﻿76 
  ON 
  THE 
  NAIADES, 
  

  

  link 
  in 
  the 
  gradual 
  change 
  of 
  the 
  characters 
  of 
  the 
  teeth. 
  It 
  ap- 
  

   proaches 
  that 
  division 
  of 
  the 
  Naiades 
  which 
  do 
  not 
  possess 
  teeth, 
  more 
  

   closely 
  than 
  any 
  species 
  which 
  has 
  come 
  under 
  my 
  notice. 
  

  

  Anodonta 
  lato-marginata. 
  Plate 
  XII. 
  fig. 
  34. 
  

  

  Testa 
  obovatd, 
  transversa, 
  insequilaterali 
  ; 
  intus 
  margine 
  lata 
  et 
  cornea; 
  sinu 
  

   longo 
  et 
  in 
  partem 
  internam 
  disci 
  vergente 
  ; 
  valvulis 
  crassis 
  ; 
  epidermide 
  rubido- 
  

   fuscd 
  ; 
  margarita 
  alba 
  et 
  iridescente. 
  

  

  Shell 
  obovate, 
  transverse, 
  inequilateral, 
  interior 
  with 
  a 
  broad 
  horn 
  coloured 
  border; 
  

   sinus 
  long, 
  and 
  pointed 
  towards 
  the 
  interior 
  of 
  the 
  disk 
  ; 
  valves 
  thick 
  ; 
  epidermis 
  red- 
  

   dish 
  brown 
  ; 
  nacre 
  pearly 
  white 
  and 
  iridescent. 
  

  

  Hab. 
  River 
  Parana, 
  South 
  America. 
  Dr 
  Burrough. 
  

  

  My 
  Cabinet. 
  

  

  Cabinet 
  of 
  the 
  Academy 
  of 
  Natural 
  Sciences 
  of 
  Philadelphia. 
  

  

  Diam. 
  1-5, 
  Length 
  2-5, 
  Breadth 
  3-5 
  inches. 
  

  

  Shell 
  obovate, 
  transverse, 
  inequilateral, 
  inflated, 
  interior 
  with 
  a 
  broad 
  

   horn 
  coloured 
  border 
  ; 
  sinus 
  long, 
  and 
  pointed 
  to 
  the 
  interior 
  of 
  the 
  

   disk; 
  substance 
  of 
  the 
  shell 
  thick: 
  beaks 
  somewhat 
  elevated; 
  ligament 
  

   long 
  and 
  thick; 
  epidermis 
  reddish 
  brown, 
  finely 
  wrinkled, 
  and 
  some- 
  

   times 
  obscurely 
  rayed; 
  anterior 
  cicatrices 
  distinct; 
  posterior 
  cicatrices 
  

   confluent 
  ; 
  palleal 
  cicatrices 
  almost 
  imperceptible 
  ; 
  dorsal 
  cicatrices 
  ap- 
  

   parently 
  none; 
  cavity 
  of 
  the 
  beaks 
  shallow 
  and 
  subangular; 
  nacre 
  

   pearly 
  white 
  and 
  iridescent, 
  extending 
  only 
  to 
  the 
  broad 
  horn 
  coloured 
  

   border. 
  

  

  Remarks. 
  — 
  In 
  the 
  collection 
  of 
  Dr 
  Burrough 
  there 
  are 
  several 
  spe- 
  

   cimens 
  of 
  this 
  species, 
  some 
  of 
  which 
  are 
  young 
  and 
  more 
  rotund 
  than 
  

   that 
  figured 
  here. 
  It 
  presents 
  several 
  characters 
  unusual 
  in 
  the 
  species 
  

   of 
  this 
  genus, 
  so 
  far 
  as 
  our 
  knowledge 
  extends. 
  The 
  horn 
  coloured 
  

   border 
  is 
  even 
  broader 
  than 
  that 
  of 
  the 
  tenebricosa 
  herein 
  described, 
  

   and 
  the 
  apparent 
  absence 
  of 
  the 
  dorsal 
  cicatrices 
  I 
  have 
  never 
  noticed 
  

   before 
  in 
  any 
  species 
  of 
  the 
  family. 
  The 
  sinus 
  of 
  this 
  species 
  is 
  very 
  

   remarkable, 
  as 
  well 
  as 
  that 
  of 
  the 
  tenebricosa. 
  It 
  does 
  not, 
  however, 
  

  

  