﻿ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  

  

  Table 
  XXV. 
  

  

  171 
  

  

  Lias. 
  

  

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  02 
  

  

  

  

  

  

  

  

  Whole 
  

  

  Genera 
  and 
  

  

  

  

  

  The 
  above 
  are 
  all 
  Mollusca 
  

  

  Lias 
  

  

  species 
  in 
  

  

  I 
  

  

  J 
  i 
  valves 
  

  

  

  ex 
  

  

  cept 
  ^ 
  Annelida 
  in 
  the 
  

  

  Fauna. 
  

  

  each 
  division. 
  

  

  

  

  

  

  Inferior 
  Oolite. 
  

  

  Three 
  Ammonites 
  only 
  are 
  known 
  to 
  pass 
  the 
  boundary 
  line 
  

   between 
  the 
  Upper 
  Lias 
  and 
  the 
  Inferior 
  Oolite 
  ; 
  they 
  are 
  Harpo- 
  

   ceras 
  inslgne, 
  Harpoceras 
  radians, 
  and 
  Harpoceras 
  concavum. 
  They 
  

   are 
  Upper- 
  Lias 
  forms, 
  and 
  lived 
  on 
  through 
  the 
  physical 
  change 
  

   that 
  took 
  place, 
  or 
  the 
  transition 
  from 
  the 
  conditions 
  of 
  argillaceous 
  

   and, 
  in 
  places, 
  arenaceous 
  deposition, 
  to 
  those 
  uuder 
  which 
  calcareous 
  

   deposits 
  were 
  formed, 
  the 
  latter 
  of 
  which 
  prevailed, 
  with 
  the 
  exception 
  

   of 
  the 
  Fuller's-earth 
  episode 
  (a 
  local 
  oue), 
  up 
  to 
  the 
  Oxfordian 
  stage. 
  

   The 
  manifest 
  change 
  in 
  the 
  molluscan 
  fauna 
  from 
  the 
  Inferior 
  

   Oolite 
  to 
  the 
  Fuller's 
  Earth 
  clearly 
  shows 
  the 
  influence 
  due 
  to 
  sedi- 
  

   mentary 
  habitat. 
  As 
  a 
  group 
  of 
  species, 
  probably 
  no 
  other 
  so 
  com- 
  

   pletely 
  died 
  out 
  at 
  a 
  special 
  age 
  as 
  did 
  that 
  of 
  the 
  Ammonitidae. 
  

   293 
  species 
  have 
  been 
  recorded 
  from 
  the 
  Liassic 
  strata 
  of 
  Britain 
  ; 
  

   173 
  of 
  these 
  occurred 
  in 
  the 
  Lower 
  Lias, 
  54 
  in 
  the 
  Middle 
  Lias, 
  and 
  

   79 
  in 
  the 
  Upper, 
  and 
  only 
  2 
  or 
  3 
  of 
  the 
  Upper-Lias 
  forms 
  passed 
  to 
  

   the 
  Inferior 
  Oolite. 
  Even 
  between 
  the 
  Lower 
  and 
  Middle 
  Lias 
  167 
  

   species 
  had 
  either 
  migrated 
  or 
  died 
  out 
  ; 
  for 
  only 
  6 
  species 
  out 
  of 
  the 
  

   173 
  passed 
  onwards 
  and 
  upwards 
  into 
  the 
  Middle 
  Lias, 
  and, 
  as 
  already 
  

   stated, 
  not 
  a 
  single 
  species 
  of 
  Ammonite 
  is 
  common 
  to 
  all 
  three 
  divi- 
  

   sions 
  of 
  the 
  Lias 
  in 
  Britain. 
  

  

  Nautili. 
  — 
  Ten 
  species 
  are 
  known 
  in 
  the 
  Lias 
  ; 
  the 
  occurrences 
  are 
  

   6 
  in 
  the 
  Lower 
  Lias, 
  4 
  in 
  the 
  Middle 
  Lias, 
  and 
  3 
  in 
  the 
  Upper. 
  The 
  

   typical 
  species 
  are 
  N. 
  intermedins, 
  N. 
  latidorsatus, 
  N. 
  striatus, 
  JV. 
  

   semistriatus, 
  and 
  N. 
  truncatus. 
  No 
  species 
  passes 
  to 
  the 
  Inferior 
  

   Oolite, 
  neither 
  do 
  we 
  know 
  of 
  any 
  species 
  being 
  common 
  to 
  all 
  

   three 
  of 
  the 
  divisions 
  of 
  the 
  Lias. 
  In 
  so 
  pelagic 
  a 
  form 
  we 
  should 
  

  

  