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DE.  J.  S.  BOWEEBAXK  OX  THE  AXAT0:HT 
Geodia  M^Andreivii,  Bowerbank,  MS.,  a new  and  remarkably  interesting  species.  In 
this  sponge  there  appeared  to  be  a greater  amount  of  silex  secreted  in  the  large  skeleton 
spicula  than  in  Tethea^  while  some  of  them  after  incineration  were  resolved  into  thin 
shells  of  silex,  others  withstood  the  operation  and  retained  their  form ; and  some  were  so 
completely  siliceous,  that  on  plunging  them  into  the  drop  of  water  for  examination  while 
red-hot  from  the  flame  of  the  lamp,  the  result  was  the  same  as  if  they  had  been  solid 
glass  rods,  and  these  were  cracked  and  shattered  in  every  direction  (Plate  XXIII.  fig.  8). 
I submitted  to  the  same  mode  of  incineration  a few  of  the  long  siliceous  spicula  or 
fibres  of  Eu])lectella  aspergillum,  Owex,  burning  about  half  of  each  fibre,  and  the 
result,  although  somewhat  different,  was  equally  satisfactory.  The  unbumed  portion 
appeared  perfectly  solid,  but  exhibited  the  usual  trace  of  concentric  structm’e.  The  end 
thoroughly  burned  became  reduced  to  a thin  filament  of  densely  black  matter  like 
charcoal,  but  the  junction  of  the  burned  and  unburned  portions  was  extremely  interesting. 
At  this  point  the  action  of  the  heat  upon  the  concentric  layers  had  separated  them  from 
each  other  in  the  form  of  a series  of  thin  curved  flakes  or  coats,  illustrating  the  thin 
concentric  structure  in  a very  satisfactory  manner ; demonstrating  that  the  outer  coat  of 
siliceous  matter  was  not  the  only  one,  and  that  probably  there  were  several  coats,  each 
containing  a sufficient  amount  of  silex  in  its  composition  to  resist  disintegration  by  inci- 
neration (Plate  XXIII.  fig.  7). 
On  operating  in  like  manner  on  the  spicula  of  Halichondria  oculata,  Johxstox,  little 
or  no  alteration  was  perceptible  in  the  spicula,  the  inner  cavity  remaining  the  same  as 
in  the  unburned  ones,  and  distinguished  only  by  a slight  broum  tint,  indicating  the 
existence  of  but  a very  small  amount  of  animal  matter  within.  This  result  might  be 
expected ; the  spicula  being,  imbedded  in  the  keratose  fibre  to  give  it  additional  firm- 
ness and  strength,  are  not  required  to  be  elastic ; they  are  therefore  short,  comparatively 
stout,  and  solid  in  their  structure. 
A specimen  of  Halichondria  panicea,  Johnston,  burned  in  the  flame  of  a spirit-lamp 
to  a white  heat,  exhibited  no  alteration  in  the  mature  spicula,  in  many  of  which  I could 
not  detect  a central  tubular  cavity ; and  I presume  in  these  cases  the  spicula  were 
entirely  filled  with  silex,  as  in  younger  spicula  it  was  more  or  less  apparent.  'When  the 
cavity  was  very  small,  the  colour  had  a very  faint  tinge  of  brown,  and,  as  in  other  cases, 
when  the  cavity  increased  in  diameter,  the  amount  of  colouring  matter  produced  by  the 
incineration  of  the  animal  matter  within  became  greater,  and  deeper  in  its  tint,  until  in 
the  young  and  immature  spicula  the  internal  cavity  occupied  the  greater  part  of  its  dia- 
meter, and  it  became  perfectly  black  and  opake ; and  in  one  spiculum  the  gaseous  matter 
generated  within  expanded  one  part  of  the  spiculum  to  such  an  extent,  as  to  cause  it  to 
resemble  exactly  a hydrometer  in  form. 
The  result  of  the  incineration  of  Halichondria  incrustans,  Johnston,  was  very  similar 
to  that  of  Hal.  pcmicea.  The  adult  spicula  remained  unaltered,  and  the  central  canal 
was  rendered  more  apparent  than  it  was  before. 
On  burning  portions  of  Spongilla  fluviatilis  and  lacustns,  Johnston,  and  oi  Spongilla 
