﻿64 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  vol.67 
  

  

  As 
  a 
  fairly 
  general 
  rule, 
  it 
  seems 
  that 
  those 
  forms 
  with 
  a 
  well 
  

   rounded 
  ovoid 
  or 
  globose 
  calyx, 
  combined 
  with 
  very 
  short 
  infra- 
  

   basals, 
  have 
  mostly 
  a 
  divided 
  base; 
  but 
  the 
  subcorneal 
  No. 
  7 
  has 
  

   it 
  also. 
  

  

  Thus 
  the 
  recognizable 
  species 
  are 
  reduced 
  to 
  eleven, 
  and 
  it 
  is 
  

   probable 
  that 
  there 
  are 
  still 
  more 
  synonyms, 
  but 
  the 
  material 
  is 
  not 
  

   at 
  hand 
  for 
  close 
  comparison 
  of 
  some 
  species. 
  

  

  THE 
  INFLATED 
  VENTRAL 
  SAC 
  

  

  The 
  leading 
  character 
  of 
  the 
  Fistulate 
  division 
  of 
  the 
  Crinoidea 
  

   Inadunata 
  is 
  the 
  great 
  development 
  of 
  the 
  posterior 
  interradius, 
  

   which 
  in 
  some 
  genera 
  takes 
  the 
  form 
  of 
  an 
  elongate 
  anal 
  tube 
  with 
  

   the 
  opening 
  at 
  the 
  distal 
  end, 
  while 
  in 
  others 
  almost 
  the 
  entire 
  teg- 
  

   men 
  is 
  extended 
  into 
  a 
  closed 
  sac, 
  in 
  which 
  the 
  anal 
  opening, 
  in- 
  

   stead 
  of 
  being 
  at 
  the 
  distal 
  end, 
  or 
  at 
  the 
  posterior 
  side, 
  is 
  located 
  

   at 
  the 
  anterior 
  side 
  of 
  the 
  tube, 
  either 
  at 
  the 
  base, 
  or 
  part 
  way 
  up, 
  

   sometimes 
  at 
  the 
  end 
  of 
  a 
  lateral 
  spout. 
  

  

  This 
  organ 
  exhibits 
  various 
  forms 
  and 
  modifications, 
  some 
  of 
  

   which 
  are 
  illustrated 
  by 
  Wachsmuth 
  and 
  Springer 
  on 
  plate 
  7 
  of 
  the 
  

   North 
  American 
  Crinoidea 
  Camerata. 
  It 
  is 
  not 
  my 
  purpose 
  to 
  

   discuss 
  these 
  structures 
  in 
  detail, 
  further 
  than 
  is 
  desirable 
  to 
  clarify 
  

   our 
  knowledge 
  in 
  regard 
  to 
  one 
  of 
  them 
  that 
  has 
  hitherto 
  been 
  ob- 
  

   scure, 
  and 
  to 
  supply 
  some 
  needed 
  information 
  regarding 
  certain 
  

   species 
  which 
  for 
  lack 
  of 
  adequate 
  illustration 
  have 
  not 
  hitherto 
  been 
  

   clearly 
  understood, 
  several 
  of 
  the 
  important 
  ones 
  never 
  having 
  been 
  

   figured 
  at 
  all. 
  The 
  modification 
  which 
  I 
  wish 
  especially 
  to 
  consider 
  

   is 
  the 
  one 
  which 
  is 
  characterized 
  by 
  a 
  peculiar 
  reversal 
  in 
  the 
  posi- 
  

   tion 
  of 
  the 
  anal 
  opening, 
  by 
  which 
  in 
  certain 
  forms 
  it 
  emerges 
  at 
  

   the 
  anterior 
  side 
  instead 
  of 
  the 
  posterior, 
  where 
  it 
  is 
  usually 
  ex- 
  

   pected. 
  This 
  has 
  been 
  a 
  perplexing 
  fact 
  in 
  the 
  morphology 
  of 
  the 
  

   group, 
  giving 
  rise 
  to 
  some 
  rather 
  far-fetched 
  theories 
  for 
  its 
  ex- 
  

   planation. 
  Later 
  investigations, 
  as 
  I 
  have 
  hitherto 
  stated 
  in 
  the 
  

   Flexibilia 
  monograph, 
  indicate 
  that 
  there 
  is 
  no 
  essential 
  difference 
  

   between 
  the 
  " 
  anal 
  tube," 
  such 
  as 
  is 
  found 
  in 
  Cyathocrinus, 
  and 
  the 
  

   " 
  ventral 
  sac," 
  as 
  in 
  Aulocrinus; 
  and 
  that 
  all 
  forms 
  of 
  tube 
  in 
  which 
  

   the 
  anus 
  is 
  not 
  at 
  the 
  distal 
  end 
  may 
  be 
  explained 
  by 
  the 
  recurving 
  

   of 
  the 
  gut 
  with 
  its 
  enveloping 
  tube 
  in 
  its 
  upward 
  or 
  distal 
  extension, 
  

   from 
  the 
  vertical 
  toward 
  the 
  anterior 
  side, 
  folding 
  or 
  doubling 
  back 
  

   upon 
  itself 
  more 
  or 
  less 
  completely, 
  so 
  that 
  the 
  opening 
  may 
  emerge 
  

   through 
  the 
  wall 
  of 
  the 
  tube 
  at 
  any 
  point 
  between 
  the 
  distal 
  end 
  and 
  

   the 
  base. 
  

  

  The 
  tendency 
  of 
  the 
  tube, 
  perhaps 
  primarily 
  owing 
  to 
  some 
  ob- 
  

   struction 
  in 
  the 
  early 
  stages, 
  is 
  to 
  expand 
  at 
  or 
  near 
  the 
  point 
  where 
  

   it 
  is 
  bent, 
  either 
  producing 
  a 
  rounded 
  or 
  nodose 
  enlargement, 
  or 
  

  

  