AJS'D  PHYSIOLOGY  OF  THE  SPONGIAD^. 
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Ctlindeical. — Having  the  shaft  of  the  same  diameter  throughout  its  length,  and 
terminating  at  each  end  hemispherically,  as  in  Pachymatisma  Johnstonia,  Boweebank 
(Plate  XXIII.  fig.  17). 
Fusieoemi-ctlindeical. — Having  both  terminations  hemispherical,  and  the  shaft 
gradually  increasing  in  diameter  to  its  middle.  Pachymatisma  Johnstonia,  Bovs^eebank 
(Plate  XXIII.  fig.  18). 
Attexuato-ctlindeical. — Terminating  hemispherically  at  both  ends,  but  the  shaft 
slightly  decreasing  from  the  base  to  the  apex.  Pachymatisma  Johnstonia,  Boweebank 
(Plate  XXIII.  fig.  19). 
Fusifoemi-attenuato-ctlindeical. — Both  terminations  being  hemispherical,  the  fusi- 
form shaft  has  a much  smaller  diameter  towards  its  apex  than  it  has  at  its  base.  From 
Tethea  rohusta,  Boweebank,  MS.  A new  species  from  Australia  in  the  British  Museum 
(Plate  XXIII.  fig.  20). 
Biclayated  ctlindeical. — The  shaft  equally  cylindrical,  with  gradually  infiated  termi- 
nations. The  infiations  are  almost  as  great  as  that  of  a spinulate  spiculum,  but  without 
sphericity  (Plate  XXIII.  fig.  21).  From  a new  and  undescribed  species  from  Australia, 
Bowerbank  Collection. 
Inequi-Biclayated  ctlindeical. — The  shaft  attenuated  from  the  base  to  the  apex, 
with  claYated  terminations  of  unequal  diameters  (Plate  XXIII.  fig.  22).  From  Pachy- 
matisma Johnstonia,  Boweebank. 
Angulated  inequi-Biclayated  ctlindeical. — This  singular  angulated  form  does  not 
appear  to  be  purely  accidental,  as  I haYe  found  other  instances  of  similar  angulation  at 
the  middle  of  the  shaft  in  other  sponges,  and  the  angle  in  each  instance  has  been  as 
nearly  as  possible  at  the  same  spot  in  the  shaft.  Pachymatisma  Johnstonia,  Boweebank 
(Plate  XXIII.  fig.  23). 
Spinulate. — Shaped  hke  a pin,  having  the  same  diameter  from  the  spherical  base  to 
ver)'  near  the  acutely  terminated  apex.  Halichondria  carnosa,  Johnston  (Plate  XXIII. 
fig.  24). 
Fusifoemi-spinulate. — The  base  being  spherical,  the  shaft  more  or  less  fusiform  and 
terminated  acutely.  Halichondria  subarea^  Johnston  (Plate  XXIII.  fig.  25). 
Attenuato-depeesso-spinulate. — Having  the  basal  infiation  considerably  depressed, 
and  the  shaft  gradually  attenuated  from  the  base  to  the  apex.  From  a new  species  of 
sponge  from  Ash  Island,  in  the  cabinet  of  Mr.  Thomas  Ingall  (Plate  XXIII.  fig.  26). 
Enoemi-spinulate. — Having  the  spherical  infiation  slightly  within  the  basal  portion 
of  the  shaft  of  the  spiculum.  Halichondria  celata,  Johnston  (Plate  XXIII.  fig.  27). 
Flexuous. — Having  the  shaft  of  the  spiculum  curved  repeatedly  (Plat^  XXHI.  fig.  28). 
Halichondria  ventilalrrum^  Johnston. 
Ensifoem. — Expanding  towards  the  apex,  but  terminating  acutely ; so  that  the  outline 
has  more  or  less  the  form  of  the  blade  of  a sword.  Sponge  unknown  (Plate  XXIII. 
fig.  29). 
The  spicula  of  the  skeleton  in  some  species  of  siliceous  sponges  are  more  or  less 
MDCCCLVIII.  2 E 
