

  

  Plate 
  6, 
  figs. 
  1-3 
  

  

  Coil 
  open, 
  with 
  stem 
  diminishing 
  but 
  little 
  distalwards. 
  Cirri 
  

   numerous, 
  long, 
  slender, 
  closely 
  apposed, 
  slightly 
  rounded 
  but 
  not 
  

   moniliform; 
  mostly 
  paired 
  on 
  successive 
  columnals. 
  Crown 
  large, 
  

   with 
  long 
  arms 
  branching 
  repeatedly; 
  its 
  bulk 
  producing 
  a 
  notice- 
  

   able 
  swelling 
  of 
  the 
  two 
  rows 
  of 
  closely 
  packed 
  cirri 
  inclosing 
  it. 
  

   Rays 
  5, 
  irregular, 
  of 
  the 
  Iocrinus 
  type, 
  the 
  anal 
  tube 
  borne 
  on 
  the 
  

   left 
  shoulder 
  of 
  r. 
  post. 
  Rs. 
  

  

  This 
  species 
  differs 
  from 
  all 
  Silurian 
  forms 
  in 
  the 
  conspicuous 
  

   bulging 
  caused 
  by 
  the 
  large 
  size 
  of 
  the 
  crown. 
  I 
  have 
  nine 
  specimens 
  

   from 
  the 
  Keyser 
  beds, 
  in 
  all 
  of 
  which 
  the 
  presence 
  of 
  the 
  crown 
  is 
  

   indicated 
  by 
  this 
  feature. 
  In 
  size, 
  shape, 
  and 
  distribution 
  of 
  the 
  

   cirri 
  this 
  form 
  does 
  not 
  differ 
  essentially 
  from 
  M. 
  convolutus, 
  but 
  

   the 
  bulkiness 
  of 
  the 
  crown 
  differentiates 
  the 
  two 
  readily. 
  

  

  In 
  two 
  of 
  the 
  specimens 
  the 
  crown 
  is 
  well 
  exposed, 
  so 
  that 
  its 
  com- 
  

   position 
  may 
  be 
  studied. 
  The 
  swelling 
  is 
  not 
  due 
  to 
  the 
  calyx, 
  but 
  

   appears 
  in 
  the 
  arm 
  region, 
  leading 
  to 
  the 
  inference 
  that 
  it 
  is 
  caused 
  

   by 
  an 
  inflated 
  anal 
  tube 
  or 
  sac, 
  such 
  as 
  occurs 
  in 
  Ohiocrinus, 
  and, 
  

   though 
  rarely 
  seen, 
  in 
  Anomalocrinus. 
  The 
  rays 
  differ 
  greatly 
  in 
  

   size 
  in 
  the 
  one 
  specimen 
  in 
  which 
  they 
  can 
  be 
  fully 
  observed 
  (pi. 
  6 
  

   figs. 
  1-lc) 
  ; 
  r. 
  post, 
  and 
  r. 
  ant. 
  being 
  narrow, 
  the 
  other 
  three 
  much 
  

   wider; 
  I. 
  ant. 
  the 
  widest 
  of 
  all, 
  and 
  branching 
  higher 
  up 
  than 
  the 
  

   others. 
  The 
  difference 
  in 
  the 
  development 
  of 
  the 
  rays 
  is 
  connected 
  

   with 
  their 
  relative 
  position 
  in 
  the 
  curvature 
  of 
  the 
  crown. 
  The 
  

   largest 
  one, 
  I. 
  ant., 
  being 
  at 
  the 
  outside 
  of 
  the 
  curve, 
  was 
  freest 
  to 
  

   develop 
  and 
  filled 
  the 
  greatest 
  space; 
  whereas 
  r. 
  post, 
  and 
  r. 
  ant. 
  

   were 
  much 
  cramped 
  at 
  the 
  inner 
  side 
  of 
  the 
  curve, 
  compressed, 
  and 
  

   dwarfed 
  in 
  their 
  growth, 
  especially 
  r. 
  ant., 
  which 
  does 
  not 
  branch 
  

   at 
  all. 
  The 
  first 
  bifurcation 
  in 
  the 
  others 
  is 
  at 
  different 
  heights, 
  

   and 
  beyond 
  that 
  the 
  arms 
  branch 
  five 
  or 
  six 
  times 
  to 
  very 
  fine 
  finials. 
  

  

  In 
  the 
  two 
  largest 
  specimens, 
  having 
  diameters 
  at 
  the 
  close 
  coil 
  of 
  

   about 
  30 
  mm., 
  the 
  stems 
  extend 
  for 
  5 
  and 
  6 
  cm. 
  bej^ond 
  that, 
  and 
  are 
  

   4.5 
  and 
  5.5 
  mm. 
  in 
  width, 
  without 
  noticeable 
  diminution; 
  in 
  these 
  

   the 
  thickness 
  of 
  the 
  swollen 
  part 
  is 
  6 
  and 
  12.5 
  mm. 
  respectively, 
  

   being 
  thus 
  about 
  double 
  the 
  width 
  of 
  the 
  stems. 
  In 
  another 
  large 
  

   incomplete 
  specimen 
  the 
  swelling 
  is 
  15 
  mm. 
  thick 
  (pi. 
  6. 
  fig. 
  3) 
  ; 
  and 
  

   a 
  smaller 
  specimen, 
  with 
  a 
  coil 
  18 
  mm. 
  in 
  diameter, 
  has 
  the 
  swelling 
  

   enlarged 
  to 
  15 
  mm. 
  

  

  Horizon 
  and 
  locality. 
  — 
  Lower 
  Devonian, 
  Helderbergian, 
  Keyser 
  

   formation; 
  Keyser, 
  West 
  Virginia. 
  

  

  