﻿DR. 
  COOKE 
  : 
  OPERCULUM 
  OF 
  THE 
  GENUS 
  BURSA, 
  I 
  

  

  Species 
  whose 
  operculum 
  g„^,^, 
  ^, 
  information. 
  ^^^"irnotTno^vr"'"" 
  

  

  Sub-genus 
  Bafonaria 
  (= 
  Tutufa, 
  Jouss.). 
  

   Sect. 
  Crossata. 
  

  

  califoniica, 
  Hinds. 
  M.B., 
  McA., 
  A.H.C. 
  

   ventricosa, 
  Brod. 
  J.il.T., 
  A.H.C. 
  

  

  Sect. 
  Bufonaria. 
  

  

  ruhefa, 
  Bolt. 
  M.B. 
  coriacea, 
  Ptve. 
  

  

  scrobiculator, 
  L. 
  J.C.iM., 
  J.R.T. 
  camingiana, 
  Dkr. 
  

  

  papulosa, 
  A. 
  Ad. 
  

   ratielloides, 
  Rve. 
  

  

  With 
  regard 
  to 
  the 
  section 
  Craspedotriton, 
  Kesteven 
  has 
  shown 
  ' 
  

   that 
  the 
  operculum 
  and 
  radula 
  of 
  convoltitus, 
  Brod., 
  are 
  those 
  of 
  

   Irophon, 
  not 
  Bursa; 
  it 
  is 
  probable, 
  therefore, 
  that 
  scalariformis, 
  

   Brod., 
  and 
  scalarina, 
  A. 
  Ad, 
  (= 
  speciosa, 
  Ang.), 
  will 
  also 
  prove 
  to 
  be 
  

   Trophons 
  : 
  the 
  section 
  therefore 
  drops 
  out. 
  

  

  Tlie 
  details 
  of 
  the 
  known 
  species 
  are 
  as 
  follows 
  : 
  — 
  

  

  A. 
  Sub-genus 
  Bursa. 
  

  

  (rt) 
  Section 
  Bursa. 
  

  

  General 
  characteristics: 
  operculum 
  rather 
  thin, 
  more 
  or 
  less 
  

  

  transparent, 
  almost 
  triangular, 
  with 
  longer 
  side 
  rounded, 
  nucleus 
  

  

  sub-lateral, 
  to 
  the 
  left 
  {i.e. 
  adjacent 
  to 
  the 
  columella), 
  nearly 
  central, 
  

  

  clear 
  of 
  the 
  margin, 
  lines 
  of 
  growth 
  prominent. 
  

  

  1. 
  albifasciata, 
  Sowb. 
  A 
  somewhat 
  broken 
  operculum 
  is 
  attached 
  

   to 
  the 
  tablet 
  in 
  M.B., 
  nucleus 
  to 
  right, 
  sub-lateral, 
  half-way 
  between 
  

   centre 
  and 
  lower 
  end. 
  In 
  other 
  words, 
  if 
  the 
  operculum 
  belongs 
  to 
  

   the 
  shell, 
  which 
  I 
  doubt 
  (the 
  shells 
  are 
  Cuming's), 
  the 
  species 
  must 
  

   be 
  removed, 
  probably 
  to 
  section 
  Ranella 
  or 
  Colubrellina, 
  from 
  which, 
  

   conchologically, 
  it 
  is 
  quite 
  distinct. 
  

  

  2. 
  crumena. 
  Lam. 
  Nucleus 
  well 
  marked, 
  lines 
  of 
  growth 
  flattened. 
  

  

  3. 
  elegans, 
  Beck. 
  As 
  in 
  spinosa, 
  not 
  transparent, 
  colour 
  deep 
  brown. 
  

  

  4. 
  margaritnla, 
  Desh. 
  Rather 
  less 
  poiuted 
  at 
  top 
  and 
  bottom 
  than 
  

   the 
  other 
  species, 
  dark 
  brown, 
  lines 
  of 
  growth 
  not 
  very 
  prominent. 
  

  

  5. 
  nayia, 
  Sowb. 
  Two 
  opercula 
  are 
  attached 
  to 
  the 
  tablet 
  in 
  M.B. 
  

   (Cuming's 
  specimens), 
  one 
  rather 
  long, 
  narrow, 
  nucleus 
  sub-terminal, 
  

   the 
  other 
  more 
  ovate, 
  light-coloured, 
  nucleus 
  sub-marginal, 
  to 
  right, 
  

   below 
  the 
  centre. 
  It 
  is 
  clear 
  that 
  both 
  of 
  these 
  cannot 
  be 
  the 
  true 
  

   opercula, 
  and 
  I 
  am 
  inclined 
  to 
  regard 
  them 
  both 
  with 
  suspicion. 
  

  

  6. 
  rana, 
  L. 
  Thin, 
  transparent, 
  lines 
  of 
  growth 
  very 
  sharply 
  

   marked, 
  and 
  occasionally 
  rising 
  into 
  broad 
  raised 
  ridges. 
  

  

  7. 
  spmosa, 
  Lam. 
  Not 
  angled, 
  but 
  rounded, 
  against 
  the 
  columella, 
  

   thicker 
  than 
  in 
  rana, 
  lines 
  of 
  growth 
  not 
  elevated. 
  

  

  8. 
  thersites, 
  Redf. 
  Rather 
  thin, 
  nucleus 
  very 
  near 
  the 
  margin, 
  

   a 
  little 
  below 
  the 
  centre. 
  

  

  ^ 
  Proc. 
  Linn. 
  Soc. 
  N.S. 
  Wales, 
  vol. 
  xxvii, 
  1902, 
  p. 
  479. 
  Dall, 
  though 
  writing 
  

   his 
  paper 
  on 
  the 
  Frog 
  Shells 
  in 
  1904, 
  does 
  not 
  seem 
  to 
  have 
  seen 
  Kesteven's 
  

   paper, 
  as 
  he 
  expressly 
  says 
  (p. 
  13), 
  with 
  reference 
  to 
  scalariformis 
  and 
  

   convolutus, 
  "their 
  operculum 
  is 
  not 
  known 
  to 
  me." 
  

  

  