﻿1863.] 
  DUNCAN 
  WEST 
  INDIAN 
  CORALS. 
  35 
  

  

  mounted 
  by 
  a 
  single 
  row 
  of 
  transversely 
  compressed 
  tubercles 
  — 
  the 
  

   upward 
  terminations 
  of 
  the 
  rows 
  of 
  lateral 
  papillae. 
  The 
  inner 
  edge 
  

   does 
  not 
  abut 
  against 
  the 
  columella 
  in 
  general, 
  being 
  separated, 
  for 
  

   the 
  greater 
  part, 
  from 
  it 
  by 
  an 
  interspace." 
  The 
  sides 
  of 
  the 
  lamellae 
  

   constantly 
  present 
  arched 
  fractured 
  laminae. 
  Fragments 
  of 
  the 
  endo- 
  

   theca, 
  and 
  the 
  vesicular 
  areas 
  bounded 
  by 
  them, 
  are 
  beset 
  with 
  

   papillae, 
  in 
  general 
  irregularly 
  distributed, 
  but 
  sometimes 
  arranged 
  

   in 
  curved 
  ascending 
  rows. 
  Out 
  of 
  the 
  range 
  of 
  the 
  endotheca 
  the 
  

   papillae 
  are 
  arranged 
  in 
  ascending 
  series 
  which 
  appear 
  to 
  radiate 
  

   from 
  below. 
  The 
  interseptal 
  loculi 
  exceed 
  the 
  lamellae 
  in 
  thickness, 
  

   and 
  are 
  crossed 
  by 
  the 
  dissepiments 
  of 
  the 
  endotheca. 
  Columella 
  : 
  

   where 
  well 
  seen 
  it 
  is 
  essential, 
  lamellar, 
  thick, 
  perforated 
  here 
  and 
  

   there, 
  and 
  connected 
  with 
  the 
  septa 
  by 
  small 
  dissepiments. 
  

  

  Wall 
  : 
  it 
  consists 
  of 
  a 
  solid 
  layer 
  which 
  crosses 
  the 
  interseptal 
  

   loculi 
  j 
  its 
  thickness 
  is 
  variable 
  but 
  never 
  great, 
  and 
  sometimes 
  the 
  

   layer 
  is 
  rudimentary, 
  indistinct, 
  or 
  wanting. 
  In 
  vertical 
  sections 
  

   a 
  perpendicular 
  layer, 
  more 
  or 
  less 
  continuous, 
  occurs 
  about 
  T 
  L 
  inch 
  

   from 
  the 
  exterior, 
  and 
  is 
  flanked 
  on 
  each 
  side 
  by 
  a 
  vesicular 
  struc- 
  

   ture 
  ; 
  it 
  is 
  sometimes 
  wanting 
  altogether, 
  or 
  is 
  represented 
  by 
  

   detached 
  points. 
  Endotheca 
  and 
  exotheca 
  : 
  " 
  these 
  structures 
  are 
  

   noticed 
  conjointly 
  on 
  account 
  of 
  the 
  position 
  they 
  occupy. 
  The 
  endo- 
  

   theca 
  consists 
  of 
  numerous 
  arched 
  laminae, 
  and 
  presents, 
  in 
  vertical 
  

   sections, 
  a 
  vesicular 
  composition 
  over 
  the 
  whole 
  surface, 
  from 
  the 
  

   columella 
  to 
  the 
  wall. 
  They 
  are 
  inclined 
  downwards 
  and 
  inwards. 
  

   Their 
  outline 
  and 
  extent 
  are 
  irregular. 
  The 
  exotheca 
  resembles 
  

   structurally 
  the 
  endotheca, 
  but 
  is, 
  of 
  course, 
  outside 
  the 
  thin 
  wall, 
  

   and 
  the 
  dissepiments 
  are 
  inclined 
  externally," 
  the 
  vesicles 
  dipping 
  in 
  

   an 
  opposite 
  direction 
  to 
  those 
  of 
  the 
  endotheca. 
  The 
  exothecal 
  disse- 
  

   piments 
  enclose 
  spaces 
  of 
  various 
  sizes, 
  extend 
  to 
  the 
  costal 
  edge, 
  

   and 
  often 
  completely 
  fill 
  up 
  the 
  intercostal 
  spaces 
  to 
  the 
  level 
  of 
  the 
  

   costae. 
  " 
  The 
  costae 
  radiate 
  in 
  every 
  direction 
  from 
  the 
  small 
  base, 
  

   and 
  extend 
  along 
  the 
  under 
  surface, 
  conforming 
  to 
  its 
  outline 
  ; 
  but 
  

   they 
  bend 
  upwards 
  on 
  arriving 
  at 
  the 
  margin 
  of 
  the 
  sides 
  and 
  ex- 
  

   tremities 
  — 
  ranging 
  thence 
  to 
  the 
  summit 
  in 
  closely 
  set 
  parallel 
  fine 
  

   ridges, 
  crested 
  with 
  a 
  single 
  row 
  of 
  transversely 
  compressed 
  tubercles. 
  

   The 
  thickness 
  of 
  the 
  costae 
  and 
  their 
  equivalent 
  septa 
  is 
  equal 
  ; 
  it 
  is 
  

   greatest 
  at 
  the 
  wall 
  and 
  least 
  at 
  the 
  free 
  edge. 
  Their 
  sides 
  are 
  

   marked 
  by 
  the 
  exotheca, 
  and 
  often 
  by 
  papillae." 
  

  

  " 
  Epitheca 
  : 
  this 
  structure 
  is 
  best 
  shown 
  on 
  the 
  under 
  surface, 
  but 
  

   patches 
  of 
  it 
  occur 
  on 
  the 
  sides 
  and 
  near 
  the 
  calicular 
  margin. 
  In 
  

   the 
  first-mentioned 
  area 
  it 
  presents 
  a 
  solid, 
  thickish, 
  detachable 
  layer 
  

   (membraniform), 
  elliptically 
  rugose, 
  and 
  marked 
  by 
  minor 
  lines 
  of 
  

   increment, 
  and 
  in 
  the 
  best-preserved 
  portions 
  the 
  subjacent 
  costae 
  are 
  

   barely 
  visible. 
  On 
  the 
  sides 
  it 
  is 
  thinner, 
  and 
  the 
  range 
  of 
  the 
  ribs 
  

   is 
  evident. 
  Reproduction 
  fissiparous." 
  Height 
  ly 
  6 
  ^ 
  inch 
  ; 
  length 
  

   5 
  inches; 
  breadth 
  -^ 
  inch 
  ; 
  16 
  large 
  and 
  11 
  rudimentary 
  septa 
  in 
  

   -j^- 
  inch 
  ; 
  from 
  2 
  to 
  3 
  endothecal 
  vesicles 
  in 
  J$ 
  inch 
  ; 
  costae 
  project 
  

   T 
  L 
  inch. 
  

  

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

  

  d2 
  

  

  