﻿24 
  ON 
  THE 
  NAIADES 
  

  

  of 
  knowledge, 
  while 
  there 
  is 
  such 
  a 
  " 
  diffusion 
  of 
  existing 
  knowledge 
  

   among 
  the 
  mass 
  of 
  mankind" 
  as 
  we 
  have 
  at 
  present. 
  

  

  We 
  can 
  only 
  account 
  for 
  the 
  almost 
  total 
  neglect 
  of 
  the 
  family 
  

   Naiades 
  by 
  writers 
  on 
  natural 
  history 
  of 
  the 
  last 
  century, 
  in 
  the 
  fact 
  

   that 
  the 
  fresh 
  w 
  T 
  aters 
  of 
  Europe 
  produce 
  so 
  few 
  species 
  that 
  they 
  had 
  

   then 
  scarcely 
  attracted 
  attention. 
  The 
  habits 
  of 
  these 
  animals 
  have 
  

   been 
  there 
  so 
  little 
  studied 
  and 
  known, 
  that 
  some 
  recent 
  writers 
  of 
  

   reputation 
  assert 
  that 
  they 
  move 
  with 
  the 
  beaks 
  of 
  the 
  shell 
  " 
  down- 
  

   ward," 
  which 
  is 
  equivalent 
  to 
  saying 
  they 
  walk 
  on 
  their 
  backs. 
  The 
  

   anterior 
  part 
  has 
  been 
  called 
  the 
  posterior 
  part, 
  which 
  is 
  as 
  much 
  as 
  

   to 
  say, 
  that 
  their 
  locomotion 
  is 
  backward. 
  

  

  These 
  facts 
  display 
  a 
  great 
  want 
  of 
  attention 
  to 
  the 
  animal 
  in 
  its 
  

   element, 
  — 
  where 
  it 
  would 
  be 
  observed 
  to 
  possess 
  many 
  curious 
  and 
  

   striking 
  characteristics. 
  The 
  great 
  systematist, 
  the 
  immortal 
  Linneus, 
  

   w 
  r 
  hose 
  name 
  will 
  be 
  found 
  recorded 
  in 
  the 
  book 
  of 
  the 
  last 
  student 
  of 
  

   natural 
  history, 
  knew 
  so 
  few 
  members 
  of 
  this 
  family 
  that 
  he 
  classed 
  

   them 
  indiscriminately 
  with 
  two 
  marine 
  genera, 
  Mya 
  and 
  Mytilus. 
  

  

  It 
  was 
  the 
  rich 
  and 
  splendid 
  productions 
  of 
  the 
  rivers 
  of 
  the 
  United 
  

   States, 
  and 
  particularly 
  those 
  w 
  r 
  hich 
  are 
  tributary 
  to 
  the 
  Mississippi, 
  

   which 
  first 
  roused 
  the 
  attention 
  of 
  the 
  zoologist 
  to 
  their 
  extraordinary 
  

   characters 
  ; 
  and 
  they 
  have 
  within 
  a 
  few 
  years 
  become 
  sought 
  after 
  by 
  

   collectors 
  as 
  eagerly 
  as 
  the 
  " 
  most 
  precious 
  jewels 
  of 
  the 
  ocean." 
  

  

  Urged 
  by 
  the 
  solicitations 
  of 
  numerous 
  scientific 
  friends, 
  I 
  have 
  

   continued 
  my 
  efforts 
  to 
  obtain 
  such 
  specimens 
  as 
  appeared 
  to 
  me 
  to 
  be 
  

   new 
  and 
  undescribed, 
  and 
  they 
  are 
  now 
  submitted 
  to 
  the 
  consideration 
  

   of 
  the 
  Society. 
  

  

  In 
  my 
  communications 
  I 
  have 
  heretofore 
  said 
  little 
  on 
  the 
  geogra- 
  

   phical 
  position 
  of 
  our 
  Naiades. 
  It 
  has, 
  however, 
  been 
  to 
  me 
  an 
  inte- 
  

   resting 
  branch 
  of 
  the 
  subject, 
  and 
  engaged 
  much 
  of 
  my 
  attention. 
  

   The 
  great 
  dividing 
  ridge 
  or 
  chain 
  of 
  mountains, 
  the 
  Alleghanies, 
  which 
  

   seems 
  so 
  completely 
  to 
  separate 
  our 
  eastern 
  from 
  our 
  western 
  waters, 
  

   almost 
  as 
  completely 
  separates 
  the 
  species 
  of 
  this 
  family 
  inhabiting 
  

   those 
  parts 
  lying 
  east 
  and 
  west 
  of 
  it. 
  It 
  is 
  a 
  matter 
  of 
  doubt 
  if 
  there 
  

   be 
  more 
  than 
  two 
  or 
  three 
  species 
  of 
  all 
  the 
  genera 
  of 
  this 
  family 
  ex- 
  

   isting 
  in 
  the 
  eastern 
  waters 
  which 
  have 
  their 
  analogues 
  in 
  the 
  western 
  

   waters. 
  That 
  shell, 
  which 
  we 
  have 
  considered 
  the 
  JJnio 
  cariosus 
  of 
  

  

  