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DE.  J.  S.  BOWEEBAJSE:  O^s  the  AXATO:^^Y 
of  curvature  forming  the  basal  commencements  of  the  hooks ; but  although  not  decur- 
rent on  the  shaft,  the  lines  of  the  inner  margins  are  projected  forward  at  an  angle  of 
about  45  degrees  to  the  axis  of  the  shaft ; and  as  the  outer  lines  are  projected  in  a 
corresponding  degree,  we  have  the  palm  produced  in  the  form  of  two  concave  conical 
teeth  or  palms  at  each  end  of  the  spiculum ; and  between  these  there  is  not  the  slightest 
appearance  of  the  ends  of  the  hami,  which  appear  to  be  equally  divided  between  the 
terminal  palms  or  teeth.  This  form  I therefore  propose  to  term  bidentate  equi- 
anchorate.  The  same  termination  occurs  among  the  inequi-anchorate  forms ; and  this 
mode  of  the  development  of  the  teeth  is  well  shown  in  the  distal  or  larger  portion  of  the 
bidentate  inequi-anchorate  spiculum,  represented  in  Plate  XXIV.  fig.  55.  In  other- 
cases  the  termination  of  each  hook  does  not  thus  merge  in  the  teeth,  but  is  canied  for- 
ward between  them  either  in  the  form  of  a simple  attenuated  termination,  as  repre- 
sented in  Plate  XXIV.  fig.  57,  or  it  expands  laterally  and  forms  a third  intei-mediate 
tooth  of  a hastate  form,  as  represented  in  Plate  XXV.  fig.  7.  In  either  of  these  cases 
I therefore  propose  to  designate  the  spiculum  as  tridentate.  In  other  cases,  the  lateral 
expansions  forming  the  palm  are  continued  along  the  shaft  of  the  spiculum  to  nearly,  or 
quite,  the  full  extent  of  the  palm,  forming  a single,  undhided,  more  or  less  concave 
termination,  as  in  Plate  XXIV.  fig.  56.  I propose  therefore  to  designate  this  fonn  as 
palmato-anchorate ; and  intermediate  forms  between  the  decidedly  dentate  or  palmate 
ones  would  be  designated  as  tridentato-palmate  (Plate  XXV.  fig.  7),  the  palmate  form 
being  in  excess  of  the  dentate  structure ; or  palmato-  tri-  or  bi-dentate,  when  the  teeth 
are  in  the  ascendant. 
Generally  speaking,  the  ends  of  the  shaft  of  each  anchorate  spiculum  either  become 
obsolete  at  the  base  of  the  teeth,  as  in  bidentate  forms,  or  they  are  continued  in  a regu- 
lar curve,  forming  the  third  tooth,  as  in  the  tridentate  form ; but  m some  cases,  as  m 
Halichondria  plumosa,  Johnston,  the  shaft  appears  to  terminate  abruptly  at  each  end, 
and  the  palms  or  teeth  are  projected  towards  each  other  at  a sharp  angle  to  the  ends  of 
the  shaft  or  bow  of  the  spiculum : in  this  case  we  should  term  the  spiculum  angulated 
anchorate,  as  represented  in  Plate  XXV.  figs.  I,  2 and  3. 
The  anchorate  spicula  are  not,  like  the  acerate,  acuate  and  other  simple  forms,  of  the 
same  shape,  or  nearly  so,  from  the  commencement  to  the  termination  of  theii-  growth, 
but,  on  the  contrary,  they  are  developed  progressively. 
In  a new  species  of  Halichondria^  for  which  I am  indebted  to  my  fi’iend  Mr.  Thomas 
Ingall,  the  course  of  their  development  is  displayed  m a very  interesting  and  instructi-s  e 
manner.  The  first  condition  in  which  we  detect  them,  is  in  the  form  of  an  exceedingly 
slender  and  elongated  simple  bihamate  spiculum,  which  is  readily  distinguished  from 
the  true  bihamate  form  by  the  straightness  of  the  shaft,  the  comparative  shortness  of  the 
hami,  and  the. obtuseness  of  their  terminations,  as  represented  m Plate  XXV.  fig.  4. 
We  next  find  the  same  form  increased  in  strength,  and  ulth  slight  lateral  fimbriae  near 
each  end  of  the  shaft  at  the  commencement  of  the  hami,  as  in  Plate  XXV.  fig.  5.  In 
a more  advanced  stage  we  find  a regularly  curved  extension  of  the  fimbriae,  slightly  so 
