﻿108 
  ON 
  THE 
  NAIADES, 
  

  

  some 
  years 
  since 
  by 
  a 
  dealer 
  in 
  Paris. 
  It 
  perhaps 
  most 
  resembles 
  the 
  

   Zeylanica 
  (Lamarck). 
  It 
  differs, 
  however, 
  in 
  being 
  more 
  compressed, 
  

   more 
  rotund, 
  in 
  having 
  longer 
  lateral 
  teeth, 
  and 
  in 
  these 
  being 
  serru- 
  

   late. 
  The 
  nacre 
  is 
  rather 
  thinner, 
  and 
  is 
  coloured. 
  On 
  comparison 
  

   it 
  will 
  be 
  observed 
  that 
  the 
  anterior 
  tooth 
  of 
  the 
  Zeylanica 
  is 
  merely 
  

   a 
  tubercle, 
  while 
  that 
  of 
  rotundata 
  is 
  long 
  and 
  lamellar. 
  The 
  nacre 
  

   is 
  disposed 
  to 
  be 
  pinkish 
  on 
  the 
  posterior 
  part. 
  

  

  Cyrena 
  Jayensis. 
  Plate 
  XVII. 
  fig. 
  52. 
  

  

  Testa 
  subrotundd, 
  subsequilaterali, 
  antice 
  rugosd; 
  valvulis 
  crassis 
  ; 
  natibus 
  par- 
  

   vis, 
  elevatis 
  ; 
  dentibus 
  cardinalibus 
  bijidis, 
  lateralibus 
  longis, 
  minute 
  serratis, 
  

   rectisque; 
  margaritd 
  purpurea. 
  

  

  Shell 
  subrotund, 
  nearly 
  equilateral, 
  transversely 
  wrinkled 
  on 
  the 
  anterior 
  part 
  ; 
  

   valves 
  rather 
  thick 
  ; 
  beaks 
  small, 
  elevated 
  ; 
  cardinal 
  teeth 
  bifid 
  ; 
  lateral 
  teeth 
  long, 
  

   nearly 
  straight, 
  and 
  minutely 
  serrulate 
  ; 
  nacre 
  purple. 
  

  

  Hab. 
  Batavia? 
  J. 
  C. 
  Jay, 
  M.D. 
  

  

  My 
  Cabinet. 
  

   Cabinet 
  of 
  Dr 
  Jay. 
  

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

  

  Shell 
  subrotund, 
  nearly 
  equilateral, 
  furnished 
  with 
  transverse 
  rather 
  

   large 
  wrinkles 
  on 
  the 
  anterior 
  part 
  ; 
  substance 
  of 
  the 
  shell 
  rather 
  thick 
  ; 
  

   beaks 
  small, 
  elevated, 
  retuse 
  ; 
  ligament 
  very 
  short 
  and 
  thick 
  : 
  epidermis 
  

   dark 
  brown, 
  shining; 
  cardinal 
  teeth 
  bifid, 
  long, 
  nearly 
  straight 
  and 
  

   minutely 
  serrulate 
  ; 
  cicatrices 
  scarcely 
  perceptible 
  ; 
  cavity 
  of 
  the 
  shell 
  

   shallow 
  ; 
  cavity 
  of 
  the 
  beaks 
  subangular 
  ; 
  nacre 
  dark 
  purple, 
  sometimes 
  

   whitish. 
  

  

  Remarks. 
  — 
  It 
  is 
  to 
  the 
  kindness 
  of 
  Dr 
  Jay 
  I 
  am 
  indebted 
  for 
  the 
  

   specimen 
  figured. 
  That 
  of 
  his 
  cabinet 
  is 
  rather 
  more 
  oblique 
  than 
  

   this. 
  The 
  Jayensis 
  has 
  some 
  resemblance 
  to 
  the 
  rotundata, 
  described 
  

   herein, 
  but 
  differs 
  in 
  having 
  rather 
  large 
  wrinkles 
  on 
  the 
  anterior 
  part, 
  

   in 
  having 
  more 
  elevated 
  beaks, 
  and 
  in 
  the 
  dark 
  purple 
  colour 
  of 
  the 
  

   nacre. 
  

  

  