﻿34 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL, 
  MUSEUM 
  vol.67 
  

  

  arms 
  upon 
  their 
  hinges 
  was 
  downward 
  rather 
  than 
  upward, 
  and 
  

   that 
  the 
  pendent 
  position, 
  with 
  the 
  dorsal 
  side 
  of 
  the 
  arms 
  pressing 
  

   backward 
  upon 
  the 
  calyx 
  and 
  stem, 
  was 
  the 
  position 
  of 
  rest, 
  or 
  of 
  

   greatest 
  fixity. 
  Then 
  the 
  arms, 
  instead 
  of 
  opening 
  out 
  from 
  the 
  top 
  

   in 
  order 
  to 
  extend 
  themselves 
  and 
  their 
  pinnules 
  for 
  the 
  maximum 
  

   of 
  contact 
  with 
  the 
  water, 
  would 
  be 
  extended 
  from 
  the 
  bottom, 
  the 
  

   ventral 
  side 
  containing 
  the 
  food 
  grooves 
  being 
  already 
  in 
  position 
  for 
  

   complete 
  connection 
  with 
  the 
  currents 
  by 
  means 
  of 
  the 
  pinnules 
  and 
  

   their 
  softer 
  appendages. 
  

  

  The 
  proof 
  of 
  this 
  is 
  found 
  in 
  the 
  fact 
  that 
  in 
  numerous 
  instances 
  

   the 
  marks 
  of 
  long 
  continued 
  pressure 
  by 
  the 
  arms 
  in 
  habitual 
  posi- 
  

   tions 
  are 
  found 
  upon 
  the 
  outer 
  wall 
  of 
  the 
  calyx 
  and 
  the 
  stem, 
  pro- 
  

   ducing 
  permanent 
  indentations 
  which 
  could 
  not 
  have 
  occurred 
  unless 
  

   the 
  arms 
  had 
  become 
  fixed 
  in 
  that 
  position 
  (pis. 
  9, 
  fig. 
  9; 
  18, 
  fig. 
  4). 
  

   In 
  the 
  most 
  conspicuous 
  cases 
  of 
  this 
  kind 
  I 
  have 
  observed 
  that 
  the 
  

   recumbent 
  arms 
  are 
  always 
  profusely 
  provided 
  with 
  long 
  and 
  

   thickly 
  studded 
  pinnules, 
  and 
  these, 
  standing 
  out 
  from 
  the 
  curving 
  

   surface 
  of 
  the 
  reversed 
  arms, 
  have 
  all 
  the 
  food-gathering 
  exposure 
  

   that 
  they 
  could 
  obtain 
  in 
  any 
  other 
  way. 
  

  

  It 
  is 
  also 
  worth 
  noting 
  that 
  the 
  entire 
  group 
  Flexiblia, 
  in 
  which 
  

   the 
  arms 
  are 
  almost 
  invariably 
  found 
  folded 
  together 
  in 
  the 
  fossil 
  

   state, 
  and 
  in 
  which 
  recumbent 
  arms 
  are 
  unknown, 
  are 
  destitute 
  of 
  

   pinnules. 
  

  

  Neither 
  are 
  the 
  recumbent 
  arms, 
  of 
  the 
  type 
  which 
  I 
  am 
  about 
  to 
  

   describe, 
  found 
  among 
  the 
  Inadunata, 
  whether 
  with 
  pinnules 
  or 
  

   without 
  ; 
  and 
  regardless 
  of 
  the 
  matter 
  of 
  pinnules 
  it 
  is 
  probable 
  that 
  

   the 
  mechanics 
  of 
  the 
  arm 
  joint, 
  both 
  in 
  the 
  Flexibilia 
  and 
  the 
  Ina- 
  

   dunata, 
  precluded 
  the 
  possibility 
  of 
  any 
  such 
  backward 
  and 
  down- 
  

   ward 
  motion 
  as 
  would 
  be 
  required 
  for 
  the 
  arms 
  to 
  become 
  settled 
  in 
  

   that 
  position. 
  

  

  While 
  it 
  is 
  true 
  that 
  among 
  the 
  Recent 
  crinoids 
  specimens 
  brought 
  

   up 
  by 
  the 
  dredge 
  frequently 
  have 
  the 
  arms 
  curved 
  backwards 
  upon 
  

   the 
  stem, 
  leaving 
  the 
  oral 
  surface 
  open 
  except 
  for 
  its 
  forest 
  of 
  pin- 
  

   nules, 
  this 
  is 
  merely 
  one 
  phase 
  of 
  arm 
  movement 
  in 
  the 
  natural 
  and 
  

   usual 
  condition, 
  due 
  to 
  their 
  enormous 
  flexibility. 
  There 
  is 
  not 
  that 
  

   complete 
  reversal 
  in 
  the 
  habitus 
  of 
  the 
  arm 
  which 
  makes 
  it 
  hang 
  

   downward 
  as 
  if 
  suspended 
  from 
  the 
  roof 
  of 
  the 
  calyx. 
  For 
  that 
  

   the 
  solid 
  dome 
  of 
  the 
  Camerata 
  is 
  needed 
  to 
  afford 
  a 
  firm 
  anchorage 
  

   for 
  the 
  suspended 
  arms, 
  often 
  projecting 
  as 
  it 
  does 
  at 
  the 
  edge 
  of 
  the 
  

   tegmen 
  out 
  over 
  the 
  dorsal 
  wall 
  below 
  it, 
  and 
  at 
  all 
  events 
  furnishing 
  

   a 
  rigid 
  means 
  of 
  support. 
  In 
  typical 
  examples 
  to 
  be 
  mentioned 
  the 
  

   covering 
  plates 
  of 
  adjacent 
  arms 
  are 
  for 
  quite 
  a 
  distance 
  suturally 
  

   connected, 
  thus 
  preventing 
  the 
  usual 
  motion 
  of 
  the 
  arms. 
  

  

  It 
  is 
  only 
  among 
  the 
  Camerata 
  that 
  such 
  a 
  well 
  supported 
  hinge 
  is 
  

   found 
  ; 
  and 
  here 
  the 
  structure 
  occurs 
  in 
  several 
  of 
  its 
  families, 
  occa- 
  

  

  