﻿HYBOcunrus, 
  baeHoceinus, 
  and 
  hybocystites. 
  307 
  

  

  is, 
  therefore, 
  no 
  " 
  articulation" 
  between 
  it 
  and 
  a 
  radial 
  plate 
  below, 
  

   as 
  is 
  the 
  case 
  with 
  the 
  bifurcating 
  plate 
  of 
  locrinus 
  ; 
  for 
  it 
  is 
  

   united 
  to 
  the 
  basals 
  by 
  suture 
  ; 
  and, 
  being 
  beloiv 
  an 
  arm-bearing 
  

   radial, 
  it 
  can 
  hardly 
  be 
  considered 
  a 
  modified 
  brachial, 
  i. 
  e. 
  as 
  

   belonging 
  to 
  the 
  series 
  above 
  the 
  radials. 
  It 
  should 
  be 
  so 
  con- 
  

   sidered, 
  however, 
  if 
  it 
  is 
  to 
  be 
  comparable 
  to 
  the 
  bifurcating 
  plate 
  

   of 
  locrinus 
  in 
  the 
  manner 
  suggested 
  by 
  Wachsmuth 
  and 
  Springer. 
  

   I 
  cannot, 
  therefore, 
  follow 
  these 
  authors 
  in 
  regarding 
  locrinus 
  as 
  

   the 
  starting-point 
  from 
  which 
  the 
  development 
  of 
  the 
  anal 
  plates 
  

   may 
  be 
  traced 
  from 
  one 
  genus 
  of 
  the 
  Cyathocrinidse 
  to 
  another. 
  

  

  Viewed 
  in 
  a 
  purely 
  embryological 
  aspect, 
  CyatJiocrinus. 
  or 
  a 
  

   Dendrocrinoid 
  form 
  with 
  the 
  two 
  halves 
  of 
  the 
  " 
  compound 
  radial 
  " 
  

   united, 
  is 
  a 
  lower 
  type 
  than 
  locrinus. 
  For 
  the 
  continuous 
  line 
  of 
  

   the 
  radials 
  is 
  broken 
  into 
  by 
  the 
  anal 
  plate, 
  which 
  is 
  in 
  direct 
  

   contact 
  with 
  a 
  basal, 
  as 
  in 
  the 
  early 
  Pentacrinoid. 
  L 
  But 
  in 
  locrinus 
  , 
  

   although 
  it 
  is 
  " 
  one 
  of 
  the 
  earliest 
  known 
  forms 
  of 
  Crinoids, 
  we 
  find 
  

   the 
  body 
  up 
  to 
  the 
  top 
  of 
  the 
  radials 
  perfectly 
  equilateral, 
  all 
  basal 
  

   and 
  radial 
  plates 
  having 
  the 
  same 
  form 
  ; 
  " 
  and 
  this 
  symmetrical 
  

   condition 
  is 
  only 
  attained 
  comparatively 
  late 
  in 
  the 
  development 
  of 
  

   the 
  recent 
  Crinoid. 
  

  

  The 
  lower 
  part 
  of 
  the 
  compound 
  radial 
  of 
  Bendrocrinus 
  (fig. 
  III. 
  a) 
  

   seems 
  to 
  me 
  to 
  be 
  fairly 
  represented 
  by 
  the 
  large 
  " 
  anal" 
  plate 
  of 
  

   Hybocrinus 
  tumidus 
  (fig. 
  I. 
  a), 
  and 
  not 
  by 
  a 
  portion 
  of 
  it 
  only, 
  as 
  

   supposed 
  by 
  "Wachsmuth 
  and 
  Springer. 
  Resting, 
  as 
  it 
  does, 
  on 
  the 
  

   basals 
  in 
  a 
  line 
  with 
  four 
  very 
  similar 
  radials, 
  it 
  should, 
  I 
  think, 
  be 
  

   regarded 
  rather 
  as 
  a 
  modified 
  radial, 
  the 
  arm-bearing 
  portion 
  of 
  

   which 
  has 
  been 
  cut 
  off, 
  than 
  as 
  a 
  true 
  "anal" 
  plate; 
  and 
  I 
  should 
  

   therefore 
  prefer 
  to 
  speak 
  of 
  it 
  as 
  the 
  " 
  azygos" 
  plate. 
  But 
  I 
  am 
  

   bound 
  to 
  say 
  that 
  the 
  condition 
  of 
  the 
  Russian 
  species 
  (fig. 
  I. 
  e), 
  

   which 
  appears 
  to 
  have 
  no 
  separate 
  anal 
  plate, 
  may 
  be 
  thought 
  to 
  

   prove 
  the 
  contrary. 
  That 
  the 
  anal 
  and 
  the 
  azygos 
  plates 
  of 
  H. 
  di- 
  

   pentas 
  may 
  have 
  fused, 
  as 
  suggested 
  by 
  Schmidt, 
  is 
  possible 
  enough 
  ; 
  

   but 
  the 
  comparison 
  of 
  c 
  and 
  d, 
  fig. 
  I., 
  seems 
  to 
  me 
  to 
  show 
  that, 
  

   like 
  its 
  fellow 
  on 
  the 
  right, 
  the 
  azygos 
  plate 
  is 
  fundamentally 
  a 
  

   modified 
  radial 
  belonging 
  to 
  the 
  right 
  posterior 
  ray. 
  

  

  These 
  conclusions 
  are 
  supported, 
  I 
  think, 
  by 
  the 
  results 
  of 
  my 
  

   study 
  of 
  Hybocystites 
  problematicus, 
  "Wetherby, 
  which 
  is 
  certainly 
  

   one 
  of 
  the 
  most 
  remarkable 
  fossil 
  Echinoderms 
  yet 
  discovered. 
  

   Both 
  Prof. 
  Wetherby 
  and 
  Mr. 
  Wachsmuth 
  have 
  been 
  good 
  enough 
  

   to 
  send 
  me 
  specimens 
  for 
  examination, 
  with 
  a 
  liberal 
  kindness 
  for 
  

   which 
  I 
  owe 
  them 
  my 
  heartiest 
  thanks. 
  Characters 
  seem 
  to 
  me 
  to 
  

   be 
  present 
  in 
  all 
  three 
  specimens 
  which 
  have 
  hitherto 
  escaped 
  

   notice, 
  and 
  are 
  of 
  very 
  considerable 
  morphological 
  importance. 
  No 
  

   two 
  of 
  them 
  are 
  exactly 
  alike 
  ; 
  and 
  I 
  have 
  therefore 
  thought 
  it 
  

   worth 
  while 
  to 
  supplement 
  Prof. 
  Wetherby's 
  representation 
  of 
  the 
  

   type 
  by 
  a 
  series 
  of 
  figures 
  which 
  have 
  been 
  executed 
  with 
  the 
  

   greatest 
  possible 
  care 
  by 
  my 
  friends 
  Messrs. 
  C. 
  Berjeau 
  and 
  P. 
  

   Highley. 
  

  

  Hybocystites 
  problcmatkus. 
  the 
  only 
  species 
  at 
  present 
  known, 
  

  

  