﻿894 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  cases 
  are 
  constantly 
  occurring 
  and 
  must 
  be 
  expected 
  to 
  occur 
  yet 
  

   more 
  frequently 
  in 
  the 
  future." 
  

  

  Mr. 
  G. 
  W. 
  Shrubsole, 
  in 
  his 
  paper 
  on 
  " 
  British 
  Upper 
  Silurian 
  

   Fenestellidse," 
  says: 
  "As 
  to 
  the 
  question 
  whether 
  Fenestella 
  

   intermedia 
  ought 
  also 
  to 
  be 
  included 
  in 
  the 
  genus 
  Polypora 
  it 
  may 
  

   fairly 
  be 
  left 
  open 
  for 
  consideration. 
  It 
  may 
  be, 
  and 
  is, 
  difficult 
  

   in 
  practice 
  to 
  draw 
  the 
  line 
  where 
  Fenestella 
  ends 
  and 
  Polypora 
  

   begins." 
  

  

  Mr. 
  E. 
  O. 
  Ulrich, 
  in 
  the 
  Palaeontology 
  of 
  Illinois, 
  Yol. 
  8, 
  p. 
  358, 
  

   mentions 
  several 
  species 
  which 
  could 
  with 
  equal 
  propriety 
  be 
  

   included 
  in 
  either 
  genus, 
  or 
  to 
  speak 
  more 
  accurately, 
  in 
  either 
  

   the 
  family 
  Fenestellidse 
  or 
  Polyporidae 
  as 
  proposed 
  by 
  Yine, 
  

   which 
  amounts 
  to 
  the 
  same 
  thing. 
  Other 
  quotations 
  could 
  be 
  

   made, 
  but 
  it 
  is 
  unnecessary. 
  

  

  It 
  remains 
  then 
  to 
  reject 
  altogether 
  the 
  genus 
  Polypora 
  or 
  to 
  

   form 
  another 
  genus 
  which 
  shall 
  include 
  those 
  forms 
  intermediate 
  

   between 
  Fenestella 
  and 
  Polypora. 
  To 
  me 
  the 
  latter 
  course 
  seems 
  

   preferable. 
  To 
  place 
  all 
  the 
  forms 
  hitherto 
  included 
  in 
  the 
  two 
  

   genera 
  in 
  one 
  genus 
  would 
  make 
  that 
  genus 
  unwieldy 
  and 
  add 
  

   greatly 
  to 
  the 
  difficulty 
  of 
  the 
  identification 
  of 
  species, 
  while 
  it 
  

   seems 
  absurd 
  to 
  have 
  two 
  genera, 
  either 
  of 
  which 
  would, 
  with 
  

   equal 
  propriety, 
  include 
  many 
  species. 
  

  

  The 
  name 
  Polyporella 
  is 
  therefore 
  proposed 
  to 
  include 
  those 
  

   species 
  which 
  are 
  intermediate 
  between 
  Fenestella 
  and 
  Polypora 
  

   and 
  which 
  have 
  on 
  some 
  portions 
  of 
  the 
  branches 
  only 
  two 
  ranges 
  

   of 
  cell 
  apertures 
  and 
  on 
  other 
  portions 
  three 
  or 
  more 
  ranges. 
  

   The 
  Polyporella 
  fistulata 
  of 
  the 
  Hamilton 
  group 
  is 
  taken 
  as 
  the 
  

   type 
  of 
  the 
  genus 
  or 
  sub-genus 
  as 
  it 
  may 
  be 
  considered. 
  

  

  The 
  advantages 
  of 
  this 
  arrangement 
  are 
  that 
  by 
  it 
  the 
  limits 
  

   of 
  the 
  genera 
  Fenestella 
  and 
  Polypora 
  in 
  regard 
  to 
  each 
  other 
  

   are 
  definitely 
  fixed 
  and 
  there 
  can 
  be 
  no 
  donbt 
  as 
  to 
  the 
  disposal 
  

   of 
  intermediate 
  forms. 
  

  

  Such 
  forms 
  as 
  0. 
  Eudora 
  of 
  the 
  Lower 
  Helderberg 
  group, 
  

   which, 
  with 
  the 
  exception 
  of 
  a 
  small 
  fractional 
  space, 
  before 
  

   bifurcation, 
  has 
  only 
  two 
  ranges 
  of 
  cell 
  apertures, 
  separated 
  by 
  a 
  

   carina, 
  I 
  should 
  unhesitatingly 
  place 
  in 
  Fenestella, 
  and 
  similarly 
  

   those 
  forms 
  which 
  have, 
  except 
  for 
  a 
  very 
  small 
  space 
  above 
  a 
  

   bifurcation, 
  three 
  or 
  more 
  ranges 
  of 
  cell-apertures 
  would 
  be 
  

   placed 
  under 
  Polypora, 
  but 
  those 
  species 
  in 
  which 
  the 
  proportion 
  

  

  