﻿aim!) 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  33 
  

  

  the 
  modifications, 
  however 
  slight 
  they 
  may 
  appear 
  in 
  the 
  fossils, 
  as 
  

   indicating 
  a 
  definite 
  specific 
  change. 
  

  

  Wachsmuth 
  and 
  Springer's 
  figure 
  13c, 
  although 
  not 
  very 
  charac- 
  

   teristic, 
  must 
  go 
  with 
  C. 
  multicirrus 
  in 
  conformity 
  with 
  the 
  horizon 
  

   from 
  which 
  the 
  specimen 
  is 
  derived. 
  

  

  The 
  extreme 
  tenuity 
  of 
  the 
  cirri 
  in 
  this 
  species 
  is 
  constant 
  in 
  sev- 
  

   eral 
  specimens, 
  in 
  which 
  thej^ 
  often 
  contain 
  as 
  many 
  as 
  forty 
  nar- 
  

   row 
  cirrals, 
  which 
  are 
  longer 
  than 
  wide. 
  

  

  Horizon 
  and 
  locality. 
  — 
  Mississippian, 
  upper 
  part 
  of 
  the 
  Chester, 
  

   Glen 
  Dean 
  formation; 
  chiefly 
  at 
  Sloan's 
  Valley, 
  Pulaski 
  County, 
  

   Kentucky, 
  but 
  also 
  at 
  Newman's 
  Ridge, 
  Bland 
  County, 
  Virginia. 
  

  

  THE 
  RECUMBENT 
  ARMS 
  

  

  Among 
  existing 
  crinoids 
  those 
  taken 
  by 
  the 
  dredge 
  or 
  otherwise 
  

   captured 
  have 
  been 
  found 
  with 
  their 
  arms, 
  when 
  preserved, 
  either 
  

   outstretched 
  or 
  folded 
  together. 
  On 
  the 
  sea 
  bottom, 
  in 
  the 
  case 
  of 
  

   stalked 
  crinoids, 
  both 
  positions 
  may 
  be 
  assumed, 
  depending 
  upon 
  

   whether 
  the 
  crinoid 
  1, 
  was 
  seeking 
  food, 
  in 
  which 
  case 
  the 
  arms 
  would 
  

   be 
  spread 
  so 
  as 
  to 
  bring 
  the 
  maximum 
  of 
  surface 
  on 
  the 
  ventral 
  side 
  

   into 
  contact 
  with 
  the 
  water 
  containing 
  the 
  organisms 
  upon 
  which 
  

   the 
  crinoid 
  feeds, 
  or 
  2, 
  was 
  in 
  a 
  state 
  of 
  rest, 
  in 
  which 
  case 
  the 
  arms 
  

   would 
  probably 
  be 
  folded 
  as 
  a 
  matter 
  of 
  protection 
  to 
  the 
  vital 
  organs. 
  

   Which 
  attitude 
  was 
  most 
  frequent, 
  or 
  longest 
  continued, 
  we 
  have 
  no 
  

   means 
  of 
  knowing, 
  but 
  among 
  the 
  specimens 
  as 
  taken 
  out 
  of 
  the 
  water 
  

   both 
  conditions 
  are 
  found. 
  When 
  disturbed 
  by 
  the 
  dredge 
  or 
  tangles, 
  

   many 
  individuals 
  respond 
  to 
  the 
  contact 
  by 
  opening 
  the 
  arms 
  widely, 
  

   while 
  others 
  seem 
  to 
  bring 
  them 
  close 
  together, 
  and 
  still 
  others 
  cast 
  

   them 
  off. 
  

  

  Among 
  fossil 
  crinoids 
  the 
  second 
  was 
  undoubtedly 
  the 
  most 
  fre- 
  

   quent 
  occurrence, 
  for 
  practically 
  nine 
  out 
  of 
  every 
  ten 
  well 
  preserved 
  

   specimens, 
  deposited 
  so 
  as 
  to 
  become 
  imbedded 
  in 
  soft 
  material, 
  

   have 
  the 
  arms 
  folded. 
  And 
  in 
  certain 
  large 
  groups, 
  such 
  as 
  the 
  

   Flexibilia, 
  they 
  are 
  scarcely 
  ever 
  found 
  in 
  any 
  other 
  condition. 
  

   Therefore 
  it 
  is 
  to 
  be 
  assumed 
  that 
  such 
  was 
  the 
  usual 
  position 
  of 
  the 
  

   fossil 
  crinoids 
  at 
  death. 
  Any 
  other 
  disposition 
  of 
  the 
  arms 
  by 
  

   which 
  they 
  become 
  so 
  firmly 
  retracted 
  as 
  to 
  remain 
  fixed 
  in 
  that 
  

   position 
  after 
  death, 
  and 
  to 
  become 
  fossilized 
  in 
  it, 
  must 
  therefore 
  

   be 
  associated 
  with 
  some 
  structural 
  modification 
  in 
  the 
  articulation 
  

   of 
  the 
  arms 
  by 
  which 
  their 
  motion 
  in 
  an 
  upward 
  direction 
  would 
  

   be 
  restricted. 
  Many 
  instances 
  have 
  been 
  observed 
  in 
  which 
  this 
  is 
  

   apparently 
  the 
  case, 
  and 
  in 
  which 
  the 
  facts 
  are 
  not 
  explained 
  by 
  sup- 
  

   posing 
  that 
  the 
  recumbent 
  arms 
  were 
  due 
  merely 
  to 
  casual 
  move- 
  

   ments 
  by 
  the 
  animal, 
  voluntary 
  or 
  involuntary. 
  It 
  is 
  evident 
  that 
  

   the 
  mechanics 
  of 
  the 
  arm 
  structure 
  was 
  such 
  that 
  the 
  motion 
  of 
  the 
  

   23832—26 
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