﻿G. 
  K. 
  VINE 
  ON 
  THE 
  WENLOCK 
  POLYZOA. 
  

  

  Pies. 
  11-13. 
  — 
  Ptilodictva 
  Lonsdalei, 
  Vine. 
  

  

  m 
  

  

  11. 
  Section 
  nearly 
  parallel 
  to 
  the 
  central 
  axis, 
  showing 
  the 
  marginal 
  cells, 
  and 
  

  

  tbe 
  compressed 
  perpendicular 
  cell 
  : 
  X 
  20. 
  

  

  12. 
  A 
  portion 
  of 
  the 
  same, 
  further 
  enlarged 
  : 
  X 
  40. 
  

  

  13. 
  A 
  portion 
  of 
  the 
  non-poriferous 
  margin 
  of 
  another 
  section 
  : 
  X 
  40. 
  

  

  Localities. 
  Though 
  rare 
  in 
  some 
  of 
  the 
  washings, 
  more 
  or 
  less 
  

   abundant 
  in 
  all 
  the 
  shales 
  below 
  the 
  Wenlock 
  Limestone. 
  Very 
  

   rare, 
  though 
  I 
  have 
  found 
  a 
  few 
  fragments, 
  in 
  the 
  shales 
  No. 
  46 
  

   over 
  the 
  Wenlock 
  Limestone. 
  

  

  Affinities. 
  This 
  species 
  resembles 
  to 
  some 
  extent 
  P.flagellum, 
  Nich. 
  

   (Ann. 
  & 
  Mag. 
  Nat. 
  Hist. 
  March 
  1875, 
  pi. 
  xiv. 
  figs. 
  3, 
  3 
  6 
  ), 
  except 
  in 
  the 
  

   fiexuous 
  character 
  of 
  .the 
  base. 
  There 
  is 
  a 
  slight 
  difference 
  in 
  the 
  

   measurements 
  of 
  the 
  two 
  species 
  ; 
  and 
  Nicholson 
  does 
  not 
  allude 
  to 
  

   any 
  distal 
  openings, 
  while 
  these 
  are 
  a 
  marked 
  feature 
  in 
  P. 
  Lonsdalei. 
  

   I 
  have 
  not 
  specimens 
  for 
  comparison 
  ; 
  but 
  I 
  have 
  not 
  the 
  least 
  doubt 
  

   that 
  it 
  will 
  be 
  found 
  that 
  the 
  Llandovery 
  and 
  Wenlock 
  P. 
  lanceo- 
  

   lata 
  may 
  be 
  placed 
  here. 
  My 
  only 
  objection 
  to 
  describing 
  the 
  frag- 
  

   ments 
  as 
  typical 
  of 
  Lonsdale's 
  species 
  is 
  that 
  the 
  Wenlock 
  Limestone 
  

   type 
  is 
  altogether 
  different 
  and 
  considerably 
  larger. 
  Under 
  these 
  

   circumstances 
  1 
  dedicate 
  the 
  species 
  to 
  Lonsdale's 
  memory. 
  

  

  In 
  the 
  description 
  of 
  this 
  type 
  I 
  have 
  indicated 
  the 
  function 
  of 
  

   the 
  " 
  non-poriferous 
  margins 
  " 
  of 
  Ptilodictya 
  by 
  speaking 
  of 
  them 
  

   as 
  the 
  "endocystal 
  layers." 
  Taking 
  the 
  endocyst 
  and 
  the 
  ectocyst 
  

   together, 
  the 
  latter 
  being 
  only 
  a 
  structureless 
  excretion 
  from 
  the 
  

   endocyst 
  charged 
  with 
  a 
  protective 
  function 
  *, 
  it 
  may 
  be 
  well 
  to 
  direct 
  

   attention 
  to 
  this 
  physiological 
  feature. 
  I 
  have 
  ascertained 
  that 
  the 
  

   enlargement 
  of 
  the 
  colony 
  of 
  Ptilodictya 
  takes 
  place 
  at 
  the 
  distal 
  

   openings 
  and 
  also 
  at 
  the 
  margins. 
  After 
  a 
  time 
  enlargement 
  at 
  the 
  

   distal 
  openings 
  becomes 
  abortive, 
  and 
  these 
  indications 
  of 
  a 
  function 
  

   remain 
  as 
  ornaments 
  only. 
  It 
  is 
  different 
  on 
  the 
  margins 
  ; 
  here 
  

   life 
  is 
  more 
  active, 
  and 
  enlargements 
  take 
  place 
  on 
  the 
  younger 
  por- 
  

   * 
  Hincks's 
  Brit. 
  Mar. 
  Polyzoa, 
  p. 
  x. 
  

   Q.J.G.S. 
  No. 
  149. 
  if 
  

  

  