﻿130 
  DE. 
  G. 
  J. 
  HINDE 
  ON 
  AECB^EOCYATHIJS 
  AND 
  OTHEE 
  GENEEA 
  

  

  found, 
  they 
  would 
  show 
  spicules. 
  Mr. 
  Walcott 
  has 
  likewise 
  referred 
  

   to 
  the 
  probable 
  obliteration 
  of 
  the 
  spicules 
  by 
  the 
  crystallization 
  of 
  

   the 
  calcite 
  of 
  which 
  their 
  skeletons 
  now 
  consist. 
  It 
  is 
  therefore 
  

   desirable 
  to 
  ascertain 
  if 
  possible 
  the 
  original 
  mineral 
  structure 
  of 
  

   these 
  fossils 
  in 
  considering 
  their 
  probable 
  zoological 
  relations. 
  First, 
  

   however, 
  we 
  may 
  exclude 
  the 
  Archceocyathus 
  minganensis, 
  Bill., 
  

   from 
  present 
  consideration, 
  since, 
  as 
  will 
  be 
  shown 
  later 
  on, 
  this 
  

   organism 
  is 
  undoubtedly 
  a 
  siliceous 
  sponge, 
  and 
  has 
  no 
  relationship 
  

   whatever 
  to 
  Archceocyathus 
  proper 
  and 
  its 
  allied 
  genera. 
  All 
  the 
  

   forms 
  of 
  this 
  group 
  which 
  I 
  have 
  seen, 
  whether 
  from 
  North 
  America, 
  

   Spain, 
  or 
  Sardinia, 
  are 
  uniformly 
  composed 
  of 
  carbonate 
  of 
  lime. 
  

   The 
  Canadian 
  specimens 
  of 
  A. 
  atlanticus 
  and 
  A. 
  profundus 
  from 
  Lab- 
  

   rador 
  consist 
  of 
  a 
  dull 
  white 
  or 
  yellowish-white 
  carbonate 
  of 
  lime, 
  

   compact 
  in 
  texture 
  and 
  opaque, 
  unless 
  in 
  very 
  thin 
  sections, 
  when 
  it 
  

   shows 
  a 
  very 
  minute 
  granular 
  character. 
  The 
  specimens 
  are 
  im- 
  

   bedded 
  in 
  a 
  hard 
  compact 
  granular 
  limestone, 
  reddish 
  in 
  tint 
  and 
  

   containing 
  numerous 
  microscopic 
  fragments 
  of 
  various 
  organisms. 
  

   This 
  matrix 
  usually 
  infills 
  the 
  cups 
  and 
  some 
  of 
  the 
  interloculi 
  in 
  

   the 
  specimens, 
  but 
  the 
  interior 
  spaces 
  frequently 
  are 
  now 
  filled 
  with 
  

   crystalline 
  calcite. 
  

  

  When 
  weathering 
  has 
  taken 
  place, 
  the 
  matrix 
  proves 
  more 
  resis- 
  

   tant 
  than 
  the 
  walls 
  and 
  septa 
  of 
  the 
  fossil, 
  which 
  consequently 
  are 
  

   now 
  indicated 
  by 
  depressed 
  lines 
  and 
  furrows. 
  In 
  all 
  the 
  specimens 
  

   which 
  I 
  have 
  seen, 
  the 
  walls 
  and 
  other 
  structures 
  of 
  the 
  fossil 
  are 
  

   well 
  defined 
  and 
  distinct 
  from 
  the 
  matrix, 
  and 
  though 
  from 
  the 
  

   lowest 
  Cambrian 
  strata, 
  their 
  characters 
  are 
  as 
  clearly 
  shown 
  as 
  if 
  

   they 
  had 
  been 
  of 
  Mesozoic 
  or 
  Tertiary 
  age. 
  

  

  The 
  type 
  specimen 
  of 
  Archceocyathus 
  marianus, 
  F. 
  Eomer, 
  from 
  

   Spain, 
  consists, 
  for 
  the 
  most 
  part, 
  of 
  a 
  dull, 
  opaque, 
  minutely 
  granu- 
  

   lar 
  carbonate 
  of 
  lime, 
  similar 
  to 
  that 
  of 
  the 
  Canadian 
  specimens 
  ; 
  but 
  

   in 
  the 
  minutely 
  reticulated 
  outer 
  surface 
  of 
  the 
  wall, 
  and 
  in 
  some 
  

   of 
  the 
  septa 
  as 
  well, 
  this 
  has 
  been 
  replaced 
  by 
  a 
  green 
  mineral, 
  not 
  

   unlike 
  glauconite 
  in 
  appearance. 
  The 
  matrix 
  is 
  a 
  granular, 
  cal- 
  

   careous, 
  shaly 
  rock, 
  somewhat 
  rusty 
  by 
  weathering. 
  The 
  spaces 
  

   within 
  the 
  fossil 
  are 
  filled 
  partially 
  by 
  the 
  matrix 
  and 
  partially 
  by 
  

   crystalline 
  calcite. 
  

  

  The 
  Sardinian 
  specimens 
  vary 
  somewhat 
  in 
  mineral 
  characters 
  

   according 
  to 
  the 
  different 
  localities 
  from 
  which 
  they 
  came. 
  Those 
  

   from 
  Canal 
  Grande 
  occur 
  as 
  dark 
  grey 
  patches 
  in 
  a 
  lighter 
  matrix 
  ; 
  

   the 
  fossils 
  themselves 
  are 
  of 
  minutely 
  granular 
  carbonate 
  of 
  lime, 
  

   and 
  their 
  interspaces 
  are 
  usually 
  filled 
  with 
  crystalline 
  calcite, 
  and 
  

   only 
  occasionlly 
  with 
  the 
  rock-matrix, 
  which 
  is 
  a 
  hard, 
  compact, 
  

   coarsely 
  granular 
  limestone 
  with 
  an 
  admixture 
  of 
  mica 
  and 
  some 
  

   other 
  minerals. 
  From 
  this 
  locality, 
  and 
  also 
  from 
  Punta 
  Pintau, 
  

   some 
  of 
  the 
  specimens 
  occur 
  as 
  casts 
  in 
  a 
  coarsely 
  granular 
  mica- 
  

   ceous 
  rock. 
  At 
  San 
  Pietro 
  di 
  Masua 
  these 
  fossils 
  are 
  enclosed 
  in 
  a 
  

   reddish 
  nodular 
  marble 
  with 
  streaks 
  and 
  veins 
  of 
  calcite. 
  They 
  

   are 
  whitish 
  by 
  ordinary 
  light, 
  and 
  the 
  carbonate 
  of 
  lime 
  is 
  minutely 
  

   granular 
  ; 
  their 
  interspaces 
  are 
  filled 
  with 
  calcite. 
  The 
  specimens 
  

   from 
  Cucuru 
  Contu 
  have 
  a 
  dark 
  appearance 
  by 
  reflected 
  light 
  ; 
  in 
  

  

  