320 
DR.  J.  S.  BOWEEBAXK  OX  THE  AXATOHT 
3rd.  Spicula  disposed  in  fasciculi  in  the  substance  of  the  gemmule  fkom  the  centee 
TO  THE  CIKCUMFEEENCE. 
Inequi-fusifoemi-aceeate  (Plate  XXVI.  fig.  39). — This  form  is  found  in  the  fasciculi 
of  spicula  that  radiate  in  all  directions  from  the  centre  to  the  surface  of  the  gemmules 
of  Tethea  cranium,  Johnston.  The  largest  diameter  of  the  spiculum  is  at  about  one- 
fourth  or  one-fifth  of  its  length  from  its  base,  and  thence  it  gradually  diminishes  in  size 
to  the  very  attenuated  apex.  They  are  about  -gVlfi  of  an  inch  in  length. 
Unihamate  attenuato-clavate  (Plate  XXVI.  fig.  40). — This  singular  form  occurs 
abundantly  in  the  gemmules  of  Tethea  cranium,  Johnston.  The  long  attenuated  shaft 
increases  gradually  in  size  from  its  proximal  end  to  its  distal  one,  where  it  rapidly  but 
progressively  increases  in  diameter,  and  terminates  hemispherically.  From  this  clavate 
mass  a single  hook  is  projected,  which  curves  slightly  towards  the  shaft  of  the  spiculum, 
so  that  its  apex  reaches  a point  at  about  45°  from  the  axis  of  the  spiculum.  The 
length  of  the  hook  is  about  equal  to  the  diameter  of  the  clavate  mass  from  which  it 
emanates.  I have  seen  a great  number  of  spicula  of  this  form  from  different  specimens 
of  Tethea  cranium,  and  never  found  more  than  one  terminal  hook ; but  it  appears  highly 
probable,  from  a comparison  of  these  spicula  with  allied  forms  from  the  gemmules  of 
Tethea  similimus,  Boweebank,  MS.,  from  the  South  Sea,  in  the  Museum  of  the  Eoyal 
College  of  Surgeons,  that  it  is  but  a permanent  variety  of  the  recmwo-ternate  form  that 
occurs  sparingly  among  the  defensive  spicula  of  T.  cranium. 
Attenuato-eecuevo-teenate  (Plate  XXVI.  figs.  41  and  42). — In  the  gemmules  of 
Tethea  similimus,  Boweebank,  MS.,  from  the  South  Sea.  There  are  numerous  spicula 
like  those  represented  by  figure  40,  from  T.  cranium,  but  not  quite  so  much  recuiTed, 
and  many  of  these  have  the  rudimentary  canal  opposite  to  the  well-developed  hook, 
indicating  a predisposition  to  eliminate  a second  one.  In  other  spicula  we  find  the 
second  hook  fully  produced,  as  represented  by  figure  41 ; and  occasionally,  though  rarely, 
we  find  a completely  ternate  termination,  as  represented  by  figure  42. 
Attenuato-poeeecto-teenate  (Plate  XXVI.  fig.  43). — This  form  is  foimd  in  abun- 
dance in  the  fasciculi  of  spicula  in  the  gemmule  of  Tethea  cranium,  Johnston.  It  is  very 
like  the  porrecto-ternate  spicula  that  are  projected  from  the  surface  of  that  sponge,  but 
it  differs  from  them  in  always  having  the  radii  expanded  to  a greater  amount,  in  many 
cases  attaining  an  angle  of  nearly  40  degrees  to  the  shaft  of  the  spiculum.  The  ternate 
termination  is  always  the  distal  one. 
The  positions  in  the  sponge  of  the  whole  of  the  spicula  hitherto  figimed  have  been 
determined  with  as  great  a degree  of  accuracy  as  chcumstauces  permitted.  Beside  these 
there  are  other  interesting  forms  of  spicula,  of  the  spongeous  origin  of  which  there  can  be 
no  reasonable  doubt,  which  have  presented  themselves  dming  the  coui’se  of  my  researches, 
and  which  I have  thought  it  advisable  to  describe  separately. 
