﻿1874.] 
  ' 
  Challenger 
  ' 
  Soundings 
  in 
  the 
  Southern 
  Sea. 
  37 
  

  

  Globigerina, 
  Orbulina 
  is 
  most 
  fully 
  developed 
  and 
  most 
  abundant 
  in 
  the 
  

   warmer 
  seas. 
  

  

  Associated 
  with 
  these 
  forms, 
  and, 
  like 
  them, 
  living 
  on 
  the 
  surface, 
  and 
  

   dead, 
  with 
  their 
  shells 
  in 
  various 
  stages 
  of 
  decay, 
  at 
  the 
  bottom, 
  

   there 
  are 
  two 
  very 
  marked 
  species 
  or 
  varieties 
  of 
  Pulvinulina, 
  P. 
  Menardii, 
  

   and 
  P. 
  Micheliniana. 
  The 
  general 
  structure 
  of 
  Pulvinulina 
  resembles 
  

   that 
  of 
  Globigerina. 
  The 
  shell 
  consists 
  of 
  a 
  congeries 
  of 
  from 
  five 
  to 
  eight 
  

   chambers 
  arranged 
  in 
  an 
  irregular 
  spiral. 
  As 
  in 
  Globigerina, 
  the 
  last 
  

   chamber 
  is 
  the 
  largest 
  ; 
  the 
  inner 
  smaller 
  chambers 
  are 
  usually 
  filled 
  

   with 
  yellow 
  sarcode 
  ; 
  and, 
  as 
  in 
  Globigerina, 
  the 
  last 
  chamber 
  is 
  frequently 
  

   nearly 
  empty, 
  a 
  small 
  irregular 
  mass 
  of 
  sarcode 
  only 
  occupying 
  a 
  part 
  of 
  

   the 
  cavity. 
  The 
  walls 
  of 
  the 
  chambers 
  are 
  closely 
  and 
  minutely 
  per- 
  

   forated. 
  The 
  external 
  surface 
  of 
  the 
  wall 
  is 
  nearly 
  smooth, 
  and 
  no 
  trace 
  

   of 
  a 
  spine 
  has 
  ever 
  been 
  detected. 
  Pulvinulina 
  Menardii 
  (PI. 
  III. 
  fig. 
  1) 
  

   has 
  a 
  large 
  discoiclal 
  depressed 
  shell, 
  consisting 
  of 
  a 
  series 
  of 
  flat 
  

   chambers 
  overlappiug 
  one 
  another, 
  like 
  a 
  number 
  of 
  coins 
  laid 
  down 
  

   somewhat 
  irregularly, 
  but 
  generally 
  in 
  a 
  spiral 
  ; 
  each 
  chamber 
  is 
  bordered 
  

   by 
  a 
  distinct 
  somewhat 
  thickened 
  solid 
  rim 
  of 
  definite 
  width. 
  On 
  the 
  lower 
  

   surface 
  of 
  the 
  shell 
  the 
  intervals 
  between 
  the 
  chambers 
  are 
  indicated 
  by 
  

   deep 
  grooves. 
  The 
  large 
  irregular 
  opening 
  of 
  the 
  final 
  chamber 
  is 
  pro- 
  

   tected 
  by 
  a 
  crescentic 
  lip, 
  which 
  in 
  some 
  specimens 
  bears 
  a 
  fringe 
  of 
  

   spine-like 
  papillaD. 
  This 
  form 
  is 
  almost 
  confined 
  to 
  the 
  warmer 
  seas. 
  It 
  

   is 
  very 
  abundant 
  on 
  the 
  surface, 
  and 
  still 
  more 
  so 
  during 
  the 
  day, 
  at 
  a 
  

   depth 
  of 
  ten 
  to 
  twenty 
  fathoms 
  in 
  the 
  Mid- 
  Atlantic 
  ; 
  and 
  it 
  enters 
  into 
  

   the 
  composition 
  of 
  the 
  very 
  characteristic 
  " 
  Globigerina-ooz^'' 
  of 
  the 
  

   " 
  Dolphine 
  Rise 
  " 
  in 
  almost 
  as 
  large 
  proportions 
  as 
  Globigerina. 
  Pulvinu- 
  

   lina 
  Micheliniana 
  is 
  a 
  smaller 
  variety 
  ; 
  the 
  upper 
  surface 
  of 
  the 
  shell 
  is 
  

   flattened 
  as 
  in 
  P. 
  Menardii, 
  but 
  the 
  chambers 
  are 
  conical 
  and 
  prolonged 
  

   downwards, 
  so 
  that 
  the 
  shell 
  is 
  deeper 
  and 
  somewhat 
  turbinate. 
  The 
  

   two 
  species 
  usually 
  occur 
  together 
  ; 
  but 
  P. 
  Micheliniana 
  has 
  apparently 
  a 
  

   much 
  wider 
  distribution 
  than 
  P. 
  Menardii 
  ; 
  for 
  while 
  the 
  latter 
  was 
  

   limited 
  to 
  the 
  region 
  of 
  the 
  trade-winds 
  and 
  the 
  equatorial 
  drift 
  current, 
  

   and 
  was 
  found 
  rarely 
  if 
  at 
  all 
  to 
  the 
  south 
  of 
  the 
  Agulhas 
  current, 
  the 
  

   former 
  accompanied 
  us 
  southward 
  as 
  far 
  as 
  Kerguelen 
  Land. 
  Both 
  forms 
  

   of 
  Pulvinulina, 
  however, 
  are 
  more 
  restricted 
  than 
  Globigerina 
  ; 
  for 
  even 
  

   P. 
  Micheliniana 
  became 
  scarce 
  after 
  leaving 
  the 
  Cape, 
  and 
  the 
  wonderfully 
  

   pure 
  calcareous 
  formation 
  in 
  the 
  neighbourhood 
  of 
  Prince 
  Edward 
  

   Island 
  and 
  #Le 
  Crozets 
  consists 
  almost 
  solely 
  of 
  Globigerina 
  bulloides, 
  

   and 
  neither 
  species 
  of 
  Pulvinulina 
  occurred 
  to 
  the 
  south 
  of 
  Kerguelen 
  

   Land. 
  

  

  Over 
  a 
  very 
  large 
  part 
  of 
  the 
  " 
  Globigerina-ooze 
  " 
  area, 
  and 
  especially 
  

   in 
  those 
  intertropical 
  regions 
  in 
  which 
  the 
  formation 
  is 
  most 
  charac- 
  

   teristically 
  developed, 
  although 
  the 
  great 
  bulk 
  of 
  the 
  ooze 
  is 
  made 
  up 
  of 
  

   entire 
  shells 
  and 
  fragments 
  of 
  shells 
  of 
  the 
  above-described 
  fora- 
  

   minifera, 
  there 
  is 
  frequently 
  a 
  considerable 
  proportion 
  (amounting 
  in 
  

  

  