﻿612 
  COLLECTIONS 
  PROM 
  THE 
  WESTERN 
  INDIAN 
  OCEAN. 
  

  

  ECTYONID^. 
  

  

  Two 
  of 
  the 
  six 
  species 
  obtained, 
  viz. 
  Clathria 
  fro^rdifera 
  and 
  

   Acaryius 
  ternatus, 
  must 
  now 
  be 
  regarded 
  as 
  characteristic 
  of 
  the 
  

   equatorial 
  parts 
  of 
  the 
  Indian 
  Ocean. 
  As 
  this 
  ocean 
  appears 
  to 
  be 
  

   the 
  main 
  focus 
  of 
  Clathria, 
  it 
  is 
  not 
  surprising 
  to 
  find 
  this 
  most 
  

   prolific 
  genus 
  further 
  represented 
  here 
  by 
  two 
  new 
  species. 
  

  

  CLATHRIA. 
  

  

  The 
  three 
  species 
  found 
  in 
  this 
  district 
  contrast, 
  by 
  their 
  decum- 
  

   bent 
  or 
  incrustiug 
  habit, 
  with 
  the 
  fine 
  arborescent 
  species 
  which 
  

   prevail 
  in 
  AustraUa. 
  

  

  34. 
  Clathria 
  frondifera, 
  Boiverhanl. 
  (Plate 
  LIII. 
  fig. 
  J.) 
  

  

  8ee 
  Part 
  I,, 
  p. 
  448, 
  of 
  this 
  Report. 
  

  

  This 
  species 
  seems 
  to 
  be 
  almost 
  as 
  abundant 
  in 
  this 
  region 
  as 
  in 
  

   the 
  North- 
  Australian 
  seas. 
  The 
  specimens 
  agree 
  well, 
  both 
  as 
  to 
  

   outward 
  form 
  and 
  size 
  and 
  in 
  their 
  fibre-characters, 
  with 
  those 
  

   described 
  by 
  me 
  (Part 
  I. 
  p. 
  448) 
  from 
  those 
  seas. 
  The 
  only 
  diver- 
  

   gent 
  points 
  which 
  they 
  present 
  are 
  found 
  in 
  the 
  spiculation, 
  viz. 
  

   the 
  slightly 
  greater 
  diameter 
  attained 
  by 
  the 
  smooth 
  deep-skeleton 
  

   acuate 
  in 
  some 
  of 
  the 
  specimens, 
  and 
  the 
  wide 
  range 
  of 
  dimensions 
  

   exhibited 
  by 
  this 
  spicule 
  : 
  it 
  ranges 
  from 
  '16 
  to 
  '25 
  miUim. 
  in 
  

   length 
  and 
  from 
  '008 
  to 
  *0l27 
  millim. 
  in 
  thickness 
  ; 
  the 
  latter 
  

   thickness 
  is 
  not 
  reached 
  by 
  the 
  Australian 
  specimens, 
  but 
  is 
  exhi- 
  

   bited 
  by 
  one 
  from 
  Gaspar 
  Strait, 
  and 
  exceeded 
  (-0158 
  millim.) 
  by 
  

   the 
  type 
  specimen, 
  from 
  the 
  Straits 
  of 
  Malacca. 
  

  

  Hah. 
  Providence 
  Reef 
  and 
  Island, 
  Mascarene 
  group 
  ; 
  Amirante 
  

   Islands 
  ; 
  Seychelle 
  Islands 
  ; 
  12-24 
  fms. 
  

  

  35. 
  Clathria 
  decumbens. 
  (Plate 
  LIII. 
  fig. 
  K 
  ; 
  Plate 
  LIV. 
  

  

  Sponge 
  massive, 
  sessile 
  ; 
  forming 
  low, 
  spreading 
  masses, 
  either 
  

   (a) 
  of 
  submonticular 
  form, 
  i. 
  e. 
  highest 
  in 
  the 
  middle 
  and 
  terminating 
  

   laterally 
  in 
  a 
  few 
  short 
  angular 
  ends, 
  or 
  (6) 
  commencing 
  as 
  a 
  hori- 
  

   zontal 
  flattened 
  cylinder, 
  sessile 
  by 
  its 
  lower 
  side, 
  terminated 
  at 
  each 
  

   end 
  by 
  rounded 
  (sometimes 
  free) 
  extremities, 
  and 
  sometimes 
  sending 
  

   oft' 
  lateral 
  lobes 
  of 
  similar 
  character. 
  Surface 
  (in 
  unmacerated 
  

   condition) 
  slightly 
  undulating, 
  either 
  (in 
  b) 
  glabrous, 
  formed 
  by 
  a 
  

   parchment-Hke 
  brown 
  membrane 
  which 
  conceals 
  the 
  honeycombed 
  

   main 
  mass 
  of 
  the 
  sponge, 
  or 
  (in 
  a) 
  much 
  grooved, 
  having 
  a 
  worm- 
  

   eaten 
  appearance, 
  the 
  surface 
  between 
  the 
  grooves 
  slightly 
  and 
  

   minutely 
  pilose 
  with 
  the 
  ends 
  of 
  the 
  skeleton-fibres, 
  the 
  bottom 
  of 
  

   the 
  grooves 
  themselves 
  smooth, 
  membranous. 
  Vents 
  moderately 
  

   abundant 
  (7 
  or 
  8 
  in 
  small 
  specimen), 
  scattered 
  on 
  all 
  parts, 
  round, 
  

   suborbicular, 
  or 
  oval 
  ; 
  opening 
  level 
  with 
  surface 
  ; 
  provided 
  with 
  

   thin 
  membranous 
  margins 
  ; 
  diameter 
  1-4 
  millim. 
  

  

  Main 
  mass 
  of 
  sponge 
  composed 
  of 
  subcylindrical 
  trabeculae, 
  5 
  to 
  

  

  