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  PROCEEDINGS 
  OP 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  Table 
  XXI. 
  — 
  Showing 
  the 
  value 
  of 
  12 
  chief 
  Genera 
  of 
  Monomy 
  avian 
  

   Mollusca 
  in 
  the 
  three 
  Divisions 
  of 
  the 
  Lias 
  with 
  relation 
  to 
  the 
  

   same 
  Group 
  in 
  the 
  whole 
  of 
  the 
  Jurassic 
  rocks. 
  

  

  .2 
  » 
  

  

  , 
  m 
  * 
  

  

  Chief 
  Monomy 
  arian 
  ^ 
  .2 
  

   genera 
  in 
  the 
  Lias. 
  

  

  

  Species 
  in 
  the 
  Lower 
  

   Middle, 
  & 
  Upper 
  Lias. 
  

  

  S 
  

  

  

  4" 
  

  

  Avicula 
  

  

  Gervillia 
  

  

  Gryphaea 
  

  

  Hinnites 
  

  

  Inoceramus 
  

  

  Lima 
  (Radula) 
  

  

  Ostrea 
  

  

  Pecten 
  I 
  90 
  

  

  Perna 
  17 
  

  

  Pinna 
  15 
  

  

  Placunopsis 
  9 
  

  

  Plicatula 
  19 
  

  

  18 
  

  

  11 
  

  

  7 
  

  

  7 
  

  

  (j 
  

  

  29 
  

  

  18 
  

  

  32 
  

  

  4 
  

  

  7 
  

  

  1 
  

  

  12 
  

  

  14 
  

   5 
  

   4 
  

   3 
  

   1 
  

  

  23 
  

  

  14 
  

  

  21 
  

  

  9 
  

  

  3 
  

   3 
  

   4 
  

   2 
  

   2 
  

  

  10 
  

   3 
  

  

  16 
  

  

  21 
  

   11 
  

   10 
  

  

  8 
  

  

  6 
  

   36 
  

   19 
  

   41 
  

  

  4 
  

   10 
  

  

  1 
  

   14 
  

  

  403 
  

  

  152 
  

  

  101 
  

  

  51 
  

  

  29 
  

  

  181 
  

  

  Carpenteria, 
  Placunopsis, 
  Posidonia, 
  Posidonomya, 
  Pteropema, 
  

   and 
  Spondylus 
  yield 
  only 
  1 
  species 
  each, 
  and 
  the 
  characteristic 
  

   genus 
  Crenatula 
  2 
  species. 
  

  

  Dimyaria. 
  — 
  This 
  great 
  and 
  important 
  group 
  of 
  the 
  Mollusca 
  

   occupies 
  a 
  prominent 
  position 
  in 
  the 
  history 
  of 
  the 
  Lias, 
  which 
  

   exceeds 
  the 
  Carboniferous 
  in 
  number 
  of 
  species, 
  the 
  numerical 
  value 
  

   of 
  the 
  genera 
  being 
  the 
  same. 
  245 
  species 
  are 
  known 
  in 
  the 
  

   Carboniferous 
  rocks 
  ; 
  and 
  the 
  Lias 
  in 
  all 
  three 
  divisions 
  has, 
  up 
  to 
  

   the 
  present 
  time, 
  yielded 
  45 
  genera 
  and 
  286 
  species, 
  

  

  the 
  Lower 
  Lias 
  yielding 
  36 
  genera 
  and 
  138 
  species, 
  

   the 
  Middle 
  „ 
  „ 
  34 
  „ 
  „ 
  108 
  „ 
  

  

  the 
  Upper 
  „ 
  „ 
  25 
  „ 
  ,, 
  69 
  

  

  with 
  comparatively 
  few 
  passing 
  to 
  the 
  higher 
  members 
  of 
  the 
  Jurassic 
  

   group. 
  

  

  11 
  genera 
  and 
  12 
  species 
  pass 
  to 
  the 
  Inferior 
  Oolite, 
  

  

  5 
  „ 
  „ 
  5 
  „ 
  „ 
  Puller's 
  Earth, 
  

  

  6 
  „ 
  „ 
  6 
  „ 
  „ 
  Great 
  Oolite, 
  

  

  1 
  genus 
  „ 
  1 
  „ 
  „ 
  Forest 
  Marble, 
  

  

  2 
  genera 
  „ 
  2 
  „ 
  „ 
  Cornbrash. 
  

  

  No 
  Lias 
  form 
  appears 
  above 
  the 
  Cornbrash. 
  

  

  The 
  preponderating 
  genera 
  (16), 
  or 
  those 
  having 
  most 
  specific 
  re- 
  

   presentatives 
  in 
  the 
  Lias, 
  are 
  given 
  in 
  the 
  following 
  Table 
  (XXII.) 
  : 
  — 
  

  

  