﻿FROM 
  THE 
  CAMBRIAN 
  STRATA 
  OF 
  NORTH 
  AMERICA, 
  ETC. 
  139 
  

  

  were, 
  by 
  Mr. 
  Billings* 
  , 
  ultimately 
  classed, 
  owing 
  to 
  his 
  unfor- 
  

   tunate 
  mistake 
  in 
  regarding 
  Arch, 
  profundus 
  and 
  Arch, 
  (now 
  

   Spirocyathus) 
  atlanticus 
  as 
  structurally 
  similar 
  to 
  the 
  A. 
  minga- 
  

   nensis, 
  which 
  is 
  a 
  true 
  siliceous 
  sponge. 
  We 
  have 
  seen 
  that 
  in 
  all 
  

   the 
  forms 
  above 
  mentioned 
  the 
  skeleton 
  is 
  composed 
  of 
  carbonate 
  of 
  

   lime 
  in 
  a 
  minutely 
  granular 
  condition, 
  and 
  there 
  is 
  every 
  indication 
  

   that 
  this 
  is 
  the 
  original 
  material, 
  and 
  that 
  it 
  is 
  not 
  a 
  replacement 
  

   after 
  silica, 
  so 
  that 
  any 
  relationship 
  to 
  siliceous 
  sponges 
  is 
  alto- 
  

   gether 
  excluded. 
  As 
  regards 
  their 
  probable 
  alliance 
  to 
  Calci- 
  

   sponges, 
  there 
  are 
  no 
  known 
  forms 
  of 
  this 
  group, 
  whether 
  fossil 
  or 
  

   recent, 
  with 
  the 
  same 
  regular 
  septate 
  build 
  of 
  the 
  skeleton 
  which 
  

   distinguishes 
  most 
  of 
  the 
  genera 
  of 
  the 
  Archaeocyathinse. 
  Spiro- 
  

   cyathus 
  and 
  Protopharetra 
  do, 
  indeed, 
  in 
  the 
  reticulate 
  and 
  partly 
  

   fibrous 
  character 
  of 
  their 
  skeletons, 
  bear 
  an 
  outward 
  resemblance 
  to 
  

   the 
  fossil 
  Pharetrones 
  f 
  , 
  and 
  it 
  has 
  been 
  suggested 
  that, 
  as 
  in 
  many 
  

   of 
  these 
  sponges, 
  the 
  fibrous 
  structures 
  may 
  have 
  originally 
  consisted 
  

   of 
  spicules 
  which 
  have 
  been 
  destroyed 
  in 
  the 
  fossilization 
  ; 
  but 
  to 
  

   this 
  supposition 
  may 
  be 
  opposed 
  the 
  fact 
  that 
  the 
  fibres 
  of 
  true 
  

   Pharetrones 
  whose 
  spicular 
  structures 
  have 
  been 
  destroyed 
  do 
  not 
  

   show 
  the 
  same 
  minute 
  granular 
  condition 
  which 
  is 
  present 
  both 
  in 
  

   the 
  Sardinian 
  and 
  Canadian 
  examples 
  of 
  the 
  two 
  above-named 
  

   genera, 
  and, 
  further, 
  in 
  no 
  example 
  of 
  Pharetrones 
  which 
  has 
  

   come 
  under 
  my 
  observation 
  is 
  there, 
  in 
  the 
  skeleton-fibres, 
  a 
  primary 
  

   layer 
  enclosed 
  by 
  successive 
  secondary 
  layers, 
  which 
  is 
  so 
  clearly 
  

   shown 
  in 
  Spirocyathus. 
  This 
  feature 
  is, 
  in 
  my 
  opinion, 
  conclu- 
  

   sively 
  opposed 
  to 
  the 
  idea 
  that 
  the 
  skeleton 
  of 
  this 
  genus, 
  like 
  that 
  

   of 
  the 
  Pharetrones, 
  consisted 
  originally 
  of 
  spicules 
  of 
  carbonate 
  of 
  

   lime. 
  

  

  Next, 
  as 
  to 
  the 
  relations 
  of 
  the 
  Archaeocyathinae 
  to 
  Foraminifera, 
  

   with 
  which 
  group 
  Archceocyaihus 
  has 
  been 
  compared 
  by 
  Sir 
  J. 
  W. 
  

   Dawson 
  %. 
  The 
  general 
  form 
  and 
  structure 
  of 
  this 
  organism 
  does 
  

   not 
  bear 
  any 
  close 
  resemblance 
  to 
  any 
  known 
  fossil 
  or 
  recent 
  genus 
  

   of 
  Foraniinifera, 
  and 
  the 
  septal 
  interloculi 
  crossed 
  by 
  dissepiments 
  

   cannot 
  be 
  compared 
  with 
  the 
  chamber-system 
  of 
  Poraminifera. 
  

  

  ArcJiceocyathus 
  has 
  been 
  included 
  in 
  the 
  ReceptaculitidsB 
  by 
  

   Prof. 
  Ferd. 
  Eomer 
  on 
  the 
  grounds 
  of 
  possessing 
  a 
  perforated 
  outer 
  

   and 
  inner 
  wall, 
  enclosing 
  a 
  central 
  cavity 
  as 
  in 
  Beceptaculites. 
  The 
  

   resemblance, 
  however, 
  is 
  of 
  too 
  slight 
  a 
  character 
  and 
  insufficient 
  to 
  

   indicate 
  any 
  close 
  relationship, 
  particularly 
  if 
  the 
  real 
  nature 
  of 
  the 
  

   skeleton 
  of 
  this 
  latter 
  genus 
  is 
  taken 
  into 
  consideration. 
  

  

  We 
  may 
  now 
  consider 
  the 
  probable 
  relationship 
  of 
  the 
  Archaeo- 
  

   cyathinae 
  to 
  Corals, 
  with 
  which 
  they 
  were 
  at 
  first 
  compared 
  both 
  by 
  

  

  * 
  Pal. 
  Foss. 
  vol. 
  i. 
  p. 
  357. 
  

  

  t 
  Versteinerungen 
  Sardiniens, 
  p. 
  37. 
  

  

  | 
  Can. 
  Nat. 
  and 
  Geologist, 
  1865, 
  p. 
  103, 
  note; 
  Pal. 
  Foss. 
  vol. 
  i. 
  p. 
  356; 
  

   Dawn 
  of 
  Life 
  (1875), 
  pp. 
  151-155. 
  Mention 
  is 
  here 
  made 
  of 
  a 
  canal-system 
  

   within 
  some 
  of 
  the 
  thicker 
  plates 
  of 
  Arch, 
  ^profundus 
  ; 
  but 
  the 
  original 
  section 
  

   from 
  which 
  fig. 
  41 
  c, 
  p. 
  154, 
  was 
  taken 
  shows 
  that 
  the 
  supposed 
  canals 
  are 
  merely 
  

   accidental 
  defects 
  in 
  the 
  preparation 
  of 
  the 
  section. 
  

  

  