﻿38 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [NoV. 
  18, 
  

  

  marked 
  by 
  costae 
  covered 
  with 
  a 
  thin 
  and 
  very 
  granular 
  epitheca 
  ; 
  

   the 
  calices 
  are 
  generally 
  equal 
  in 
  size, 
  and 
  are 
  more 
  numerous 
  above 
  

   than 
  at 
  the 
  sides, 
  where 
  their 
  costal 
  prolongations, 
  more 
  or 
  less 
  

   covered 
  by 
  epitheca, 
  reach 
  downwards 
  to 
  the 
  base. 
  Septa 
  crowded 
  

   and 
  very 
  slightly 
  exsert 
  ; 
  those 
  of 
  the 
  first 
  and 
  second 
  orders 
  are 
  sub- 
  

   equal, 
  and 
  are 
  thicker 
  at 
  the 
  wall 
  than 
  at 
  the 
  columella 
  ; 
  all 
  have 
  

   lateral 
  spiniform 
  granules, 
  and 
  the 
  tertiary 
  orders 
  rarely 
  curve 
  to- 
  

   wards 
  the 
  secondary. 
  In 
  six 
  systems 
  of 
  three 
  cycles, 
  with 
  occasionally 
  

   a 
  septum 
  of 
  the 
  fourth 
  cycle 
  interpolated. 
  Pali 
  wedge-shaped 
  and 
  

   subequal, 
  placed 
  before 
  the 
  primary 
  and 
  secondary 
  septa. 
  Colu- 
  

   mella 
  papillary. 
  Calicular 
  fossa 
  very 
  shallow. 
  Costae 
  subequal 
  at 
  

   the 
  surface, 
  extending 
  on 
  to 
  the 
  intercalicular 
  space, 
  and 
  covered 
  

   with 
  a 
  finely 
  and 
  profusely 
  granular 
  epitheca 
  ; 
  they 
  appear 
  large 
  in 
  

   relation 
  to 
  the 
  septa, 
  and 
  are 
  separated 
  by 
  linear 
  grooves. 
  In 
  trans- 
  

   verse 
  sections, 
  and 
  in 
  vertical 
  views 
  of 
  fractured 
  corallites, 
  the 
  costae 
  

   are 
  seen 
  to 
  be 
  very 
  small, 
  and 
  to 
  be 
  represented 
  by 
  longitudinal 
  

   series 
  of 
  sharp 
  granules 
  ; 
  their 
  appearance 
  on 
  the 
  surface 
  is 
  accounted 
  

   for 
  by 
  the 
  great 
  development 
  of 
  the 
  exothecal 
  tissue, 
  which 
  consti- 
  

   tutes, 
  as 
  in 
  the 
  genus 
  Solenastrcea, 
  the 
  means 
  of 
  corallite 
  junction. 
  

   Occasionally 
  the 
  exothecal 
  cells, 
  which 
  are 
  convex 
  above, 
  appear 
  to 
  

   form 
  dense 
  transverse 
  bands. 
  The 
  endotheca 
  is 
  delicate 
  ; 
  the 
  dissepi- 
  

   ments 
  are 
  but 
  slightly 
  inclined, 
  and 
  extend 
  well 
  to 
  the 
  columella. 
  

   The 
  laminae 
  of 
  the 
  septa 
  are 
  very 
  granular. 
  The 
  wall 
  is 
  distinct 
  and 
  

   well 
  developed. 
  Height 
  of 
  corallum 
  l 
  T 
  8 
  yinch; 
  diameter 
  of 
  calices 
  -Af 
  

   inch 
  ; 
  distance 
  between 
  calices 
  -^ 
  (more 
  or 
  less) 
  inch. 
  

  

  From 
  the 
  silt 
  of 
  the 
  Sandstone 
  plain, 
  San 
  Domingo. 
  Coll. 
  Geol. 
  

   Soc. 
  

  

  23. 
  Plesiastr^a 
  globosa, 
  spec. 
  nov. 
  PI. 
  IV. 
  fig. 
  5. 
  

  

  Corallum 
  globose 
  and 
  large, 
  with 
  a 
  small 
  base. 
  Calices 
  close, 
  but 
  

   not 
  crowded, 
  circular, 
  and 
  but 
  very 
  little 
  above 
  the 
  surface, 
  equally 
  

   distributed 
  over 
  the 
  whole 
  corallum, 
  and 
  very 
  equal 
  in 
  size. 
  Septa 
  but 
  

   slightly 
  exsert, 
  largest 
  at 
  the 
  wall, 
  granular 
  on 
  the 
  sides, 
  slightly 
  den- 
  

   tate 
  above 
  and 
  unequal. 
  In 
  six 
  systems 
  of 
  three 
  cycles, 
  the 
  primary 
  

   and 
  secondary 
  reaching 
  the 
  columella 
  and 
  having 
  small 
  pali, 
  whilst 
  

   the 
  tertiary 
  do 
  not 
  extend 
  so 
  far. 
  The 
  costae 
  are 
  subequal, 
  short, 
  

   and 
  covered 
  with 
  epitheca, 
  which 
  is 
  hardly 
  granular. 
  In 
  transverse 
  

   sections 
  they 
  are 
  small 
  but 
  not 
  granular. 
  Columella 
  lax, 
  but 
  pa- 
  

   pillary 
  above. 
  Fossa 
  deeper 
  than 
  in 
  the 
  last 
  species. 
  Exotheca 
  

   cellular, 
  connecting 
  the 
  corallites, 
  but 
  not 
  so 
  abundant 
  as 
  in 
  the 
  last 
  

   form. 
  Endotheca 
  very 
  scanty. 
  The 
  epitheca 
  covers-in 
  the 
  inter- 
  

   calicular 
  spaces, 
  and 
  often 
  has 
  a 
  groove 
  in 
  it 
  midway 
  between 
  the 
  

   calices. 
  The 
  youngest 
  corallites 
  have 
  twelve 
  equally 
  developed 
  septa. 
  

   Height 
  of 
  corallum 
  34- 
  inches 
  ; 
  diameter 
  of 
  calices 
  -JL- 
  inch 
  ; 
  width 
  of 
  

   intercalicular 
  spaces 
  ^L. 
  i 
  ncn# 
  

  

  From 
  the 
  silt 
  of 
  the 
  Sandstone 
  plain, 
  San 
  Domingo. 
  Coll. 
  Geol. 
  

   Soc. 
  

  

  Several 
  specimens 
  are 
  semifossil, 
  and 
  in 
  one 
  the 
  formation 
  of 
  casts 
  

   has 
  been 
  completed. 
  

  

  