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DE.  J.  S.  BOWEEBAJS^K  ON  THE  ANATOMY 
BiROTULATE  : EOTUL^  irregularly  AISTD  deeply  dentate,  SHAPT  medially  SPINED 
(Plate  XXVI.  fig.  29). — This  form  occurs  in  the  gemmules  of  Spongilla  Meyeni,  Car- 
ter, from  the  water-tanks  of  Bombay.  It  is  the  largest  spiculum  of  that  form  that  I 
have  yet  seen.  It  differs  from  the  congenerous  form  in  S])ongilla  fluviatilis,  inasmuch 
as  the  spination  of  the  shaft  in  Sp.  Meyeni  is  the  rule,  while  in  Sp.  fluviatilis  it  is  a 
rare  exception. 
Recurvo-dentate  BIROTULATE  (Plate  XXVI.  figs.  21  and  22). — This  elegant  form  of 
spiculum  is  from  the  coat  of  the  gemmule  oi  Spongilla  plumosa.  Carter,  from  the  water- 
tanks  of  Bombay.  It  is  the  most  perfectly  developed  form  of  its  class  with  which  we 
are  acquainted.  It  varies  to  some  extent  in  size  and  form.  The  length  of  the  shaft  is 
from  three  to  three-and-a-half  times  the  diameter  of  the  rotulse,  and  it  is  covered  pro- 
fusely with  stout  acutely-conical  spines,  which  frequently  exceed  the  diameter  of  the 
shaft  in  length. 
The  rotulse  are  internally  concave,  and  considerably  and  regularly  convex  on  the  outer 
surface,  and  they  have  their  margins  u’regularly  dentate,  the  dents  in  fully-developed 
specimens  being  much  recurved.  The  shaft  is  usually  regularly  cylindrical  throughout 
its  length,  but  in  very  fully-developed  spicula  it  sometimes  increases  considerably  in  its 
diameter  at  a slight  distance  from  its  junctions  -with  the  rotulse. 
In  this  spiculum,  as  it  occurs  in  Spongilla  plumosa^  Carter,  the  gradual  development 
of  the  birotulate  form  is  beautifully  displayed,  as  I have  described  at  length  in  my  intro- 
ductory observations,  page  316:  figs.  18,  19  and  20  exhibit  progressive  stages  of  deve- 
lopment. 
Multihamate  birotulate  (Plate  XXVI.  fig.  30). — This  singular  form  of  spiculum  is 
from  the  outer  portion  of  the  gemmules  of  a new  species  of  freshwater  sponge  from  the 
River  Amazon,  Spongilla  recurmta,  Bowerbank,  MS. 
The  external  surfaces  of  the  rotulee  are  smooth,  very  convex,  and  in  many  cases  almost 
hemispherical;  so  that  the  points  of  the  curved  spines  are  in  the  direction  of  lines 
parallel  to  the  shaft  of  the  spiculum,  and  the  rotulee  are  cleft  almost  to  the  point  of 
union  with  the  shaft.  The  number  of  the  curved  spines  vary;  in  one  rotula  there 
were  as  many  as  ten,  but  the  usual  number  is  five  or  six.  An  average-sized  specimen 
measured  of  i^ich  long ; diameter  of  the  rotulae,  of  an  mch ; and  dia- 
meter of  the  shaft,  42^8  6^^  of  an  inch. 
Inequi-birotulate  (Plate  XXVI.  figs.  31  and  32). — This  spiculum  exhibits  a gradiud 
transition  from  the  fully  developed  birotulate  to  the  completely  boletiform  tribe  of 
spicula.  It  occurs  in  a new  species  of  freshwater  sponge,  Spongilla  paulida,  Bourebanr, 
MS.,  from  the  River  Amazon.  It  is  a stout  fully  developed  form,  and  the  whole  of 
them  exhibited,  as  nearly  as  possible,  the  same  proportions,  which  are  as  follows : — 
Length  of  an  inch,  diameter  of  largest  rotula  ysTs-th  of  an  inch,  and  diameter 
of  the  shaft  at  the  middle  of  an  inch.  The  shaft  increases  shghtly  and  gradually 
in  its  diameter  from  the  middle  to  each  of  the  rotulae.  The  central  caAty  of  the  shaft  is 
very  distinct,  and  has  a diameter  equal  to  about  one-fifth  that  of  the  medial  one  of  the 
