﻿30 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [-NOV. 
  18, 
  

  

  lines 
  whicli 
  denote 
  the 
  intercostal 
  spaces, 
  a 
  slightly 
  convex 
  elevation 
  

   between 
  the 
  lines 
  being 
  over 
  the 
  rib. 
  In 
  transverse 
  views 
  the 
  costae 
  

   are 
  wedge-shaped, 
  their 
  bases 
  being 
  continuous 
  with 
  the 
  lamellae 
  ; 
  the 
  

   angle 
  is 
  external, 
  rounded, 
  and 
  marked 
  by 
  a 
  series 
  of 
  small 
  blunt 
  

   tubercles, 
  whilst 
  the 
  sides 
  are 
  papillated 
  like 
  the 
  lamellae, 
  and 
  

   marked 
  by 
  the 
  exothecal 
  dissepiments, 
  which 
  moreover 
  pass 
  in 
  front 
  

   of 
  the 
  costae. 
  There 
  is 
  but 
  one 
  row 
  of 
  tubercles 
  to 
  each 
  rib, 
  and 
  the 
  

   free 
  extremity 
  is 
  often 
  sharply 
  spined. 
  The 
  costae, 
  inferiorly, 
  are 
  

   more 
  delicate 
  than 
  superiorly, 
  and 
  are 
  thinner 
  and 
  closer; 
  the 
  distinc- 
  

   tion 
  between 
  their 
  orders 
  is 
  moreover 
  greater 
  at 
  the 
  base 
  than 
  above, 
  

   where 
  they 
  are 
  nearly 
  equal. 
  The 
  costae 
  project 
  at 
  least 
  -^ 
  inch 
  

   from 
  the 
  wall, 
  and 
  the 
  intercostal 
  furrows 
  are 
  well 
  marked. 
  Endo- 
  

   theca 
  abundant, 
  vesicular, 
  and 
  uniting 
  the 
  lamellae, 
  especially 
  exter- 
  

   nally. 
  The 
  dissepiments 
  are 
  very 
  inclined, 
  bound 
  unequal 
  areas 
  on 
  

   the 
  sides 
  of 
  the 
  lamellae, 
  and 
  stretch 
  across 
  the 
  interseptal 
  loculi 
  ; 
  they 
  

   do 
  not 
  form 
  a 
  spiral 
  arrangement, 
  but 
  separate 
  each 
  interseptal 
  space 
  

   into 
  several 
  compartments. 
  The 
  dissepiments 
  unite 
  with 
  the 
  tissue 
  

   of 
  the 
  columella. 
  The 
  exotheca 
  is 
  well 
  developed 
  ; 
  the 
  dissepiments 
  

   are 
  inclined 
  downwards 
  and 
  outwards 
  between 
  the 
  costae, 
  and 
  range 
  

   across 
  these, 
  being 
  there 
  transversely 
  arched 
  or 
  straight 
  ; 
  here 
  and 
  

   there 
  they 
  form 
  oblique 
  layers, 
  which 
  fill 
  up 
  the 
  intercostal 
  space 
  

   and 
  even 
  hide 
  the 
  costae. 
  The 
  epitheca 
  is 
  membraniform 
  and 
  fully 
  

   developed, 
  extending 
  upwards 
  close 
  to 
  the 
  calicular 
  margin 
  ; 
  it 
  is 
  

   marked 
  by 
  transverse 
  bands 
  and 
  by 
  growth-rings, 
  as 
  well 
  as 
  by 
  lon- 
  

   gitudinal 
  striae. 
  The 
  epitheca 
  is 
  evidently 
  closely 
  attached 
  to 
  the 
  

   costae, 
  but 
  has 
  been 
  separated 
  by 
  the 
  violence 
  to 
  which 
  fossils 
  are 
  

   often 
  subjected. 
  The 
  wall 
  is 
  distinct, 
  and 
  flanked 
  by 
  exothecal 
  and 
  

   endothecal 
  dissepiments. 
  

  

  A 
  very 
  interesting 
  point 
  in 
  the 
  development 
  of 
  this 
  species 
  is 
  the 
  

   fact 
  that, 
  when 
  very 
  young, 
  the 
  septal 
  and 
  costal 
  numerical 
  'deve- 
  

   lopment 
  is 
  nearly 
  if 
  not 
  quite 
  as 
  great 
  as 
  in 
  the 
  full-grown 
  form. 
  

   A 
  younger 
  specimen 
  than 
  the 
  type, 
  which 
  has 
  not 
  yet 
  commenced 
  

   its 
  upward 
  and 
  cylindrical 
  growth, 
  suggests 
  the 
  close 
  alliance 
  be- 
  

   tween 
  A. 
  ponderosa 
  and 
  the 
  species 
  under 
  consideration. 
  Height 
  

   2-j^j- 
  inches, 
  of 
  small 
  form 
  1A 
  inch 
  ; 
  breadth 
  of 
  calice 
  1 
  T 
  6 
  ^ 
  inch 
  ; 
  

   length 
  1 
  T 
  9 
  ^ 
  inch 
  ; 
  length 
  of 
  columella 
  y 
  7 
  ^ 
  inch 
  ; 
  breadth 
  y 
  2 
  ^ 
  inch 
  ; 
  

   height 
  of 
  inner 
  septal 
  margin 
  y 
  2 
  ^ 
  inch. 
  

  

  From 
  the 
  Nivaje 
  shale, 
  San 
  Domingo. 
  Coll. 
  Geol. 
  Soc. 
  

  

  15. 
  Axtillia 
  Loxsdaleia, 
  spec. 
  nov. 
  PI. 
  III. 
  figs. 
  4a-4e. 
  

  

  Circopliyllia 
  , 
  species 
  2, 
  Lonsdale 
  MS. 
  

  

  **Corallum 
  straight, 
  tall, 
  subturbinate, 
  slightly 
  compressed, 
  with 
  a 
  

   constricted 
  calicular 
  margin 
  and 
  a 
  sharp 
  mammilliform 
  pedicel. 
  Calice 
  

   rounded 
  at 
  each 
  end, 
  and 
  more 
  or 
  less 
  flat 
  and 
  compressed 
  laterally. 
  

   Septa 
  numerous, 
  crowded, 
  thin, 
  long, 
  exsert, 
  having 
  an 
  external 
  and 
  

   internal 
  arched 
  lobe, 
  the 
  last 
  being 
  on 
  a 
  lower 
  plane 
  than 
  the 
  first, 
  

   and 
  terminating 
  in 
  a 
  vertical 
  inner 
  edge 
  which 
  bounds 
  the 
  fossula. 
  

   Upper 
  margin 
  of 
  the 
  external 
  lobe 
  finely 
  dentate, 
  that 
  of 
  the 
  internal 
  

   and 
  paliform 
  lobe 
  being 
  less 
  so. 
  The 
  septa 
  of 
  the 
  first 
  three 
  cycles 
  

   are 
  equal, 
  and 
  reach 
  to 
  and 
  bound 
  the 
  fossula 
  ; 
  they 
  are 
  distinctly 
  

  

  