﻿136 
  DE. 
  G. 
  J. 
  HINDE 
  ON 
  AECH^OCYATHUS 
  AKD 
  OTHEE 
  GENEEA 
  

  

  supposed 
  higher 
  stage 
  of 
  the 
  organism 
  has 
  been 
  discovered 
  ; 
  and 
  for 
  

   such 
  forms, 
  which, 
  in 
  places, 
  Dr. 
  Borneinann 
  states, 
  fill 
  entire 
  beds 
  

   of 
  rock, 
  the 
  provisional 
  genus 
  Protopharetra 
  is 
  proposed. 
  It 
  includes 
  

   bodies 
  of 
  very 
  varying 
  forms, 
  either 
  cylindrical 
  or 
  growing 
  in 
  ex- 
  

   tended 
  masses, 
  from 
  which 
  simple 
  or 
  furcated 
  stems 
  are 
  given 
  off. 
  

   The 
  stems 
  have 
  a 
  tube-like, 
  axial 
  cavity, 
  crossed 
  by 
  tabulae 
  (Boden, 
  

   Borneni.) 
  and 
  bounded 
  by 
  the 
  porous 
  walls. 
  These 
  consist 
  of 
  a 
  

   delicate, 
  fibrous, 
  calcareous 
  tissue, 
  of 
  dull, 
  nearly 
  opaque, 
  milk-white 
  

   aspect 
  in 
  thin 
  sections. 
  The 
  fibres 
  may 
  be 
  cylindrical 
  or 
  flattened, 
  

   and 
  they 
  anastomose 
  with 
  each 
  other, 
  and 
  thus 
  bear 
  a 
  consi- 
  

   derable 
  outward 
  resemblance 
  to 
  the 
  structure 
  of 
  the 
  group 
  of 
  fossil 
  

   Calcisponges 
  named 
  Pharetrones 
  by 
  v. 
  Zittel 
  ; 
  but, 
  unlike 
  these, 
  no 
  

   traces 
  of 
  spicules 
  occur 
  in 
  the 
  fibres, 
  and 
  their 
  minutely 
  granular 
  

   homogeneous 
  character 
  is 
  opposed 
  to 
  the 
  idea 
  that 
  they 
  originally 
  

   consisted 
  of 
  spicules. 
  

  

  Prom 
  microscopic 
  sections 
  of 
  the 
  Sardinian 
  specimens 
  kindly 
  pre- 
  

   sented 
  to 
  me 
  by 
  Dr. 
  Bornemann 
  I 
  am 
  enabled 
  to 
  confirm 
  the 
  

   description 
  given 
  by 
  him 
  of 
  the 
  structure 
  of 
  Protopharetra. 
  I 
  am 
  

   not 
  satisfied, 
  however, 
  that 
  these 
  fossils 
  are 
  merely 
  the 
  lower 
  stage 
  

   of 
  development 
  of 
  Archceocyathus-forms. 
  Yery 
  small 
  specimens, 
  

   both 
  of 
  this 
  latter 
  genus 
  and 
  of 
  Protopharetra, 
  are 
  present 
  in 
  the 
  

   same 
  rock-fragments, 
  and 
  the 
  distinctive 
  characters 
  of 
  each 
  are 
  well 
  

   marked. 
  Fairly 
  large 
  examples 
  of 
  ProtopJiaretra 
  also 
  occur, 
  which 
  

   show 
  no 
  traces 
  of 
  the 
  regular 
  septal 
  structure 
  of 
  Archceocyathus. 
  

  

  Five 
  species 
  of 
  this 
  genus 
  have 
  been 
  described 
  by 
  Dr. 
  Bornemann 
  

   from 
  the 
  Lower 
  Cambrian 
  strata 
  of 
  Sardinia. 
  

  

  Genus 
  Spieoctathus 
  *, 
  gen. 
  nov. 
  (Plate 
  V. 
  figs. 
  8, 
  9, 
  10.) 
  

   Generic 
  characters. 
  Infundibuliform 
  or 
  subcylindrical 
  forms, 
  with 
  

   an 
  axial 
  subcylindrical 
  tube 
  or 
  cavity 
  bounded 
  by 
  thick 
  walls. 
  

   These 
  are 
  built 
  up 
  of 
  relatively 
  thick, 
  solid, 
  inosculating 
  plates 
  or 
  

   lamina?, 
  partially 
  connected 
  by 
  delicate 
  fibres, 
  which 
  form 
  a 
  reticu- 
  

   late 
  tissue 
  with 
  irregular 
  lacunae 
  or 
  canals. 
  The 
  lamina 
  forming 
  

   the 
  outer 
  surface, 
  and 
  that 
  next 
  the 
  axial 
  tube, 
  are 
  much 
  stouter 
  

   than 
  those 
  of 
  the 
  central 
  portions 
  of 
  the 
  wall. 
  The 
  outer 
  lamina 
  

   is 
  apparently 
  perforated 
  by 
  minute 
  apertures, 
  and 
  larger 
  canals 
  

   connect 
  the 
  interspaces 
  of 
  the 
  wall-tissue 
  with 
  the 
  central 
  cavity. 
  

   In 
  places 
  the 
  cavity 
  is 
  partially 
  filled 
  up 
  with 
  fibrous 
  outgrowths 
  

   from 
  the 
  wall. 
  The 
  wall-plates 
  consist 
  of 
  a 
  primary 
  central 
  layer 
  

   enclosed 
  by 
  successive 
  secondary 
  layers 
  of 
  a 
  minutely 
  granular 
  

   carbonate 
  of 
  lime. 
  

  

  This 
  genus 
  is 
  based 
  on 
  the 
  type 
  specimen 
  of 
  Archceocyathus 
  

   atlanticus, 
  Bill.f 
  The 
  form 
  had 
  not 
  previously 
  been 
  studied 
  in 
  

  

  * 
  GTreipa, 
  a 
  twisted 
  coil, 
  KvaOos, 
  cup. 
  

  

  t 
  New 
  species 
  of 
  Lower 
  Silurian 
  Fossils, 
  1861, 
  p. 
  4, 
  figs. 
  1-3 
  ; 
  Pal. 
  .Fossils, 
  

   vol. 
  i. 
  (1865) 
  p. 
  5, 
  fig. 
  5. 
  Mr. 
  Walcott 
  (Bull. 
  no. 
  30, 
  p. 
  73) 
  regards 
  this 
  species 
  

   as 
  the 
  type 
  of 
  Archceocyathus, 
  Bill. 
  ; 
  but 
  I 
  have 
  pointed 
  out 
  already 
  (p. 
  126, 
  note): 
  

   that 
  for 
  very 
  good 
  reasons 
  Mr. 
  Billings, 
  in 
  a 
  revised 
  reference 
  to 
  the 
  genus 
  in 
  

   1865, 
  distinctly 
  placed 
  A. 
  'profundus 
  as 
  the 
  type, 
  and 
  that 
  the 
  characters 
  of 
  

   A. 
  atlanticus 
  will 
  not 
  allow 
  of 
  its 
  inclusion 
  in 
  Archceocyathus, 
  as 
  defined 
  

   by 
  Mr. 
  Billings. 
  

  

  