﻿FOURTH 
  REPORT 
  OF 
  THE 
  DIRECTOR 
  IO/D7 
  63 
  

  

  made 
  to 
  solve 
  the 
  difficult 
  problem 
  of 
  removal 
  of 
  the 
  matrix 
  and 
  

   exposure 
  of 
  structural 
  details. 
  Roemer 
  figured 
  the 
  best 
  but 
  not 
  the 
  

   largest 
  of 
  his 
  specimens 
  [pi. 
  28] 
  and 
  the 
  number 
  of 
  arms 
  assigned 
  

   by 
  him 
  to 
  this 
  species 
  is 
  16. 
  Stiirtz 
  finds 
  this 
  number 
  also 
  (14-16). 
  

   At 
  all 
  events 
  the 
  species 
  is 
  large 
  and 
  its 
  arms 
  relatively 
  numerous 
  

   in 
  contrast 
  with 
  other 
  Paleozoic 
  ophiurans. 
  The 
  disk 
  is 
  mostly 
  

   covered 
  by 
  the 
  converging 
  arms 
  and 
  the 
  length 
  of 
  any 
  one 
  of 
  the 
  

   latter 
  from 
  the 
  point 
  where 
  it 
  becomes 
  free 
  to 
  its 
  tip 
  is 
  almost 
  equal 
  

   to 
  the 
  axis 
  of 
  the 
  disk 
  which 
  in 
  both 
  the 
  German 
  and 
  American 
  

   specimens 
  seems 
  not 
  to 
  be 
  normally 
  circular 
  but 
  often 
  elliptical. 
  

  

  The 
  New 
  York 
  specimens, 
  Helianthaster 
  gyalum 
  

   nov. 
  are 
  smaller 
  than 
  H 
  . 
  rhenanus. 
  The 
  arms 
  are 
  more 
  

   numerous 
  and 
  appear 
  to 
  be 
  quite 
  uniformly 
  24-25. 
  Compare! 
  to 
  

   H 
  . 
  rhenanus 
  they 
  are 
  relatively 
  short, 
  but 
  very 
  long 
  compared 
  

   with 
  the 
  size 
  of 
  the 
  disk 
  which 
  is 
  much 
  suppressed, 
  and 
  on 
  none 
  

   of 
  the 
  specimens, 
  all 
  showing 
  the 
  oral 
  surface, 
  is 
  any 
  distinct 
  evi- 
  

   dence 
  of 
  it 
  visible, 
  so 
  deeply 
  do 
  the 
  arms 
  cut 
  into 
  it 
  and 
  so 
  closely 
  

   do 
  they 
  lie 
  together. 
  Notwithstanding 
  this 
  apparent 
  retreat 
  of 
  the 
  

   disk 
  the 
  madreporiform 
  plate 
  is 
  very 
  large. 
  This 
  organ 
  is 
  preserved 
  

   in 
  but 
  one 
  example 
  and 
  but 
  here 
  it 
  overlaps 
  two 
  adjoining 
  inter- 
  

   brachial 
  angles 
  and 
  the 
  mouth 
  parts 
  pertaining 
  thereto. 
  Instead 
  of 
  

   being 
  a 
  flat 
  or 
  concave 
  elongate 
  plate 
  as 
  in 
  H 
  . 
  rhenanus 
  it 
  is 
  

   highly 
  convex 
  and 
  circular 
  ; 
  its 
  surface 
  markings 
  less 
  distinct 
  and 
  

   coarse 
  than 
  in 
  that 
  species. 
  

  

  The 
  great 
  oral 
  aperture 
  is 
  margined 
  by 
  a 
  series 
  of 
  pronounced 
  

   I 
  jaws 
  " 
  or 
  sharp 
  projecting 
  elevated 
  angles 
  the 
  sides 
  of 
  which 
  take 
  

   Drigin 
  from 
  the 
  margins 
  of 
  adjoining 
  arms. 
  These 
  oral 
  projections 
  

   are 
  slightly 
  expanded 
  at 
  their 
  tips 
  into 
  blunt 
  points 
  comparable 
  t*> 
  

   but 
  smaller 
  than 
  the 
  " 
  Hocker 
  " 
  of 
  H 
  . 
  rhenanus 
  but 
  like 
  thc^- 
  

   carry 
  small 
  spines 
  projecting 
  inward. 
  The 
  solidity 
  and 
  strength 
  ol 
  

   these 
  mouth 
  parts 
  is 
  indicated 
  by 
  their 
  prominence 
  and 
  elevation 
  as 
  

   shown 
  in 
  figure. 
  It 
  is 
  probable 
  that 
  in 
  this 
  expression 
  there 
  is 
  repre- 
  

   sented 
  a 
  combination 
  of 
  dorsal 
  and 
  ventral 
  structure 
  with 
  the 
  latter 
  

   predominant 
  by 
  compression. 
  Stiirtz 
  has 
  been 
  able 
  to 
  distinguish 
  

   the 
  dorsal 
  and 
  ventral 
  details 
  in 
  H. 
  rhenanus 
  and 
  assigns 
  to 
  

   the 
  former 
  a 
  pair 
  of 
  divergent 
  thickened 
  crescentic 
  narrow 
  and 
  

   vertical 
  plates 
  departing 
  from 
  the 
  axis 
  of 
  each 
  arm 
  and 
  each 
  member 
  

   joining 
  one 
  of 
  the 
  adjacent 
  pair, 
  thus 
  producing 
  the 
  projecting 
  oral 
  

   processes. 
  In 
  our 
  specimens 
  it 
  is 
  not 
  possible 
  to 
  discriminate 
  these 
  

   structures 
  further 
  than 
  to 
  recognize 
  in 
  them 
  a 
  combination 
  of 
  these 
  

   oral 
  plates 
  with 
  the 
  spinous 
  oral 
  processes. 
  The 
  reentrant 
  angle 
  at 
  

   the 
  base 
  of 
  each 
  arm 
  is 
  narrow, 
  long 
  and 
  acute, 
  much 
  more 
  extreme 
  

  

  