﻿64 
  ON 
  THE 
  NAIADES, 
  

  

  trices 
  confluent 
  ; 
  dorsal 
  cicatrices 
  in 
  the 
  centre 
  of 
  the 
  cavity 
  of 
  the 
  

   beaks 
  ; 
  cavity 
  of 
  the 
  beaks 
  shallow 
  and 
  tinged 
  with 
  brownish 
  purple 
  ; 
  

   nacre 
  white 
  anteriorly, 
  thinner 
  and 
  very 
  iridescent 
  posteriorly. 
  

  

  Remarks. 
  — 
  I 
  owe 
  to 
  the 
  kindness 
  of 
  professor 
  Troost 
  this 
  little 
  

   species, 
  and 
  name 
  it 
  after 
  an 
  indefatigable 
  naturalist, 
  Mr 
  T. 
  A. 
  Con- 
  

   rad. 
  It 
  belongs 
  to 
  that 
  group 
  which 
  is 
  distinguished 
  by 
  an 
  imma- 
  

   ture 
  hinge, 
  and 
  which 
  I 
  have 
  noticed 
  in 
  my 
  remarks 
  on 
  the 
  U. 
  Hil- 
  

   drethius. 
  The 
  U. 
  Conradius 
  certainly 
  resembles 
  that 
  shell 
  closely. 
  It 
  

   is, 
  however, 
  less 
  cylindrical, 
  and 
  has 
  the 
  teeth 
  more 
  perfect. 
  It 
  also 
  

   has 
  rays 
  and 
  undulations 
  which 
  I 
  have 
  not 
  observed 
  on 
  the 
  other. 
  In 
  

   outline 
  it 
  more 
  closely 
  resembles 
  the 
  U. 
  iris 
  (nobis), 
  but 
  differs 
  in 
  the 
  

   teeth 
  and 
  in 
  the 
  rays. 
  Having 
  but 
  two 
  specimens 
  of 
  this 
  species 
  to 
  

   examine, 
  some 
  of 
  the 
  characters 
  may 
  be 
  found 
  to 
  differ 
  in 
  other 
  speci- 
  

   mens. 
  One 
  of 
  these 
  is 
  slightly 
  emarginate 
  at 
  the 
  basal 
  margin. 
  

  

  Unio 
  divaricatus. 
  Plate 
  IX. 
  fig. 
  24. 
  

  

  Testa 
  ellipticd, 
  transversa, 
  subcompressd, 
  valde 
  insequilaterd 
  ; 
  valvulis 
  tenuibus 
  ; 
  

   natibus 
  plicis 
  pulchris 
  divaricatis 
  ; 
  dentibus 
  cardinalibus 
  parvis, 
  compressis 
  ; 
  

   lateralibus 
  longis 
  et 
  subtenuibus 
  ; 
  margaritd 
  albd 
  et 
  iridescente. 
  

  

  Shell 
  elliptical, 
  transverse, 
  rather 
  compressed, 
  very 
  inequilateral 
  ; 
  valves 
  thin 
  ; 
  beaks 
  

   with 
  beautiful 
  divaricating 
  folds 
  ; 
  cardinal 
  teeth 
  small, 
  compressed 
  ; 
  lateral 
  teeth 
  long 
  

   and 
  rather 
  thin 
  ; 
  nacre 
  white 
  and 
  iridescent. 
  

  

  Hab. 
  Egypt. 
  Duke 
  de 
  Rivoli. 
  

  

  My 
  Cabinet. 
  

   Diam. 
  -5, 
  Length 
  -9, 
  Breadth 
  1*4 
  inches. 
  

  

  Shell 
  elliptical, 
  transverse, 
  somewhat 
  compressed, 
  very 
  inequilate- 
  

   ral 
  ; 
  substance 
  of 
  the 
  shell 
  thin 
  ; 
  beaks 
  covered 
  with 
  beautiful 
  folds 
  

   diverging 
  from 
  their 
  apex; 
  ligament 
  rather 
  short 
  and 
  slender; 
  epi- 
  

   dermis 
  greenish, 
  smooth 
  ; 
  cardinal 
  teeth 
  small, 
  compressed, 
  double 
  

   in 
  the 
  right 
  valve, 
  and 
  single 
  in 
  the 
  left; 
  lateral 
  teeth 
  long, 
  rather 
  

   thin 
  and 
  nearly 
  straight 
  ; 
  anterior 
  cicatrices 
  slightly 
  confluent 
  ; 
  pos- 
  

   terior 
  cicatrices 
  confluent 
  ; 
  dorsal 
  cicatrices 
  situated 
  in 
  the 
  centre 
  of 
  

  

  