﻿AND 
  OTHER 
  FAMILIES. 
  63 
  

  

  extensive 
  dealer 
  in 
  London. 
  He 
  could 
  not 
  give 
  me 
  the 
  least 
  idea 
  of 
  

   its 
  native 
  country. 
  From 
  its 
  general 
  appearance 
  I 
  should 
  presume 
  it 
  

   to 
  come 
  from 
  a 
  southern 
  latitude, 
  perhaps 
  from 
  New 
  Holland. 
  It 
  is 
  

   rather 
  peculiar 
  in 
  its 
  outline, 
  being 
  more 
  emarginate 
  at 
  base 
  than 
  any 
  

   species 
  with 
  which 
  I 
  am 
  acquainted. 
  The 
  emargination 
  is 
  not, 
  how- 
  

   ever, 
  so 
  great 
  as 
  in 
  the 
  My 
  a 
  margaritifera 
  (Lin.), 
  JLlasmodonta 
  arcuata 
  

   (Barnes). 
  It 
  approaches 
  most 
  closely 
  the 
  Unio 
  subtentus 
  (Say), 
  but 
  

   differs 
  from 
  it 
  in 
  the 
  total 
  absence 
  of 
  folds 
  or 
  " 
  ribs" 
  on 
  the 
  posterior 
  

   slope. 
  In 
  the 
  two 
  valves 
  which 
  I 
  possess 
  there 
  appear 
  to 
  be 
  no 
  rays, 
  

   unless 
  the 
  green 
  of 
  the 
  posterior 
  slope 
  be 
  denominated 
  a 
  single 
  broad 
  

   one. 
  The 
  emargination 
  and 
  compression 
  of 
  the 
  base 
  cause 
  the 
  poste- 
  

   rior 
  part 
  of 
  the 
  cavity 
  of 
  the 
  shell 
  to 
  be 
  effuse. 
  

  

  Unio 
  Conradicus. 
  Plate 
  IX. 
  fig. 
  23. 
  

  

  Testa 
  ellipticd, 
  transversa, 
  insequilaterd, 
  parte 
  posteriori 
  plicatd 
  ; 
  valvulis 
  tenui- 
  

   bus; 
  natibus 
  ad 
  apices 
  nitide 
  undulatis 
  ; 
  dentibus 
  cardinalibus 
  parvis 
  et 
  erectis 
  ; 
  

   lateralibus 
  indistinctis 
  ; 
  margaritd 
  antice 
  albd, 
  postice 
  iridescente 
  et 
  in 
  cavofusco 
  

   purpurea. 
  

  

  Shell 
  elliptica], 
  transverse, 
  inequilateral, 
  folded 
  on 
  the 
  posterior 
  parts 
  ; 
  valves 
  thin 
  ; 
  

   beaks 
  finely 
  undulated 
  at 
  tip 
  ; 
  cardinal 
  teeth 
  small 
  and 
  erect 
  ; 
  lateral 
  teeth 
  not 
  perfectly- 
  

   defined 
  ; 
  nacre 
  white 
  anteriorly, 
  iridescent 
  posteriorly, 
  and 
  brownish 
  purple 
  in 
  the 
  

   cavity. 
  

  

  Hab 
  Professor 
  Troost. 
  

  

  My 
  Cabinet. 
  

  

  Cabinet 
  of 
  Professor 
  Troost. 
  

  

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

  

  Shell 
  elliptical, 
  transverse, 
  inequilateral, 
  indistinctly 
  folded 
  on 
  the 
  

   posterior 
  parts 
  ; 
  substance 
  of 
  the 
  shell 
  thin 
  behind, 
  thicker 
  before 
  ; 
  

   beaks 
  slightly 
  elevated 
  and 
  finely 
  undulated 
  at 
  tip 
  ; 
  ligament 
  rather 
  

   long 
  and 
  thin 
  ; 
  epidermis 
  finely 
  wrinkled, 
  yellowish 
  brown, 
  with 
  nu- 
  

   merous 
  indistinct 
  greenish 
  rays, 
  which 
  on 
  the 
  posterior 
  part 
  are 
  dis- 
  

   posed 
  to 
  be 
  clouded 
  ; 
  cardinal 
  teeth 
  small, 
  erect, 
  disposed 
  to 
  be 
  lobed 
  ; 
  

   lateral 
  teeth 
  long, 
  slightly 
  curved, 
  not 
  perfectly 
  defined, 
  having 
  but 
  a 
  

   small 
  cleft 
  in 
  the 
  left 
  valve 
  ; 
  anterior 
  cicatrices 
  distinct 
  ; 
  posterior 
  cica- 
  

  

  