﻿24 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Nov. 
  18, 
  

  

  very 
  slightly 
  indented 
  in 
  more 
  than 
  one 
  spot. 
  Costae 
  converge 
  from 
  

   the 
  calice 
  to 
  the 
  pedicel, 
  are 
  very 
  distinct 
  and 
  crowded, 
  those 
  of 
  the 
  

   higher 
  orders 
  not 
  reaching 
  far 
  down, 
  all 
  nearly 
  equal 
  and 
  linear 
  ; 
  

   they 
  are 
  convex 
  and 
  not 
  papillated. 
  Epitheca 
  almost 
  rudimentary. 
  

   Height 
  probably 
  2 
  inches 
  ; 
  length 
  1^- 
  inch 
  ; 
  breadth 
  -^ 
  inch. 
  

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

  

  Variety 
  3. 
  — 
  Corallum 
  small 
  and 
  heavy. 
  Costae 
  converging 
  and 
  

   granular. 
  Epitheca 
  well 
  developed, 
  and 
  marked 
  by 
  series 
  of 
  granules 
  

   (3 
  or 
  4) 
  over 
  the 
  path 
  of 
  the 
  costae, 
  where 
  these 
  are 
  not 
  produced. 
  

  

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

  

  Variety 
  4. 
  — 
  A 
  form 
  intermediate 
  between 
  the 
  type 
  and 
  variety 
  3. 
  

   It 
  has 
  a 
  large 
  corallum 
  and 
  an 
  indented 
  calice, 
  which 
  is 
  very 
  open, 
  

   and 
  the 
  pali 
  are 
  indistinct. 
  Epitheca 
  well 
  developed. 
  

  

  Erom 
  the 
  silt 
  of 
  the 
  Sandstone 
  plain, 
  San 
  Domingo. 
  Coll. 
  Geol. 
  Soc. 
  

  

  The 
  next 
  species 
  has 
  a 
  greater 
  affinity 
  with 
  the 
  recent 
  Placocyathus 
  

   apertus, 
  Edwards 
  & 
  Haime, 
  than 
  any 
  other 
  of 
  the 
  genus 
  ; 
  but 
  the 
  

   structural 
  differences 
  are 
  specific. 
  Mr. 
  Lonsdale 
  has 
  described 
  it 
  as 
  

   " 
  Placocyathus, 
  species 
  2." 
  It 
  differs 
  from 
  the 
  var. 
  2 
  of 
  P. 
  Barretti, 
  

   nob. 
  (Foss. 
  Cor. 
  West. 
  Ind., 
  &c, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xix. 
  

   p. 
  428), 
  in 
  having 
  more 
  prominent 
  and 
  subcristiform 
  costae. 
  

  

  4. 
  Placocyathus 
  costatus, 
  spec. 
  nov. 
  PL 
  II. 
  figs. 
  3 
  a, 
  3 
  b. 
  

   Placocyathus, 
  species 
  2, 
  Lonsdale 
  MS. 
  

  

  **Corallum 
  nabeHiform, 
  compressed, 
  curved 
  in 
  the 
  direction 
  of 
  the 
  

   major 
  axis, 
  especially 
  inferiorly, 
  and 
  finely 
  pedicellated. 
  It 
  is 
  marked 
  

   by 
  irregular 
  lines 
  of 
  growth. 
  The 
  sides 
  are 
  lobed 
  unequally, 
  and 
  

   they 
  expand 
  rapidly 
  in 
  the 
  upper 
  half 
  of 
  the 
  specimen. 
  The 
  extre- 
  

   mities 
  are 
  irregularly 
  rounded, 
  and 
  diverge 
  greatly 
  as 
  well 
  as 
  sud- 
  

   denly 
  in 
  their 
  upward 
  range. 
  Pedicel 
  small. 
  Calicular 
  margin 
  hori- 
  

   zontal, 
  and 
  with 
  a 
  wavy 
  lobed 
  outline. 
  Calice 
  irregularly 
  elliptical, 
  

   and 
  widely 
  open 
  at 
  the 
  extremities, 
  but 
  less 
  so 
  midway. 
  Septa 
  

   numerous, 
  crowded, 
  often 
  wavy, 
  thin, 
  broad, 
  rounded, 
  and 
  but 
  little 
  

   exsert 
  ; 
  in 
  six 
  systems 
  of 
  six 
  cycles, 
  the 
  orders 
  of 
  a 
  seventh 
  being 
  

   occasionally 
  noticed. 
  Septa 
  of 
  the 
  first, 
  second, 
  and 
  third 
  cycles 
  

   nearly 
  equal, 
  those 
  of 
  the 
  fourth 
  narrower 
  and 
  thinner 
  ; 
  those 
  of 
  

   the 
  higher 
  order 
  are 
  small, 
  in 
  accordance 
  with 
  their 
  rule. 
  Laminae 
  

   very 
  little 
  thicker 
  at 
  the 
  wall 
  than 
  elsewhere, 
  granulated 
  laterally 
  

   and 
  on 
  the 
  free 
  rounded 
  margin. 
  Pali 
  rounded, 
  small, 
  thin, 
  and 
  

   irregularly 
  developed; 
  very 
  generally 
  placed 
  before 
  the 
  penultimate, 
  

   and 
  rarely 
  before 
  the 
  antepenultimate 
  series. 
  The 
  columella 
  is 
  a 
  

   thin 
  granulated 
  plate 
  with 
  an 
  undulating 
  edge, 
  and 
  is 
  very 
  feebly 
  

   developed. 
  The 
  costae, 
  except 
  those 
  of 
  the 
  higher 
  orders, 
  are 
  sharp 
  

   from 
  the 
  point 
  of 
  their 
  appearance 
  or 
  interpolation; 
  the 
  largest 
  

   are 
  visible 
  throughout 
  and 
  are 
  subcristiform; 
  the 
  lateral 
  costae 
  

   are 
  not 
  more 
  developed 
  than 
  the 
  others 
  ; 
  all 
  are 
  somewhat 
  wavy, 
  

   and, 
  where 
  not 
  abraded, 
  are 
  granular. 
  The 
  varying 
  length 
  of 
  the 
  

   costae 
  is 
  remarkable 
  : 
  the 
  principal 
  project 
  slightly 
  at 
  the 
  calicular 
  

   margin, 
  Epitheca 
  pellicular 
  and 
  papillated. 
  The 
  wall 
  is 
  dense 
  

  

  