﻿art 
  9 
  UNUSUAL. 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  81 
  

  

  ZEACRINUS 
  WORTHENI 
  Hall 
  

  

  Plate 
  23, 
  figs. 
  1-8 
  

  

  Zeacrinus 
  tcortheni 
  Hall, 
  Geol. 
  Iowa, 
  pt. 
  2, 
  1858, 
  p. 
  6S3, 
  also 
  p. 
  545. 
  

   Chester 
  group, 
  Okaw 
  and 
  Glen 
  Dean 
  formations 
  ; 
  Randolph 
  County, 
  

   Illinois, 
  Pulaski, 
  Grayson, 
  Todd 
  and 
  Breckinridge 
  counties, 
  Kentucky. 
  

  

  ZEACRINUS 
  MAGNOLIAEFORMIS 
  (Troost) 
  Hall 
  

  

  Plate 
  22, 
  figs. 
  4-11 
  

  

  Zeacrinus 
  magnoliaeformis, 
  Hall, 
  Geol. 
  Iowa, 
  pt. 
  2, 
  1858, 
  p. 
  684, 
  also 
  p. 
  545. 
  

   Chester 
  group, 
  Gasper 
  formation 
  ; 
  Huntsville, 
  Alabama. 
  

  

  The 
  two 
  typical 
  species 
  of 
  the 
  genus, 
  in 
  which 
  is 
  introduced 
  the 
  

   pyramidal 
  form 
  of 
  sac, 
  acuminate 
  instead 
  of 
  rounded 
  distally, 
  which 
  

   is 
  most 
  commonly 
  associated 
  with 
  the 
  genus, 
  and 
  which 
  was 
  the 
  basis 
  

   of 
  the 
  description 
  of 
  the 
  sac 
  in 
  Revision 
  of 
  Paleocrinoidea, 
  (l,p. 
  126). 
  

   It 
  is 
  best 
  shown 
  in 
  Z. 
  wortheni, 
  which 
  is 
  the 
  more 
  widely 
  distributed 
  

   and 
  in 
  better 
  preservation. 
  From 
  this 
  we 
  now 
  know 
  the 
  location 
  

   of 
  the 
  anal 
  opening, 
  about 
  midway, 
  clearly 
  shown 
  in 
  several 
  speci- 
  

   mens, 
  from 
  which 
  the 
  instructive 
  illustrations 
  are 
  selected. 
  In 
  these 
  

   species, 
  especially 
  Z. 
  wortheni, 
  is 
  introduced 
  the 
  long, 
  slender 
  radi- 
  

   anal, 
  producing 
  the 
  narrow 
  anal 
  side 
  which 
  is 
  so 
  different 
  from 
  that 
  

   of 
  the 
  earlier 
  species. 
  

  

  As 
  the 
  two 
  species 
  are 
  among 
  the 
  important 
  fossils 
  of 
  their 
  forma- 
  

   tions, 
  and 
  their 
  names 
  have 
  been 
  used 
  rather 
  indiscriminately 
  by 
  

   geologists 
  in 
  listing 
  the 
  fossils 
  collected 
  in 
  various 
  localities 
  of 
  the 
  

   Chester 
  area, 
  it 
  is 
  very 
  desirable 
  to 
  ascertain 
  which 
  is 
  which. 
  

  

  There 
  is 
  nothing 
  in 
  Hall's 
  formal 
  description 
  of 
  the 
  species 
  to 
  

   separate 
  them. 
  The 
  principal 
  discussion 
  is 
  on 
  page 
  545, 
  where 
  it 
  is 
  

   said 
  that 
  Z. 
  wortheni 
  " 
  has 
  a 
  narrow 
  and 
  less 
  rotund 
  base, 
  with 
  the 
  

   cavity 
  much 
  less 
  deep, 
  and 
  the 
  subradial 
  and 
  first 
  radial 
  plates 
  (BB 
  

   and 
  RR) 
  proportionately 
  shorter 
  and 
  the 
  latter 
  narrower, 
  while 
  the 
  

   anterior 
  ray 
  has 
  two 
  intermediate 
  radial 
  plates." 
  This 
  might 
  be 
  

   true 
  as 
  between 
  two 
  individual 
  specimens, 
  but 
  will 
  not 
  hold 
  good 
  

   for 
  the 
  numbers 
  that 
  are 
  now 
  in 
  hand. 
  In 
  a 
  note 
  he 
  says 
  that 
  Z. 
  

   wortheni 
  is 
  distinct 
  from 
  Z. 
  magnoliaeformis, 
  " 
  with 
  shorter 
  first 
  

   radials, 
  extending 
  a 
  little 
  above 
  the 
  plane 
  of 
  the 
  base, 
  and 
  arms 
  

   much 
  shorter 
  and 
  less 
  robust." 
  He 
  gives 
  a 
  diagram 
  of 
  each, 
  that 
  of 
  

   Z. 
  magnoliaeformis 
  from 
  Troost's 
  type; 
  it 
  does 
  not 
  show 
  the 
  anal 
  

   side. 
  

  

  The 
  diagram 
  of 
  Z. 
  wortheni 
  shows 
  the 
  anal 
  side 
  with 
  post. 
  B 
  acumi- 
  

   nate 
  like 
  the 
  other 
  BB, 
  not 
  connecting 
  with 
  x 
  (next 
  anal 
  above), 
  

   and 
  RA 
  narrow, 
  passing 
  low 
  down 
  between 
  BB 
  — 
  that 
  is, 
  a 
  narrow 
  

   anal 
  area. 
  

  

  