﻿CKICK 
  : 
  ON 
  AMMONITES 
  NAVICULARIS, 
  JIANTELt. 
  157 
  

  

  the 
  following 
  dimensions: 
  diameter 
  of 
  shell, 
  117mm. 
  (1); 
  height 
  

   of 
  outer 
  whorl, 
  50 
  mm. 
  (0'43) 
  ; 
  thickness 
  of 
  outer 
  whorl, 
  about 
  

   58 
  mm. 
  (0-49); 
  width 
  of 
  umbilicus, 
  35 
  mm. 
  (0-30). 
  The 
  fossil 
  is 
  

   fairly 
  well 
  represented 
  (but 
  reversed) 
  of 
  the 
  natural 
  size 
  in 
  his 
  

   fig. 
  1. 
  The 
  ribs 
  are 
  alternately 
  longer 
  and 
  shorter; 
  the 
  longer 
  

   commence 
  at 
  the 
  suture 
  of 
  the 
  shell, 
  cross 
  the 
  inner 
  or 
  umbilical 
  

   area 
  of 
  the 
  whorl, 
  and 
  increasing 
  in 
  strength 
  form 
  a 
  tubercle 
  at 
  the 
  

   edge 
  of 
  the 
  umbilicus, 
  and 
  sometimes 
  bear 
  a 
  second 
  tubercle 
  on 
  each 
  

   side 
  of 
  the 
  whorl 
  at 
  about 
  one-third 
  of 
  the 
  width 
  of 
  the 
  lateral 
  area 
  

   from 
  this 
  umbilical 
  margin 
  ; 
  the 
  shorter 
  ribs 
  rise 
  on 
  the 
  side 
  of 
  the 
  

   whorl, 
  nearer 
  the 
  umbilicus 
  than 
  the 
  periphery 
  ; 
  all 
  the 
  ribs 
  cross 
  

   the 
  periphery, 
  but 
  are 
  slightly 
  angular 
  or 
  feebly 
  tuberculated 
  at 
  each 
  

   margin 
  of 
  the 
  periphery, 
  even 
  at 
  the 
  anterior 
  end 
  of 
  the 
  specimen, 
  

   «.(?. 
  at 
  a 
  diameter 
  of 
  117 
  mm. 
  Between 
  the 
  two 
  tubercles 
  near 
  the 
  

   umbilical 
  margin 
  the 
  longer 
  ribs 
  are 
  straight 
  and 
  have 
  an 
  almost 
  

   radial 
  direction 
  or 
  are 
  but 
  feebly 
  reclined, 
  but 
  between 
  the 
  second 
  

   row 
  of 
  tubercles 
  and 
  the 
  row 
  at 
  the 
  margin 
  of 
  the 
  periphery, 
  both 
  

   the 
  longer 
  ribs 
  and 
  the 
  intervening 
  shorter 
  ribs 
  have 
  a 
  slight 
  

   forwardly 
  concave 
  curve, 
  and 
  at 
  a 
  point 
  rather 
  nearer 
  the 
  tubercle 
  

   at 
  the 
  margin 
  of 
  the 
  periphery 
  than 
  the 
  tubercle 
  in 
  the 
  second 
  row 
  

   from 
  the 
  umbilicus 
  each 
  rib 
  is 
  angular 
  and 
  feebly 
  raised, 
  and 
  in 
  the 
  

   earliest 
  part 
  of 
  the 
  outer 
  whorl 
  bears 
  a 
  small 
  but 
  distinct 
  tubercle 
  ; 
  

   all 
  the 
  ribs 
  are 
  straight 
  on 
  the 
  periphery. 
  The 
  ribs 
  are 
  prominent, 
  

   rounded, 
  and 
  at 
  the 
  commencement 
  of 
  the 
  oiiter 
  whorl 
  not 
  quite 
  so 
  

   wide 
  as 
  the 
  interspaces, 
  whilst 
  near 
  the 
  anterior 
  end 
  of 
  the 
  specimen 
  

   they 
  are 
  only 
  one-half 
  the 
  width 
  of 
  the 
  interspaces. 
  Thus 
  there 
  are 
  

   differences 
  between 
  this 
  fossil 
  and 
  Mantell's 
  type-specimen, 
  differences 
  

   which 
  we 
  think 
  must 
  be 
  regarded 
  as 
  of 
  specific 
  value. 
  

  

  The 
  specimen 
  h;is 
  been 
  labelled 
  " 
  Grey 
  Chalk 
  : 
  Dover". 
  According 
  

   to 
  the 
  Museum 
  register, 
  tlie 
  fossil 
  was 
  obtained 
  from 
  Mr. 
  Mackie, 
  

   but 
  both 
  the 
  horizon 
  and 
  locality 
  of 
  the 
  fossil 
  are 
  unrecorded. 
  Upon 
  

   the 
  specimen 
  is 
  written 
  in 
  ink 
  (apparently 
  in 
  the 
  handwriting 
  of 
  

   Daniel 
  Sharpe), 
  " 
  Fig. 
  1, 
  PL 
  18. 
  Mr. 
  Mackie." 
  Although 
  Sharpe's 
  

   figure 
  is 
  reversed 
  and 
  a 
  little 
  restored, 
  there 
  can 
  be 
  no 
  doubt 
  about 
  

   its 
  being 
  the 
  figured 
  example. 
  Sharpe 
  does 
  not 
  specially 
  refer 
  to 
  

   the 
  fossil 
  in 
  the 
  text 
  of 
  his 
  work, 
  but 
  in 
  the 
  explanation 
  of 
  the 
  plate 
  

   he 
  states 
  that 
  the 
  specimen 
  is 
  " 
  from 
  the 
  Grey 
  Chalk 
  of 
  "White 
  Nore, 
  

   Dorsetshire 
  " 
  and 
  that 
  it 
  is 
  " 
  in 
  the 
  collection 
  of 
  E. 
  H. 
  Bunbury, 
  Esq." 
  

   He 
  cites 
  the 
  species 
  as 
  being 
  "common 
  in 
  the 
  Lower 
  Chalk 
  of 
  the 
  

   South 
  of 
  England". 
  

  

  In 
  the 
  explanation 
  of 
  his 
  figures 
  Sharpe 
  states 
  that 
  the 
  original 
  of 
  

   fig. 
  2 
  came 
  "from 
  the 
  Grey 
  Chalk 
  near 
  Lewes", 
  and 
  that 
  it 
  was 
  

   " 
  in 
  the 
  collection 
  of 
  Henry 
  Catt 
  [afterwards 
  Willett], 
  Esq." 
  This 
  

   collection 
  is 
  now 
  in 
  the 
  Brighton 
  Museum, 
  and 
  in 
  the 
  Catalogue 
  of 
  

   Types 
  and 
  Figured 
  Specimens 
  in 
  that 
  Museum, 
  published 
  in 
  the 
  

   Museum 
  Report 
  for 
  the 
  years 
  1891-2, 
  a 
  specimen 
  in 
  the 
  Willett 
  

   collection 
  is 
  recorded 
  (p. 
  16) 
  as 
  the 
  original 
  of 
  Sharpe's 
  figure. 
  

   Although 
  this 
  specimen, 
  for 
  the 
  loan 
  of 
  which 
  we 
  ore 
  indebted 
  to 
  

   the 
  Chairman 
  and 
  Committee 
  of 
  the 
  Brighton 
  Museum, 
  has 
  been 
  

   labelled 
  as 
  having 
  been 
  described 
  and 
  figured 
  by 
  Sharpe 
  in 
  "Pal. 
  

  

  