﻿60 
  ON 
  THE 
  NAIADES. 
  

  

  Unio 
  parallelopipedon. 
  Plate 
  VIII. 
  fig. 
  20. 
  

  

  Testa 
  ob/ongd, 
  subcylindraced, 
  transversa, 
  valde 
  insequilaterali, 
  postice 
  angu- 
  

   lutd, 
  inflcttd, 
  marginibus 
  dorsi 
  et 
  baseos 
  parallelis 
  ; 
  valvulis 
  subcrassis 
  ; 
  natibus 
  

   prominulis, 
  retusis 
  ; 
  epidermide 
  fere 
  nigra; 
  dentibus 
  cardinalibus 
  obliquis, 
  cris- 
  

   tutis 
  ; 
  lateralibiis 
  longis 
  rectisque 
  ; 
  margaritd 
  albd 
  et 
  iridescente. 
  

  

  Shell 
  oblong, 
  subcylindrical, 
  dorsal 
  and 
  basal 
  margins 
  parallel, 
  transverse, 
  very 
  in- 
  

   equilateral, 
  angular 
  behind, 
  inflated 
  ; 
  valves 
  rather 
  thick 
  ; 
  beaks 
  somewhat 
  elevated, 
  

   rctuse 
  ; 
  epidermis 
  almost 
  black 
  ; 
  cardinal 
  teeth 
  oblique, 
  crested 
  ; 
  lateral 
  teeth 
  long 
  and 
  

   straight 
  ; 
  nacre 
  pearl}' 
  white 
  and 
  iridescent. 
  

  

  Hab. 
  River 
  Parana, 
  Province 
  of 
  Corrientes. 
  

  

  My 
  Cabinet. 
  

  

  Cabinet 
  of 
  Dr 
  Burrough. 
  

  

  Cabinet 
  of 
  the 
  Academy 
  of 
  Natural 
  Sciences 
  of 
  Philadelphia. 
  

  

  Diam. 
  "9. 
  Length 
  1*2, 
  Breadth 
  2-7 
  inches. 
  

  

  Shell 
  oblong, 
  subcylindrical, 
  dorsal 
  and 
  basal 
  margins 
  parallel, 
  trans- 
  

   verse, 
  very 
  inequilateral, 
  flattish 
  on 
  the 
  sides, 
  angular 
  behind, 
  inflated 
  ; 
  

   substance 
  of 
  the 
  shell 
  rather 
  thick 
  ; 
  beaks 
  rather 
  elevated 
  and 
  placed 
  

   near 
  the 
  anterior 
  margin; 
  ligament 
  long 
  and 
  thin; 
  umbones 
  flattened; 
  

   umbonial 
  slope 
  carinate 
  ; 
  posterior 
  slope 
  elevated 
  into 
  a 
  carina 
  ; 
  epider- 
  

   mis 
  finely 
  wrinkled 
  and 
  almost 
  black 
  ; 
  cardinal 
  teeth 
  oblique 
  and 
  crested, 
  

   larger 
  in 
  the 
  right 
  valve; 
  lateral 
  teeth 
  long 
  and 
  straight; 
  anterior 
  cica- 
  

   trices 
  distinct 
  ; 
  posterior 
  cicatrices 
  confluent 
  ; 
  dorsal 
  cicatrices 
  placed 
  

   in 
  the 
  centre 
  of 
  the 
  cavity 
  of 
  the 
  beaks; 
  cavity 
  of 
  the 
  beaks 
  shallow; 
  

   nacre 
  pearly 
  white 
  and 
  iridescent. 
  

  

  Remarks. 
  — 
  This 
  species 
  is 
  from 
  the 
  Burrough 
  collection, 
  and 
  is 
  dis- 
  

   tinct 
  from 
  any 
  I 
  have 
  seen. 
  It 
  resembles 
  somewhat, 
  in 
  the 
  outline 
  of 
  

   the 
  margin, 
  the 
  nasutus 
  of 
  Say. 
  The 
  posterior 
  slope 
  does 
  not, 
  how- 
  

   ever, 
  decline 
  so 
  much, 
  the 
  dorsal 
  and 
  basal 
  margins 
  being 
  nearly 
  

   parallel. 
  In 
  being 
  subcylindrical 
  it 
  resembles 
  the 
  cylindricus 
  of 
  Say 
  ; 
  

   it 
  has 
  not, 
  however, 
  either 
  tubercles 
  or 
  arrow-headed 
  markings. 
  The 
  

   very 
  dark 
  colour 
  of 
  its 
  epidermis 
  is 
  peculiar.* 
  

  

  * 
  Since 
  the 
  above 
  description 
  and 
  the 
  figure 
  were 
  made, 
  I 
  have 
  seen 
  a 
  more 
  perfect 
  

   specimen 
  in 
  the 
  possession 
  of 
  Dr 
  Burrough, 
  which 
  has 
  the 
  beaks 
  but 
  little 
  eroded. 
  In 
  

  

  