﻿84 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  vol.67 
  

  

  Mr. 
  Wright 
  49 
  has 
  given 
  further 
  particulars 
  of 
  the 
  occurrence 
  of 
  the 
  

   genus 
  in 
  that 
  region, 
  which 
  he 
  finds 
  to 
  be 
  quite 
  abundant 
  in 
  two 
  

   localities. 
  He 
  has 
  noted 
  variations 
  in 
  the 
  anal 
  area 
  analogous 
  to 
  

   those 
  which 
  I 
  have 
  recorded 
  for 
  the 
  two 
  Chester 
  species, 
  and 
  it 
  i& 
  

   interesting 
  to 
  observe 
  that 
  out 
  of 
  45 
  specimens 
  examined 
  by 
  him 
  41 
  

   have 
  the 
  post. 
  B 
  acuminate 
  with 
  RA 
  more 
  or 
  less 
  elongate, 
  all 
  from 
  

   one 
  locality, 
  and 
  3 
  have 
  post. 
  B 
  truncate, 
  with 
  shorter 
  RA, 
  and 
  are 
  

   from 
  a 
  different 
  locality. 
  The 
  similarity 
  in 
  this 
  respect 
  to 
  the 
  Ameri- 
  

   can 
  species 
  adds 
  another 
  significant 
  fact 
  toward 
  the 
  correlation 
  of 
  

   the 
  two 
  horizons, 
  and 
  we 
  shall 
  await 
  with 
  interest 
  the 
  description 
  

   of 
  the 
  crowns 
  to 
  see 
  what 
  further 
  resemblance 
  is 
  disclosed. 
  

  

  ZEACRINUS 
  GIRTYI, 
  new 
  species 
  

  

  Plate 
  23, 
  figs. 
  9, 
  9a 
  

  

  This 
  is 
  the 
  latest 
  known 
  occurrence 
  of 
  the 
  genus, 
  having 
  a 
  low 
  

   cup, 
  long 
  truncate 
  posterior 
  basal, 
  strongly 
  heterotomous 
  arms, 
  

   partly 
  uniserial; 
  but 
  to 
  some 
  extent 
  with 
  cuneiform 
  brachials, 
  and 
  

   balloon-shaped 
  ventral 
  sac. 
  The 
  species 
  is 
  founded 
  on 
  a 
  single 
  very 
  

   well 
  preserved 
  specimen 
  from 
  the 
  basal 
  Pennsylvanian 
  of 
  Oklahoma, 
  

   of 
  larger 
  size 
  than 
  is 
  usual 
  in 
  the 
  genus, 
  the 
  length 
  of 
  crown 
  being 
  

   6.5 
  cm. 
  

  

  Specifically 
  it 
  is 
  exceedingly 
  well 
  marked 
  by 
  the 
  fact 
  that 
  the 
  

   heterotomy 
  and 
  the 
  inflated 
  sac 
  are 
  developed 
  to 
  an 
  extent 
  unknown 
  

   in 
  any 
  other 
  species. 
  The 
  rays 
  divide 
  on 
  the 
  second 
  plate 
  above 
  

   the 
  radial 
  into 
  two 
  main 
  and 
  equal 
  branches 
  ; 
  each 
  of 
  these 
  bifurcates 
  

   further, 
  but 
  unequally 
  — 
  the 
  outer 
  branch 
  of 
  the 
  ray 
  continuing 
  

   strong 
  and 
  dividing 
  several 
  times, 
  giving 
  off 
  to 
  the 
  inner 
  side 
  of 
  

   the 
  dichotom 
  successive 
  branches, 
  the 
  lowest 
  about 
  one-third 
  the 
  

   thickness 
  of 
  the 
  main 
  branch 
  at 
  the 
  point 
  of 
  bifurcation, 
  and 
  con- 
  

   tinuing 
  simple 
  to 
  the 
  full 
  height 
  of 
  the 
  ray. 
  The 
  differences 
  in 
  size 
  

   between 
  the 
  outer 
  arm 
  and 
  the 
  inner 
  ramules 
  become 
  less 
  and 
  less 
  

   until 
  the 
  last 
  division 
  is 
  about 
  equal. 
  This 
  type 
  of 
  heterotomy 
  is 
  

   the 
  same 
  as 
  that 
  of 
  Z. 
  wortheni 
  of 
  the 
  Chester, 
  but 
  it 
  is 
  more 
  marked 
  

   in 
  this 
  specimen 
  than 
  in 
  any 
  of 
  that 
  species, 
  the 
  taper 
  of 
  the 
  main 
  

   arms 
  is 
  more 
  pronounced, 
  and 
  the 
  bifurcations 
  more 
  numerous 
  — 
  

   there 
  being 
  seven 
  here, 
  whereas 
  I 
  have 
  never 
  seen 
  more 
  than 
  five 
  

   in 
  the 
  largest 
  Chester 
  specimen. 
  

  

  This 
  species 
  has 
  also 
  two 
  primibrachs, 
  so 
  that 
  the 
  ray 
  bifurcates 
  

   on 
  the 
  second 
  plate 
  above 
  the 
  radial, 
  instead 
  of 
  the 
  first 
  as 
  is 
  the 
  

   rule 
  in 
  the 
  genus 
  except 
  in 
  the 
  anterior 
  ray, 
  which 
  usually 
  has 
  one 
  

   or 
  more 
  additional 
  brachials. 
  In 
  Scytalocrinus 
  and 
  similar 
  genera 
  

   closely 
  allied 
  to 
  Pachylocrinus 
  both 
  structures 
  are 
  found, 
  with 
  many 
  

   species 
  of 
  each 
  ; 
  but 
  in 
  Zeacrinus 
  and 
  the 
  closely 
  related 
  Coeliocrinus 
  

  

  40 
  Trans. 
  Geol. 
  Soc. 
  Glasgow, 
  vol. 
  16, 
  pt. 
  3, 
  1917-18, 
  p. 
  380. 
  

  

  