AND  PHYSIOLOGY  OF  THE  SPONGIAD^. 
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All  the  simple  rectangulated  hexradiate  forms  of  spicula  hitherto  described  are  large, 
compared  with  the  rectangulated  hexradiate  spicula  which  form  the  central  bases  of  the 
compound  stellate  forms,  and  excepting  the  disparity  in  size,  the  transition  from  the  last 
form  described,  to  the  complicated  and  beautiful  compound  stellate  ones,  is  easy  and 
natm’al ; the  apices  of  the  hexradiate  form  becoming  the  bases  of  the  numerous  radii  of 
the  stellate  ones.  This  transition  from  the  simple  to  the  compound  forms  is  admirably 
illustrated  in  a bifurcated  spiculum  that  occurs  in  the  new  species  of  Eiijplectella  in  the 
Museum  of  the  Jardin  des  Plantes,  which  I propose  to  designate  as  follows : — 
Bifuecated  eectaagulated  hexeadiate  stellate  (Plate  XXV.  fig.  38). — It  is 
minute  and  slender,  and  the  bifurcating  rays  are  irregular,  often  tortuous,  and  are 
frequently  not  produced  on  one  or  two  of  the  primary  radii.  These  indecisive 
characters,  common  to  all  the  specimens  of  this  form  of  spiculum  that  I have  seen, 
combined  with  the  elongate  characters  of  the  radii,  seem  strongly  to  mark  this  spiculum 
as  the  connecting  link  betw^een  the  simple  hexradiate  and  the  compound  stellate  forms 
of  spicula. 
Teifuecato-hexeadiate  stellate  (Plate  XXV.  fig.  39). — The  central  radii  consist  of 
six  rectangulated  primary  rays  of  equal  length,  each  of  which  terminates  in  three 
equidistant  secondary  attenuating  rays,  which  are  projected  from  the  apices  of  the 
primary  ones  at  an  angle  of  about  45  degrees  to  the  common  basal,  or  primary  ray. 
These  spicula  occur  in  abundance  in  Eiiplectella  aspergillum,  Owen,  and  in  Dactylocalyx 
pumicea,  Stetchbuey.  I observed  them  first  in  some  fragments  of  the  magnificent 
specimen  of  I),  pumicea,  half  of  which  is  in  the  possession  of  Dr.  J.  E.  Geay  ; and  the 
other  half  is,  I believe,  in  the  Museum  of  the  Bristol  Institution ; and  subsequently  in  a 
second  specimen  in  the  possession  of  my  friend  Mr.  Thomas  Ingall,  in  whose  sponge 
there  are  remains  of  the  sarcodous  structure,  which  is  literally  crowded  with  them  and 
the  spinulo-hexi’adiate  stellate  ones.  They  are  also  abundant  in  a specimen  of,  1 
believe,  a different  species  in  the  Museum  of  the  Jardin  des  Plantes  at  Paris,  where 
the  sponge  is  designated  Ipliiteon.  There  is  a slight  difference  in  the  form  and  mode 
of  radiation  of  the  secondary  rays  in  the  specimens  of  these  spicula  that  occur  in 
Mr.  Cuming’s  beautiful  specimen  of  Euplectella  aspergillum  and  those  from  Dactylocalyx, 
and  they  are  not  in  the  former  species  accompanied  by  the  spinulo-hexradiate  ones,  as 
in  Eactylocalyx  pumicea.  In  my  friend  Dr.  A.  Faeee’s  beautiful  specimen  of  Euplectella 
they  are  to  be  found,  but  not  so  abundantly  as  in  Mr.  Cuming’s  sponge,  but  they  are  of 
precisely  the  same  form  as  the  spicula  from  that  specimen. 
Spinulo-teifuecated  hexeadiate  stellate  (Plate  XXVI.  fig.  I). — The  central  radii 
consist  of  six  rectangular  primary  rays  of  equal  length,  each  of  which  terminates  in 
three  equidistant  cylindi’o-spinulate  radii,  projected  from  the  apices  of  the  primary  ones 
at  an  angle  of  about  45  degrees  to  the  axis  of  the  common  basal  primary  ray. 
Occasionally  we  find  four  secondary  radii  in  place  of  three,  but  this  is  not  of  common 
occurrence ; and  in  the  fully  developed  spicula  the  spinulate  terminations  are  usually  not 
globular,  but  of  a more  or  less  depressed  form.  This  spiculum  I have  found  only  in 
MDCCCLVIII.  2 u 
