AND  PHYSIOLOGY  OF  THE  SPONGIAD^. 
293 
Fusifoemi-aceeate. — Geodia  Barretti,  Boweebajstk,  MS.  On  this  remarkably  fine 
species  of  Geodia  this  form  of  defensive  spiculum  occurs  in  parts  in  such  abundance, 
that  they  completely  cover  and  obscure  the  surface  of  the  sponge,  from  which  they  pro- 
ject nearly  the  whole  of  their  length,  the  proximal  ends  of  many  of  them  scarcely  pass- 
ing through  the  dermal  crust  of  the  sponge.  This  sponge  has  also  a secondary  series  of 
defensive  spicula,  of  the  same  form  as  the  larger  ones ; the  latter  often  exceeding  |^th  of 
an  inch  in  length,  while  the  secondary  spicula  do  not  exceed  ^th  of  an  inch  in  length. 
For  the  form  of  this  spiculum  see  Plate  XXIII.  fig.  10. 
Attenuato-acuate  : extieelt  spined. — Bictyocylindrus  ventilabrum,  Bov^eebank,  MS. 
This  short  form  of  spiculum  is  of  very  frequent  occurrence  in  the  interior  of  sponges  of 
several  different  genera.  They  are  usually  profusely  spinous,  and  especially  at  the  base, 
which  is  firmly  imbedded  in  the  keratode  of  the  skeleton.  The  spines  are  irregularly 
dispersed  over  all  parts  of  the  shaft,  to  the  very  apex  of  the  spiculum ; they  are  pro- 
jected into  the  interstitial  cavities  and  canals  of  the  sponge  at  all  angles  to  the  axis  of 
the  skeleton  on  which  they  are  based,  and  no  degree  of  regularity  exists  in  their  mode  of 
dispersion.  In  some  sponges  they  occur  in  considerable  numbers ; but  in  others,  where 
the  animal  is  well  protected  by  the  abundance  of  the  large  radial  spicula,  they  are  few 
in  number,  and  are  not  to  be  detected  without  a very  careful  search  (Plate  XXIV.  fig.  1). 
Acuate  : extieely  axd  veeticillately  spixed  (Plate  XXIV.  fig.  2). — This  form  of 
spiculum  is  one  of  the  most  remarkable  and  beautiful  of  its  tribe.  I have  found  it  in 
two  distinct  species  of  sponge  from  the  West  Indies.  In  one  it  is  irregularly  dispersed, 
and  in  the  other  it  is  collected  into  radiating  groups.  The  form  of  the  spiculum  is 
short,  stout,  and  regularly  acuate,  haVng  the  acutely-conical  spines  arranged  in  nearly 
equidistant  rings  of  a single  series  each,  from  the  base  to  the  apex  of  the  spiculum. 
Cylixdeical  : extieely  axd  veeticillately  spixed  (Plate  XXIV.  fig.  3). — I am  not 
acquainted  with  the  sponge  whence  this  beautiful  spiculum  came.  I found  it  in  the 
refuse  matter  from  the  base  of  a specimen  of  Oculina  rosea,  from  the  South  Seas.  The 
shaft  of  the  spiculum,  from  end  to  end,  has  equidistant  rings  of  single  series  of  acute 
conical  spines,  and  the  base  and  apex  of  the  spiculum  are  each  equally  crowded  with 
spines.  I have  arranged  it  as  a defensive  spiculum,  from  its  near  approximation  to  the 
characters  of  the  spiculum  last  described;  but  it  is  subject  to  the  doubt  whether  it  may 
not  ultimately  prove  to  have  belonged  to  the  skeleton,  as  we  have  in  HalicJiondria 
incrustans,  Johxstox,  entirely  spined  acuate  spicula  forming  the  skeleton,  the  charac^- 
ters  of  which  are  so  closely  allied  to  the  attenuato-acuate  defensive  spicula  so  common 
in  the  interior  of  some  sponges,  that  had  we  found  but  a single  spiculum  of  the  skeleton 
of  that  sponge,  we  should  very  naturally  have  concluded  it  to  have  been  an  inteimal 
defensive  spiculum. 
Spixulo-eecuevo-quateexate. — I have  found  this  remarkable  form  of  spiculum  in  one 
sponge  only,  and  I am  indebted  to  my  friend  Mr.  Thomas  Ixgall,  in  whose  cabinet  it 
is,  for  my  knowledge  of  it.  They  occur  in  great  profusion  in  the  cavities  of  the  sponge, 
clusters  of  them  consisting  frequently  of  as  many  as  twelve  or  fifteen  radiate  from  the 
