﻿SPONGIIDA. 
  609 
  

  

  30. 
  Desmacidon 
  rimosa 
  *. 
  (Plate 
  LIII. 
  fig. 
  F 
  ; 
  Plate 
  LIV. 
  

   figs, 
  m-m".) 
  

  

  Erect, 
  stipitate 
  ; 
  stem 
  and 
  branches 
  solid, 
  more 
  or 
  less 
  antero- 
  

   postoriorly 
  compressed, 
  except 
  the 
  extreme 
  apices 
  of 
  the 
  latter, 
  which 
  

   are 
  cylindrical 
  and 
  terminally 
  rounded, 
  finger-like. 
  Branching 
  

   very 
  irregular, 
  not 
  confined 
  to 
  one 
  plane, 
  the 
  first 
  division 
  approxi- 
  

   mately 
  dichotomous 
  ; 
  the 
  resulting 
  (secondary) 
  axes 
  are 
  either 
  

   flattened 
  strongly 
  (2-4 
  times 
  as 
  broad 
  as 
  they 
  are 
  long), 
  with 
  but 
  

   short 
  subcylindrical 
  marginal 
  branchlets, 
  or 
  subcylindrical, 
  giving 
  

   off 
  several 
  subcylindrical 
  (tertiary) 
  branches 
  ; 
  the 
  largest 
  of 
  these 
  

   branches 
  may 
  attain 
  a 
  length 
  of 
  35 
  millim. 
  ; 
  diameter 
  of 
  tips 
  

   of 
  branches, 
  just 
  before 
  termination, 
  4-5 
  millim. 
  Surface 
  of 
  stem 
  

   and, 
  to 
  a 
  less 
  extent, 
  of 
  branches 
  scored 
  by 
  winding 
  furrows, 
  1-3 
  

   millim. 
  deep, 
  1-3 
  millim. 
  wide, 
  generally 
  directed 
  transversely 
  when 
  

   on 
  the 
  fiat 
  surface 
  of 
  the 
  branch, 
  more 
  longitudinally 
  when 
  they 
  

   have 
  reached 
  its 
  margin 
  ; 
  they 
  either 
  vanish 
  by 
  becoming 
  gradually- 
  

   shallower 
  distally, 
  or 
  end 
  abruptly 
  in 
  an 
  oscular 
  opening. 
  Vents 
  

   •5 
  to 
  1-5 
  millim. 
  in 
  diameter, 
  circular, 
  deep, 
  numerous, 
  scattered 
  

   along 
  the 
  above-mentioned 
  grooves. 
  Surface 
  pilose, 
  like 
  coarse 
  

   velvet, 
  owing 
  to 
  projection 
  of 
  primary 
  skeleton-fibres 
  to 
  a 
  height 
  of 
  

   •25 
  to 
  1 
  milUm., 
  at 
  distances 
  of 
  -25 
  to 
  1 
  millim. 
  apart. 
  Texture 
  

   in 
  spirit 
  firm, 
  tough, 
  subelastic, 
  the 
  surface 
  slightly 
  harsh 
  to 
  the 
  

   touch 
  ; 
  colour 
  in 
  spirit 
  normally 
  brown, 
  inclining 
  to 
  grey, 
  and 
  

   to 
  rufous 
  where 
  skrinkage 
  or 
  abrasion 
  of 
  sarcode 
  has 
  more 
  or 
  less 
  

   exposed 
  the 
  skeleton. 
  

  

  Main 
  skeleton 
  — 
  primary 
  fibres 
  vertical 
  to 
  surface, 
  about 
  -07 
  

   millim. 
  thick, 
  •28-'35 
  milhm. 
  apart 
  ; 
  the 
  secondaries 
  vertical 
  to 
  the 
  

   primaries, 
  about 
  -05 
  millim. 
  thick, 
  •28--35 
  millim. 
  apart: 
  fibres 
  

   cored 
  by 
  spicule 
  no. 
  2, 
  with 
  a 
  few 
  of 
  no. 
  1 
  near 
  the 
  centre 
  of 
  the 
  

   sponge 
  ; 
  the 
  horny 
  fibre 
  is 
  almost 
  wholly 
  obscured 
  by 
  spicules 
  ; 
  

   near 
  the 
  surface 
  a 
  distinct 
  clear 
  pale 
  brown 
  transparent 
  margin 
  

   of 
  about 
  a 
  quarter 
  the 
  thickness 
  of 
  the 
  fibre 
  is 
  usually 
  left. 
  

   Dermal 
  skeleton 
  made 
  up 
  of 
  triangular 
  to 
  polygonal 
  meshes 
  (•28-*8 
  

   millim. 
  wide) 
  of 
  spiculo-fibre, 
  •035-*09 
  millim. 
  thick, 
  strength- 
  

   ened 
  by 
  much 
  pale 
  brown 
  transparent 
  horny 
  substance, 
  which 
  is 
  

   seen 
  outside 
  the 
  spicules 
  in 
  the 
  narrower 
  fibres 
  ; 
  the 
  contained 
  spi- 
  

   cules 
  are 
  chiefly 
  no. 
  1 
  ; 
  the 
  stouter 
  fibres 
  contain 
  also, 
  superficially, 
  

   no. 
  2. 
  Sarcode 
  transparent, 
  pale 
  yellowish 
  brown. 
  

  

  Spicules 
  of 
  skeleton: 
  — 
  (1) 
  Acuate, 
  smooth, 
  slightly 
  curved, 
  tapering 
  

   gradually, 
  more 
  rapidly 
  towards 
  apex, 
  to 
  moderately 
  sharp 
  point, 
  and 
  

   diminishing 
  slightly 
  in 
  diameter 
  towards 
  the 
  rounded 
  base 
  ; 
  length 
  

   about 
  -yS 
  milhm. 
  ; 
  diameter, 
  base 
  "Ol!), 
  middle 
  of 
  shaft 
  "022 
  millim. 
  

   (most 
  abundant 
  in 
  the 
  fibre 
  near 
  surface, 
  occasionally 
  free 
  in 
  sarcode). 
  

   (2) 
  Acuate, 
  approximately 
  straight, 
  tapering 
  gradually 
  from 
  near 
  

   head 
  to 
  sharp 
  point 
  ; 
  the 
  base 
  occasionally 
  provided 
  with 
  a 
  small 
  

   number 
  of 
  minute 
  spines 
  ; 
  size 
  •23--33 
  by 
  •005--01 
  millim. 
  (some- 
  

   times 
  loose 
  in 
  sarcode, 
  especially 
  in 
  dermis). 
  

  

  « 
  Rimosus, 
  full 
  of 
  furrows, 
  referring 
  to 
  the 
  appearance 
  of 
  the 
  sui'face. 
  

  

  2r 
  

  

  