﻿36 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  corners 
  but 
  slightly 
  truncated 
  by 
  the 
  interbrachials. 
  Arms 
  usually 
  ten, 
  long, 
  

   biserial, 
  simple 
  throughout. 
  Tegmen 
  low, 
  composed 
  of 
  numerous 
  irregular 
  

   plates. 
  

  

  The 
  genus 
  stands 
  out 
  distinctly 
  from 
  all 
  the 
  other 
  Melocrinidae 
  

   by 
  having 
  three 
  basals, 
  and 
  in 
  the 
  anal 
  interradius 
  three 
  plates 
  in 
  

   the 
  first 
  range 
  above 
  the 
  closed 
  radial 
  ring, 
  instead 
  of 
  only 
  one. 
  

   The 
  form 
  is 
  typically 
  Silurian, 
  six 
  species 
  having 
  thus 
  far 
  been 
  

   recognized, 
  of 
  which 
  two 
  are 
  from 
  the 
  Rochester 
  shale, 
  three 
  from 
  

   the 
  Waldron, 
  and 
  one 
  from 
  the 
  Louisville 
  limestone. 
  The 
  speci- 
  

   mens 
  of 
  these 
  species 
  are 
  rather 
  small. 
  The 
  arms, 
  so 
  far 
  as 
  known, 
  

   are 
  two 
  to 
  the 
  ray, 
  rather 
  heavy, 
  and 
  of 
  the 
  normal 
  type. 
  

  

  When 
  the 
  remarkable 
  Devonian 
  material 
  upon 
  which 
  the 
  present 
  

   species 
  is 
  described 
  was 
  first 
  seen, 
  its 
  generic 
  affinities 
  were 
  not 
  ap- 
  

   parent, 
  because 
  the 
  calyx 
  was 
  completely 
  enveloped 
  in 
  the 
  downward 
  

   hanging 
  arms, 
  and 
  its 
  composition 
  was 
  thereby 
  hidden; 
  there 
  was 
  

   no 
  thought 
  of 
  its 
  belonging 
  to 
  a 
  form 
  of 
  which 
  the 
  superficial 
  ap- 
  

   pearance 
  was 
  so 
  widely 
  different. 
  It 
  was 
  only 
  after 
  removing 
  part 
  

   of 
  the 
  arms 
  from 
  two 
  specimens 
  that 
  I 
  was 
  able 
  to 
  determine 
  the 
  

   essential 
  elements 
  which 
  fixed 
  its 
  position 
  as 
  now 
  recognized. 
  Com- 
  

   parison 
  of 
  the 
  two 
  figures 
  on 
  plate 
  9 
  with 
  the 
  foregoing 
  statement 
  

   of 
  generic 
  characters 
  leaves 
  not 
  the 
  slighest 
  doubt 
  that 
  we 
  have 
  here 
  

   a 
  well 
  marked 
  representative 
  of 
  Macro 
  stylo 
  crinus, 
  which 
  on 
  pass- 
  

   ing 
  over 
  from 
  the 
  Silurian 
  to 
  the 
  Devonian 
  has 
  undergone 
  some 
  

   striking 
  changes. 
  

  

  The 
  outstanding 
  difference 
  from 
  all 
  previously 
  described 
  species 
  

   lies 
  in 
  the 
  number 
  of 
  arms, 
  and 
  their 
  recumbent 
  habitus. 
  Instead 
  

   of 
  being 
  limited 
  to 
  10, 
  the 
  arms 
  occur 
  in 
  clusters 
  of 
  5 
  to 
  the 
  ray, 
  per- 
  

   haps 
  4 
  in 
  two 
  of 
  them, 
  given 
  a 
  total 
  of 
  23 
  to 
  25 
  arms, 
  the 
  bifurca- 
  

   tions 
  being 
  indicated 
  in 
  the 
  tegmen 
  by 
  nodose 
  axillary 
  ambulacrals. 
  

   The 
  mode 
  of 
  articulation 
  is 
  such 
  that 
  their 
  facets 
  are 
  directed 
  

   downwards 
  from 
  underneath 
  a 
  projection, 
  or 
  overhang, 
  from 
  the 
  

   edge 
  of 
  the 
  tegmen, 
  which 
  is 
  thus 
  broader 
  by 
  at 
  least 
  a 
  fourth 
  than 
  

   the 
  calyx 
  at 
  the 
  arm 
  bases. 
  Accordingly 
  the 
  tegmen 
  is 
  left 
  free 
  

   and 
  clear 
  as 
  a 
  smooth 
  roof, 
  and 
  the 
  arms, 
  heavy 
  and 
  closely 
  apposed, 
  

   form 
  a 
  closed 
  fringe 
  or 
  curtain 
  about 
  the 
  calyx, 
  meeting 
  by 
  their 
  

   distal 
  ends 
  around 
  the 
  stem, 
  and 
  having 
  their 
  outer 
  sides 
  thickly 
  

   studded 
  with 
  strong 
  pinnules. 
  They 
  do 
  not, 
  however, 
  in 
  this 
  

   species 
  press 
  closely 
  against 
  the 
  calyx 
  wall 
  so 
  as 
  to 
  leave 
  indentations, 
  

   as 
  in 
  some 
  other 
  forms, 
  but 
  there 
  is 
  an 
  open 
  space 
  between 
  the 
  calyx 
  

   and 
  the 
  dorsal 
  side 
  of 
  the 
  arms, 
  so 
  that 
  in 
  case 
  of 
  fracture 
  in 
  the 
  

   region 
  of 
  the 
  arm 
  bases 
  the 
  calyx 
  may 
  come 
  loose 
  and 
  separate 
  freely 
  

   from 
  the 
  curtain 
  of 
  arms 
  which 
  surrounds 
  it, 
  as 
  actually 
  happened 
  

   with 
  the 
  two 
  largest 
  specimens. 
  

  

  