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DE.  J.  S.  BOWEEBAISTC  OX  THE  AXATOIVIT 
Euplectella  aspergillum.  They  are  abundant  in  that  sponge,  frequently  filling  up  the 
interstices  of  the  network  of  the  siliceous  skeleton,  or  otherwise  entangled  in  the  tissues. 
In  Dr,  A.  Faree’s  specimen  of  Euplectella  they  are  equally  abundant,  and  are  not  to  be 
distinguished  from  those  in  Mr.  Cuming’s  specimen.  They  are,  like  the  great  external 
prehensile  spicula,  and  the  fibre  of  the  skeleton,  composed  of  numerous  concentric- 
layers  of  silex,  which  readily  separate  from  each  other  by  decompositicm. 
I cannot  say  with  absolute  certainty  that  this  tribe  of  spicula  belong  really  to  the 
sarcode,  as  I have  never  seen  specimens  of  either  of  the  species  I have  named,  in  which 
they  occur  in  profusion,  in  such  a state  of  preservation  as  to  allow  of  their-  position  being 
positively  determined ; but  as  in  another  specimen  of  sponge  with  a siliceous  skeleton 
like  tliat  of  Bactylocalyx  pumicea,  Stutchbury,  the  sarcode  is  preserved  in  excellent  con- 
dition, and  occurs  in  such  abundance,  filling  all  the  interstices  of  the  skeleton  of  the 
sponge,  and  affording  ample  space  for  the  imbedment  of  such  spicula  in  its  substance, 
I am,  therefore,  induced  to  think  it  probable  that  a similar  abundance  of  sarcode  may 
exist  in  Bactylocalyx  and  other  similarly  constituted  sponges,  and  that  hereafter  even 
the  largest  of  this  tribe  of  spicula  will  be  found  completely  imbedded  in  the  sai-code. 
Slender  attenuated  rectangulated  hexradiate  (Plate  XXY.  fig.  34). — Beside 
the  large  and  stout  attenuato-hexradiate  spicula  in  Euplectella  aspergillum,  there  are 
comparatively  small  and  very  slender  ones,  many  of  which  are  nearly  of  the  same  pro- 
portions as  the  larger  ones ; but  generally  speaking  the  axial  radii  are  more  elongated, 
and  in  some  cases  the  basal  end  is  extended  to  four  or  six  times  the  length  of  the  apical 
portion. 
These  spicula  do  not  present  the  same  irregularity  in  their  development  that  we 
observe  in  the  stout  ones,  and  it  is  a rare  occurrence  to  find  one  without  the  full  number 
of  rays.  They  are  exceedingly  numerous  in  the  sponge,  and  they  occiu’  in  closely  packed 
fasciculi,  the  axes  of  the  spicula  nearly  touching  each  other.  Amidst  these  fasciculi 
we  find  the  large  stout  forms  imbedded,  the  whole  of  them  apparently  having  been 
completely  enveloped  by  the  sarcode  of  the  sponge. 
Cylindeo-rectangulated  hexradiate  : APiCALLY  SPINED  (Plate  XXY.  fig.  35). — This 
form  is  very  abundant  in  an  undescribed  species  of  Euplectella  in  the  Museum  of  the 
Jardin  des  Plantes,  Paris.  The  figure  represents  the  upper  portion  of  the  spiculiun 
only,  the  lower  portion  of  the  axial  shaft  being  exceedingly  elongated.  Mlien  examined 
with  a power  of  400  linear,  the  apices  of  the  radii  are  seen  to  be  abundantly,  but 
minutely  spined.  The  axial  shaft  of  this  spiculum  mthout  any  of  the  lateral  radii 
developed,  is  also  abundant ; it  is  exceedingly  long,  and  at  the  proper  distance  below 
the  apex  we  often  observe  a gradual  enlargement  of  the  diameter,  as  represented  in 
fig.  37,  and  the  rudimentary  canals  for  the  lateral  radii  are  frequently  apparent. 
This  form  of  spiculum  is  also  very  abundant  in  Bactylocalyx  pumicea,  Stutchbury, 
Iphiteon  of  the  French  Museum.  In  general  character  they  are  very  similar  to  those 
of  the  Euplectella  described  above,  with  the  addition  of  the  apices  of  the  radii  being 
more  or  less  clavated. 
