﻿44 
  THE 
  ZOOLOGIST. 
  

  

  it 
  has 
  to 
  be 
  remembered 
  that 
  it 
  was 
  formerly 
  known 
  in 
  the 
  

   eastern 
  part 
  of 
  that 
  sea 
  and 
  off 
  Morocco.* 
  Besides 
  the 
  fore- 
  

   going, 
  pearl 
  fisheries 
  are 
  also 
  carried 
  on 
  in 
  the 
  Gulf 
  of 
  Mexico, 
  

   various 
  contiguous 
  islands, 
  in 
  Panama, 
  and 
  California. 
  The 
  true 
  

   Pearl-Oyster 
  (M. 
  vulgaris) 
  is 
  a 
  comparatively 
  small 
  species, 
  but 
  

   has 
  a 
  beautiful 
  pearly 
  lustre. 
  Like 
  the 
  larger 
  pearl-shells, 
  it 
  is 
  

   fixed 
  by 
  a 
  byssus 
  or 
  beard 
  (as 
  in 
  the 
  Common 
  Mussel), 
  whereas 
  

   the 
  Tamblegam 
  Oyster 
  (Placuna) 
  has 
  none. 
  

  

  In 
  addition, 
  two 
  other 
  forms 
  of 
  Oyster 
  are 
  conspicuous 
  in 
  

   Australian 
  waters, 
  viz. 
  the 
  " 
  black 
  lip 
  " 
  and 
  the 
  " 
  silver 
  or 
  gold 
  

   lip," 
  and 
  both 
  produce 
  pearls, 
  whilst 
  they 
  are 
  valuable 
  in 
  other 
  

   respects. 
  The 
  latter 
  shell 
  reaches 
  nearly 
  a 
  foot 
  in 
  diameter, 
  and 
  

   may 
  weigh 
  ten 
  pounds. 
  A 
  third 
  Australian 
  form 
  is 
  the 
  " 
  Shark's 
  

   Bay" 
  shell.! 
  

  

  Similar 
  Pearl-Oysters 
  are 
  found 
  at 
  the 
  Cape, 
  West 
  Indies, 
  

   and 
  both 
  sides 
  of 
  Central 
  America. 
  1 
  In 
  some 
  of 
  these 
  the 
  pearls 
  

   (e. 
  g. 
  M. 
  cetra, 
  Beeves) 
  are 
  valuable, 
  whilst 
  the 
  shell 
  is 
  less 
  so, 
  

   the 
  reverse 
  being 
  the 
  case 
  in 
  others. 
  Moreover, 
  S. 
  Grand§ 
  is 
  of 
  

   opinion 
  that 
  in 
  shallow 
  water 
  the 
  shells 
  are 
  small, 
  but 
  pearls 
  

   more 
  frequent 
  ; 
  whilst 
  in 
  deep 
  water 
  the 
  shells 
  are 
  more 
  valuable, 
  

   but 
  the 
  pearls 
  fewer. 
  

  

  In 
  our 
  own 
  seas 
  the 
  pearl-producing 
  species 
  are 
  few 
  in 
  num- 
  

   ber, 
  and 
  their 
  pearls 
  of 
  little 
  value. 
  One 
  of 
  these 
  occurs 
  in 
  vast 
  

   numbers 
  viz. 
  the 
  Common 
  Mussel, 
  whilst 
  the 
  larger 
  Horse-Mussel 
  

   is 
  not 
  uncommon 
  in 
  deeper 
  water. 
  The 
  great 
  majority 
  of 
  the 
  

   pearls 
  in 
  the 
  former 
  are 
  white 
  or 
  dull 
  white, 
  a 
  few 
  beiijg 
  bluish 
  

   or 
  mauve, 
  and 
  some 
  blackish 
  blue. 
  In 
  the 
  Horse-Mussel 
  they 
  

   often 
  have 
  a 
  nacreous 
  lustre, 
  and 
  may 
  be 
  fixed 
  like 
  tears 
  to 
  the 
  

   valves. 
  

  

  On 
  the 
  other 
  hand, 
  two 
  forms, 
  viz. 
  Margaritana 
  and 
  Anodonta, 
  

   have 
  kmg 
  been 
  known 
  in 
  the 
  fresh 
  waters 
  of 
  Britain 
  and 
  of 
  

   Europe 
  for 
  the 
  beauty 
  of 
  their 
  pearls, 
  and 
  the 
  vast 
  variety 
  and 
  

   great 
  numbers 
  of 
  the 
  Unios 
  of 
  American 
  fresh 
  waters 
  have 
  a 
  

   similar 
  distinction. 
  

  

  Formation 
  of 
  Pearls. 
  — 
  One 
  feature 
  all 
  pearls 
  have 
  in 
  common, 
  

  

  * 
  M. 
  llaoul 
  Postel 
  (quoted 
  by 
  M. 
  Grand). 
  

  

  | 
  Fine 
  examples 
  of 
  these 
  have 
  been 
  presented 
  to 
  the 
  Museum 
  of 
  the 
  

   University 
  by 
  Mr. 
  J. 
  E. 
  Josh, 
  M.A., 
  B.Sc. 
  

  

  | 
  Fisheries 
  for 
  these 
  go 
  on 
  from 
  July 
  till 
  October. 
  

   ( 
  '/'• 
  cit. 
  

  

  