﻿aktO 
  UNUSUAL, 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  85 
  

  

  and 
  Hydreionocrinus 
  I 
  do 
  not 
  remember 
  to 
  have 
  seen 
  before, 
  except 
  

   in 
  a 
  few 
  specimens 
  of 
  Z. 
  com?naticus, 
  an 
  exception 
  to 
  the 
  rule 
  of 
  a 
  

   single 
  primibrach 
  to 
  all 
  the 
  rays 
  other 
  than 
  the 
  anterior. 
  

  

  The 
  ventral 
  sac, 
  which 
  in 
  other 
  species 
  except 
  commaticus 
  is 
  only 
  

   about 
  half 
  the 
  height 
  of 
  the 
  arms, 
  is 
  here 
  of 
  extraordinary 
  size 
  for 
  

   the 
  genus, 
  approaching 
  rather 
  the 
  structure 
  of 
  Coeliocrinus 
  in 
  this 
  

   respect; 
  it 
  rises 
  entirely 
  above 
  the 
  ends 
  of 
  the 
  arms, 
  which 
  are 
  them- 
  

   selves 
  unusually 
  long 
  and 
  slender. 
  

  

  While 
  the 
  arm 
  structure, 
  as 
  above 
  stated, 
  is 
  like 
  that 
  of 
  the 
  Chester 
  

   species, 
  Z. 
  wortkeni, 
  it 
  is 
  curious 
  that 
  the 
  calyx 
  of 
  this 
  species 
  is 
  

   more 
  like 
  that 
  of 
  the 
  earlier 
  forms 
  of 
  the 
  Burlington 
  limestone, 
  such 
  

   as 
  Z. 
  elegans, 
  in 
  having 
  quite 
  large 
  and 
  prominent 
  basals 
  instead 
  of 
  

   small 
  ones 
  almost 
  concealed 
  in 
  the 
  basal 
  cavity, 
  and 
  also 
  a 
  short 
  

   radianal. 
  

  

  On 
  the 
  whole, 
  this 
  may 
  be 
  termed 
  an 
  acmic 
  species, 
  recapitulating 
  

   to 
  some 
  extent 
  the 
  characters 
  found 
  in 
  the 
  genus 
  in 
  earlier 
  periods; 
  

   and 
  it 
  doubtless 
  represents 
  the 
  culmination 
  of 
  the 
  genus, 
  which 
  has 
  

   not 
  hitherto 
  been 
  recognized 
  later 
  than 
  the 
  Chester. 
  

  

  The 
  specific 
  name 
  of 
  this 
  remarkable 
  species 
  is 
  given 
  in 
  honor 
  

   of 
  Dr. 
  George 
  T. 
  Girty, 
  in 
  charge 
  of 
  Carboniferous 
  researches 
  for 
  

   the 
  U. 
  S. 
  Geological 
  Survey, 
  to 
  whom 
  I 
  am 
  indebted 
  for 
  the 
  use 
  

   of 
  the 
  material. 
  

  

  Horizon 
  and 
  Locality. 
  — 
  Morrow 
  formation 
  of 
  the 
  basal 
  Pennsyl- 
  

   vanian; 
  near 
  Crittenden 
  in 
  northeastern 
  Oklahoma. 
  Found 
  by 
  Dr. 
  

   E. 
  O. 
  Ulricji 
  associated 
  with 
  Ulrichicrinus 
  Oklahoma. 
  

  

  Genus 
  COELIOCRINUS 
  White 
  

   Plates 
  24, 
  25 
  

  

  Coeliocrinus 
  White, 
  Boston 
  Journ. 
  Nat. 
  Hist., 
  vol. 
  7, 
  1863, 
  p. 
  499. 
  

   Coeliocrinus, 
  subgenus 
  of 
  Poteriocrinus, 
  Meek 
  and 
  Worthen, 
  Proc, 
  Acad. 
  

  

  Nat. 
  Sci. 
  Phila., 
  1869, 
  p. 
  138. 
  

   Coeliocrinus, 
  subgenus 
  of 
  HydreionocHnus, 
  Wachsmuth 
  and 
  Springer, 
  Rev. 
  

  

  Pal., 
  pt. 
  1, 
  1879, 
  p. 
  131. 
  

   Mississippian 
  ; 
  Lower 
  Burlington 
  to 
  Keokuk. 
  

  

  The 
  prominent 
  features 
  of 
  this 
  genus 
  are 
  stated 
  by 
  the 
  author 
  as 
  

   f 
  olows 
  : 
  

  

  First, 
  the 
  large 
  inflated 
  ventral 
  sack, 
  varying 
  in 
  size 
  in 
  different 
  species, 
  

   from 
  four 
  or 
  five 
  times 
  the 
  capacity 
  of 
  the 
  calyx 
  to 
  ten 
  or 
  twenty 
  times 
  that 
  

   capacity. 
  It 
  is 
  widest 
  at 
  the 
  top, 
  in 
  some 
  cases* 
  extending 
  above 
  the 
  tips 
  of 
  

   the 
  arms 
  — 
  the 
  lower 
  part 
  being 
  contracted 
  between 
  the 
  arms 
  like 
  the 
  neck 
  of 
  

   a 
  balloon 
  — 
  and 
  joins 
  by 
  this 
  the 
  anal 
  series. 
  

  

  Second, 
  the 
  proportionally 
  small 
  calyx 
  formed 
  by 
  the 
  basal, 
  subradial, 
  radial, 
  

   and 
  first 
  anal 
  plates, 
  which 
  is 
  so 
  small 
  as 
  to 
  render 
  it 
  certain 
  that 
  could 
  not 
  

   contain 
  the 
  necessary 
  internal 
  organs 
  for 
  the 
  support 
  of 
  the 
  other 
  parts. 
  These 
  

   organs 
  must 
  have 
  been 
  located 
  in 
  the 
  plated 
  sack, 
  which 
  I 
  have 
  denominated 
  

   the 
  ventral 
  sack 
  ; 
  thus 
  reversing 
  their 
  usual 
  order 
  of 
  operation, 
  as 
  the 
  mouth 
  

  

  