﻿486 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  " 
  This 
  Urchin 
  is 
  not 
  uncommon 
  in 
  the 
  upper 
  portion 
  of 
  No. 
  5. 
  The 
  

   different 
  colouring 
  of 
  the 
  tests 
  is 
  the 
  result 
  of 
  the 
  colour 
  of 
  the 
  rock. 
  

   The 
  white 
  specimens 
  were 
  from 
  the 
  white 
  stratum 
  ; 
  the 
  reddish 
  from 
  

   the 
  red 
  coralline 
  limestone 
  above 
  the 
  red 
  sand, 
  where 
  the 
  two 
  blend 
  

   almost 
  imperceptibly 
  ; 
  the 
  darker, 
  from 
  the 
  soft 
  drab-coloured 
  rock, 
  

   often 
  found 
  overlying 
  the 
  clay, 
  where 
  No. 
  2 
  is 
  seemingly 
  wanting. 
  

   The 
  bed 
  No. 
  2 
  is 
  not 
  apparently 
  uniformly 
  distributed 
  over 
  the 
  

   Island. 
  

  

  " 
  I 
  have 
  not 
  hitherto 
  met 
  with 
  this 
  Urchin 
  in 
  any 
  of 
  the 
  other 
  

   beds." 
  (A. 
  L. 
  A.) 
  

  

  Collections. 
  — 
  Museum 
  of 
  the 
  Royal 
  School 
  of 
  Mines 
  and 
  of 
  the 
  

   Geological 
  Society 
  ; 
  Marquis 
  of 
  Northampton's, 
  the 
  Earl 
  of 
  Ducie's, 
  

   and 
  my 
  cabinet. 
  

  

  29. 
  Brissus 
  imbricatus, 
  Wright. 
  PI. 
  XXII. 
  fig. 
  2. 
  

  

  Affinities 
  and 
  differences. 
  — 
  It 
  differs 
  from 
  all 
  the 
  preceding 
  species 
  

   in 
  having 
  the 
  anterior 
  pair 
  of 
  petaloid 
  ambulacra 
  directed 
  obliquely 
  

   forwards 
  and 
  outwards, 
  and 
  with 
  the 
  posterior 
  pair 
  forming 
  a 
  St. 
  

   Andrew's 
  cross 
  on 
  the 
  dorsum 
  or 
  upper 
  surface. 
  It 
  differs 
  from 
  

   Brissus 
  Scillce 
  in 
  having 
  a 
  depressed 
  test, 
  with 
  the 
  base 
  much 
  more 
  

   highly 
  ornamented, 
  and 
  likewise 
  in 
  the 
  direction 
  of 
  the 
  anterior 
  

   ambulacra. 
  

  

  Stratigraphical 
  position. 
  — 
  Both 
  specimens 
  were 
  collected 
  from 
  bed 
  

   No. 
  1, 
  the 
  Upper 
  Limestone, 
  at 
  Malta. 
  

  

  Collections. 
  — 
  The 
  Bristol 
  Museum 
  contains 
  the 
  type, 
  and 
  the 
  Mu- 
  

   seum 
  of 
  the 
  Geological 
  Society 
  of 
  London 
  the 
  most 
  perfect 
  specimen. 
  

  

  30. 
  Brissus 
  tuberculatus, 
  Wright, 
  sp. 
  no 
  v. 
  PL 
  XXII. 
  fig. 
  1. 
  

  

  Test 
  ovoid, 
  depressed, 
  tapering 
  behind 
  ; 
  the 
  two 
  pairs 
  of 
  petaloid 
  

   ambulacra 
  long, 
  narrow, 
  lanceolate, 
  and 
  extending 
  over 
  two-thirds 
  

   of 
  the 
  dorsum 
  ; 
  anterior 
  pair 
  curved 
  forwards, 
  posterior 
  pair 
  directed 
  

   outwards 
  and 
  backwards 
  ; 
  poriferous 
  zones 
  wide, 
  depressed 
  ; 
  inter- 
  

   poriferous 
  zone 
  convex 
  ; 
  peripetalous 
  fasciole 
  narrow 
  ; 
  anterior 
  border, 
  

   sides, 
  and 
  upper 
  surface, 
  within 
  and 
  without 
  the 
  peripetalous 
  fasciole, 
  

   covered 
  with 
  large 
  crenulated 
  and 
  perforated 
  tubercles, 
  among 
  which 
  

   smaller 
  ones 
  are 
  scattered 
  ; 
  no 
  an 
  teal 
  sulcus 
  ; 
  posterior 
  border 
  slightly 
  

   truncated 
  ; 
  vent 
  large, 
  oblong 
  ; 
  subanal 
  fasciole 
  having 
  a 
  cordate 
  

   figure 
  beneath 
  the 
  opening. 
  

  

  Dimensions. 
  — 
  Length 
  5 
  inches 
  ; 
  breadth 
  4| 
  inches. 
  

  

  These 
  measurements 
  are 
  only 
  approximate, 
  as 
  the 
  two 
  specimens 
  I 
  

   have 
  are 
  both 
  much 
  distorted. 
  

  

  Affinities 
  and 
  differences. 
  — 
  This 
  species 
  differs 
  from 
  all 
  the 
  other 
  

   Miocene 
  species 
  of 
  Brissus 
  in 
  having 
  much 
  larger 
  tubercles 
  on 
  its 
  upper 
  

   surface 
  : 
  from 
  B. 
  latus, 
  Wright, 
  in 
  having 
  the 
  ambulacra 
  level 
  with 
  

   the 
  surface, 
  and 
  no 
  anteal 
  sulcus 
  ; 
  the 
  same 
  characters 
  distin- 
  

   guish 
  it 
  from 
  B. 
  cylindricus, 
  Ag. 
  ; 
  and 
  it 
  differs 
  from 
  B. 
  imbricatus, 
  

   Wright, 
  in 
  having 
  large 
  tubercles 
  without 
  as 
  well 
  as 
  within 
  the 
  peripe- 
  

   talous 
  fasciole. 
  The 
  tuberculated 
  character 
  of 
  the 
  upper 
  surface 
  is 
  a 
  

   good 
  diagnostic 
  character. 
  The 
  imperfection 
  of 
  the 
  only 
  two 
  frag- 
  

   ments 
  I 
  possess 
  prevents 
  a 
  more 
  extended 
  comparison 
  with 
  other 
  forms. 
  

  

  