﻿HYBOCKINUS, 
  BAEROCRIXUS, 
  AND 
  HYBOCYSTITES. 
  309 
  

  

  but 
  I 
  would 
  point 
  out 
  that 
  they 
  are 
  almost 
  equally 
  comparable 
  to 
  

   the 
  ambulacra 
  of 
  the 
  Blastoids 
  ; 
  and 
  I 
  am 
  inclined 
  to 
  think 
  that 
  

   the 
  relations 
  of 
  Hybocystites 
  are 
  rather 
  with 
  this 
  group 
  and 
  with 
  the 
  

   Crinoids 
  than 
  with 
  the 
  Cystids. 
  For 
  I 
  cannot 
  make 
  out 
  that 
  it 
  had 
  

   any 
  arms 
  at 
  all, 
  in 
  the 
  ordinary 
  acceptance 
  of 
  this 
  term 
  in 
  Crinoid 
  

   anatomy. 
  In 
  the 
  only 
  figure* 
  which 
  shows 
  any 
  thing 
  of 
  the 
  arms 
  

   described 
  by 
  Prof. 
  'Wetherby, 
  two 
  joints 
  only 
  are 
  represented 
  above 
  

   the 
  radials 
  (PL 
  XI. 
  fig. 
  6) 
  ; 
  and 
  he 
  nowhere 
  speaks 
  of 
  having 
  found 
  

   any 
  specimen 
  with 
  a 
  larger 
  number 
  of 
  arm-joints 
  still 
  in 
  connexion 
  

   with 
  the 
  calyx, 
  such 
  as 
  are 
  shown 
  in 
  his 
  figure 
  of 
  Hyhocrinus. 
  

  

  But 
  he 
  describes 
  " 
  a 
  more 
  or 
  less 
  obscure 
  furrow 
  " 
  upon 
  the 
  

   outer 
  surface 
  of 
  each 
  arm, 
  " 
  of 
  which 
  nothing 
  further 
  is 
  known." 
  

  

  This 
  furrow 
  is 
  in 
  reality 
  a 
  recurrent 
  ambulacrum, 
  as 
  may 
  be 
  seen 
  

   in 
  figs. 
  8-24. 
  It 
  is 
  most 
  clearly 
  seen 
  in 
  figs. 
  8, 
  14, 
  and 
  20, 
  which 
  

   respectively 
  represent 
  a 
  direct 
  view 
  of 
  the 
  anterior 
  ambulacrum 
  in 
  

   each 
  of 
  the 
  three 
  specimens. 
  They 
  should 
  be 
  compared 
  with 
  figs. 
  

   9, 
  12, 
  15, 
  18, 
  21, 
  23, 
  representing 
  identical 
  views 
  of 
  the 
  right 
  

   and 
  left 
  anterior 
  ambulacra, 
  viz. 
  the 
  appressed 
  ones, 
  to 
  which 
  they 
  

   are 
  similar 
  in 
  all 
  respects. 
  

  

  I 
  believe 
  the 
  supposed 
  " 
  arms" 
  to 
  be 
  merely 
  upward 
  prolonga- 
  

   tions 
  of* 
  the 
  radials, 
  which 
  are 
  possibly 
  more 
  or 
  less 
  segmented 
  in 
  

   the 
  same 
  way 
  as 
  the 
  downward- 
  extending 
  radials 
  are 
  in 
  Pentacrinus 
  

   briar 
  eus. 
  There 
  seems, 
  however, 
  to 
  be 
  much 
  variation 
  in 
  this 
  

   respect; 
  for 
  while 
  two 
  segments 
  seem 
  clearly 
  visible 
  in 
  the 
  left 
  

   posterior 
  ray 
  of 
  Wachsmuth's 
  smaller 
  specimen 
  (figs. 
  20, 
  21, 
  23, 
  

   24), 
  there 
  are 
  but 
  faint 
  traces 
  of 
  grooves 
  marking 
  off 
  a 
  second 
  

   segment 
  in 
  either 
  of 
  the 
  other 
  two 
  rays. 
  In 
  Prof. 
  ""NVetherby's 
  

   specimen, 
  again, 
  delicate 
  lines 
  are 
  visible 
  crossing 
  the 
  radial 
  exten- 
  

   sions 
  ; 
  but 
  I 
  have 
  great 
  doubts 
  as 
  to 
  whether 
  they 
  are 
  really 
  to 
  be 
  

   regarded 
  as 
  indicating 
  segmentation. 
  

  

  Of 
  the 
  five 
  ambulacra, 
  therefore, 
  which 
  diverge 
  from 
  the 
  peri- 
  

   stome, 
  the 
  right 
  and 
  left 
  anterior 
  ones 
  pass 
  directly 
  downwards 
  

   from 
  the 
  summit 
  onto 
  the 
  corresponding 
  radial 
  plates, 
  and 
  from 
  

   them 
  onto 
  the 
  basals 
  as 
  described 
  by 
  Prof. 
  "\Yetherby. 
  The 
  other 
  

   three 
  ascend 
  the 
  inner 
  faces 
  of 
  the 
  short 
  radial 
  extensions, 
  pass 
  

   over 
  their 
  tops, 
  and 
  down 
  their 
  outer 
  faces. 
  They 
  are 
  least 
  visible 
  

   in 
  Wachsmuth's 
  larger 
  specimen 
  (figs. 
  14-19), 
  which 
  has 
  lost 
  the 
  

   upper 
  ends 
  of 
  its 
  radial 
  extensions. 
  But 
  in 
  his 
  smaller 
  one 
  the 
  two 
  

   posterolateral 
  ambulacra 
  are 
  very 
  distinct 
  (figs. 
  23, 
  24), 
  more 
  so 
  in 
  

   fact 
  than 
  the 
  appressed 
  anterolateral 
  pair 
  ; 
  and 
  they 
  are 
  to 
  be 
  seen, 
  

   though 
  not 
  clearly, 
  passing 
  over 
  the 
  upper 
  ends 
  of 
  the 
  radial 
  exten- 
  

   sions 
  on 
  the 
  way 
  from 
  their 
  inner 
  to 
  their 
  outer 
  faces. 
  This 
  feature 
  

   is 
  best 
  seen 
  in 
  Prof. 
  "Wetherby's 
  specimen, 
  as 
  is 
  shown 
  in 
  fig. 
  10. 
  

  

  In 
  reference 
  to 
  this 
  question, 
  I 
  may 
  mention 
  that 
  I 
  have 
  shown 
  

   these 
  specimens 
  to 
  several 
  palaeontologists, 
  including 
  Mr. 
  R. 
  Ether- 
  

   idge, 
  F.B.S., 
  and 
  his 
  accomplished 
  son, 
  and 
  also 
  to 
  other 
  naturalists 
  

   who 
  have 
  made 
  a 
  special 
  study 
  of 
  Echinoderm 
  structure. 
  All 
  of 
  

   them, 
  I 
  am 
  glad 
  to 
  say, 
  have 
  confirmed 
  my 
  interpretation 
  of 
  the 
  

   "more 
  or 
  less 
  obscure 
  furrows" 
  upon 
  the 
  outer 
  surfaces 
  of 
  the 
  

   * 
  Loc. 
  cit. 
  pi. 
  t. 
  fig. 
  la, 
  

  

  Q.J.G.S. 
  No. 
  151. 
  y 
  

  

  