298 
DE.  J.  S.  BOWEEBA^S'K  ON  THE  ANATOHT 
Tubeeculated  fusipoemi-cylindeical  (Plate  XXIV.  fig.  24). — These  minute  spicula 
are  profusely  dispersed  on  the  inner  surface  of  the  dermal  and  interstitial  membranes 
of  Pachymatisma  Johnstonia.  They  are  short  and  stout,  and  are  covered  very  irregularly 
with  ill-defined  tubercles.  They  vary  very  considerably  in  form  and  proportions.  Their 
average  dimensions  are,  length  -g^th  of  an  inch,  diameter  ^^q-^th  of  an  inch. 
Inplato-cylindeical  (Plate  XXIV.  fig.  25). — This  form  of  spiculum  is  very  minute. 
It  is  slightly  curved,  and  has  a single,  well-defined  bulbous  infiation  near  the  middle  of 
the  shaft,  but  in  this  respect,  as  well  as  in  size,  there  is,  comparatively,  a considerable 
amount  of  variation.  The  normal  condition  of  the  infiation  is  equidistant  from  the  ends 
of  the  spiculum,  but  in  some  cases  it  is  not  more  than  a thh’d  of  the  length  of  the  spicu- 
lum from  one  end  of  it.  The  only  sponge  m which  I have  found  this  form  is  Halichon- 
dria  ficus^  Johnston,  where  it  occurs  in  the  dermal  membrane  in  great  profusion. 
Teicuevato-aceeate  (Plate  XXIV.  figs.  26,  27,  and  28). — This  form  of  spiculum  has 
always  three  curves  in  the  course  of  its  length,  one  at  the  centre  of  the  shaft,  and  one  near 
each  termination,  the  terminal  ones  curving  in  the  same  direction,  and  always  opposite  to 
that  of  the  central  curve. 
These  spicula  vary  greatly  in  form  and  proportions  m different  sponges,  and  frequently 
even  in  the  same  species.  The  normal  form  is  that  of  three  curves  of  about  equal  value 
(Plate  XXIV.  fig.  26),  but  sometimes,  as  in  fig.  27,  the  central  curve  is  very  much  the 
larger  of  the  three,  while  in  fig.  28  we  find  the  extreme  condition  of  the  form,  the  spicu- 
lum being  comparatively  straight,  mth  a very  small  curve  in  the  centre  of  the  shaft,  and 
the  terminations  exhibiting  only  the  rudiments  of  curves  in  an  opposite  dh-ection  to  the 
middle  one.  They  are  usually  very  much  more  slender  than  the  spicula  of  the  skeleton, 
and  are  comparatively  of  rare  occurrence  in  every  species  in  which  I have  foimd  them. 
I have  never  seen  them  in  situ  with  the  terminal  curves  elevated  above  the  siu’face  of 
the  membrane,  but  always  reposing  on  one  side,  with  all  parts  of  the  shaft  closely  attached 
to  its  surface.  The  three  forms  figured  are  from  the  same  specimen  of  sponge. 
Unicuevo-ceucifoem  (Plate  XXIV.  fig.  29). — This  form  occurs  abundantly  on  the 
membrane  lining  the  great  cloacal  cavities  of  (drantia  nivea^  Johnston.  The  axial  radii 
are  disposed  very  nearly  in  the  direction  of  the  long  axis  of  those  organs,  and  the  cuiA  es 
formed  by  the  lunate  radii  always  have  their  points  towards  the  mouth  of  the  cloaca. 
Falcato-aceeate  (Plate  XXIV.  fig.  30). — This  form  is  abundant  in  a small  species 
of  Grantia  from  Austraha,  which  is  found  on  several  species  of  Fuci  in  the  collections 
brought  home  by  Dr.  Haevey.  The  sponges  do  not  frequently  exceed  the  eighth  of  an 
inch  in  length. 
Bicuevo-aceeate  (Plate  XXIV.  fig.  31). — This  form  is  from  a small  parasitical 
Grantia  from  Algoa  Bay,  in  my  collection.  The  sponge  is  about  the  size  of  a large  pea, 
and  is  not  uncommon  on  Zoophytes  from  that  locality. 
Foliato-peltate  Sjjicida. 
These  spicula  have  the  shaft  exceedingly  short  and  conical ; the  basal  "termination 
being  acute,  and  the  shaft  dilating  rapidly  to  its  distal  end,  to  the  extent  of  an  angle 
