﻿art 
  9 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  45 
  

  

  The 
  following 
  species 
  are 
  also 
  illustrated 
  for 
  comparison 
  : 
  

  

  ACROCRINUS 
  SHUMARDI 
  Yandell 
  

  

  Plate 
  12, 
  figs 
  6, 
  7 
  

  

  Acrocrinus 
  shumardi 
  Yandell, 
  Amer. 
  Journ. 
  Sci., 
  vol. 
  20, 
  1S55, 
  p. 
  135. 
  — 
  

   Wachsmuth 
  and 
  Springer, 
  North 
  Amor. 
  Crin. 
  Cam., 
  1S97, 
  p. 
  806, 
  

   pi. 
  80, 
  figs. 
  1-3. 
  

  

  Upper 
  Chester, 
  Glen 
  Dean 
  formation 
  ; 
  Grayson 
  Comity, 
  Kentucky. 
  

  

  ACROCRINUS 
  AMPHORA 
  Wachsmuth 
  and 
  Springer 
  

  

  Plates 
  9, 
  figs. 
  8, 
  9 
  ; 
  plate 
  12, 
  figs. 
  8, 
  9 
  ; 
  plate 
  18, 
  fig. 
  4 
  

  

  Aa-ocrinus 
  amphora 
  Wachsmuth 
  and 
  Springer, 
  North 
  Amer. 
  Crin. 
  Cam., 
  

  

  1897, 
  p. 
  808, 
  pi. 
  80, 
  figs. 
  4-9. 
  

   Lower 
  Chester, 
  Ohara 
  formation 
  ; 
  Huntsville, 
  Alabama. 
  

  

  ACROCRINUS 
  WORTHENI 
  Wachsmuth 
  

  

  Plate 
  12, 
  fig. 
  10 
  

  

  Acrocrinus 
  wortheni 
  Wachsmuth, 
  Geol. 
  Surv. 
  Illinois, 
  vol. 
  7, 
  1882, 
  p. 
  343, 
  

   pi. 
  30, 
  fig. 
  13. 
  — 
  Wachsmuth 
  and 
  Springer, 
  N. 
  A. 
  Crin. 
  Cam., 
  1897, 
  

   p. 
  807, 
  pi. 
  SO, 
  figs. 
  10(7, 
  &. 
  

  

  Coal 
  Measures 
  ; 
  Peoria 
  County, 
  Illinois. 
  

  

  THE 
  WING-LIKE 
  RADIAL 
  PROCESSES 
  

  

  There 
  still 
  remains 
  to 
  point 
  out 
  another 
  line 
  of 
  productive 
  modi- 
  

   fication 
  furnished 
  by 
  this 
  fertile 
  genus 
  Dichocrimis, 
  leading 
  to 
  a 
  

   specialization 
  of 
  an 
  entirely 
  different 
  type. 
  In 
  this 
  the 
  major 
  de- 
  

   velopment 
  takes 
  place 
  in 
  the 
  tegmen, 
  at 
  the 
  expense 
  of 
  the 
  arms 
  and 
  

   the 
  dorsal 
  cup. 
  The 
  arms 
  become 
  short 
  and 
  relatively 
  inconspicu- 
  

   ous; 
  the 
  radiajs 
  small 
  and 
  no 
  longer 
  dominating 
  the 
  cup; 
  the 
  two 
  

   fair-sized 
  primibrachs 
  of 
  the 
  parent 
  genus 
  have 
  been 
  reduced 
  to 
  a 
  

   single 
  minute 
  triangular 
  piece, 
  which 
  is 
  often 
  invisible; 
  the 
  large 
  

   anal 
  plate, 
  which 
  was 
  of 
  similar 
  form 
  and 
  size 
  to 
  the 
  radials, 
  is 
  now 
  

   a 
  pentangular 
  or 
  more 
  or 
  less 
  wedge-formed 
  piece, 
  narrowing 
  up- 
  

   ward, 
  sometimes 
  to 
  an 
  apex 
  below 
  the 
  level 
  of 
  the 
  radials. 
  The 
  

   chief 
  developmental 
  activity 
  of 
  the 
  skeleton 
  is 
  concentrated 
  in 
  the 
  

   ambulacral 
  region 
  of 
  the 
  tegmen, 
  where 
  the 
  axillary 
  plate, 
  or 
  radial 
  

   dome 
  plate, 
  is 
  hypertrophied 
  into 
  a 
  variety 
  of 
  forms, 
  some 
  thin 
  and 
  

   knife-like; 
  some 
  thick, 
  rounded, 
  club-shaped, 
  or 
  spatulate; 
  and 
  still 
  

   others 
  bifurcating, 
  until 
  there 
  is 
  produced 
  the 
  wing-like 
  processes 
  

   of 
  Pterotocrinus, 
  structures 
  unlike 
  those 
  seen 
  in 
  any 
  other 
  crinoid. 
  

   They 
  are 
  analogous 
  to 
  the 
  spines 
  of 
  Dorycrinus, 
  but 
  far 
  more 
  spe- 
  

   cialized 
  and 
  complex; 
  their 
  different 
  forms 
  are 
  shown 
  upon 
  plate 
  

   79 
  of 
  the 
  Camerata 
  monograph. 
  

  

  