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  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  Besides 
  these 
  16 
  genera 
  quoted 
  from 
  the 
  Lias, 
  there 
  are 
  others 
  

   of 
  much 
  importance, 
  zoologically 
  considered, 
  having 
  first 
  appeared 
  

   with 
  these 
  in 
  time. 
  Amongst 
  them 
  must 
  be 
  named 
  Anatina, 
  Ar- 
  

   comya, 
  Carclita, 
  Ceromya, 
  Hippopodium, 
  Ilomomya, 
  Macrodon, 
  Myo- 
  

   concha, 
  Opis, 
  Protocardium, 
  Trigonia, 
  Unicardium, 
  &c. 
  Most 
  of 
  

   these 
  genera 
  play 
  an 
  importaDt 
  part 
  in 
  the 
  history 
  of 
  the 
  Lower 
  

   and 
  Upper 
  Secondary 
  rocks, 
  especially 
  the 
  Jurassic, 
  which 
  will 
  be 
  

   alluded 
  to 
  under 
  their 
  respective 
  horizons. 
  These 
  12 
  genera 
  include 
  

   195 
  species, 
  all 
  of 
  which 
  occur 
  in 
  the 
  Jurassic 
  group, 
  including 
  the 
  

   Lias, 
  which 
  forms 
  so 
  important 
  an 
  integer 
  at 
  the 
  base 
  : 
  51 
  of 
  the 
  

   195 
  are 
  Lias 
  species 
  generally, 
  22 
  are 
  Lower-Lias 
  proper, 
  24 
  Middle- 
  

   Lias, 
  and 
  only 
  9 
  occur 
  in 
  the 
  Upper 
  Lias. 
  Cyprina, 
  Gastrocliama, 
  

   Isocardia, 
  Lithodomus, 
  Myophoria, 
  Quenstedtia, 
  Sowerbya, 
  Solen, 
  

   and 
  Thracia 
  are 
  only 
  represented 
  in 
  the 
  Lias 
  by 
  1 
  species 
  each. 
  

   Closer 
  search 
  will 
  doubtless 
  add 
  to 
  this 
  scanty 
  specific 
  fauna. 
  The 
  

   accompanying 
  Table 
  (XXIY.) 
  illustrates 
  the 
  distribution 
  of 
  the 
  

   above 
  12 
  genera 
  through 
  the 
  Lias. 
  

  

  Table 
  XXIV. 
  — 
  Additional 
  Genera 
  to 
  the 
  16 
  before 
  tabulated 
  occurring 
  

  

  in 
  the 
  Lias. 
  

  

  Genera. 
  

  

  Anatina 
  .... 
  

   Arcomya 
  — 
  

  

  Cardita 
  

  

  Ceroniya 
  .... 
  

   Hippopodium 
  

   Homomya.... 
  

   Macrodon 
  .... 
  

   Myoconcha 
  . 
  

  

  Opis 
  

  

  Protocardium 
  

   Trigonia 
  .... 
  

   Unicardium 
  . 
  

  

  cL.2 
  

  

  O 
  u 
  

  

  u 
  

  

  11 
  

  

  5 
  

  

  (> 
  

  

  18 
  

  

  4 
  

  

  6 
  

  

  7 
  

  

  14 
  

  

  20 
  

  

  4 
  

  

  88 
  

  

  12 
  

  

  195 
  

  

  51 
  

  

  a 
  

  

  L>4 
  

  

  P 
  

  

  P/3 
  

  

  55 
  

  

  Following 
  on 
  the 
  analysis 
  made 
  of 
  the 
  Monomyarian 
  group 
  from 
  

   the 
  Lias 
  of 
  Yorkshire, 
  I 
  now 
  do 
  the 
  same 
  for 
  the 
  Diniyaria 
  from 
  the 
  

   same 
  area, 
  which 
  important 
  district 
  cannot 
  be 
  overlooked, 
  first 
  on 
  

   account 
  of 
  the 
  high 
  development 
  and 
  stratigraphical 
  value 
  of 
  the 
  

   whole 
  of 
  the 
  Lias 
  formation 
  there, 
  and, 
  secondly, 
  owing 
  to 
  the 
  exhaus- 
  

   tive 
  nature 
  of 
  the 
  researches 
  of 
  Messrs. 
  Tate 
  and 
  Blake, 
  which 
  have 
  

   caused 
  the 
  Lias 
  of 
  Yorkshire 
  to 
  be 
  regarded 
  as 
  a 
  type 
  to 
  which 
  we 
  

   must 
  now 
  refer 
  the 
  rest 
  of 
  Britain. 
  Accepting 
  then, 
  as 
  I 
  do, 
  the 
  

   value 
  of 
  the 
  Ammonite-zones 
  as 
  a 
  means 
  of 
  registering 
  the 
  fauna 
  of 
  

  

  