296 
DE.  J.  S.  BOWEEBAOTC  OX  THE  AXATO^klY 
of  its  length,  giving  its  outline  very  much  the  form  of  an  ancient  sword  (fig.  15,  Plate 
XXIV.).  In  Grantia  tessellata,  Boweeba]S"^k,  MS.,  a new  species  from  the  Island  of 
Sark,  the  spicular  ray  is  short,  veiy  stout,  and  cuiwed  throughout  its  whole  length  in 
the  form  of  a sabre,  as  represented  by  fig.  16,  Plate  XXIV. 
Equiajvgulated  spiculated  teipodate. — Vdien  the  basal  radii  are  projected  back- 
ward so  that  their  apices  only  are  in  the  same  plane,  and  the  spicular  ray  at  right 
angles  to  that  plane.  The  short  spicular  ray  in  this  case  is  not  based  on  a tiii-adiate 
skeleton  one,  but  the  whole  spiculum  is  essentially  a defensive  one  only.  They  occur 
in  the  lining  membrane  of  the  cloaca  of  Grantia  nivea.  and  are  very  minute  (fig.  17. 
Plate  XXIV.). 
Equiangulated  teieadiate  : unieadially  spia'ED. — I obtained  a considerable  number 
of  this  form  of  spiculum  from  the  dissolution  in  nitric  acid  of  a small  fragment  of  a 
parasitical  sponge,  in  the  collection  of  the  late  Mr.  Chaeles  Stokes.  I have  not  seen 
it  in  situ,  but  I have  very  little  doubt  from  its  structui-e  that  the  spiculated  ray  is  a 
defensive  one,  while  the  two  spineless  rays  formed  part  of  the  skeleton  (fig.  18. 
Plate  XXIV.). 
Attenuato-clavate  : incipiently  spined. — The  enlargement  of  the  base  of  this  spicu- 
lum is  not  spherical  as  in  a spinulate  form,  but  it  expands  more  or  less  gradually  and  is 
usually  exaxial.  They  are  projected  m abundance  into  all  parts  of  the  mterstitial  cavities 
of  a new  species  of  British  sponge,  Hyineniacidon  clavigera,  Boweebakk,  jNIS.  (Plate 
XXIV.  fig.  19). 
Equiakgulae  teieadiate  : veeticillately  spixed. — This  beautiful  spiculum  was  foimd 
among  minute  fragments  of  various  sponges  scraped  from  the  bases  of  specimens  of 
Oculina  rosea.  I have  never  found  verticillately  spined  sponge  spicula  under  any  other 
character  than  that  of  defensive  spicula,  and  I have  therefore  arranged  this  one  as  such 
until  further  information  shall  be  obtained  regarding  it  (fig.  20,  Plate  XXIV.).  Other 
forms  are  frequently  found  disposed  as  defensive  spicula,  but  as  they  do  not  differ  in 
shape  from  the  skeleton  spicula  already  described  and  figimed,  it  is  uimecessary  to  figiu’e 
them  again. 
Spicula  of  the  Membranes. 
There  are  two  distinct  classes  of  spicula  appropriated  to  the  membranous  tissues  of 
sponges.  The  office  of  the  first  of  these  is  simply  to  strengthen  and  support  those 
delicate  tissues  when  necessary,  and  to  commimicate  to  them  a certain  amount  of  ten- 
sion when  it  is  required.  The  forms  are  few  in  number,  and  their  structure  compara- 
tively simple. 
The  office  of  the  second  class  is  that  of  assisting  in  the  retention  of  the  sarcode  on  the 
interstitial  and  other  membranous  structures.  They  are  usually  minute  in  size,  and 
often  very  complicated  in  form. 
I propose  to  designate  these  organs  as, — 
1st.  Tension  Spicula. 
2nd.  Ketentive  Spicula. 
