﻿898 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  PTILOPORELLA, 
  Hall. 
  

   (See 
  Pal. 
  N". 
  Y., 
  vol. 
  YI, 
  pi. 
  xliii, 
  figs. 
  7-9.) 
  

  

  In 
  1874, 
  H. 
  A. 
  Nicholson 
  (Pal. 
  Ohio, 
  vol. 
  2, 
  p. 
  264, 
  pi. 
  xxv, 
  

   figs. 
  11, 
  11a) 
  described 
  a 
  peculiar 
  fenestelloid 
  form 
  from 
  the 
  

   Niagara 
  group 
  as 
  Fenestella 
  nervata. 
  

  

  Forms 
  of 
  this 
  particular 
  mode 
  of 
  growth 
  do 
  not, 
  so 
  far 
  as 
  I 
  

   know, 
  again 
  occur 
  until 
  the 
  Upper 
  Helderberg 
  formation 
  is 
  

   reached. 
  

  

  The 
  peculiarity 
  of 
  this 
  form 
  is 
  the 
  method 
  of 
  branching. 
  In. 
  

   the 
  ordinary 
  fenestelloid 
  form 
  the 
  branches 
  are 
  of 
  essentially 
  

   the 
  same 
  size 
  and 
  increase 
  by 
  bifurcation. 
  In 
  this 
  form 
  there 
  

   are 
  a 
  number 
  of 
  prominent 
  or 
  main 
  branches, 
  from 
  which 
  

   smaller 
  branches 
  proceed 
  laterally, 
  either 
  from 
  one 
  or 
  both 
  

   sides. 
  At 
  intervals 
  one 
  of 
  the 
  lateral 
  branches 
  increases 
  in 
  size 
  

   and 
  becomes 
  one 
  of 
  the 
  main 
  brarches, 
  having 
  lateral 
  branches 
  

   in 
  the 
  same 
  manner 
  as 
  the 
  primary 
  main 
  branches. 
  This 
  

   method 
  of 
  growth 
  is 
  repeated 
  as 
  long 
  as 
  the 
  expansion 
  of 
  the 
  

   frond 
  continues. 
  

  

  As 
  is 
  the 
  case 
  in 
  all 
  other 
  forms 
  of 
  Fenestellidge 
  some 
  of 
  the 
  

   species 
  have 
  only 
  two 
  ranges 
  of 
  cells 
  on 
  a 
  branch 
  while 
  others 
  

   have 
  three 
  or 
  more. 
  

  

  Those 
  forms 
  which 
  have 
  only 
  two 
  ranges 
  of 
  cell 
  apertures 
  

   have 
  been 
  placed 
  in 
  the 
  genus 
  Ptiloporina. 
  

  

  Those 
  which 
  have 
  three 
  or 
  more 
  ranges 
  of 
  cell 
  apertures 
  have 
  

   been 
  placed 
  in 
  the 
  genus 
  Ptiloporella, 
  the 
  latter 
  genus 
  having 
  

   the 
  same 
  relation 
  to 
  the 
  former 
  as 
  Polypora 
  has 
  to 
  Fenestella. 
  

   The 
  typical 
  species 
  are 
  represented 
  on 
  plate 
  xliii. 
  

  

  Both 
  of 
  these 
  genera 
  are 
  infundibuliform. 
  There 
  are 
  other 
  

   species 
  which 
  always 
  have 
  a 
  flabellate 
  growth, 
  and 
  the 
  lateral 
  

   arrangement 
  of 
  the 
  secondary 
  branches 
  is 
  even 
  more 
  pronounced 
  

   than 
  in 
  the 
  infundibuliform 
  fronds. 
  If 
  one 
  of 
  the 
  main 
  branches 
  

   with 
  its 
  lateral 
  branches 
  is 
  broken 
  away 
  from 
  the 
  main 
  frond 
  

   the 
  fragment 
  has 
  precisely 
  the 
  appearance 
  as 
  a 
  fragment 
  of 
  

   Ptilopora. 
  

  

  Following 
  the 
  same 
  process 
  of 
  reasoning 
  by 
  which 
  the 
  genera 
  

   FlabelliporeUa 
  and 
  Flabelliporina 
  have 
  been 
  formed 
  I 
  propose 
  

   to 
  separate 
  these 
  flabellate 
  species 
  from 
  the 
  infundibuliform 
  and 
  

   the 
  term 
  Pmnaporella 
  may 
  be 
  applied 
  to 
  them. 
  

  

  