﻿56 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [N"oV. 
  18, 
  

  

  I 
  have 
  named 
  this 
  species 
  after 
  my 
  friend 
  Dr. 
  Duncan, 
  who 
  first 
  

   detected 
  the 
  operculum 
  in 
  its 
  interior, 
  and 
  who 
  has 
  assisted 
  me 
  in 
  

   arriving 
  at 
  a 
  definite 
  conclusion 
  respecting 
  the 
  age 
  of 
  these 
  fossils 
  by 
  

   furnishing 
  me 
  with 
  concurrent 
  testimony 
  drawn 
  from 
  an 
  examina- 
  

   tion 
  of 
  the 
  East 
  Indian 
  Tertiary 
  Corals. 
  

  

  Dimensions. 
  — 
  Large 
  specimen 
  : 
  length 
  ly 
  1 
  ^ 
  inch, 
  breadth 
  ±-1 
  inch 
  ; 
  

   length 
  of 
  aperture 
  fy 
  inch, 
  breadth 
  -fy 
  inch. 
  Small 
  specimen: 
  

   length 
  T 
  7 
  2 
  inch, 
  breadth 
  T 
  6 
  ^- 
  inch 
  ; 
  length 
  of 
  aperture 
  J- 
  inch, 
  breadth 
  

   / 
  T 
  inch. 
  

  

  Matrix. 
  — 
  Acoarse 
  greenish-grey 
  marl, 
  with 
  black 
  cinder-like 
  grains. 
  

  

  10. 
  jSTatica 
  rostalina, 
  spec. 
  nov. 
  PI. 
  VI. 
  fig. 
  8. 
  

  

  Shell 
  subglobose, 
  largely 
  and 
  perspectively 
  umbilicate, 
  with 
  a 
  

   short 
  but 
  protruding 
  spire 
  and 
  a 
  distinctly 
  impressed 
  suture. 
  Whorls 
  

   rounded, 
  smooth, 
  somewhat 
  flattened 
  near 
  the 
  suture, 
  and 
  then 
  con- 
  

   vexly 
  descending, 
  produced 
  downwards, 
  and 
  rapidly 
  increasing 
  in 
  

   size. 
  Aperture 
  narrow, 
  not 
  quite 
  a 
  semicircle, 
  equally 
  tapering 
  above 
  

   and 
  below 
  ; 
  basal 
  portion 
  of 
  the 
  peristome 
  produced 
  so 
  as 
  to 
  form 
  an 
  

   almost 
  horizontal, 
  but 
  slightly 
  descending, 
  obtuse 
  spout. 
  Umbilicus 
  

   with 
  a 
  distinct 
  raised 
  margin, 
  which 
  descends 
  below 
  the 
  mouth 
  and 
  

   beyond 
  the 
  columella, 
  and 
  then 
  curves 
  upwards 
  so 
  as 
  to 
  include 
  the 
  

   spout. 
  Columella 
  thin, 
  enamelled 
  above, 
  and 
  with 
  a 
  small, 
  flat, 
  rather 
  

   broad, 
  striated 
  callosity 
  entering 
  the 
  umbilicus. 
  

  

  Operculum 
  half-heart-shaped 
  ; 
  convex 
  margin 
  turned 
  outwards, 
  

   unevenly 
  serrated 
  outwardly, 
  and 
  succeeded 
  by 
  a 
  narrow 
  platform 
  

   projecting 
  beyond 
  the 
  rest 
  of 
  the 
  outer 
  surface 
  of 
  the 
  operculum, 
  and 
  

   separated 
  from 
  it, 
  first 
  by 
  an 
  obliquely 
  descending 
  rim, 
  and 
  below 
  

   this 
  by 
  a 
  groove 
  cut 
  horizontally 
  into 
  the 
  side 
  of 
  the 
  platform. 
  The 
  

   rest 
  of 
  the 
  outer 
  surface 
  of 
  the 
  operculum 
  is 
  flat, 
  with 
  the 
  exception 
  

   of 
  a 
  nearly 
  semicircular 
  tumidity, 
  which 
  begins 
  at 
  the 
  nucleus, 
  and 
  

   extends, 
  with 
  the 
  growth 
  of 
  the 
  operculum, 
  almost 
  parallel 
  to 
  the 
  

   convex 
  margin, 
  but 
  at 
  a 
  gradually 
  increasing 
  distance, 
  and 
  becoming 
  

   gradually 
  less 
  prominent. 
  The 
  inner 
  or 
  columellar 
  margin 
  of 
  the 
  

   operculum, 
  like 
  that 
  of 
  the 
  preceding 
  species, 
  is 
  thick 
  in 
  the 
  middle 
  

   and 
  becomes 
  thinner 
  at 
  each 
  end. 
  

  

  This 
  species, 
  of 
  which 
  there 
  are 
  two 
  specimens 
  (one 
  nearly 
  perfect 
  

   contained 
  the 
  operculum 
  just 
  described) 
  in 
  M. 
  de 
  Groot's 
  collection, 
  

   is 
  allied 
  to 
  Natica 
  jpellis-tigrina, 
  Chemn., 
  a 
  Swan-River 
  species. 
  

   Were 
  other 
  evidence 
  wanting, 
  the 
  differences 
  in 
  their 
  opercula 
  would 
  

   alone 
  be 
  sufficient 
  to 
  establish 
  their 
  specific 
  distinctness 
  ; 
  but 
  these 
  

   differences 
  are 
  also 
  associated, 
  as 
  would 
  be 
  expected, 
  with 
  differences 
  

   in 
  the 
  shells. 
  Thus, 
  the 
  aperture 
  of 
  N. 
  pellis-tigrina 
  is 
  much 
  more 
  

   dilated, 
  the 
  umbilicus 
  smaller, 
  and 
  the 
  spire 
  longer 
  than 
  the 
  corre- 
  

   sponding 
  structures 
  in 
  the 
  Javan 
  fossil. 
  There 
  is, 
  however, 
  a 
  very 
  

   great 
  general 
  resemblance 
  in 
  form 
  between 
  the 
  two 
  species. 
  

  

  Dimensions. 
  — 
  Length 
  ^J 
  inch, 
  breadth 
  |^ 
  inch 
  ; 
  length 
  of 
  aper- 
  

   ture 
  | 
  inch, 
  breadth 
  ^ 
  inch. 
  

  

  Matrix. 
  — 
  A 
  reddish 
  calcareous 
  sand, 
  partly 
  composed 
  of 
  fragments 
  

   of 
  shell, 
  and 
  containing 
  a 
  Foraminifer, 
  referred 
  to 
  below 
  (p. 
  62) 
  as 
  

   Amphistegina 
  vulgaris. 
  

  

  