﻿1864.] 
  

  

  SALTER 
  LINGTTLA-FLAG 
  FOSSILS. 
  

  

  239 
  

  

  which 
  the 
  branches 
  are 
  arranged 
  in 
  more 
  than 
  

   one 
  plane, 
  and 
  hence 
  there 
  is 
  no 
  danger 
  of 
  

   confounding 
  the 
  Primordial 
  form 
  with 
  those 
  

   Silurian 
  genera*. 
  

  

  There 
  are 
  many 
  unpublished 
  Spongiadse 
  

   from 
  true 
  Silurian 
  Bocks 
  t 
  ; 
  and 
  it 
  is 
  at 
  least 
  

   satisfactory 
  to 
  find 
  that 
  these 
  had 
  their 
  ante- 
  

   cedents 
  in 
  a 
  formation 
  whose 
  much 
  greater 
  

   antiquity 
  is 
  now 
  well 
  established. 
  The 
  fauna 
  

   of 
  the 
  Lingula-flags 
  is 
  even 
  yet 
  a 
  scanty 
  one. 
  

   In 
  some 
  few 
  of 
  its 
  genera 
  it 
  shows 
  an 
  ap- 
  

   proximation 
  to 
  Lower 
  Silurian 
  forms 
  ; 
  and 
  

   some 
  Shells 
  and 
  a 
  Cystidean 
  are 
  of 
  genera 
  

   common 
  to 
  both 
  formations. 
  But 
  the 
  Crus- 
  

   tacea 
  here, 
  as 
  elsewhere 
  in 
  the 
  Pakeozoic 
  

   rocks, 
  are 
  our 
  surest 
  indices 
  of 
  age 
  ; 
  and 
  the 
  

   entire 
  distinctness 
  of 
  the 
  Trilobite 
  fauna 
  

   overbalances 
  the 
  fact 
  that 
  species 
  of 
  Orthis, 
  

   of 
  Distinct, 
  of 
  Theca, 
  and 
  of 
  Trochocystites 
  are 
  

   found 
  both 
  in 
  Silurian 
  strata 
  and 
  in 
  the 
  great 
  

   Primordial 
  formation 
  which 
  lies 
  near 
  the 
  base 
  

   of 
  the 
  fossiliferous 
  rocks 
  of 
  "Wales. 
  With 
  the 
  

   exception 
  of 
  Agnostus 
  and 
  Leperditia, 
  not 
  a 
  

   single 
  Crustacean 
  genus 
  is 
  known 
  to 
  pass 
  from 
  

  

  * 
  In 
  a 
  letter 
  from 
  Dr. 
  Bowerbank, 
  to 
  whom 
  I 
  sent 
  

   specimens 
  of 
  Protospongia, 
  he 
  refers 
  to 
  his 
  recent 
  

   genus 
  Spongionella 
  (Phil. 
  Trans. 
  1862, 
  plate 
  74. 
  fig. 
  

   10) 
  as 
  the 
  nearest 
  ally. 
  The 
  pyritized 
  state 
  of 
  the 
  

   fossil 
  favours 
  the 
  view 
  which 
  he 
  takes, 
  that 
  this 
  is 
  

   one 
  of 
  the 
  true 
  horny 
  sponges 
  allied 
  to 
  the 
  genus 
  

   just 
  quoted, 
  sponge-fibre 
  decomposing 
  but 
  slowly. 
  

   The 
  remains 
  here 
  figured 
  are 
  not, 
  in 
  Dr. 
  Bower- 
  

   bank's 
  view, 
  the 
  spiculae, 
  but 
  the 
  sponge-fibre 
  itself 
  

   replaced 
  by 
  pyrites 
  ; 
  and, 
  if 
  so, 
  the 
  size 
  of 
  the 
  fibres 
  

   would 
  be 
  nothing 
  remarkable, 
  since 
  it 
  maybe 
  paralleled 
  

   in 
  many 
  recent 
  species. 
  While 
  I 
  do 
  not 
  share 
  Dr. 
  

   Bowerbank's 
  opinion 
  (I 
  believe 
  these 
  are 
  true 
  spiculae), 
  

   I 
  feel 
  bound 
  to 
  give 
  his 
  authority 
  for 
  a 
  contrary 
  view, 
  

   the 
  more 
  so 
  as 
  there 
  seem 
  to 
  be 
  several 
  Silurian 
  and 
  

   other 
  palaeozoic 
  forms 
  which 
  may 
  be 
  better 
  explained 
  

   in 
  this 
  way, 
  such 
  as 
  Ischadites, 
  Tetragonis, 
  &c. 
  The 
  

   remarkable 
  genus 
  Arch<20cyathus, 
  Billings 
  (Geology 
  of 
  

   Canada, 
  pp. 
  283, 
  285, 
  286), 
  described 
  in 
  1861, 
  has 
  no 
  

   relation 
  to 
  our 
  fossil, 
  and 
  was 
  probably 
  calcareous. 
  

   There 
  is, 
  I 
  think, 
  much 
  doubt 
  if 
  the 
  limestones 
  there 
  

   described 
  truly 
  belong 
  to 
  the 
  Primordial 
  group, 
  though 
  

   included 
  with 
  the 
  Potsdam 
  Sandstone. 
  Eospongia, 
  

   published 
  in 
  the 
  same 
  year, 
  does 
  not 
  need 
  com- 
  

   parison. 
  

  

  t 
  I 
  may 
  mention 
  here 
  that 
  a 
  fine 
  species 
  of 
  Astylo- 
  

   spongia, 
  very 
  like 
  A. 
  incisolobata, 
  Eoem. 
  (pi. 
  1. 
  f. 
  3), 
  

   was 
  found 
  by 
  myself, 
  years 
  ago, 
  at 
  Sholes 
  Hook, 
  near 
  

   Haverfordwest, 
  in 
  the 
  Caradoc 
  strata. 
  It 
  is 
  in 
  the 
  

   Museum 
  of 
  Practical 
  Greology. 
  The 
  genus 
  is 
  new 
  to 
  

   Britain. 
  

  

  k: 
  

  

  GQ 
  

  

  Cb 
  

  

  m 
  

  

  m.fr 
  

  

  pq 
  

  

  .2 
  p. 
  

  

  