﻿SPONGHDA. 
  623 
  

  

  longer 
  and 
  has 
  more 
  bends 
  than 
  the 
  stout 
  form, 
  which 
  could 
  thus 
  

   only 
  have 
  been 
  derived 
  from 
  it 
  by 
  fission 
  or 
  retrogressive 
  absorption, 
  

   methods 
  unknown, 
  so 
  far 
  as 
  I 
  am 
  aware, 
  in 
  the 
  normal 
  development 
  

   of 
  siliceous 
  sponge-spicules. 
  

  

  46. 
  Spirastrella 
  transitoria. 
  (Plate 
  LIV. 
  figs, 
  q, 
  q'.) 
  

  

  Sessile, 
  incrusting. 
  Surface 
  broken 
  up 
  by 
  slight 
  intercrossing 
  

   ridges 
  into 
  very 
  shallow 
  angular 
  areas 
  1 
  to 
  2 
  millim. 
  wide 
  ; 
  surface 
  

   between 
  and 
  over 
  ridges 
  subglabrous. 
  Consistence 
  in 
  spirit 
  tough, 
  

   elastic 
  ; 
  colour 
  pale 
  pinkish 
  brown. 
  

  

  Main 
  skeleton 
  chiefly 
  composed 
  of 
  dense 
  fascicles 
  of 
  the 
  skcleton- 
  

   spicule, 
  with 
  the 
  points 
  radiating 
  outwards, 
  set 
  at 
  various 
  angles 
  to 
  

   the 
  surface, 
  viz. 
  from 
  right 
  angles 
  to 
  a 
  horizontal 
  jiosition 
  ; 
  the 
  

   points 
  of 
  the 
  bundles 
  frequently 
  project 
  slightly 
  beyond 
  the 
  surface. 
  

   Sarcode 
  dense 
  ; 
  that 
  of 
  surface 
  sub 
  transparent, 
  dark 
  greenish 
  yellow 
  ; 
  

   of 
  subjacent 
  tissues 
  very 
  pale 
  yellow, 
  transparent. 
  

  

  Spicules: 
  — 
  (1) 
  Skeleton 
  spinulate, 
  straight 
  or 
  nearly 
  so; 
  head 
  

   spherical, 
  neck 
  distinct 
  ; 
  head 
  and 
  centre 
  of 
  shaft 
  of 
  about 
  the 
  same 
  

   diameter, 
  viz. 
  '016 
  millim. 
  ; 
  shaft 
  tapering 
  to 
  sharp 
  point 
  from 
  about 
  

   7 
  diameters 
  from 
  apex 
  ; 
  length 
  of 
  spicule 
  about 
  '9 
  millim. 
  (2) 
  Spini- 
  

   spirular, 
  extremely 
  conceutrated, 
  composed 
  of 
  only 
  one 
  entire 
  bend 
  ; 
  

   spines 
  numerous, 
  closely 
  aggregated, 
  strong 
  and 
  sharp 
  ; 
  shaft 
  about 
  

   •004 
  millim. 
  thick 
  ; 
  spines 
  "004 
  millim. 
  long; 
  length 
  of 
  spicule, 
  

   includiug 
  spines, 
  -OIG 
  millim. 
  

  

  Hub. 
  Darros 
  Island, 
  Amirante 
  group, 
  22 
  fms. 
  ; 
  bottom 
  broken 
  

   coral. 
  

  

  This 
  species 
  is 
  represented 
  by 
  a 
  specimen 
  of 
  about 
  1 
  square 
  inch 
  

   in 
  superficial 
  extent, 
  covering 
  and 
  following 
  the 
  iu 
  equalities 
  of 
  a 
  

   small 
  mass 
  of 
  shells 
  and 
  Polyzoa 
  ; 
  the 
  thickness 
  varies 
  from 
  about 
  

   •5 
  to 
  2 
  millim. 
  It 
  appears 
  to 
  be 
  most 
  nearly 
  related 
  to 
  the 
  form 
  

   termed 
  by 
  Mr. 
  Carter 
  (Ann. 
  & 
  Mag. 
  N. 
  H. 
  1882, 
  ix. 
  p. 
  352) 
  

   " 
  Spirastrella 
  cunctatrix, 
  variety," 
  from 
  Mauritius 
  ; 
  but 
  this 
  form 
  is 
  

   stated 
  to 
  be 
  white, 
  to 
  have 
  a 
  spinispirular 
  with 
  tivo 
  bends, 
  of 
  a 
  length 
  

   of 
  about 
  "036 
  millim. 
  It 
  differs 
  from 
  S. 
  cunctatrix, 
  Schmidt, 
  in 
  the 
  

   shorter 
  spinispirular, 
  and 
  the 
  globular, 
  not 
  oval, 
  head 
  of 
  the 
  spinulate. 
  

   In 
  S. 
  transitoria 
  we 
  have 
  the 
  spinispirular 
  almost 
  in 
  the 
  form 
  of 
  the 
  

   stellate, 
  with 
  which 
  Schmidt 
  (Spong. 
  Atl. 
  Geb. 
  p. 
  5) 
  and 
  Carter 
  

   (op. 
  cit. 
  1879, 
  iii. 
  p. 
  355) 
  consider 
  it 
  to 
  be 
  homologous. 
  

  

  47. 
  Spirastrella 
  punctulata. 
  (Plate 
  LIV. 
  figs. 
  p,p'.) 
  

  

  " 
  Suberites 
  P 
  sp. 
  undesciibed, 
  Mauritius," 
  Carter, 
  Ann. 
  iSf 
  Mag. 
  N. 
  H. 
  

   1882, 
  ix. 
  p. 
  352. 
  

  

  Elongated, 
  subconical. 
  Vents 
  single 
  or 
  few, 
  terminal, 
  oval, 
  about 
  

   2 
  millim. 
  in 
  greatest 
  diameter. 
  Surface 
  obscurely 
  nodose, 
  and 
  

   covered 
  besides 
  on 
  the 
  upper 
  parts 
  of 
  the 
  sponge 
  with 
  a 
  minute, 
  but 
  

   close 
  and 
  regular 
  pitting, 
  giving 
  the 
  appearance 
  of 
  shagreen 
  ; 
  pits 
  

   and 
  intermediate 
  elevations 
  low, 
  each 
  about 
  -3 
  millim. 
  in 
  diameter 
  ; 
  

  

  