ol.  49.]  MADREPORARIA  FROM  THE  SUTTOX  STOXE.  577 
trabecule.  They  have  pseudo-synapticulae  which  are  numerous,  have 
little  prominence,  and  closely  resemble  those  of  Clausastrcea.  The 
dissepiments  are  distant,  straight,  or  oblique,  and  feebly  developed. 
Columella  large,  and  the  primary  septa  fused  into  it.  Increase  takes 
place  by  fissiparity  and  by  gemmation  between  the  corallites,  as  in 
Stylocoenia  and  Bcithycoenia. 
In  neither  of  the  specimens  examined  are  the  external  characters 
of  the  calices  determinable.  T\  hether  the  edges  of  the  septa  were 
denticulate,  and  whether  the  columella  was  prominent  or  the  reverse, 
are  particulars  which  can  only  be  known  when  specimens  having 
the  external  characters  better  preserved  have  been  examined. 
I  he  genus  will  take  its  place  near  to  Clausastrcea ,  with  which  it 
agrees  pretty  closely,  excepting  in  the  very  important  particular  of 
possessing  a  well-developed  columella,  and  having  both  modes  of 
increase,  i.  e.  fissiparity  and  gemmation.  In  the  latter  particulars  it 
differs  from  all  the  genera  to  which  it  is  in  any  way  related. 
Although  the  present  is  obviously  distinct  as  a  species  from  that 
described  as  Astrocoenia  gibbosa  by  the  late  Prof.  Duncan,  I  retain 
the  same  specific  name,  and  give  the  following  definition  — 
Stelidioseris  gibbosa,  sp.  nov. 
Astrocoenia  gibbosa ,  Duncan,  Quart.  Journ.  Geol.  Soc.  vol.  xlii. 
(1886)  p.  101,  pi.  viii.,  not  A.  gibbosa  of  ‘  Suppl.  to  Brit.  Toss.  Corals.’ 
The  septa  are  rather  stout,  straight,  from  twenty  to  thirty  in 
number,  of  which  ten  pass  into  the  columella,  and  all  the  others  are 
more  or  less  rudimentary.  The  inside  or  openings  of  the  corallites 
are  more  or  less  polygonal,  but  with  the  angles  so  much  rounded 
that  they  are  often  irregularly  ovoid  or  even  circular.  The  lateral 
fusing  into  each  other  of  the  septal  cost®  iu  the  mural  region  varies 
from  one-sixth  of  the  diameter  of  the  remaining  opening  in  the 
corallite  to  nearly  its  whole  diameter. 
Diameter  of  a  large  calice  —  inch. 
Hcib.  The  Sutton  Stone  of  Glamorganshire. 
EXPLANATION  OF  PLATE  XX. 
Pig.  1.  Stelidioseris  gibbosa.  A  horizontal  section  of  some  calices  magnified 
four  times,  and  seen  by  transmitted  light.  The  dark  markings  between 
the  calices  in  this  figure  and  in  figs.  2  &  4  are  due  to  greater  opacity, 
and  they  represent  the  cycles  of  septa,  which,  however,  are  difficult 
to  enumerate. 
Fig.  2.  Stelidioseris  gibbosa.  Two  contiguous  corallites,  cut  through  horizontally 
and  seen  by  transmitted  light.  They  show  fissiparous  increase  very 
clearly,  and  are  magnified  eight  times. 
Fig.  3.  Astrocoenia  tourtiensis,  Bolsche.  A  horizontal  section  of  some  coral¬ 
lites  seen  by  transmitted  light,  showing  the  thin  rudimentary  wall 
and  the  great  development  of  stereoplasm  within  the  corallites,  reducing 
their  diameter  by  nearly  one  half,  and  from  a  polygonal  to  a  circular 
form.  Magnified  eight  times. 
Fig.  4.  Stelidioseris  gibbosa.  A  corallite  cut  though  very  obliquely,  and  seen  by 
transmitted  light.  In  the  fragments  of  septa  on  the  right  and  left- 
hand  of  the  figure  the  pseudo-synapticulaa  appear  as  horizontal  lines, 
as  in  the  genus  Clausastrcea.  The  septa  shown  at  the  top  and  bottom 
2q  2 
