﻿AND 
  OTHER 
  FAMILIES. 
  79 
  

  

  Diam. 
  1*5, 
  Length 
  1-9, 
  Breadth 
  3-3 
  inches. 
  

  

  Shell 
  elliptical, 
  transverse, 
  inequilateral, 
  with 
  a 
  broad 
  horn 
  coloured 
  

   border, 
  emarginate 
  at 
  base 
  ; 
  sinus 
  incurved 
  ; 
  substance 
  of 
  the 
  shell 
  thick 
  ; 
  

   beaks 
  scarcely 
  prominent; 
  ligament 
  long 
  and 
  thick; 
  epidermis 
  dark 
  

   olive 
  brown, 
  wrinkled, 
  obscurely 
  rayed 
  on 
  the 
  posterior 
  slope 
  ; 
  anterior 
  

   cicatrices 
  distinct 
  ; 
  posterior 
  cicatrices 
  confluent 
  ; 
  palleal 
  cicatrix 
  large 
  

   and 
  partially 
  tinted 
  with 
  bluish 
  purple 
  ; 
  dorsal 
  cicatrix 
  situated 
  in 
  the 
  

   centre 
  of 
  the 
  cavity 
  of 
  the 
  beaks 
  ; 
  cavity 
  of 
  the 
  beaks 
  very 
  shallow 
  : 
  

   nacre 
  pearly 
  white 
  clouded 
  with 
  bluish 
  purple, 
  extending 
  only 
  to 
  the 
  

   broad 
  horn 
  coloured 
  border, 
  iridescent. 
  

  

  Remarks.— 
  This 
  curious 
  species 
  is 
  from 
  the 
  collection 
  sent 
  to 
  the 
  

   Academy 
  of 
  Natural 
  Sciences 
  by 
  Dr 
  Burrough. 
  It 
  diners 
  distinctly 
  

   from 
  any 
  species 
  known 
  to 
  me. 
  The 
  horn 
  coloured 
  broad 
  border, 
  and 
  

   the 
  absence 
  of 
  nacreous 
  matter 
  on 
  this 
  part 
  is 
  very 
  remarkable, 
  as 
  is 
  

   also 
  the 
  close 
  approximation 
  to 
  a 
  perfect 
  ellipsis, 
  the 
  posterior 
  and 
  an- 
  

   terior 
  margins 
  being 
  nearly 
  of 
  the 
  same 
  curve. 
  The 
  clouded 
  bluish 
  

   purple 
  colour 
  I 
  have 
  never 
  seen 
  in 
  the 
  nacre 
  of 
  any 
  other 
  species. 
  The 
  

   sinus 
  is 
  so 
  peculiar 
  in 
  the 
  two 
  specimens 
  examined, 
  that 
  I 
  would 
  

   impress 
  it 
  as 
  important 
  in 
  the 
  character 
  of 
  this 
  species. 
  In 
  the 
  Jin. 
  

   exotica 
  (Lam.), 
  a 
  South 
  American 
  species, 
  the 
  sinus 
  is 
  generally 
  of 
  

   the 
  form 
  of 
  an 
  equilateral 
  triangle, 
  the 
  inferior 
  angle 
  being 
  sharp 
  and 
  

   well 
  defined. 
  In 
  the 
  present 
  species 
  the 
  sinus 
  is 
  still 
  more 
  remark- 
  

   able, 
  curving 
  in 
  towards 
  the 
  cavity 
  of 
  the 
  beak 
  and 
  terminating 
  with 
  

   quite 
  an 
  acute 
  angle. 
  The 
  line 
  of 
  the 
  opening 
  of 
  the 
  two 
  specimens 
  

   is 
  curved 
  and 
  not 
  a 
  plane, 
  as 
  usual 
  with 
  the 
  Naiades 
  ; 
  and 
  the 
  right 
  

   beak 
  and 
  margin 
  anterior 
  to 
  it, 
  overwrap 
  in 
  a 
  small 
  degree 
  the 
  left 
  

   beak 
  and 
  valve. 
  In 
  the 
  old 
  specimen 
  this 
  extension 
  of 
  the 
  margin 
  

   passes 
  the 
  other 
  more 
  than 
  an 
  eighth 
  of 
  an 
  inch 
  — 
  consequently 
  the 
  

   shell 
  might 
  almost 
  be 
  said 
  to 
  be 
  inequivalve. 
  In 
  its 
  general 
  characters 
  

   this 
  species 
  most 
  resembles 
  the 
  sinuosa 
  of 
  Lamarck. 
  

  

  