﻿74 
  ON 
  THE 
  NAIADES, 
  

  

  Shell 
  elliptical, 
  compressed, 
  inequilateral 
  ; 
  valves 
  rather 
  thin 
  ; 
  beaks 
  compressed 
  and 
  

   undulated 
  at 
  tip 
  ; 
  epidermis 
  yellow 
  with 
  interrupted 
  dark 
  green 
  rays 
  ; 
  cardinal 
  teeth 
  

   small 
  ; 
  lateral 
  teeth 
  long 
  and 
  slightly 
  curved 
  ; 
  nacre 
  pearly 
  white 
  and 
  iridescent. 
  

  

  Hab. 
  Harpeth 
  River, 
  Tennessee. 
  Professor 
  Troost. 
  

  

  My 
  Cabinet. 
  

  

  Cabinet 
  of 
  Professor 
  Troost. 
  

  

  Diam. 
  *8, 
  Length 
  1-6, 
  Breadth 
  2*6 
  inches. 
  

  

  Shell 
  elliptical, 
  compressed, 
  inequilateral; 
  substance 
  of 
  the 
  shell 
  

   rather 
  thin, 
  thicker 
  before 
  ; 
  beaks 
  compressed 
  and 
  finely 
  undulated 
  at 
  

   the 
  tip 
  ; 
  ligament 
  short 
  and 
  rather 
  thick 
  ; 
  epidermis 
  fine 
  yellow 
  with 
  

   numerous 
  oblique 
  interrupted 
  rays, 
  which 
  are 
  strongly 
  pencilled 
  at 
  the 
  

   commencement 
  of 
  each 
  stage 
  of 
  growth 
  ; 
  cardinal 
  teeth 
  very 
  small 
  and 
  

   erect; 
  lateral 
  teeth 
  long 
  and 
  slightly 
  curved, 
  in 
  the 
  left 
  valve 
  enlarged 
  

   near 
  the 
  termination 
  ; 
  anterior 
  cicatrices 
  distinct 
  ; 
  posterior 
  cicatrices 
  

   confluent 
  ; 
  dorsal 
  cicatrices 
  in 
  the 
  centre 
  of 
  the 
  cavity 
  of 
  the 
  beaks, 
  and 
  

   deeply 
  impressed 
  ; 
  cavity 
  of 
  the 
  beaks 
  very 
  shallow 
  and 
  rounded 
  ; 
  nacre 
  

   pearly 
  white 
  and 
  iridescent. 
  

  

  Remarks. 
  — 
  This 
  species, 
  so 
  beautiful 
  and 
  so 
  peculiar 
  in 
  its 
  painted 
  

   exterior, 
  I 
  owe 
  to 
  the 
  kindness 
  of 
  professor 
  Troost. 
  The 
  fine 
  specimen 
  

   figured 
  belongs 
  to 
  the 
  museum 
  of 
  that 
  gentleman 
  in 
  Nashville, 
  and 
  I 
  

   am 
  indebted 
  to 
  him 
  for 
  the 
  loan 
  of 
  it 
  to 
  insert 
  it 
  here. 
  It 
  belongs 
  to 
  

   a 
  group, 
  the 
  peculiar 
  character 
  of 
  which 
  seems 
  to 
  be 
  in 
  the 
  singular 
  

   interruption 
  of 
  the 
  rays, 
  which 
  are 
  obsolete, 
  except 
  at 
  the 
  commence- 
  

   ment 
  of 
  each 
  stage 
  of 
  growth, 
  where 
  they 
  are 
  strongly 
  pencilled 
  with 
  

   green. 
  The 
  U. 
  planulatus 
  (nobis), 
  U. 
  patulus 
  (nobis) 
  and 
  U. 
  perdix 
  

   (herein 
  described) 
  belong 
  to 
  this 
  group. 
  The 
  U. 
  pictus 
  has 
  some 
  re- 
  

   semblance 
  to 
  the 
  U. 
  cariosus 
  (Say), 
  but 
  differs 
  in 
  being 
  more 
  com- 
  

   pressed, 
  and 
  in 
  having 
  rays 
  over 
  the 
  whole 
  disk. 
  It 
  perhaps 
  more 
  

   closely 
  resembles 
  the 
  younger 
  specimens 
  of 
  U. 
  crassus 
  (Say). 
  It 
  dif- 
  

   fers, 
  however, 
  in 
  being 
  thinner, 
  smaller, 
  and 
  in 
  the 
  character 
  of 
  the 
  

   rays. 
  

  

  