﻿MICROSCOPIC 
  SCULPTURE 
  OF 
  PEARLY 
  FRESH-WATER 
  

  

  MUSSEL 
  SHELLS 
  

  

  By 
  William 
  B. 
  Marshall 
  

  

  Assistant 
  Curator, 
  Division 
  of 
  Mollusks, 
  United 
  States 
  National 
  Museum 
  

  

  In 
  a 
  note 
  under 
  the 
  description 
  of 
  Diplodontites 
  cookei 
  1 
  special 
  

   attention 
  was 
  called 
  to 
  its 
  minute 
  sculpture 
  in 
  the 
  following 
  words 
  : 
  

   " 
  The 
  sculpture 
  of 
  the 
  exterior 
  is 
  remarkable 
  and 
  of 
  great 
  beauty. 
  

   The 
  radiating 
  striae 
  between 
  the 
  impressed 
  radiating 
  lines 
  are 
  of 
  a 
  

   fineness 
  rarely 
  if 
  ever 
  equaled 
  in 
  shells 
  with 
  the 
  rude 
  structure 
  of 
  

   the 
  naiads." 
  In 
  the 
  same 
  paper 
  the 
  new 
  species 
  M 
  onoco 
  ndylaea 
  

   felipponei 
  was 
  described, 
  but 
  nothing 
  was 
  said 
  of 
  its 
  possessing 
  

   minute 
  radiating 
  striae. 
  In 
  fact, 
  the 
  fine 
  sculpture 
  of 
  this 
  shell 
  was 
  

   not 
  detected 
  as 
  it 
  was 
  not 
  shown 
  by 
  the 
  fairly 
  strong 
  hand 
  lens 
  used 
  

   in 
  making 
  an 
  examination. 
  Later 
  the 
  use 
  of 
  a 
  two-thirds 
  inch 
  

   objective 
  on 
  a 
  compound 
  microscope 
  showed 
  that 
  this 
  species 
  has 
  

   microscopic 
  sculpture 
  of 
  the 
  same 
  general 
  character 
  as 
  that 
  of 
  Diplo- 
  

   dontites 
  cookei. 
  Even 
  with 
  a 
  two-thirds 
  inch 
  objective 
  careful 
  

   focusing 
  is 
  needed 
  to 
  reveal 
  the 
  fine 
  striae. 
  The 
  new 
  species 
  Ano- 
  

   dontites 
  colombiensis 
  described 
  in 
  the 
  same 
  paper 
  was 
  then 
  sub- 
  

   jected 
  to 
  microscopic 
  examination 
  and 
  was 
  found 
  to 
  possess 
  minute 
  

   striae 
  of 
  the 
  same 
  nature 
  as 
  in 
  the 
  two 
  species 
  mentioned 
  above. 
  

  

  The 
  presence 
  of 
  microscopic 
  striae 
  in 
  the 
  three 
  species 
  mentioned 
  

   above 
  led 
  to 
  an 
  examination 
  of 
  many 
  other 
  species 
  of 
  South 
  Ameri- 
  

   can 
  shells, 
  and 
  it 
  was 
  found 
  that 
  in, 
  those 
  belonging 
  to 
  the 
  family 
  

   Mutelidae 
  the 
  striae 
  were 
  generally 
  present, 
  while 
  in 
  Diplodon 
  and 
  

   other 
  genera 
  of 
  the 
  Unionidae 
  they 
  were 
  lacking. 
  The 
  investigation 
  

   was 
  then 
  broadened 
  to 
  include 
  an 
  examination 
  of 
  many 
  species 
  repre- 
  

   senting 
  practically 
  all 
  genera 
  of 
  naiads 
  from 
  all 
  parts 
  of 
  the 
  world. 
  

   The 
  results 
  have 
  been 
  thought 
  sufficiently 
  interesting 
  and 
  important 
  

   to 
  warrant 
  publishing 
  them. 
  The 
  results 
  are 
  of 
  value 
  in 
  themselves 
  

   and 
  the 
  discovery 
  of 
  the 
  minute 
  striae 
  will 
  call 
  attention 
  to 
  the 
  fact 
  

   that 
  many 
  details 
  may 
  lie 
  close 
  at 
  hand 
  and 
  yet 
  remain 
  unnoticed 
  

   for 
  years. 
  The 
  genera 
  Anodontites 
  and 
  M 
  onocondylaea 
  have 
  been 
  

   known 
  for 
  many 
  years, 
  but. 
  so 
  far 
  as 
  I 
  have 
  been 
  able 
  to 
  determine,, 
  

  

  1 
  I'roc. 
  U. 
  S. 
  Nat. 
  Mus., 
  vol. 
  61. 
  1922. 
  

  

  No. 
  2576— 
  Proceedings 
  U. 
  S. 
  National 
  Museum, 
  Vol. 
  67, 
  Art. 
  4. 
  

  

  22247—25 
  1 
  

  

  