﻿476 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  middle 
  of 
  the 
  areas 
  ; 
  interambulacra 
  with 
  two 
  rows 
  of 
  primary 
  

   tubercles 
  on 
  the 
  centre 
  of 
  the 
  plates, 
  and 
  one 
  short 
  irregular 
  row 
  

   of 
  secondary 
  tubercles 
  on 
  each 
  side 
  of 
  the 
  primaries 
  ; 
  base 
  convex, 
  

   peristome 
  small. 
  

  

  Dimensions. 
  — 
  Height 
  1 
  inch 
  and 
  1 
  line 
  ; 
  transverse 
  diameter 
  1| 
  

   inch. 
  

  

  Description. 
  — 
  The 
  globular 
  form 
  of 
  this 
  Urchin, 
  with 
  the 
  few 
  rows 
  

   of 
  primary 
  tubercles 
  on 
  the 
  interambulacra, 
  seem 
  to 
  indicate 
  that 
  it 
  

   was 
  a 
  large 
  individual 
  of 
  this 
  species 
  which 
  Scilla 
  figured 
  in 
  the 
  

   plates 
  already 
  referred 
  to. 
  The 
  ambulacral 
  tubercles 
  are 
  uniform 
  

   in 
  size 
  and 
  placed 
  on 
  the 
  margin 
  of 
  the 
  areas 
  ; 
  within 
  these 
  only 
  

   a 
  very 
  few 
  small 
  tubercles 
  are 
  irregularly 
  scattered 
  ; 
  there 
  are 
  in 
  

   reality 
  only 
  two 
  rows 
  of 
  primary 
  tubercles 
  in 
  the 
  interambulacra, 
  

   for 
  all 
  the 
  others 
  are 
  of 
  secondary 
  size 
  and 
  limited 
  to 
  a 
  portion 
  of 
  

   the 
  area 
  ; 
  of 
  these, 
  the 
  rows 
  between 
  the 
  primary 
  tubercles 
  and 
  the 
  

   poriferous 
  zones 
  contain 
  the 
  smallest, 
  and 
  the 
  two 
  rows 
  near 
  the 
  

   median 
  suture 
  the 
  largest 
  secondary 
  tubercles. 
  

  

  Affinities 
  and 
  differences. 
  — 
  The 
  globular 
  form 
  of 
  the 
  test 
  and 
  the 
  

   sparseness 
  of 
  its 
  tubercles 
  readily 
  distinguish 
  it 
  from 
  P. 
  Duciei, 
  Wr. 
  

  

  StratigrapJiical 
  position. 
  — 
  It 
  was 
  collected 
  from 
  bed 
  No. 
  1, 
  the 
  

   Upper 
  Limestone 
  at 
  Malta, 
  where 
  it 
  appears 
  to 
  be 
  rare. 
  

  

  Genus 
  Cltpeaster, 
  Lamarck, 
  1801. 
  

  

  Eorm 
  oval, 
  inclining 
  to 
  pentagonal, 
  rostrated 
  before, 
  truncated 
  

   Tbehind 
  ; 
  upper 
  surface 
  more 
  or 
  less 
  inflated, 
  sometimes 
  campanulate, 
  

   eonieal 
  or 
  subcorneal 
  ; 
  inferior 
  surface 
  flat, 
  always 
  concave 
  around 
  

   the 
  mouth, 
  with 
  fine 
  straight 
  simple 
  ambulacral 
  furrows 
  proceeding 
  

   from 
  the 
  angles 
  of 
  the 
  mouth 
  to 
  the 
  border. 
  Dorsal 
  ambulacra 
  

   largely 
  petaloidal, 
  greatly 
  exceeding 
  the 
  interambulacra 
  in 
  size, 
  and 
  

   forming 
  elegant 
  leaf-like 
  expansions, 
  in 
  general 
  convex, 
  arched, 
  and 
  

   prominent, 
  bounded 
  on 
  each 
  side 
  by 
  wide 
  poriferous 
  zones, 
  the 
  holes 
  

   of 
  which 
  are 
  set 
  far 
  apart 
  and 
  united 
  by 
  transverse 
  sulci. 
  Apical 
  

   disk 
  small, 
  formed 
  of 
  five 
  genital 
  and 
  five 
  ocular 
  plates. 
  Madrepori- 
  

   form 
  body 
  central, 
  and 
  covering 
  over 
  the 
  other 
  elements 
  of 
  the 
  disc 
  

   with 
  its 
  spongy 
  tissue. 
  Tubercles 
  small, 
  numerous, 
  uniform 
  in 
  

   :size, 
  and 
  equally 
  distributed 
  over 
  the 
  test, 
  those 
  on 
  the 
  upper 
  being- 
  

   smaller 
  than 
  those 
  on 
  the 
  under 
  surface 
  ; 
  summits 
  perforated, 
  and 
  

   surrounded 
  by 
  deep 
  areolas. 
  Mouth 
  S3 
  r 
  mmetrical, 
  central, 
  penta- 
  

   gonal, 
  lodged 
  in 
  a 
  concave 
  depression 
  in 
  the 
  middle 
  of 
  the 
  base. 
  

   Auricles 
  composed 
  of 
  ten 
  distinct 
  processes 
  set 
  in 
  pairs 
  : 
  the 
  jaws 
  re- 
  

   semble 
  a 
  pentagonal 
  pyramid 
  composed 
  of 
  ten 
  separate 
  pieces 
  united 
  

   in 
  pairs 
  to 
  form 
  the 
  five 
  jaws 
  ; 
  they 
  contain 
  five 
  large 
  teeth 
  enamelled 
  

   on 
  the 
  outer 
  surface 
  and 
  lodged 
  in 
  a 
  groove 
  formed 
  between 
  the 
  two 
  

   halves 
  of 
  each 
  jaw. 
  Anus 
  small, 
  round, 
  and 
  inframarginal. 
  Interior 
  

   of 
  the 
  test 
  with 
  a 
  number 
  of 
  pillar-like 
  processes 
  towards 
  the 
  border. 
  

  

  All 
  the 
  great 
  divisions 
  of 
  the 
  globe 
  contain 
  a 
  certain 
  number 
  of 
  

   Oypeasters. 
  In 
  Europe 
  they 
  are 
  found 
  only 
  in 
  a 
  fossil 
  state, 
  while 
  

   in 
  Asia, 
  Africa, 
  America, 
  and 
  Oceania 
  both 
  living 
  and 
  fossil 
  species 
  

   tire 
  found. 
  The 
  fossil 
  European 
  species 
  characterize 
  the 
  Miocene 
  

   deposits 
  of 
  the 
  great 
  Mediterranean 
  basin, 
  especially 
  those 
  of 
  the 
  

  

  