﻿66 
  <x. 
  R. 
  VTNTE 
  Oj* 
  THE 
  WEDLOCK 
  POLYZOA. 
  

  

  tion 
  of 
  the 
  growing 
  colony 
  ; 
  but 
  even 
  here 
  it 
  seems 
  to 
  me 
  that 
  much 
  

   of 
  this 
  marginal 
  growth 
  also 
  becomes 
  abortive 
  after 
  a 
  time, 
  and 
  it, 
  

   too, 
  remaius 
  as 
  ornament. 
  It 
  may 
  be 
  wise 
  to 
  extend 
  these 
  remarks 
  

   so 
  as 
  to 
  elucidate 
  facts 
  connected 
  with 
  the 
  zoarium 
  of 
  other 
  species 
  

   as 
  well 
  ; 
  but 
  this 
  would 
  be 
  out 
  of 
  place 
  in 
  a 
  general 
  paper. 
  I 
  have 
  

   referred 
  to 
  the 
  subject 
  for 
  the 
  express 
  purpose 
  of 
  drawing 
  to 
  it 
  the 
  

   attention 
  of 
  biologists 
  and 
  palaeontologists. 
  I 
  refuse 
  to 
  say 
  cells 
  

   " 
  separated 
  by 
  a 
  thin 
  laminar 
  axis 
  " 
  because 
  this 
  is 
  not 
  so 
  in 
  this 
  

   species 
  at 
  least. 
  The 
  " 
  axis," 
  if 
  such 
  it 
  may 
  be 
  called, 
  is 
  formed 
  

   by 
  the 
  bases 
  of 
  the 
  cells, 
  both 
  in 
  transverse 
  and 
  in 
  longitudinal 
  

   section. 
  I 
  have 
  it 
  on 
  the 
  authority 
  of 
  Mr. 
  John 
  Young 
  of 
  Glasgow 
  

   that 
  some 
  of 
  the 
  rough 
  fractures 
  of 
  Ptilodictya 
  from 
  the 
  Scottish 
  

   Silurian 
  Series 
  show 
  the 
  wrinkled 
  septal 
  layer 
  which 
  intervenes 
  

   between 
  the 
  two 
  layers 
  of 
  cells. 
  There 
  are 
  also 
  specimens 
  in 
  the 
  

   School 
  of 
  Mines 
  which 
  show 
  the 
  same 
  wrinkled 
  aspect 
  ; 
  and 
  Professor 
  

   Nicholson 
  makes 
  a 
  point 
  of 
  showing 
  this 
  septal 
  layer 
  in 
  nearly 
  all 
  his 
  

   species. 
  This 
  being 
  a 
  matter 
  of 
  extreme 
  importance, 
  I 
  shall 
  return 
  

   to 
  its 
  discussion 
  at 
  some 
  future 
  time 
  when 
  other 
  investigations 
  

   which 
  I 
  am 
  making 
  are 
  completed. 
  

  

  19. 
  Ptilodictya 
  scalpellum, 
  Lonsdale. 
  

  

  Escliara 
  scaljoellum, 
  Lonsd. 
  Descriptive 
  Text 
  of 
  Sil. 
  Syst. 
  pi. 
  15. 
  

   figs. 
  25-25 
  a, 
  p. 
  679. 
  

  

  Zoarium 
  lancet-shaped. 
  Zooecia 
  more 
  or 
  less 
  oval, 
  nearly 
  oppo- 
  

   site 
  on 
  the 
  two 
  surfaces 
  ; 
  outer 
  rows, 
  cells 
  smaller 
  and 
  more 
  distant 
  

   than 
  in 
  the 
  other 
  rows 
  : 
  edge 
  of 
  zoarium, 
  when 
  perfect, 
  solid, 
  faintly 
  

   striated 
  and 
  sharp 
  ; 
  outer 
  covering 
  and 
  opening 
  of 
  cells 
  unknown. 
  

  

  Locality 
  and 
  Formation. 
  Wenlock 
  Limestone, 
  Dudley. 
  

  

  The 
  above 
  is 
  a 
  slight 
  modification 
  of 
  Lonsdale's 
  description 
  of 
  

   Eschara 
  scalpellum, 
  which, 
  by 
  general 
  consent 
  is 
  placed 
  in 
  the 
  genus 
  

   Ptilodictya. 
  In 
  his 
  remarks 
  he 
  says 
  that 
  his 
  species 
  " 
  is 
  placed 
  in 
  

   the 
  genus 
  Escliara 
  on 
  account 
  of 
  the 
  apparent 
  thickening 
  of 
  the 
  sur- 
  

   face 
  of 
  the 
  outer 
  cells, 
  and 
  the 
  cells 
  being 
  nearly 
  opposite 
  on 
  the 
  

   two 
  sides. 
  In 
  some 
  specimens 
  the 
  thickening 
  of 
  the 
  surface 
  of 
  the 
  

   outer 
  row 
  is 
  so 
  great 
  as 
  nearly 
  to 
  obliterate 
  the 
  opening 
  of 
  the 
  

   cells." 
  

  

  I 
  have 
  copied 
  nearly 
  the 
  whole 
  of 
  Lonsdale's 
  diagnosis 
  and 
  re- 
  

   marks, 
  on 
  account 
  of 
  the 
  minute 
  details 
  which 
  he 
  gives. 
  I 
  am 
  not 
  

   acquainted 
  with 
  specimens 
  from 
  the 
  Wenlock 
  Limestone, 
  Dudley 
  ; 
  

   and 
  the 
  Upper 
  Llandovery 
  specimen 
  in 
  the 
  School 
  of 
  Mines 
  is 
  only 
  

   a 
  cast. 
  The 
  several 
  fragments 
  which 
  I 
  have 
  found 
  in 
  the 
  shales 
  

   undoubtedly 
  belong 
  to 
  this 
  species. 
  One 
  character 
  of 
  the 
  genus 
  

   Ptilodictya 
  is 
  present 
  ; 
  otherwise 
  there 
  would 
  be 
  a 
  difficulty 
  in 
  placing 
  

   it 
  in 
  the 
  genus. 
  This 
  is 
  the 
  divergent 
  arrangement 
  of 
  the 
  outer 
  

   cells 
  obliquely 
  from 
  the 
  middle 
  longitudinal 
  cells. 
  As 
  Lonsdale 
  says, 
  

   there 
  is 
  around 
  the 
  openings 
  such 
  a 
  mass 
  of 
  thickening 
  material 
  

   that 
  the 
  true 
  area 
  cannot 
  be 
  seen 
  to 
  advantage. 
  The 
  margins 
  of 
  

   the 
  zoarium 
  are 
  solid 
  ; 
  and 
  in 
  sections 
  the 
  structure 
  is 
  different 
  from 
  

   that 
  of 
  P. 
  Lonsdalei. 
  Not 
  having 
  other 
  species 
  of 
  a 
  similar 
  nature 
  

   to 
  compare 
  it 
  with, 
  I 
  leave 
  it 
  temporarily 
  with 
  Ptilodictya. 
  

  

  