﻿226 
  Scientific 
  Intelligence. 
  

  

  extreme 
  of 
  nodal 
  development 
  is 
  seen 
  in 
  Botryodictya, 
  where 
  

   these 
  prominences 
  become 
  pendulous 
  lobes 
  arranged 
  in 
  numerous 
  

   whorls 
  along 
  the 
  cylindrical 
  body 
  of 
  the 
  sponge. 
  

  

  Lastly 
  there 
  may 
  be 
  modifications 
  of 
  the 
  body 
  into 
  a 
  stalk 
  

   below 
  and 
  an 
  expanded 
  cup 
  above, 
  and 
  again, 
  as 
  in 
  Phragmo- 
  

   dictya, 
  there 
  may 
  be 
  a 
  basal 
  disk 
  for 
  attachment, 
  with 
  a 
  frill 
  

   about 
  the 
  margin, 
  the 
  general 
  effect 
  resembling 
  a 
  sea-anemone 
  in 
  

   basal 
  outline. 
  

  

  The 
  spicular 
  network 
  gives 
  the 
  clue 
  to 
  classification. 
  The 
  

   family, 
  as 
  now 
  defined, 
  falls 
  under 
  the 
  subclass 
  Silicea 
  and 
  the 
  

   order 
  Hexactinellida. 
  Since 
  the 
  elements 
  of 
  the 
  spicular 
  bundles 
  

   are 
  not 
  fused 
  together, 
  the 
  family 
  further 
  belongs 
  in 
  Zittel's 
  sub- 
  

   order 
  Lyssacina. 
  The 
  specimens 
  from 
  New 
  York 
  and 
  Pennsyl- 
  

   vania 
  are 
  molds 
  and 
  it 
  is 
  extremely 
  rare 
  to 
  find 
  the 
  individual 
  

   spicules 
  preserved, 
  but 
  in 
  the 
  examples 
  from 
  Crawfordsville, 
  the 
  

   spicules, 
  which 
  in 
  all 
  siliceous 
  sponges 
  are 
  composed 
  of 
  hydrated 
  

   amorphous 
  silica, 
  have 
  here 
  been 
  altered 
  to 
  pyrite, 
  and 
  this 
  has 
  

   often 
  escaped 
  oxidation. 
  The 
  conspicuous 
  feature 
  of 
  the 
  skeletal 
  

   frame 
  is 
  the 
  inner 
  meshwork 
  surrounding 
  the 
  gastric 
  cavity, 
  

   which 
  has 
  been 
  already 
  alluded 
  to 
  in 
  discussing 
  the 
  pyramidal 
  

   forms. 
  This 
  meshwork 
  consists 
  of 
  horizontal 
  and 
  vertical, 
  nar- 
  

   row 
  and 
  often 
  flattened 
  bundles 
  of 
  rod-like 
  spicules, 
  regularly 
  

   spaced 
  and 
  forming 
  a 
  pattern 
  of 
  squares 
  over 
  the 
  entire 
  surface. 
  

   These 
  primary 
  squares, 
  which 
  may 
  be 
  upward 
  of 
  an 
  inch 
  in 
  

   diameter, 
  are 
  bisected 
  by 
  secondary 
  spicular 
  bundles 
  and 
  these 
  in 
  

   turn 
  are 
  subdivided 
  until 
  a 
  fine 
  network 
  of 
  squares, 
  which 
  may 
  

   be 
  of 
  the 
  sixth 
  order, 
  is 
  reached. 
  

  

  The 
  vertical 
  spicular 
  bundles 
  extend 
  the 
  entire 
  length 
  of 
  the 
  

   sponge 
  and 
  the 
  horizontal 
  ones 
  form 
  complete 
  rings. 
  The 
  

   memoir 
  does 
  not 
  go 
  into 
  the 
  genesis 
  of 
  the 
  individual 
  spicular 
  

   rods 
  and 
  perhaps 
  with 
  the 
  character 
  of 
  material 
  available 
  noth- 
  

   ing 
  definite 
  could 
  be 
  learned 
  regarding 
  it. 
  As 
  commonly 
  seen, 
  

   these 
  rods 
  are 
  hair-like 
  and 
  are 
  spoken 
  of 
  as 
  diactins, 
  though 
  it 
  

   is 
  possible 
  they 
  may 
  be 
  tetractins 
  in 
  which 
  the 
  rays 
  become 
  

   enormously 
  elongated, 
  and 
  in 
  growing 
  parallel 
  and 
  adjacent 
  to 
  

   one 
  another 
  form 
  the 
  bundles. 
  The 
  entire 
  thickness 
  ot 
  the 
  wall 
  

   is 
  slight 
  compared 
  with 
  the 
  diameter 
  of 
  the 
  vase. 
  The 
  interior 
  

   surface 
  is 
  formed 
  of 
  the 
  rectangular 
  network, 
  while 
  the 
  outer 
  

   surface 
  contains 
  large, 
  free 
  pentactins 
  standing 
  opposite 
  each 
  

   intersection 
  of 
  the 
  spicular 
  bundles. 
  Various 
  forms 
  of 
  smaller 
  

   modified 
  hexactins 
  have 
  been 
  noted 
  scattered 
  among 
  those 
  of 
  

   normal 
  character. 
  The 
  fossils 
  sometimes 
  show 
  tufts 
  of 
  rod-like 
  

   spicules 
  protruding 
  half 
  an 
  inch 
  or 
  more 
  from 
  the 
  nodes. 
  

  

  The 
  preceding 
  notes 
  have 
  been 
  based 
  on 
  the 
  Devonian 
  Dictyo- 
  

   spongidse. 
  Having 
  obtained 
  an 
  idea 
  of 
  their 
  characteristics, 
  it 
  

   may 
  be 
  well, 
  in 
  order 
  to 
  bring 
  out 
  the 
  progress 
  in 
  differentiation 
  

   shown 
  within 
  this 
  family, 
  to 
  point 
  out 
  the 
  striking 
  features 
  of 
  

   the 
  Lower 
  Carboniferous 
  forms 
  and 
  their 
  derivation 
  from 
  Devonian 
  

   ancestors. 
  

  

  In 
  the 
  lowest 
  sub-Carboniferous 
  faunas, 
  the 
  Waverly 
  and 
  

  

  