﻿The 
  Faux 
  a 
  of 
  the 
  Niagaka 
  Group. 
  131 
  

  

  feature 
  of 
  an 
  anal 
  side. 
  The 
  surface 
  markings 
  are 
  character- 
  

   istic 
  of 
  the 
  species, 
  and 
  in 
  some 
  specimens 
  the 
  fasciculate 
  striae 
  

   are 
  raised 
  into 
  strong 
  ridges 
  of 
  a 
  more 
  prominent 
  character 
  

   than 
  those 
  represented 
  in 
  the 
  figure. 
  In 
  a 
  single 
  specimen 
  

   observed 
  the 
  strise 
  are 
  subdued 
  and 
  separated, 
  with 
  the 
  inter- 
  

   spaces 
  marked 
  by 
  fine 
  granulse. 
  The 
  preceding 
  diagram 
  

   illustrates 
  the 
  structure 
  so 
  far 
  as 
  it 
  has 
  been 
  observed. 
  

  

  Observations 
  upon 
  the 
  genera 
  Glyptocrintts, 
  Glyptaster, 
  

   Balanocrintjs 
  and 
  Lampterocrlxus. 
  

  

  In 
  the 
  first 
  volume 
  of 
  the 
  Palceontology 
  of 
  New 
  York, 
  I 
  

   proposed 
  the 
  genus 
  Glyptocrixus 
  for 
  a 
  lower 
  Silurian 
  form, 
  

   common 
  in 
  the 
  blue 
  shaly 
  limestone 
  of 
  the 
  Hudson 
  River 
  group 
  

   at 
  Cincinnati 
  and 
  elsewhere 
  in 
  the 
  west. 
  This 
  genus 
  is 
  char- 
  

   acterized 
  by 
  the 
  presence 
  of 
  iive 
  basal 
  or 
  subradial 
  plates, 
  suc- 
  

   ceeded 
  by 
  five 
  series 
  of 
  radial 
  plates 
  of 
  three 
  each, 
  below 
  the 
  

   first 
  subdivision 
  of 
  the 
  ray. 
  The 
  column 
  at 
  its 
  junction 
  with 
  

   the 
  body 
  is 
  pentalobate. 
  The 
  genus 
  has 
  been 
  recognized 
  and 
  

   several 
  other 
  species 
  described 
  by 
  different 
  authors. 
  A 
  care- 
  

   ful 
  examination 
  of 
  the 
  basal 
  cavity 
  of 
  some 
  of 
  the 
  specimens 
  

   gives 
  indication 
  that 
  the 
  last 
  joint 
  of 
  the 
  column 
  may 
  be 
  

   divided, 
  representing 
  five 
  undeveloped 
  basal 
  plates. 
  

  

  In 
  the 
  genus 
  Glyptaster, 
  five 
  basal 
  plates 
  and 
  iive 
  subra- 
  

   dials 
  are 
  distinguished, 
  with 
  the 
  rays 
  consisting 
  of 
  three 
  plates 
  

   each, 
  below 
  the 
  first 
  subdivision. 
  

  

  The 
  distinction 
  between 
  these 
  genera 
  is, 
  therefore, 
  as 
  fol- 
  

   lows 
  : 
  In 
  the 
  first, 
  the 
  non-development 
  of 
  true 
  basal 
  plates, 
  

   while 
  the 
  ray 
  is 
  twice 
  subdivided 
  before 
  becoming 
  free 
  ; 
  and 
  

   in 
  the 
  typical 
  species 
  the 
  arms 
  are 
  not 
  again 
  subdivided. 
  In 
  

   the 
  second, 
  a 
  moderate 
  development 
  of 
  the 
  true 
  basal 
  plates, 
  

   with 
  subradials 
  above, 
  while 
  the 
  ray 
  is 
  but 
  once 
  subdivided 
  

   before 
  becoming 
  free.* 
  

  

  At 
  the 
  time 
  of 
  proposing 
  the 
  genus 
  Glyptaster, 
  I 
  was 
  not 
  

   acquainted, 
  with 
  the 
  structure 
  of 
  Balaxocrixus 
  of 
  Troost. 
  

   The 
  latter 
  genus 
  I 
  recognized 
  in 
  the 
  Wisconsin 
  Report 
  of 
  I860. 
  

   Upon 
  further 
  examination, 
  it 
  appears 
  that 
  Balaxocrixus 
  of 
  

   Troost 
  has 
  the 
  structure 
  of 
  Glyptaster, 
  with 
  this 
  exception, 
  

   that 
  the 
  basal 
  plates 
  are 
  much 
  more 
  fully 
  developed, 
  while 
  

   the 
  rays 
  do 
  not 
  bifurcate 
  before 
  becoming 
  free. 
  Notwith- 
  

   standing, 
  therefore, 
  the 
  great 
  similarity 
  and 
  near 
  identity 
  of 
  

   structure 
  in 
  these 
  forms, 
  there 
  seems 
  good 
  reason 
  for 
  the 
  

   generic 
  separation. 
  

  

  The 
  genus 
  Lampterocrixus 
  of 
  Roemer 
  is 
  identical 
  with 
  

  

  * 
  See 
  illustrations 
  of 
  structure, 
  on 
  pp. 
  206, 
  207, 
  2ith 
  Report 
  on 
  the 
  State 
  Museum 
  

   of 
  Natural 
  History. 
  1872. 
  

  

  