﻿608 
  COLLECTIONS 
  FBOM 
  THE 
  WESTEKN 
  INDIAN 
  OCEAN. 
  

  

  Islands 
  give 
  the 
  following 
  measurements 
  : 
  acuato 
  -2 
  to 
  "25 
  by 
  '007 
  

   millim. 
  ; 
  tibiella 
  -2 
  to 
  -25 
  by 
  -004 
  millim. 
  

  

  Hah. 
  Mozambique 
  ; 
  Marie 
  Louise 
  Island, 
  Amirante 
  group 
  ; 
  tide- 
  

   marks 
  to 
  17 
  fms. 
  

  

  DESMACIDINID^. 
  

  

  The 
  occurrence 
  of 
  a 
  true 
  Desmacidon 
  in 
  the 
  Indian 
  Ocean 
  is 
  per- 
  

   haps 
  for 
  the 
  first 
  time 
  indicated 
  by 
  the 
  new 
  species 
  described 
  below. 
  

   The 
  two 
  species 
  assigned 
  to 
  the 
  genus 
  by 
  Ehlers 
  (' 
  Die 
  Esperschen 
  

   Spongien') 
  appear 
  to 
  belong 
  respectively 
  to 
  Ampliilectus 
  and 
  Clatliria. 
  

   The 
  wide 
  range 
  possessed 
  by 
  species 
  of 
  the 
  new 
  genus 
  lotrocliota 
  is 
  

   shown 
  also 
  by 
  the 
  occurrence 
  of 
  our 
  two 
  new 
  Australian 
  species, 
  

   one 
  of 
  them 
  being 
  abundant 
  in 
  both 
  localities. 
  

  

  RHIZOCHALINA. 
  

  

  The 
  scarcity 
  of 
  this 
  genus, 
  so 
  common 
  in 
  the 
  tropical 
  waters 
  of 
  

   Australia, 
  and 
  well 
  represented 
  also 
  in 
  the 
  south 
  of 
  that 
  continent, 
  

   is 
  probably 
  due 
  to 
  the 
  absence 
  of 
  mud 
  from 
  the 
  localities 
  investi- 
  

   gated 
  ; 
  slightly 
  deeper 
  dredging, 
  clear 
  of 
  the 
  reefs, 
  might 
  be 
  ex- 
  

   pected 
  to 
  reveal 
  more 
  of 
  this 
  interesting 
  genus, 
  which 
  had 
  not 
  

   hitherto 
  been 
  noted 
  from 
  any 
  localities 
  nearer 
  than 
  Ceylon 
  (Carter, 
  

   Ann. 
  & 
  Mag. 
  N. 
  H. 
  1880, 
  vi. 
  p. 
  37, 
  under 
  the 
  name 
  of 
  Desmacidon 
  

   jeffreysi). 
  

  

  29. 
  EMzochalina 
  pellucida. 
  (Plate 
  LIV. 
  fig. 
  j.) 
  

  

  Elongate, 
  tapering 
  gradually 
  from 
  base 
  of 
  sponge 
  to 
  summit 
  of 
  

   fistula. 
  Fistula 
  single, 
  straight. 
  Surface 
  even, 
  glabrous. 
  Consis- 
  

   tence 
  in 
  spirit 
  soft, 
  brittle 
  ; 
  colour 
  very 
  pale 
  brown 
  ; 
  appearance 
  

   semitransparent. 
  Body 
  of 
  sponge 
  oval, 
  compressed 
  ; 
  includes 
  foreign 
  

   bodies. 
  

  

  Main 
  skeleton 
  a 
  somewhat 
  confused 
  mass 
  of 
  moderately 
  closely 
  

   felted 
  and 
  irregularly 
  crossing 
  spicules, 
  traversed 
  at 
  intervals 
  by 
  

   tracts 
  of 
  compact 
  spiculo-fibre, 
  4-8 
  spicules 
  broad, 
  running 
  parallel 
  

   to 
  the 
  surface. 
  Dermal 
  skeleton 
  consisting 
  of 
  long, 
  straight, 
  compact 
  

   spiculo-fibres, 
  4-20 
  spicules 
  broad, 
  branching 
  at 
  acute 
  angles, 
  and 
  

   thus 
  spreading 
  over 
  the 
  surface 
  ; 
  the 
  intervals 
  occupied 
  by 
  a 
  loose 
  

   open 
  reticulation 
  of 
  single 
  spicules 
  or 
  of 
  fascicles 
  two 
  or 
  three 
  spicules 
  

   broad, 
  crossing 
  at 
  various 
  angles. 
  Sarcode 
  pale 
  yellowish 
  brown, 
  

   subtransparent. 
  Spicule 
  accrate, 
  slightly 
  curved, 
  tapering 
  gradually 
  

   to 
  sharp 
  points 
  from 
  about 
  middle 
  of 
  spicule 
  ; 
  size 
  '26 
  by 
  -01 
  millim. 
  

  

  Hab. 
  Providence 
  Island, 
  Mascarene 
  group, 
  19 
  fms, 
  ; 
  bottom 
  coral. 
  

  

  A 
  single 
  specimen, 
  87 
  millim. 
  (3| 
  inches) 
  long, 
  12 
  miUim. 
  in 
  

   greatest 
  basal 
  diameter 
  ; 
  greatest 
  diameter 
  of 
  present 
  end 
  of 
  fistula 
  

   3 
  millim. 
  

  

  In 
  its 
  svibtranspareucy, 
  and 
  in 
  the 
  great 
  thinness 
  of 
  the 
  dermal 
  

   layer 
  of 
  the 
  skeleton, 
  as 
  well 
  as 
  in 
  its 
  having 
  been 
  apparently 
  sessile 
  

   by 
  a 
  bulbous 
  base, 
  this 
  differs 
  from 
  all 
  described 
  species 
  of 
  the 
  

   genus. 
  

  

  