﻿592 
  COLLECTIONS 
  FROM 
  THE 
  WESTERN 
  INDIAN 
  OCEAK. 
  

  

  fibres, 
  meeting 
  the 
  surface 
  at 
  various 
  angles, 
  and 
  projecting 
  slightly- 
  

   above 
  it, 
  and 
  of 
  a 
  system 
  of 
  crossing 
  fibres 
  connecting 
  the 
  two 
  and 
  

   forming 
  approximately 
  rectangular 
  meshes, 
  their 
  direction 
  being 
  

   roughly 
  vertical 
  to 
  one 
  or 
  other 
  of 
  the 
  above 
  systems. 
  The 
  mesh 
  

   is 
  very 
  variable 
  in 
  diameter, 
  viz. 
  from 
  -07 
  to 
  -24 
  millim., 
  the 
  former 
  

   chiefly 
  at 
  the 
  surface. 
  The 
  diameter 
  of 
  the 
  main 
  fibre 
  is 
  'OSS-'O? 
  

   millim., 
  not 
  including 
  the 
  ditelous 
  network 
  of 
  fibres 
  of 
  small 
  dia- 
  

   meter 
  which 
  often 
  surrounds 
  the 
  bases 
  of 
  the 
  large 
  primary 
  fibres. 
  

   Colour 
  of 
  fibre 
  pale 
  amber-yellow 
  ; 
  no 
  foreign 
  bodies 
  imbedded 
  in 
  

   any 
  part 
  of 
  the 
  skeleton 
  ; 
  the 
  fibre 
  is 
  homogeneous 
  in 
  appearance, 
  

   with 
  the 
  occasional 
  exception 
  of 
  a 
  faint 
  granular 
  axial 
  line. 
  Size 
  

   of 
  sponge, 
  80-95 
  millim. 
  (3-3| 
  inches) 
  in 
  greatest 
  diameter. 
  

  

  Hah. 
  African 
  Island, 
  Amirante 
  group 
  (gathered 
  on 
  beach). 
  

  

  Distribution. 
  "Indian 
  Ocean?" 
  (Pallas); 
  Indian 
  Ocean 
  (Za???rtrfZ;); 
  

   Mauritius 
  (Hyatt). 
  

  

  Hippospongia 
  sinuosa, 
  Pallas, 
  var. 
  decidua, 
  Hi/ait. 
  

  

  The 
  other 
  variety 
  of 
  the 
  species 
  is 
  very 
  distinct 
  in 
  its 
  external 
  

   appearance, 
  but 
  on 
  examination 
  this 
  is 
  found 
  to 
  be 
  due 
  merely 
  to 
  

   modifications 
  of 
  the 
  same 
  structural 
  arrangements 
  as 
  those 
  of 
  var. 
  

   mawitiana. 
  The 
  surface 
  is 
  entirely 
  broken 
  up 
  into 
  small 
  isolated 
  

   tufts, 
  or 
  short 
  meandrine 
  ridges, 
  llattened 
  externally, 
  about 
  1-2 
  

   miUim. 
  in 
  diameter 
  (the 
  ridges 
  of 
  mauritiana 
  being 
  3 
  or 
  4 
  millim. 
  

   across), 
  rising 
  from 
  a 
  considerable 
  depth, 
  viz. 
  7-15 
  millim., 
  and 
  

   commencing 
  below 
  by 
  very 
  narrow 
  bases, 
  and 
  not 
  expanding 
  until 
  

   close 
  to 
  the 
  surface. 
  By 
  the 
  juxtaposition 
  of 
  these 
  tall 
  walls 
  and 
  

   tufts, 
  a 
  number 
  of 
  freely 
  intercommunicating, 
  very 
  narrow 
  (2 
  to 
  2-5 
  

   millim. 
  wide) 
  and 
  deep 
  channels 
  are 
  formed, 
  very 
  different 
  in 
  appear- 
  

   ance 
  from 
  the 
  subcjdindrical 
  and 
  semi-tubular 
  canals 
  which 
  repre- 
  

   sent 
  them 
  in 
  var. 
  mauritiana. 
  The 
  outward 
  form 
  of 
  the 
  sponge 
  

   is 
  essentially 
  similar 
  to 
  that 
  of 
  the 
  other 
  variety, 
  but 
  the 
  speci- 
  

   mens 
  are 
  much 
  larger 
  ; 
  the 
  largest, 
  an 
  example 
  of 
  incrusting 
  growth 
  

   about 
  30 
  millim. 
  in 
  average 
  vertical 
  thickness, 
  measures 
  275 
  millim. 
  

   (11 
  inches) 
  in 
  greatest 
  diameter; 
  some 
  smaller 
  specimens 
  attain 
  

   about 
  twice 
  the 
  thickness. 
  As 
  in 
  var. 
  mauritiana, 
  the 
  tubular 
  cha- 
  

   racter 
  of 
  the 
  channels 
  of 
  the 
  skeleton 
  is 
  much 
  more 
  strongly 
  marked 
  

   on 
  the 
  lower 
  surface, 
  where 
  (as 
  observed 
  by 
  Hyatt) 
  connecting 
  

   laminae 
  of 
  horny 
  fibre 
  frequently 
  bridge 
  over 
  the 
  spaces 
  between 
  the 
  

   summits 
  of 
  the 
  tufts 
  and 
  ridges. 
  The 
  colour 
  of 
  well-preserved 
  

   skeletons 
  is 
  a 
  rather 
  pale 
  aml}er-yellow 
  ; 
  those 
  which 
  have 
  suffered 
  

   much 
  washing 
  on 
  the 
  beach 
  are 
  almost 
  white. 
  

  

  The 
  general 
  arrangement 
  of 
  the 
  skeleton 
  is 
  similar 
  to 
  that 
  of 
  the 
  

   other 
  variety 
  ; 
  but 
  the 
  following 
  important 
  differences 
  are 
  to 
  be 
  

   noted 
  : 
  — 
  (1) 
  It 
  is 
  the 
  primary 
  and 
  not 
  the 
  secondary 
  fibres 
  which 
  

   are 
  the 
  most 
  distinct 
  elements 
  of 
  the 
  deep 
  skeleton 
  ; 
  they 
  foi 
  m 
  

   continuous, 
  almost 
  straight 
  lines, 
  •4--5 
  millim. 
  apart, 
  and 
  are 
  

   placed 
  vertically 
  to 
  the 
  surface. 
  The 
  primary 
  fibres 
  of 
  the 
  

   outer 
  surface 
  form 
  a 
  decided 
  pile 
  of 
  short 
  projecting 
  points, 
  being 
  

   much 
  more 
  numerous 
  than 
  in 
  var. 
  mauritiana. 
  (2) 
  Owing 
  to 
  the 
  

  

  