﻿FROM 
  THE 
  CAMBRIAN 
  STRATA 
  OF 
  NORTH 
  AMERICA, 
  ETC. 
  129 
  

  

  tion 
  of 
  Mr. 
  Billings, 
  and 
  regards 
  A. 
  atlanticus 
  as 
  the 
  legitimate 
  type 
  

   of 
  Archceocyatlius. 
  But 
  as 
  it 
  is 
  impossible 
  to 
  make 
  A. 
  atlanticus 
  con- 
  

   form 
  to 
  the 
  generic 
  diagnosis 
  given 
  by 
  Billings, 
  Mr. 
  Waleott 
  

   radically 
  altered 
  it 
  for 
  the 
  purpose, 
  and 
  thus 
  it 
  is 
  only 
  nominally 
  

   the 
  same 
  genus 
  which 
  Mr. 
  Billings 
  described. 
  

  

  The 
  structure 
  of 
  A. 
  atlanticus 
  is 
  described 
  by 
  Mr. 
  Waleott 
  as 
  con- 
  

   sisting 
  of 
  a 
  more 
  or 
  less 
  irregular 
  system 
  of 
  rounded 
  and 
  irregular 
  

   passages 
  or 
  canals, 
  many 
  of 
  them 
  terminating 
  as 
  culs-de-sac 
  or 
  little 
  

   chambers 
  in 
  the 
  mass 
  of 
  the 
  skeleton. 
  In 
  longitudinal 
  section 
  the 
  

   skeleton 
  is 
  stated 
  to 
  be 
  arranged 
  on 
  arching 
  transverse 
  lines, 
  and 
  vertical 
  

   and 
  slightly 
  radiating 
  lines, 
  but 
  its 
  minute 
  structure 
  is 
  unknown. 
  If 
  

   spicula 
  existed 
  in 
  A. 
  atlanticus, 
  they 
  were 
  probably 
  destroyed 
  by 
  the 
  

   crystallization 
  of 
  the 
  calcareous 
  matter 
  of 
  which 
  the 
  skeleton 
  now 
  

   consists 
  ; 
  but 
  in 
  A. 
  Billingsi, 
  a 
  new 
  species, 
  spicula 
  are 
  stated 
  to 
  be 
  

   present 
  in 
  the 
  interseptal 
  spaces, 
  the 
  cup, 
  and 
  about 
  the 
  specimens, 
  

   and 
  are 
  regarded 
  as 
  constituent 
  parts 
  of 
  the 
  organism. 
  The 
  author 
  

   gives 
  for 
  the 
  first 
  time 
  a 
  separate 
  definition 
  of 
  the 
  genus 
  Ethmo- 
  

   phyllum, 
  Meek, 
  and 
  figures 
  the 
  type 
  forms. 
  The 
  skeleton 
  is 
  said 
  to 
  

   consist 
  of 
  fine 
  branching 
  spicula 
  in 
  one 
  species 
  (E. 
  minganensis), 
  

   and 
  undetermined 
  in 
  others, 
  owing 
  probably 
  to 
  the 
  replacement 
  of 
  

   the 
  parts 
  by 
  calcite. 
  Both 
  A. 
  profundus, 
  Bill., 
  and 
  A. 
  minganensis, 
  

   Bill., 
  are 
  by 
  this 
  author 
  included 
  in 
  Meek's 
  genus, 
  and 
  it 
  comprises 
  

   also 
  Arcliaiocyathellus, 
  Ford, 
  and 
  Protocyathus, 
  Ford. 
  All 
  these 
  

   forms 
  are 
  regarded 
  as 
  sponges, 
  and 
  the 
  spicula, 
  in 
  several 
  of 
  the 
  

   species, 
  are 
  supposed 
  to 
  have 
  been 
  lost 
  in 
  the 
  crystallization 
  of 
  the 
  

   calcite. 
  

  

  In 
  1886 
  * 
  Prof. 
  C. 
  Schliiter 
  compared 
  some 
  fossils 
  from 
  the 
  drift 
  

   of 
  Sadewitz 
  in 
  Silesia 
  to 
  Arcliceocyatlius, 
  but 
  their 
  state 
  of 
  preser- 
  

   vation 
  is 
  altogether 
  too 
  imperfect 
  to 
  allow 
  of 
  any 
  satisfactory 
  con- 
  

   clusions 
  as 
  to 
  their 
  structure 
  or 
  relations. 
  

  

  In 
  the 
  May 
  number 
  of 
  the 
  ' 
  Geological 
  Magazine 
  ' 
  for 
  the 
  present 
  

   year 
  (1888), 
  p. 
  226, 
  1 
  described 
  the 
  detached 
  siliceous 
  spicules 
  present 
  

   in 
  specimens 
  of 
  A. 
  minganensis, 
  and 
  referred 
  them 
  to 
  several 
  distinct 
  

   species 
  of 
  siliceous 
  sponges 
  ; 
  consequently, 
  as 
  Mr. 
  Billings 
  had 
  sus- 
  

   pected, 
  they 
  did 
  not 
  belong 
  to 
  the 
  form 
  with 
  which 
  they 
  are 
  found. 
  

   I 
  also 
  expressed 
  the 
  opinion 
  that 
  the 
  so-called 
  branching 
  spicules 
  

   were 
  probably 
  only 
  siliceous 
  replacements 
  of 
  the 
  outer 
  surface 
  of 
  the 
  

   wall 
  of 
  the 
  fossil, 
  but 
  I 
  had 
  not 
  then 
  seen 
  specimens 
  of 
  these 
  ; 
  from 
  

   a 
  subsequent 
  examination 
  of 
  the 
  type 
  forms 
  it 
  is 
  evident 
  that 
  they 
  

   are 
  genuine 
  spicules 
  belonging 
  to 
  the 
  form 
  itself, 
  and 
  thus 
  the 
  

   opinion 
  I 
  expressed 
  about 
  them 
  was 
  erroneous. 
  

  

  2. 
  The 
  Mineral 
  Nature 
  of 
  Archaeocyathus 
  and 
  its 
  allies. 
  

  

  The 
  mineral 
  nature 
  of 
  this 
  genus, 
  whether 
  calcareous 
  or 
  siliceous, 
  

   has 
  not 
  been 
  specially 
  referred 
  to 
  by 
  previous 
  writers, 
  though 
  it 
  has 
  

   been 
  implied 
  that 
  the 
  present 
  condition 
  of 
  some 
  of 
  the 
  specimens 
  is 
  

   not 
  the 
  original 
  one, 
  and 
  that 
  if 
  siliceous 
  examples 
  of 
  these 
  were 
  

  

  * 
  " 
  Archaeoeyathus 
  im 
  russischen 
  Silur 
  ? 
  " 
  Zeitschr. 
  deutsch. 
  geol. 
  Gesellsch. 
  

   (1886), 
  pp. 
  899-909. 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  177. 
  k 
  

  

  