﻿38 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL, 
  MUSEUM 
  vol.07 
  

  

  Genus 
  GILBERTSOCRINUS 
  Phillips 
  

  

  Devonian 
  to 
  Keokuk. 
  

  

  GILBERTSOCRINUS 
  DISPANSUS 
  Wachsmuth 
  and 
  Springer 
  

  

  Plate 
  10, 
  fig. 
  1 
  

   GWbertsocrinus 
  dispansus 
  Wachsmuth 
  and 
  Springer. 
  North 
  Amer. 
  Crin- 
  

   Cam., 
  1897, 
  p. 
  233. 
  

  

  In 
  most 
  of 
  the 
  species 
  of 
  this 
  genus 
  in 
  which 
  the 
  arms 
  are 
  known 
  

   they 
  tend 
  to 
  hang 
  downward 
  over 
  the 
  cup, 
  emerging 
  beneath 
  an 
  

   overhang 
  at 
  the 
  edge 
  of 
  the 
  tegmen. 
  One 
  of 
  the 
  species 
  in 
  which 
  

   the 
  arms 
  are 
  not 
  pendent, 
  G. 
  tuberculatum 
  of 
  the 
  Burlington 
  lime- 
  

   stone, 
  is 
  so 
  closely 
  similar 
  to 
  one 
  of 
  the 
  same 
  formation 
  in 
  which 
  they 
  

   are 
  that 
  the 
  two 
  can 
  scarcely 
  be 
  differentiated 
  by 
  other 
  characters. 
  

   In 
  a 
  species 
  from 
  the 
  Keokuk 
  limestone 
  of 
  Indiana, 
  G. 
  dispansus™ 
  

   it 
  now 
  appears 
  from 
  specimens 
  obtained 
  since 
  the 
  description 
  was 
  

   made 
  that 
  sometimes 
  the 
  arms, 
  which 
  are 
  extremely 
  long 
  and 
  slender, 
  

   after 
  extending 
  downward 
  for 
  a 
  part 
  of 
  their 
  length 
  bend 
  backward 
  

   upon 
  themselves 
  and 
  are 
  directed 
  upward 
  toward 
  the 
  tegmen, 
  with 
  

   the 
  result 
  that 
  the 
  ambulacral 
  furrows 
  and 
  pinnules 
  in 
  one 
  part 
  of 
  

   the 
  arm 
  appear 
  to 
  be 
  upon 
  the 
  outside, 
  and 
  in 
  another 
  upon 
  the 
  in- 
  

   side 
  (pi. 
  10, 
  fig. 
  1). 
  It 
  is 
  rare 
  to 
  find 
  these 
  two 
  conditions 
  com- 
  

   pletely 
  shown 
  in 
  one 
  specimen, 
  as 
  is 
  fortunately 
  the 
  case 
  in 
  the 
  ono 
  

   I 
  have 
  figured; 
  and 
  their 
  presence 
  separately 
  in 
  different 
  specimens 
  

   has 
  led 
  to 
  some 
  curious 
  theories 
  touching 
  the 
  properties 
  of 
  arms 
  pe- 
  

   culiar 
  to 
  this 
  crinoid. 
  This 
  was 
  probably 
  the 
  occasion 
  of 
  the 
  erro- 
  

   neous 
  figure 
  by 
  Meek 
  and 
  "Worthen 
  in 
  the 
  second 
  volume 
  of 
  the 
  Geo- 
  

   logical 
  Survey 
  of 
  Illinois 
  (p. 
  220), 
  in 
  which 
  the 
  arms 
  are 
  pictured 
  

   as 
  recumbent 
  over 
  the 
  dorsal 
  cup, 
  but 
  with 
  the 
  ventral 
  side 
  under- 
  

   neath, 
  and 
  as 
  to 
  which 
  the 
  authors 
  say, 
  on 
  page 
  221 
  : 
  

  

  In 
  the 
  above 
  cut 
  the 
  minute 
  true 
  arms 
  of 
  the 
  typical 
  species 
  of 
  Gonias- 
  

   teroidocrinus 
  are 
  seen 
  to 
  branch 
  so 
  as 
  to 
  form 
  nine 
  to 
  each 
  ray. 
  The 
  cut 
  

   shows 
  only 
  their 
  outside, 
  on 
  which 
  we 
  have 
  seen 
  no 
  indications 
  of 
  ambulacral 
  

   furrows 
  ; 
  these 
  may 
  have 
  been 
  obliterated 
  in 
  cleaning 
  the 
  specimen, 
  or 
  possi- 
  

   bly 
  they 
  may 
  present 
  the 
  anomalous 
  character 
  of 
  being 
  on 
  the 
  under 
  side 
  and 
  

   thus 
  differ 
  from 
  those 
  of 
  all 
  other 
  known 
  crinoids. 
  

  

  Horizon 
  and 
  locality. 
  — 
  Mississippian, 
  Keokuk 
  limestone, 
  lower 
  

   horizon; 
  Indian 
  Creek, 
  Indiana. 
  

  

  Genus 
  PLATYCRINUS 
  Miller 
  

  

  Devonian 
  through 
  Lower 
  Carboniferous. 
  

  

  PLATYCRINUS 
  PENDENS 
  Wachsmuth 
  and 
  Springer 
  

  

  Plate 
  9, 
  figs. 
  5, 
  5a 
  

  

  Platycrinus 
  pendens 
  Wachsmuth 
  and 
  Springer, 
  North 
  Amer. 
  Crin. 
  Cam., 
  

   1897, 
  p. 
  G47. 
  

   Among 
  the 
  vast 
  number 
  of 
  species 
  of 
  Platycrinus 
  which 
  were 
  

   treated 
  by 
  Wachsmuth 
  and 
  Springer 
  in 
  the 
  Camerata 
  Monograph, 
  

  

  17 
  Wachsmuth 
  and 
  Springer, 
  N. 
  A. 
  Crin. 
  Cam., 
  p. 
  240, 
  pi. 
  15, 
  figs. 
  2a-d. 
  

  

  