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DR.  J.  S.  BOWEEBAJ^E:  on  the  ANATO:\rT 
hami  being  distended  in  the  form  of  large  round  or  ovoid  masses,  as  represented  in 
Plate  XXIV.  figs.  47,  48  and  49.  I found  the  remains  of  the  membranous  structures 
crowded  with  these  very  minute  spicula,  which  varied  exceedingly  in  form  and  in  amount 
of  development,  and  among  them  were  a great  variety  of  other  forms  of  bihamate  spi- 
cula. 
Uriclavate  bihamate  (Plate  XXIV.  fig.  47),  I believe  to  be  an  ainest  of  develop- 
ment rather  than  a separate  form ; for  although  I found  many  specimens  of  it  inter- 
mixed with  the  biclavate  forms,  I also  found  others  assuming  transitional  forms,  that 
appeared  ultimately  to  connect  it  with  the  biclavate  spicula. 
Biclavate  bihamate  (Plate  XXIV.  figs.  48  and  49). — There  is  a considerable  varia- 
tion in  the  shape  of  this  spiculum.  The  form  represented  by  figime  48  is  perhaps  the 
most  numerous,  but  that  of  figure  49  is  the  largest  and  most  fully  developed. 
In  a new  species  of  British  sponge,  Halicliondria  Hyndmani^  Boweebaxk,  MS.,  we 
find  another  form  of  expanded  termination  to  the  hami,  the  pocillated  bihamate,  which 
gradually  leads  us  to  the  true  anchorate  forms. 
In  the  simple  form  of  pocillated  bihamate  spicula,  the  temiinations  of  the  cmwed 
shaft  resolve  themselves  into  two  nearly  equal,  circular,  concavo-convex  plates,  the 
convex  surfaces  being  in  each  case  outward,  and  the  sides  of  each  plate  ciu'^Tng  con- 
siderably towards  the  other,  their  planes  being  at  a right  angle  to  the  axis  of  the  shaft. 
In  other  cases,  one  cup  will  be  developed  with  its  plane  in  the  same  direction  as  the 
axis  of  the  shaft,  while  the  other  cup  is  produced  with  its  plane  at  right  angles  to  the 
axis  and  also  of  the  plane  of  the  first  cup.  In  these  variations  of  development,  there- 
fore, this  form  of  spiculum  may  be  compared  to  the  simple  and  contort  forms  of  biha- 
mate spicula;  and  in  truth  they  differ  from  them  only  in  this,  that  in  the  one  the 
terminations  of  the  hami  are  attenuated  and  acute,  and  in  the  other  they  are  expanded 
into  concavo-convex  discs. 
These  two  modes  of  development  appear  to  be  subject  to  a considerable  amoimt  of 
variation  in  the  growth  of  the  terminal  discs ; as  in  some  cases  we  find  the  distal  part 
of  the  terminal  plate  to  consist  of  a uniform  curve,  while  in  other  cases  the  shaft  is 
carried  through  the  centre  of  that  curve,  forming,  as  it  were,  a supplemental  hook. 
These  variations  are  in  perfect  accordance  with  the  general  laws  of  de-s'elopment  in  this 
class  of  spicula,  as  we  find,  both  in  the  bihamate  and  anchorate  forms,  a considerable 
amount  of  difference  in  the  structure  and  position  of  these  organs  in  the  same  species 
of  sponge. 
Unipocillated  bihamate  (Plate  XXIV.  fig.  50). — One  termination  fully  developed 
in  the  form  of  a cup,  while  the  other  is  only  produced  to  the  extent  of  the  two  lateral 
curves,  and  a terminal  umbo  to  the  shaft. 
Simple  bipocillated  bihamate  (Plate  XXIV.  fig.  51). — Haring  both  terminations 
developed  in  the  form  of  cups  in  coincident  planes. 
CoNTOET  BIPOCILLATED  BIHAMATE  (Plate  XXIV.  fig.  52). — Two  cups  being  developed, 
but  in  planes  at  right  angles  to  each  other. 
