﻿PROPAGATION 
  OF 
  FRESH-WATEK 
  MUSSELS. 
  9 
  

  

  The 
  Warty-back, 
  Quadrula 
  pustulosa 
  (Lea). 
  [PI. 
  i, 
  fig. 
  1, 
  2. 
  J 
  

  

  This 
  mussel, 
  with 
  allied 
  species, 
  is 
  commonly 
  called 
  the 
  warty- 
  

   back 
  and 
  pimple-back 
  because 
  of 
  the 
  pustules 
  on 
  the 
  shell. 
  It 
  is 
  a 
  

   shell 
  of 
  good 
  luster 
  and 
  texture, 
  and 
  therefore 
  is 
  ranked 
  high 
  by 
  

   manufacturers. 
  

  

  Distribution. 
  — 
  Its 
  range 
  is 
  throughout 
  the 
  Mississippi 
  drainage 
  and 
  

   into 
  Michigan, 
  extending 
  east 
  into 
  the 
  Alabama 
  River 
  system 
  and 
  

   west 
  into 
  central 
  Texas. 
  

  

  Habitat. 
  — 
  It 
  is 
  found 
  in 
  streams 
  of 
  some 
  size 
  either 
  in 
  gravel 
  or 
  on 
  

   mud 
  bottom 
  (Scammon, 
  1906). 
  

  

  Juvenile. 
  — 
  The 
  juvenile, 
  of 
  10 
  to 
  20 
  mm. 
  in 
  length, 
  can 
  be 
  recog- 
  

   nized 
  by 
  a 
  broad 
  triangular 
  green 
  ray 
  upon 
  the 
  lateral 
  slope. 
  I 
  have 
  

   found 
  it 
  chiefly 
  in 
  fine 
  gravel 
  or 
  sand 
  in 
  a 
  strong 
  current. 
  

  

  No 
  byssus 
  was 
  observed 
  in 
  a 
  considerable 
  number 
  ot 
  specimens 
  

   taken 
  and 
  none 
  has 
  been 
  reported 
  tor 
  this 
  species 
  to 
  my 
  knowledge; 
  

   apparently, 
  however, 
  there 
  is 
  a 
  byssus 
  gland 
  present. 
  In 
  the 
  very 
  

   early 
  stages 
  (less 
  than 
  1 
  mm. 
  in 
  length) 
  a 
  mucilaginous 
  secretion 
  is 
  

   produced 
  which 
  serves 
  to 
  anchor 
  the 
  young 
  mussel. 
  I 
  think 
  it 
  doubt- 
  

   ful 
  if 
  this 
  species 
  at 
  any 
  stage 
  produces 
  the 
  hard 
  hyaline 
  byssus 
  

   threads 
  which 
  are 
  found 
  in 
  some 
  of 
  the 
  Lampsihn?e. 
  Among 
  the 
  

   Quadrulus 
  here 
  described 
  the 
  only 
  case 
  of 
  a 
  true 
  byssus 
  observed 
  

   was 
  in 
  that 
  of 
  a 
  specimen 
  of 
  Q. 
  plicata 
  having 
  a 
  length 
  of 
  4.5 
  mm. 
  

  

  Glochidium 
  (pi. 
  v, 
  fig. 
  36). 
  — 
  The 
  warty-back 
  is 
  a 
  summer 
  breeder, 
  

   or 
  tachytictic, 
  the 
  glochidia 
  being 
  found 
  daring 
  the 
  months 
  of 
  June, 
  

   July, 
  and 
  August. 
  The 
  earliest 
  record 
  that 
  I 
  have 
  for 
  a 
  season 
  is 
  

   June 
  12, 
  and 
  the 
  latest 
  August 
  23, 
  when 
  I 
  found 
  two 
  gravid 
  out 
  of 
  46 
  

   examined. 
  The 
  glochidia 
  occupy 
  all 
  four 
  gills 
  in 
  the 
  female, 
  and 
  are 
  

   white 
  in 
  color. 
  They 
  are 
  of 
  the 
  bookless 
  type, 
  and 
  as 
  seen 
  flatwise, 
  

   the 
  usual 
  position 
  for 
  examination 
  under 
  the 
  microscope, 
  have 
  the 
  

   form 
  of 
  an 
  elongated 
  purse 
  (pi. 
  v, 
  fig. 
  36). 
  

  

  Dimensions: 
  Height, 
  0.28 
  mm. 
  to 
  0.3 
  mm.; 
  length, 
  0.22 
  mm. 
  to 
  

   0.23 
  mm.; 
  length 
  of 
  hinge 
  line, 
  0.08 
  mm., 
  or 
  2.75 
  times 
  in 
  length. 
  

   The 
  difi'erence 
  in 
  height 
  observed 
  (0.28 
  mm. 
  -0.3 
  mm.) 
  gives 
  a 
  vari- 
  

   ation 
  of 
  less 
  than 
  8 
  per 
  cent; 
  more 
  than 
  10 
  per 
  cent 
  seems 
  to 
  be 
  

   uncommon 
  in 
  glochidia 
  of 
  one 
  species, 
  although 
  I 
  have 
  seen 
  12 
  per 
  

   cent. 
  This 
  species 
  should 
  not 
  be 
  confused 
  with 
  any 
  others 
  in 
  the 
  

   region 
  investigated 
  because 
  of 
  unique 
  form 
  and 
  size. 
  The 
  only 
  

   glochidia 
  here 
  at 
  all 
  resembling 
  it 
  are 
  those 
  of 
  Lampsilis 
  luteola 
  and 
  

   Plagiola 
  securis. 
  L. 
  luteola 
  can 
  be 
  distinguished 
  by 
  its 
  relatively 
  

   greater 
  width 
  (0.25 
  mm.) 
  and 
  hinge 
  line 
  (0.118 
  mm.), 
  and 
  Plagiola 
  

   securis 
  by 
  its 
  greater 
  length 
  (0.31 
  mm. 
  to 
  0.33 
  mm.) 
  and 
  different 
  

   proportions. 
  

  

  Natural 
  infection. 
  — 
  The 
  first 
  record 
  for 
  a 
  natural 
  infection 
  by 
  this 
  

   species 
  was 
  found 
  upon 
  a 
  catfish 
  obtained 
  July 
  5. 
  This 
  was 
  the 
  

   channel 
  cat, 
  Ictalurus 
  punctatus, 
  and 
  was 
  the 
  first 
  record 
  of 
  infection 
  

  

  