﻿114 
  Thirtieth 
  Repokt 
  on 
  the 
  State 
  Museum. 
  

  

  forms 
  of 
  cup 
  sponges, 
  which 
  are 
  fixed, 
  that 
  these 
  sponges 
  must 
  

   have 
  grown 
  with 
  the 
  concave 
  side 
  up. 
  There 
  appear 
  to 
  be 
  

   other 
  reasons 
  in 
  favor 
  of 
  this 
  theory 
  in 
  regard 
  to 
  their 
  position, 
  

   for 
  instance, 
  as 
  has 
  already 
  been 
  mentioned, 
  the 
  stars 
  upon 
  the 
  

   concave 
  side 
  are 
  in 
  a 
  better 
  state 
  of 
  preservation, 
  perhaps 
  

   indicating 
  the 
  newest 
  growth 
  of 
  the 
  sponge, 
  while 
  the 
  appear- 
  

   ance 
  of 
  the 
  other 
  side 
  might 
  seem 
  to 
  indicate 
  a 
  loss 
  of 
  organic 
  

   action 
  and 
  gradual 
  absorption 
  or 
  deposition 
  of 
  calcareous 
  or 
  

   silicious 
  particles. 
  

  

  Nevertheless, 
  upon 
  examination 
  of 
  the 
  vertical 
  section 
  repre- 
  

   sented 
  in 
  fig. 
  3, 
  of 
  Plate 
  3, 
  we 
  discover 
  lines 
  of 
  tubes, 
  the 
  con- 
  

   struction 
  of 
  which 
  we 
  will 
  hereafter 
  describe, 
  commencing 
  at 
  the 
  

   concave 
  margin 
  and 
  gradually 
  diverging 
  as 
  they 
  approach 
  the 
  

   convex 
  surface; 
  and 
  supposing 
  the 
  growth 
  of 
  the 
  sponge 
  to 
  be 
  

   upward, 
  there 
  seems 
  to 
  be 
  but 
  one 
  conclusion, 
  and 
  that 
  is, 
  that 
  

   the 
  concave 
  must 
  have 
  been 
  the 
  first 
  or 
  lower 
  side. 
  

  

  This 
  position 
  would 
  also 
  account 
  for 
  the 
  stars 
  upon 
  this 
  sur- 
  

   face 
  being 
  in 
  a 
  better 
  state 
  of 
  preservation, 
  on 
  account 
  of 
  the 
  

   protection 
  it 
  would 
  afford 
  them 
  from 
  external 
  wear 
  and 
  acci- 
  

   dent. 
  It 
  is 
  well 
  known 
  that 
  nearly 
  all 
  fossils, 
  when 
  discovered, 
  

   show 
  the 
  lower 
  side 
  to 
  have 
  been 
  better 
  protected. 
  

  

  We 
  regret 
  that 
  we 
  have 
  no 
  data 
  from 
  the 
  collector 
  showing 
  

   the 
  actual 
  position 
  of 
  these 
  specimens 
  in 
  the 
  strata; 
  but, 
  so 
  far 
  

   as 
  we 
  know, 
  they 
  have 
  been 
  found 
  separate 
  among 
  the 
  debris 
  

   and 
  decomposed 
  rock 
  upon 
  the 
  surface. 
  

  

  The 
  stars, 
  which 
  go 
  to 
  make 
  up 
  the 
  most 
  noticeable 
  feature 
  

   of 
  the 
  sponge, 
  are 
  superficially 
  tangential 
  ; 
  and 
  from 
  weather- 
  

   ing 
  and 
  gradual 
  dissolution 
  of 
  the 
  intertilling 
  substance 
  stand 
  

   in 
  relief. 
  The 
  star 
  may 
  be 
  described 
  as 
  follows 
  : 
  From 
  a 
  

   central 
  bead 
  spring 
  six 
  arms, 
  at 
  equal 
  distances, 
  each 
  measur- 
  

   ing 
  from 
  two 
  to 
  four 
  millimetres 
  in 
  length, 
  depending 
  upon 
  

   the 
  individual 
  star 
  from 
  which 
  the 
  measurement 
  has 
  been 
  taken, 
  

   and 
  each 
  branch 
  diverging 
  from 
  the 
  next 
  at 
  an 
  angle 
  of 
  sixty 
  

   degrees. 
  

  

  The 
  central 
  bead 
  is 
  a 
  hollow 
  globule 
  bearing 
  a 
  strong 
  

   resemblance 
  to 
  the 
  independent 
  or 
  originating 
  cell 
  of 
  a 
  recent 
  

   sponge 
  as 
  figured 
  by 
  Bronn 
  in 
  his 
  " 
  Thier 
  Reichs" 
  (Table 
  1, 
  

   fig. 
  9). 
  Sometimes 
  this 
  globule 
  is 
  slightly 
  compressed 
  upon 
  the 
  

   upper 
  surface. 
  It 
  has 
  six 
  principal 
  pores 
  (seeming 
  to 
  be 
  six 
  

   sided) 
  which 
  form 
  the 
  direct 
  communication 
  with 
  the 
  arms 
  or 
  

  

  