﻿abt9 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  49 
  

  

  In 
  this 
  species 
  the 
  basal 
  plates 
  are 
  very 
  small 
  and 
  flat, 
  while 
  the 
  

   radials 
  are 
  of 
  enormous 
  size, 
  larger 
  than 
  all 
  the 
  other 
  plates 
  of 
  the 
  

   cup 
  combined 
  ; 
  this 
  being 
  the 
  reverse 
  of 
  the 
  structure 
  in 
  P. 
  capitalis 
  

   and 
  all 
  other 
  known 
  species. 
  In 
  fact, 
  the 
  relative 
  smallness 
  of 
  the 
  

   radials 
  is 
  one 
  of 
  the 
  striking 
  differences 
  between 
  this 
  genus 
  in 
  its 
  

   usual 
  form 
  and 
  its 
  predecessors, 
  Dichocrinus 
  and 
  Talarocrinus, 
  while 
  

   here 
  the 
  radials 
  completely 
  dominate 
  the 
  dorsal 
  side; 
  but 
  instead 
  of 
  

   having 
  a 
  cylindrical 
  exterior 
  they 
  form 
  large 
  gibbous 
  protuberances, 
  

   which 
  occupy 
  the 
  greater 
  part 
  of 
  the 
  surface 
  of 
  the 
  cup. 
  The 
  single 
  

   primibrach 
  and 
  the 
  secundibrachs 
  are 
  relatively 
  large, 
  and, 
  as 
  usual 
  

   in 
  the 
  ginus, 
  the 
  latter 
  are 
  articulated 
  directly 
  with 
  the 
  radial 
  facet. 
  

  

  I 
  am 
  giving 
  figures 
  of 
  the 
  three 
  important 
  specimens 
  upon 
  which 
  

   the 
  foregoing 
  statements 
  are 
  based. 
  The 
  species 
  is 
  exceedingly 
  rare, 
  

   no 
  others 
  having 
  been 
  found 
  since 
  Lyon's 
  time 
  among 
  all 
  the 
  ex- 
  

   tensive 
  collections 
  made 
  from 
  the 
  Chester 
  group, 
  except 
  some 
  isolated 
  

   plates 
  now 
  thought 
  to 
  belong 
  to 
  it. 
  

  

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

   Chester, 
  Golconda 
  formation; 
  Crittenden 
  County, 
  Kentucky. 
  Lyon 
  

   stated 
  that 
  the 
  species 
  was 
  associated 
  with 
  Pt. 
  {Asterocrinus) 
  capi- 
  

   talis, 
  another 
  unusual 
  form 
  described 
  by 
  him 
  at 
  the 
  same 
  time. 
  Ex- 
  

   tensive 
  investigations 
  of 
  the 
  Chester 
  formations 
  in 
  recent 
  years 
  by 
  

   Doctor 
  Weller 
  have 
  shown 
  that 
  the 
  latter 
  species 
  is 
  an 
  exceedingly 
  

   characteristic 
  fossil 
  of 
  the 
  Golconda 
  formation 
  of 
  Southern 
  Illinois 
  

   and 
  Kentucky, 
  which 
  he 
  correlates 
  with 
  the 
  lower 
  Okaw 
  division 
  of 
  

   the 
  Upper 
  Chester, 
  and 
  that 
  it 
  is 
  limited 
  to 
  that 
  horizon. 
  He 
  has 
  

   found 
  the 
  plates 
  of 
  capitalis 
  in 
  Johnson 
  and 
  Pope 
  counties, 
  Illinois. 
  27 
  

   And 
  in 
  a 
  letter 
  of 
  December 
  29, 
  1921, 
  he 
  informed 
  me 
  that 
  he 
  had 
  

   since 
  found 
  fragments 
  of 
  Pt. 
  coronarius 
  in 
  the 
  same 
  beds. 
  A 
  species 
  

   described 
  by 
  Hall 
  in 
  1858 
  28 
  as 
  Dichocrinus 
  protuberans, 
  from 
  a 
  frag- 
  

   mentary 
  base, 
  probably 
  is 
  identical 
  with 
  this. 
  It 
  was 
  said 
  to 
  be 
  from 
  

   Chester, 
  Illinois, 
  which, 
  as 
  collections 
  were 
  made 
  at 
  that 
  time, 
  might 
  

   mean 
  anywhere 
  in 
  that 
  region. 
  

  

  PTEROTOCRINUS 
  CAPITALIS 
  (Lyon) 
  

  

  Plate 
  13, 
  fig. 
  23 
  

  

  Asterocrinus 
  capitalis 
  Lyon, 
  Geol. 
  Rep. 
  Kentucky, 
  vol. 
  3, 
  1857, 
  p. 
  472, 
  pi. 
  3, 
  

  

  figs. 
  la-h. 
  

   Pterotocrinus 
  capitalis, 
  Lyon 
  and 
  Casseday, 
  Proc. 
  Amer. 
  Acad. 
  Arts 
  and 
  

  

  Sci., 
  1859, 
  p. 
  301. 
  — 
  Wachsmuth 
  and 
  Springer, 
  North 
  Amer. 
  Crin. 
  

  

  Cam., 
  1897, 
  p. 
  794, 
  pi. 
  79, 
  figs. 
  6a, 
  o. 
  

  

  Lower 
  part 
  of 
  upper 
  Chester, 
  Golconda 
  formation 
  ; 
  Crittenden 
  County, 
  Ken- 
  

   tucky, 
  Johnson 
  and 
  Pope 
  Counties, 
  Illinois. 
  

  

  27 
  Illinois 
  State 
  Geol. 
  Surv. 
  Bull. 
  41, 
  1920, 
  p. 
  184. 
  

  

  28 
  Geol. 
  Rep. 
  Iowa, 
  pt. 
  2, 
  p. 
  689, 
  pi. 
  25, 
  fig. 
  7. 
  

  

  