﻿112 
  ON 
  THE 
  NAIADES, 
  

  

  lamellar; 
  cicatrices 
  smooth, 
  impressed, 
  showing 
  the 
  mark 
  of 
  their 
  ad- 
  

   vancement; 
  palleal 
  impression 
  indistinct, 
  broad; 
  cavity 
  of 
  the 
  shell 
  

   rather 
  shallow 
  ; 
  cavity 
  of 
  the 
  beaks 
  angular 
  ; 
  nacre 
  yellowish 
  white 
  and 
  

   shining. 
  

  

  Remarks. 
  — 
  This 
  is 
  certainly 
  a 
  very 
  interesting 
  shell. 
  It 
  is 
  difficult 
  

   to 
  find 
  any 
  one 
  to 
  compare 
  it 
  with. 
  On 
  the 
  inside 
  of 
  the 
  anterior 
  

   margin 
  there 
  appears 
  to 
  be 
  a 
  disposition 
  to 
  crenulation, 
  caused 
  by 
  the 
  

   longitudinal 
  striae. 
  Its 
  habitat 
  I 
  am 
  not 
  acquainted 
  with, 
  having 
  pur- 
  

   chased 
  my 
  specimens 
  at 
  a 
  dealer's 
  in 
  Europe, 
  who 
  could 
  not 
  inform 
  

   me 
  from 
  what 
  country 
  they 
  came. 
  

  

  Io 
  spinosa. 
  Plate 
  XIX. 
  fig. 
  79. 
  

  

  Testa 
  obtuse 
  turritd, 
  latd, 
  corned, 
  sub 
  epidermide 
  fasciatd, 
  spinis 
  magnis 
  ; 
  cm- 
  

   fractibus 
  septenis 
  ; 
  aperturd 
  elo?igald, 
  dimidium 
  longitudinis 
  testa; 
  hubente. 
  

  

  Shell 
  obtusely 
  turrited, 
  wide, 
  horn 
  colour, 
  under 
  the 
  epidermis 
  banded, 
  furnished 
  

   with 
  large 
  spines 
  ; 
  whorls 
  seven 
  ; 
  mouth 
  elongate, 
  one 
  half 
  the 
  length 
  of 
  the 
  shell. 
  

  

  Hab. 
  Holston 
  River, 
  Washington 
  County, 
  Virginia. 
  Professor 
  

   Troost. 
  

  

  My 
  Cabinet. 
  

  

  Cabinet 
  of 
  Professor 
  Troost. 
  

  

  Diam. 
  1-2, 
  Length 
  2-2 
  inches. 
  

  

  Remarks. 
  — 
  This 
  species 
  resembles 
  very 
  much 
  the 
  Io 
  fusiformis 
  

   (nobis), 
  Fusus 
  jluviatilis 
  (Say), 
  but 
  may 
  be 
  distinguished 
  by 
  its 
  large 
  

   transversely 
  compressed 
  spines, 
  the 
  fusiformis 
  having 
  somewhat 
  longi- 
  

   tudinal 
  tubercles. 
  I 
  am 
  not 
  acquainted 
  with 
  any 
  fluviatile 
  shell 
  which 
  

   has 
  such 
  large 
  spines 
  (there 
  being 
  about 
  seven 
  on 
  each 
  whorl), 
  nor 
  any 
  

   which 
  has 
  such 
  a 
  general 
  resemblance 
  to 
  a 
  marine 
  shell. 
  Professor 
  

   Troost 
  informs 
  me 
  they 
  are 
  rare 
  in 
  the 
  river, 
  that 
  they 
  had 
  been 
  

   observed 
  in 
  the 
  graves 
  of 
  the 
  aborigines 
  ; 
  and 
  as 
  it 
  was 
  generally 
  be- 
  

  

  