﻿16 
  

  

  GROWTH 
  AND 
  MIGRATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  

  

  table 
  8, 
  grandis 
  (floater), 
  4 
  specimens; 
  tetralasmus, 
  2 
  specimens; 
  

   gracilis 
  (paper-shell), 
  2 
  specimens; 
  anodontoides 
  (yellow 
  sand-shell), 
  

   1 
  specimen. 
  ' 
  

  

  Average 
  Increases 
  in 
  Weight 
  and 
  Length, 
  by 
  Species. 
  

  

  AVERAGES 
  FOR 
  ONE 
  YEAR. 
  

  

  Species. 
  

  

  Average 
  

   weight. 
  

  

  Average 
  

   increase 
  

  

  in 
  

   weight. 
  

  

  Average 
  

   length. 
  

  

  Average 
  

   Increase 
  

  

  in 
  

   length. 
  

  

  Lachrymosa 
  (maule-leaf) 
  

  

  Undulata 
  (three-fidge) 
  

  

  Rubiginosa 
  

  

  Pusttilosa 
  (warty-baclc 
  or 
  pimple-back) 
  . 
  

  

  Grandis 
  a 
  ( 
  floater) 
  

  

  Tetralasmus 
  ii 
  

  

  Grams. 
  

   100 
  

  

  124 
  

  

  74 
  

   67 
  

   194 
  

   28 
  

  

  Orams. 
  

   30.8 
  

   28 
  

   11.4 
  

   11. 
  ,5 
  

   48.6 
  

   8.5 
  

  

  Mm. 
  

   70 
  

   82 
  

  

  68.8 
  

   60 
  

   128 
  

   67 
  

  

  Mm. 
  

  

  7.5 
  

  

  7.2 
  

  

  3.4 
  

  

  2.7 
  

  

  5 
  

  

  4 
  

  

  AVERAGES 
  FOR 
  THREE 
  SUMMER 
  MONTHS. 
  

  

  Gracilis 
  (paper-shell) 
  

  

  Anodontoides 
  (yeUow 
  sand-shell) 
  . 
  

  

  22.5 
  

   4.5 
  

  

  a 
  Large 
  mature 
  specimens, 
  still 
  the 
  increase 
  is 
  good. 
  

   b 
  In 
  an 
  unusual 
  environment 
  lor 
  this 
  species 
  (p. 
  9). 
  

  

  Juvenile 
  Quadrulse 
  "■ 
  of 
  the 
  above 
  species 
  double 
  in 
  size 
  in 
  a 
  year, 
  

   as 
  shown 
  by 
  a 
  number 
  of 
  examples 
  (149, 
  158, 
  349, 
  323, 
  in 
  table 
  1; 
  

   281, 
  564, 
  413, 
  in 
  table 
  8). 
  Averages 
  here 
  given 
  and 
  those 
  taken 
  

   from 
  other 
  sources 
  mdicate 
  that 
  a 
  100-gram, 
  75-mLllimeter 
  undulata 
  

   (three-ridge) 
  (p. 
  14) 
  or 
  lachrymosa 
  (maple-leaf) 
  can 
  develop 
  in 
  the 
  

   Shoofly 
  in 
  about 
  four 
  years 
  (averages 
  for 
  tables 
  1, 
  2, 
  4, 
  and 
  5). 
  A 
  

   300-gram 
  specimen 
  of 
  undulata 
  (three-ridge) 
  or 
  lachrymosa 
  (maple- 
  

   leaf) 
  would 
  doubtless 
  be 
  close 
  to 
  15 
  years 
  old. 
  The 
  largest 
  undulata 
  

   (three-ridge) 
  rechecked 
  weighed 
  407 
  grams 
  in 
  June, 
  1910, 
  and 
  421 
  

   in 
  June, 
  1911. 
  This 
  specimen 
  was 
  123 
  millimeters 
  long, 
  and 
  increased 
  

   1 
  millimeter 
  in 
  length. 
  In 
  undulata 
  (three-ridge) 
  and 
  lachrymosa 
  

   (maple-leaf), 
  after 
  the 
  100-millimeter 
  length 
  is 
  reached, 
  the 
  increase 
  

   in 
  length 
  is 
  slow, 
  and 
  growth 
  lhi.es 
  follow 
  one 
  another 
  so 
  closely 
  that 
  

   the 
  differentiation 
  of 
  Imes 
  is 
  difficult. 
  Pustulosa 
  (warty-back, 
  pimple- 
  

   back) 
  and 
  rubiginosa 
  grow 
  more 
  slowly 
  than 
  the 
  two 
  preceding 
  species. 
  

   A 
  SO-millimeter 
  pustulosa 
  (warty-back, 
  pimple-back) 
  has 
  passed 
  the 
  

   age 
  of 
  rapid 
  growth, 
  and 
  from 
  this 
  size 
  on 
  additions 
  come 
  slowly. 
  

  

  A 
  light-shelled 
  form, 
  as 
  L. 
  gracilis 
  (paper-shell) 
  grows 
  very 
  rapidly; 
  

   this 
  would 
  seem 
  to 
  indicate 
  that 
  the 
  shell 
  is 
  built 
  up 
  at 
  greater 
  

   expense 
  of 
  food 
  and 
  energy 
  than 
  the 
  soft 
  parts 
  of 
  the 
  mussel. 
  In 
  

   table 
  8, 
  specimen 
  X, 
  during 
  the 
  three 
  summer 
  months, 
  shows 
  an 
  

   increase 
  of 
  over 
  four 
  times 
  in 
  weight 
  and 
  27 
  miUimeters 
  in 
  length; 
  

   566, 
  L. 
  anodontoides 
  (yellow 
  sand-sheU), 
  m 
  the 
  same 
  time, 
  makes 
  an 
  

   increase 
  of 
  one-fifth 
  its 
  original 
  weight, 
  and 
  4.5 
  millimeters 
  increase 
  

   in 
  length. 
  

  

  a 
  Early 
  juvenile 
  forms 
  grow 
  even 
  more 
  rapidly 
  as 
  experimentally 
  found 
  (foot-note, 
  p. 
  5) 
  by 
  Coker. 
  

  

  