﻿50 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  PTEROTOCRINUS 
  PYRAMIDALIS 
  Lyon 
  and 
  Casseday 
  

  

  Plate 
  13, 
  figs. 
  21, 
  22 
  

  

  Pterotocrinus 
  pyramidalis 
  Lyon 
  and 
  Casseday, 
  Anier. 
  Journ. 
  Sci., 
  vol. 
  29, 
  

   1860, 
  p. 
  69. 
  — 
  Wachsmuth 
  and 
  Springer, 
  North 
  Amer. 
  Crin. 
  Cam., 
  

   1897, 
  p. 
  798, 
  figs. 
  4a, 
  b. 
  

  

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

  

  PTEROTOCRINUS 
  DEPRESSUS 
  Lyon 
  and 
  Casseday 
  

  

  Plate 
  14, 
  figs. 
  4, 
  4a 
  

  

  Pterotocrinus 
  depressus 
  Lyon 
  and 
  Casseday, 
  Amer. 
  Journ. 
  Sci., 
  vol. 
  29, 
  

   1S60, 
  p. 
  68. 
  — 
  Wachsmuth 
  and 
  Springer, 
  North 
  Amer. 
  Crin. 
  Cam., 
  

   1897, 
  p. 
  796, 
  pi. 
  79, 
  figs. 
  2a-e. 
  

  

  Upper 
  Chester, 
  Glen 
  Dean 
  formation 
  ; 
  Grayson, 
  Pulaski, 
  and 
  Breckin- 
  

   ridge 
  Counties, 
  Kentucky. 
  

  

  PTEROTOCRINUS 
  ACUTUS 
  Wetherby 
  

  

  Plate 
  13, 
  fig. 
  16 
  

  

  Ptei'ocrinus 
  acutus 
  Wetherby, 
  Journ. 
  Cincinnati 
  Soc. 
  Nat. 
  Hist., 
  vol. 
  2, 
  

   1879, 
  pi. 
  11, 
  figs. 
  2a-c. 
  — 
  Wachsmuth 
  and 
  Springer, 
  North 
  Amer. 
  Crin. 
  

   Cam., 
  1897, 
  p. 
  799, 
  pi. 
  79, 
  figs. 
  3a-g. 
  

  

  Upper 
  Chester, 
  Glen 
  Dean 
  formation 
  ; 
  Pulaski 
  and 
  Breckinridge 
  Counties, 
  

   Kentucky. 
  

  

  PTEROTOCRINUS 
  BIFURCATUS 
  Wetherby 
  

  

  Plate 
  14, 
  fig. 
  5 
  

  

  Pterotocrinus 
  bifurcatus 
  Wetherby, 
  Journ. 
  Cincinnati 
  Soc. 
  Nat. 
  Hist., 
  vol. 
  

  

  2, 
  1S79, 
  p. 
  136, 
  pi. 
  11, 
  figs. 
  la-c. 
  — 
  Wachsmuth 
  and 
  Springer, 
  North 
  

  

  Amer. 
  Crin. 
  Cam., 
  1S97, 
  p. 
  801, 
  pi. 
  79, 
  figs. 
  9a, 
  b. 
  

   Upper 
  Chester, 
  Glen 
  Dean 
  formation 
  ; 
  Sloan's 
  Valley, 
  Pulaski 
  County, 
  

  

  Kentucky. 
  

  

  HETEROTOMOUS 
  BRANCHING 
  OF 
  THE 
  ARMS 
  

  

  In 
  order 
  to 
  complete 
  the 
  story 
  of 
  the 
  ramifications 
  of 
  Dichocrinus, 
  

   attention 
  should 
  be 
  called 
  to 
  the 
  species 
  D. 
  polydactylus 
  Casseday 
  

   and 
  Lyon, 
  29 
  from 
  the 
  Keokuk 
  limestone, 
  which 
  has 
  gone 
  off 
  upon 
  a 
  

   new 
  line 
  in 
  regard 
  to 
  arm 
  structure. 
  All 
  other 
  species 
  have 
  dichoto- 
  

   mous 
  arms, 
  branching 
  by 
  approximately 
  equal 
  bifurcations. 
  In 
  this 
  

   one, 
  however, 
  the 
  ray 
  divides 
  into 
  two 
  main 
  branches, 
  from 
  which 
  

   usually 
  three 
  subordinate 
  branches 
  are 
  given 
  off 
  to 
  the 
  outer 
  side 
  

   of 
  the 
  dichotom, 
  thus 
  producing 
  one 
  form 
  of 
  unilateral 
  heterotom}^ 
  — 
  

   a 
  difference 
  which 
  in 
  other 
  groups 
  has 
  been 
  regarded 
  as 
  sufficient 
  for 
  

   generic 
  separation. 
  This 
  is 
  not 
  an 
  isolated 
  or 
  sporadic 
  occurrence, 
  

   for 
  it 
  is 
  one 
  of 
  the 
  strongest 
  species 
  of 
  the 
  genus, 
  from 
  the 
  great 
  

  

  29 
  Proc 
  Airer. 
  Acad. 
  Arts 
  and 
  Sci., 
  vol. 
  5, 
  1SG0, 
  p. 
  18. 
  Wachsmuth 
  and 
  Springer, 
  

   North 
  Amer. 
  Crin. 
  Cam., 
  1807, 
  i>. 
  750, 
  pi. 
  77, 
  figs, 
  la, 
  b. 
  

  

  