﻿72 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  vol.67 
  

  

  rounded 
  end 
  of 
  the 
  sac 
  as 
  shown 
  in 
  the 
  figures 
  is 
  constant 
  in 
  form 
  and 
  

   position 
  in 
  many 
  specimens, 
  and 
  the 
  opening 
  just 
  below 
  it 
  in 
  several. 
  

   The 
  species 
  belongs 
  to 
  the 
  intermediate 
  type 
  of 
  arm 
  branching, 
  which 
  

   has 
  caused 
  it 
  sometimes 
  to 
  be 
  labeled 
  Zeacrinus, 
  while 
  the 
  resem- 
  

   blance 
  in 
  form 
  of 
  the 
  inflated 
  sac 
  has 
  also 
  led 
  to 
  a 
  reference 
  to 
  Coelio- 
  

   crinus. 
  

  

  PACHYLOCRINUS 
  FLOREALIS 
  (Yandell 
  and 
  Shumard) 
  

  

  Plate 
  16, 
  figs. 
  8, 
  9 
  

  

  Cyathocrinus 
  florealis 
  Yandell 
  and 
  Shumard, 
  Cont. 
  Geol. 
  Kentucky, 
  1847, 
  

  

  p. 
  24, 
  pi. 
  1, 
  fig. 
  1. 
  

   Zeacrinus 
  florealis, 
  Shumard, 
  Cat. 
  Pal. 
  Foss., 
  1S66, 
  pt. 
  1 
  p. 
  399. 
  

   Chester 
  group, 
  Glen 
  Dean 
  formation 
  ; 
  Grayson 
  Springs, 
  Kentucky. 
  

  

  Three 
  specimens 
  of 
  this 
  rare 
  species 
  show 
  the 
  same 
  peculiar 
  small 
  

   spiniferous 
  termination 
  of 
  the 
  sac 
  above 
  the 
  ends 
  of 
  the 
  arms, 
  with 
  

   the 
  anal 
  opening 
  near 
  the 
  distal 
  end. 
  The 
  wide 
  difference 
  in 
  the 
  

   structure 
  of 
  the 
  sac 
  between 
  this 
  and 
  the 
  preceding 
  species 
  empha- 
  

   sizes 
  the 
  extreme 
  variability 
  of 
  this 
  character. 
  

  

  Genus 
  ABROTOCRINUS 
  Miller 
  and 
  Gurley 
  

  

  Plates 
  16, 
  17 
  

  

  Abrotocrinus 
  Miller 
  and 
  Gurley, 
  Journ. 
  Cin. 
  Soc. 
  Nat. 
  Hist., 
  vol. 
  13, 
  

  

  1S90, 
  p. 
  30 
  ; 
  16th 
  Rep. 
  Geol. 
  Surv. 
  Indiana, 
  1891, 
  p. 
  350. 
  

   Mississippian 
  ; 
  Lower 
  Burlington 
  to 
  Keokuk. 
  

  

  As 
  already 
  mentioned, 
  I 
  have 
  utilized 
  this 
  genus, 
  heretofore 
  

   ranked 
  as 
  a 
  synonym, 
  to 
  include 
  those 
  species 
  of 
  Pachylocrinus 
  which 
  

   have 
  a 
  pentagonal 
  stem. 
  It 
  offers 
  the 
  medium 
  of 
  a 
  convenient 
  and 
  

   much 
  needed 
  subdivision 
  of 
  that 
  genus. 
  The 
  character 
  is 
  not 
  a 
  very 
  

   reliable 
  one, 
  some 
  intermediate 
  forms 
  having 
  the 
  stem 
  pentagonal 
  

   near 
  the 
  calyx 
  and 
  round 
  lower 
  down. 
  The 
  type 
  species, 
  Abroto- 
  

   crinus' 
  cy 
  mo 
  sus 
  Miller 
  and 
  Gurley, 
  45 
  from 
  the 
  Keokuk 
  limestone 
  of 
  

   Canton, 
  Indiana, 
  is 
  in 
  its 
  arm 
  structure 
  a 
  beautiful 
  example 
  of 
  the 
  

   Pachylocrinus 
  type. 
  I 
  am 
  illustrating 
  two 
  species, 
  one 
  from 
  the 
  

   Upper 
  Burlington 
  which 
  has 
  never 
  been 
  figured, 
  and 
  one 
  from 
  the 
  

   Keokuk, 
  showing 
  the 
  median 
  position 
  of 
  the 
  anal 
  opening. 
  

  

  ABROTOCRINUS 
  RUSTICELLUS 
  (White) 
  

  

  Plate 
  16, 
  fig. 
  11 
  

  

  Poterioc?-inus 
  rusticellus 
  White, 
  Boston 
  Journ. 
  Nat. 
  Hist., 
  vol. 
  7, 
  1863, 
  

  

  p. 
  505. 
  

   Upper 
  Burlington 
  limestone; 
  Burlington, 
  Iowa. 
  

  

  Another 
  prominent 
  Burlington 
  species, 
  not 
  hitherto 
  understood. 
  

   There 
  are 
  several 
  specimens 
  even 
  more 
  conspicuous 
  than 
  the 
  one 
  

  

  45 
  Journ. 
  Cin. 
  Soc. 
  Nat. 
  Hist. 
  1800, 
  pi. 
  5, 
  fig. 
  2. 
  

  

  