﻿EROM 
  THE 
  CAMBRIAN 
  STRATA 
  OF 
  NORTH 
  AMERICA, 
  ETC. 
  143 
  

  

  in 
  it 
  in 
  places, 
  but 
  no 
  distinct 
  spicules. 
  Where 
  the 
  smooth 
  surface- 
  

   layer 
  has 
  been 
  worn 
  away, 
  small 
  canal-apertures, 
  about 
  -5 
  millim. 
  wide, 
  

   are 
  exposed 
  (PL 
  Y. 
  fig. 
  12). 
  It 
  is 
  only 
  in 
  certain 
  weathered 
  places 
  on 
  

   the 
  outer 
  surface 
  of 
  the 
  sponge 
  that 
  the 
  spicular 
  structure 
  can 
  be 
  

   clearly 
  seen. 
  The 
  spicules 
  are 
  very 
  small, 
  the 
  rays 
  vary 
  from 
  *1 
  to 
  -2 
  

   millim. 
  in 
  length, 
  and 
  about 
  '03 
  millim. 
  in 
  thickness. 
  They 
  appear 
  

   to 
  have 
  been 
  united 
  together 
  by 
  the 
  intertwining 
  of 
  the 
  branching 
  

   extremities 
  of 
  the 
  rays, 
  but 
  no 
  prominent 
  nodes 
  are 
  formed 
  by 
  the 
  

   junction 
  as 
  in 
  the 
  majority 
  of 
  the 
  Mesozoic 
  tetracladine 
  sponges. 
  In 
  

   most 
  of 
  the 
  spicules 
  only 
  three 
  rays 
  can 
  be 
  distinguished, 
  but 
  in 
  

   some 
  the 
  normal 
  four 
  rays 
  are 
  developed 
  (PI. 
  Y. 
  fig. 
  14). 
  The 
  

   irregular 
  spicules 
  consist 
  of 
  a 
  single 
  straight 
  or 
  curved 
  axis, 
  with 
  

   branching 
  ends. 
  That 
  the 
  entire 
  sponge 
  was 
  built 
  up 
  of 
  similar 
  

   spicules 
  to 
  those 
  on 
  the 
  surface, 
  is 
  proved 
  by 
  the 
  traces 
  of 
  them 
  in 
  

   thin 
  sections 
  of 
  the 
  interior 
  of 
  the 
  wall. 
  

  

  The 
  peculiar 
  form 
  of 
  the 
  outer 
  surface 
  and 
  the 
  strongly 
  marked 
  

   septum-like 
  disposition 
  of 
  the 
  spicular 
  skeleton 
  readily 
  distinguish 
  

   this 
  genus 
  from 
  other 
  fossil 
  and 
  recent 
  Lithistids. 
  This 
  septum-like 
  

   arrangement, 
  however, 
  is 
  not 
  peculiar 
  to 
  Archceoscyphia, 
  since 
  it 
  is 
  

   present, 
  though 
  in 
  a 
  less 
  marked 
  degree, 
  in 
  the 
  Mesozoic 
  genera 
  

   Cnemidiastrum, 
  Zitt., 
  and 
  CoraUidium, 
  Zitt. 
  

  

  Archceoseypliia 
  minganensis 
  was 
  first 
  described 
  by 
  Mr. 
  Billings* 
  

   as 
  the 
  cast 
  of 
  the 
  interior 
  of 
  a 
  coral 
  belonging 
  to 
  the 
  genus 
  Petraia. 
  

   In 
  1861 
  this 
  author 
  f 
  included 
  it 
  in 
  Archoeocyatlius, 
  and 
  stated 
  that 
  it 
  

   occurred 
  in 
  the 
  Calciferous 
  Formation 
  of 
  the 
  Mingan 
  Islands, 
  and 
  

   also 
  in 
  the 
  Potsdam 
  Limestone 
  of 
  Anse 
  au 
  Loup, 
  Labrador. 
  In 
  

   1865 
  %, 
  however, 
  the 
  Potsdam 
  specimens 
  were 
  regarded 
  as 
  distinct, 
  

   and 
  the 
  specific 
  name 
  was 
  restricted 
  to 
  the 
  specimens 
  from 
  the 
  

   Mingan 
  Islands. 
  In 
  these 
  Mr. 
  Billings 
  discovered 
  numerous 
  rod-like 
  

   spicules 
  which 
  were 
  regarded 
  as 
  adventitious, 
  and 
  branching 
  spicules 
  

   belonging 
  to 
  the 
  organism 
  itself. 
  Mr. 
  Billings 
  then 
  described 
  it, 
  

   and 
  rightly, 
  as 
  a 
  sponge, 
  but 
  he 
  retained 
  it 
  still 
  in 
  Archceocyatlius, 
  

   though 
  beyond 
  a 
  rude 
  correspondence 
  in 
  form 
  there 
  is 
  nothing 
  in 
  

   common 
  between 
  A. 
  minganensis 
  and 
  A. 
  profundus, 
  the 
  type 
  of 
  

   Archceocyathus. 
  In 
  the 
  former 
  of 
  these 
  the 
  skeleton 
  is 
  siliceous 
  and 
  

   consists 
  of 
  spicules 
  ; 
  in 
  the 
  latter 
  it 
  is 
  compact 
  carbonate 
  of 
  lime, 
  

   and 
  there 
  are 
  no 
  traces 
  whatever 
  of 
  spicules. 
  

  

  Only 
  a 
  single 
  species 
  of 
  this 
  genus, 
  A. 
  minganensis, 
  Bill., 
  sp., 
  has 
  

   been 
  definitely 
  recognized 
  from 
  the 
  Calciferous 
  Formation 
  of 
  the 
  

   Mingan 
  Islands, 
  Lower 
  St. 
  Lawrence. 
  In 
  the 
  Durness 
  Limestones 
  

   of 
  Sutherlandshire 
  some 
  weathered-out 
  siliceous 
  sponges 
  occur, 
  

   which, 
  so 
  far 
  as 
  their 
  imperfect 
  state 
  of 
  preservation 
  allows 
  of 
  com- 
  

   parison, 
  appear 
  to 
  belong 
  to 
  Archceoscyphia, 
  and 
  possibly 
  to 
  a 
  species 
  

   distinct 
  from 
  A. 
  minganensis. 
  

  

  * 
  Canadian 
  Nat. 
  and 
  Geol. 
  vol. 
  iv. 
  1859, 
  p. 
  346. 
  

   t 
  New 
  Species 
  of 
  Lower 
  Silurian 
  Fossils, 
  1861, 
  p. 
  5. 
  

   | 
  Pal. 
  Foss. 
  vol. 
  i. 
  pp. 
  5, 
  354. 
  

  

  