﻿Report 
  U. 
  S. 
  F. 
  C. 
  1903. 
  

  

  Plate 
  VII. 
  

  

  ARTIFICIAL 
  CLAM 
  BED. 
  

  

  2. 
  SURFACE 
  OF 
  ARTIFICIAL 
  CLAM 
  BED. 
  

  

  