﻿autO 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  &FRING/ER 
  51 
  

  

  crinoid 
  colony 
  at 
  Crawfordsville, 
  Indiana, 
  as 
  is 
  evidenced 
  by 
  up- 
  

   wards 
  of 
  fifty 
  good 
  specimens 
  in 
  my 
  own 
  collection, 
  all 
  thoroughly 
  

   constant 
  in 
  this 
  character. 
  

  

  Furthermore, 
  I 
  have 
  in 
  recent 
  }^ears 
  acquired 
  some 
  specimens 
  of 
  

   this 
  type 
  from 
  the 
  lower 
  horizon 
  at 
  Indian 
  Creek, 
  which 
  per- 
  

   sistently 
  differ 
  from 
  the 
  Crawfordsville 
  form 
  in 
  characters 
  sufficient 
  

   for 
  specific 
  definition. 
  Both 
  species 
  attain 
  a 
  large 
  size, 
  far 
  larger 
  

   than 
  any 
  others 
  that 
  have 
  been 
  referred 
  to 
  Dichocrinus, 
  the 
  crown 
  in 
  

   mature 
  specimens 
  being 
  upwards 
  of 
  10 
  cm. 
  in 
  height; 
  and 
  in 
  both 
  

   the 
  posterior 
  interradius 
  in 
  the 
  tegmen 
  is 
  raised 
  into 
  a 
  pyramid 
  

   as 
  high 
  as 
  the 
  cup, 
  the 
  summit 
  of 
  which 
  lodges 
  the 
  anus. 
  

  

  In 
  view 
  of 
  this 
  pronounced 
  differentiation 
  in 
  arm 
  structure 
  

   represented 
  by 
  two 
  species, 
  one 
  of 
  which 
  has 
  to 
  be 
  described 
  as 
  new, 
  

   it 
  seems 
  advisable 
  to 
  place 
  them 
  in 
  a 
  separate 
  genus 
  based 
  on 
  the 
  

   foregoing 
  characters, 
  for 
  which 
  I 
  propose 
  the 
  name 
  Paradicho- 
  

   crinus, 
  with 
  P. 
  polydactylus 
  as 
  genotype. 
  

  

  PARADICHOCRINUS, 
  new 
  genus 
  

  

  Mississippian. 
  Keokuk. 
  

  

  PARADICHOCRINUS 
  PLANUS, 
  new 
  species 
  

  

  Plate 
  10, 
  figs. 
  2, 
  3, 
  4 
  

  

  Similar 
  to 
  P. 
  polydactylus, 
  except 
  that 
  the 
  dorsal 
  cup 
  plates 
  are 
  

   smooth, 
  without 
  nodes 
  or 
  tubercles 
  with 
  which 
  that 
  species 
  is 
  pro- 
  

   fusely 
  ornamented, 
  and 
  the 
  arms 
  usually 
  give 
  off 
  four 
  subordinate 
  

   branches 
  to 
  the 
  outer 
  side 
  of 
  the 
  dichotom, 
  making 
  ten 
  arms 
  to 
  the 
  

   ray; 
  also 
  the 
  specimens 
  average 
  rather 
  larger 
  than 
  those 
  of 
  that 
  

   species, 
  a 
  maximum 
  crown 
  being 
  10.5 
  cm. 
  in 
  height. 
  Five 
  speci- 
  

   mens 
  have 
  appeared, 
  all 
  from 
  the 
  Indian 
  Creek 
  colony, 
  in 
  which 
  

   these 
  characters 
  are 
  well 
  maintained. 
  Three 
  have 
  the 
  arms 
  com- 
  

   plete, 
  showing 
  with 
  but 
  a 
  single 
  exception 
  the 
  number 
  constant 
  at 
  

   ten 
  to 
  the 
  ray, 
  whereas 
  in 
  P. 
  polydactylus 
  36 
  out 
  of 
  44 
  specimens 
  

   with 
  arms, 
  or 
  80 
  per 
  cent 
  of 
  the 
  whole, 
  have 
  8 
  arms 
  to 
  the 
  ray, 
  five 
  

   of 
  the 
  others 
  having 
  9. 
  and 
  one 
  or 
  two 
  10. 
  All 
  the 
  specimens 
  agree 
  

   in 
  lacking 
  the 
  pustulose 
  ornament 
  so 
  conspicuous 
  in 
  P. 
  polydactylus, 
  

   of 
  which 
  for 
  comparison 
  I 
  give 
  a 
  figure 
  showing 
  the 
  base, 
  and 
  an- 
  

   other 
  a 
  posterior 
  view 
  of 
  the 
  calyx 
  (pi. 
  10, 
  figs. 
  5, 
  6). 
  

  

  Horizon 
  and 
  locality. 
  — 
  The 
  genus 
  and 
  both 
  species 
  are 
  restricted 
  

   to 
  the 
  Keokuk 
  limestone 
  of 
  the 
  Mississippian. 
  P. 
  planus 
  occurring 
  

   at 
  Indian 
  Creek, 
  and 
  P. 
  polydactylus 
  at 
  Crawfordsville. 
  Indiana. 
  

  

  UNEQUAL 
  RADIALS 
  

  

  Usually 
  the 
  radial 
  plates 
  of 
  a 
  crinoid, 
  as 
  well 
  as 
  the 
  arm 
  struc- 
  

   tures 
  which 
  they 
  support, 
  are 
  symmetrically 
  arranged, 
  and 
  substan- 
  

  

  