﻿U. 
  S. 
  B. 
  F.— 
  Doc. 
  804. 
  

  

  Plate 
  III 
  

  

  AN 
  EXTERIOR 
  VIEW 
  OF 
  A 
  WASHBOARD 
  (QUADRULA 
  HEROS), 
  SHOWING 
  THE 
  ABNORMAL 
  RIDGE 
  

   ON 
  THE 
  RIGHT 
  VALVE 
  AND 
  THE 
  VALLEY 
  ON 
  THE 
  LEFT 
  VALVE, 
  WHICH 
  ARE 
  SIGNS 
  OF 
  THE 
  

   PRESENCE 
  OF 
  A 
  PEARL 
  WITHIN. 
  

  

  In 
  this 
  example 
  Ihe 
  pearl 
  evidently 
  began 
  to 
  form 
  when 
  the 
  shell 
  w- 
  about 
  1 
  y-^^'^^^-J^Hf^ 
  °' 
  ''' 
  '''" 
  

   when 
  taken 
  was 
  about 
  20 
  years. 
  This 
  shell 
  was 
  found 
  at 
  Bath, 
  111,, 
  by 
  Harry 
  Lockwooa. 
  

  

  