﻿crick: 
  on 
  crioceratites 
  bowerbankii. 
  139 
  

  

  thicker 
  but 
  not 
  quite 
  so 
  prominent. 
  The 
  last 
  two, 
  however, 
  show 
  

   a 
  considerable 
  diminution 
  in 
  size. 
  About 
  40 
  mm. 
  in 
  front 
  of 
  the 
  last 
  

   complete 
  rib 
  there 
  is 
  another 
  obscure 
  rib, 
  most 
  apparent 
  near 
  the 
  

   periphery, 
  and 
  about 
  20 
  mm. 
  in 
  front 
  of 
  this 
  a 
  portion 
  of 
  the 
  peristome 
  

   is 
  visible. 
  The 
  peristome 
  was 
  plain, 
  and 
  in 
  the 
  fossil, 
  which 
  it 
  must 
  

   be 
  remembered 
  is 
  an 
  internal 
  cast, 
  there 
  are 
  several 
  fairly-coarse 
  

   lines 
  of 
  growth 
  immediately 
  posterior 
  and 
  parallel 
  to 
  it. 
  

  

  j^ot 
  only 
  are 
  the 
  ornaments 
  much 
  more 
  feeble, 
  but 
  the 
  body- 
  

   chamber 
  itself 
  is 
  very 
  much 
  reduced 
  in 
  front 
  of 
  the 
  third 
  (counting 
  

   from 
  the 
  aperture) 
  large 
  rib. 
  True 
  the 
  (morphological) 
  left 
  side 
  of 
  

   the 
  fossil 
  is 
  abraded, 
  but 
  the 
  fossil 
  does 
  not 
  appear 
  here 
  to 
  be 
  either 
  

   distorted 
  or 
  crushed. 
  This 
  condition 
  of 
  the 
  anterior 
  end 
  of 
  the 
  bodv- 
  

   chamber 
  is 
  evidently 
  a 
  senile 
  character 
  and 
  indicates 
  the 
  extremely 
  

   feeble 
  condition 
  of 
  the 
  animal 
  and 
  its 
  approaching 
  death. 
  

  

  Although 
  the 
  rough 
  surface 
  of 
  the 
  specimen, 
  which 
  is 
  an 
  internal 
  

   cast, 
  is 
  not 
  favourable 
  for 
  the 
  preservation 
  of 
  delicate 
  lines, 
  there 
  is 
  

   what 
  appears 
  to 
  be 
  an 
  obscure 
  indication 
  of 
  one 
  of 
  the 
  muscle-scars. 
  

   AVhen 
  complete 
  the 
  scar 
  seems 
  to 
  have 
  been 
  an 
  oval 
  area 
  truncated 
  

   posteriorly, 
  approximately 
  45 
  mm. 
  long 
  and 
  40 
  mm. 
  wide, 
  but 
  only 
  

   its 
  anterior 
  and 
  inner 
  boundaries 
  are 
  preserved 
  as 
  an 
  obscure 
  

   impressed 
  line. 
  Commencing 
  on 
  the 
  umbilical 
  margin 
  at 
  a 
  point 
  

   half-way 
  between 
  the 
  sixth 
  and 
  seventh 
  (counting 
  from 
  the 
  aperture) 
  

   ribs 
  the 
  line 
  passes 
  forward 
  and 
  inward 
  over 
  the 
  margin 
  to 
  witliin 
  

   about 
  30 
  mm. 
  of 
  the 
  suture 
  of 
  the 
  shell, 
  it 
  then 
  curves 
  backward 
  still 
  

   passing 
  inward 
  until 
  at 
  about 
  28 
  mm. 
  from 
  its 
  most 
  anterior 
  part 
  it 
  is 
  

   only 
  10 
  mm. 
  from 
  the 
  suture 
  of 
  the 
  shell, 
  then 
  curving 
  slowly 
  outward 
  

   it 
  can 
  be 
  traced 
  nearly 
  as 
  far 
  as 
  the 
  last 
  septal-suture. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  VII. 
  

  

  Crioceratites 
  hoioerhankii, 
  J. 
  de 
  C. 
  Sowerby, 
  from 
  the 
  Lower 
  Greensand, 
  

   Aptian, 
  Isle 
  of 
  Wight. 
  Type-spechnen. 
  British 
  Museum 
  Collection, 
  

   register 
  number 
  46474. 
  

  

  Fig. 
  1. 
  — 
  Lateral 
  aspect, 
  showing 
  the 
  rapid 
  decrease 
  in 
  size 
  of 
  the 
  anterior 
  part 
  

   of 
  the 
  body-chamber. 
  The 
  body-chamber 
  commences 
  immediately 
  

   above 
  the 
  left-hand 
  edge 
  of 
  the 
  scale, 
  m.sc. 
  anterior 
  boundary 
  of 
  

   muscle-scar. 
  

  

  ,, 
  2. 
  — 
  Peripheral 
  view, 
  showing 
  the 
  enormously-enlarged 
  ribs 
  on 
  the 
  body- 
  

   chamber. 
  

  

  ,, 
  3. 
  — 
  Apertural 
  view 
  (with 
  the 
  aperture 
  turned 
  slightly 
  to 
  the 
  right), 
  

   showing 
  the 
  rapid 
  decrease 
  in 
  size 
  of 
  the 
  anterior 
  part 
  of 
  the 
  body- 
  

   chamber 
  and 
  {vi.sc.) 
  the 
  boundary 
  of 
  the 
  muscle-scar. 
  

   (In 
  each 
  figure 
  the 
  scale 
  represents 
  4 
  inches 
  = 
  10*15 
  cm.) 
  

  

  VOL. 
  XII. 
  — 
  APRIL, 
  1917. 
  11 
  

  

  