﻿ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  

  

  159 
  

  

  a 
  given 
  set 
  of 
  beds 
  thus 
  characterized, 
  I 
  give 
  the 
  value 
  of 
  the 
  

   Dimyarian 
  fauna 
  of 
  the 
  Yorkshire 
  Lias 
  in 
  the 
  following 
  12 
  zones 
  

   adopted 
  by 
  the 
  above 
  authors 
  : 
  — 
  

  

  The 
  zone 
  of 
  

  

  

  

  

  ( 
  Mgoccras 
  planorbis 
  

  

  ,, 
  angulatum 
  

  

  contains 
  7 
  genera 
  and 
  8 
  species 
  

  

  „ 
  

  

  17 
  

  

  31 
  „ 
  

  

  Lower 
  Lias. 
  \ 
  Arietites 
  BucMandi 
  

  

  3> 
  

  

  19 
  ; 
  

  

  33 
  „ 
  

  

  | 
  Amaltkeus 
  oxynotus 
  

  

  )5 
  

  

  12 
  

  

  U 
  „ 
  

  

  ^ 
  AEgoceras 
  Jameson 
  i 
  

  

  ,, 
  

  

  20 
  

  

  28 
  „ 
  

  

  f 
  ,, 
  capricomus 
  ... 
  

  

  „ 
  

  

  11 
  

  

  17 
  „ 
  

  

  Middle 
  Lias, 
  j 
  Amaltkeus 
  margaritatus 
  ., 
  

  

  » 
  

  

  17 
  

  

  30 
  „ 
  

  

  „ 
  spinatus 
  

  

  

  24 
  

  

  40 
  , 
  

  

  f 
  Stephanoceras 
  annxdatum 
  

  

  „ 
  

  

  12 
  

  

  13 
  „ 
  

  

  XT 
  T 
  Harpoceras 
  serventinum 
  .. 
  

  

  „ 
  

  

  5 
  

  

  5 
  „ 
  

  

  Stephanoceras 
  commune 
  .. 
  

  

  )! 
  

  

  5 
  ? 
  

  

  6 
  „ 
  

  

  1 
  Li/toccras 
  jurense 
  

  

  

  5 
  

  

  5 
  

  

  

  

  154 
  

  

  230 
  „ 
  

  

  The 
  affinity 
  between 
  the 
  Liassic 
  Dimyarian 
  Laniellibranchs 
  and 
  

   those 
  of 
  the 
  succeeding 
  Inferior 
  Oolite 
  is 
  manifested 
  only 
  through 
  

   11 
  genera 
  and 
  12 
  species. 
  This 
  emphatically 
  shows 
  a 
  great 
  change 
  

   in 
  the 
  physical 
  condition 
  of 
  the 
  sea-bed, 
  when 
  the 
  whole 
  of 
  the 
  

   Dimyarian 
  Bivalves, 
  numbering 
  286 
  species, 
  less 
  the 
  12 
  (274), 
  

   ceased 
  to 
  exist 
  or 
  otherwise 
  migrated. 
  The 
  11 
  genera 
  and 
  12 
  

   species 
  are 
  Astarte 
  modiolaris, 
  Cypricardia 
  acutangula, 
  Goniomya 
  

   angulifera, 
  Homomya 
  crassiuscula, 
  Leda 
  lacJiryma, 
  Modiola 
  Sower- 
  

   hyana, 
  Myadtes 
  tenuistriatus, 
  Myoconcha 
  crassa, 
  Mytilus 
  lunularis, 
  

   Pholadomya 
  jidicula, 
  Trigonia 
  formosa, 
  and 
  T. 
  spinulosa. 
  The 
  de- 
  

   termination 
  of 
  these 
  connecting 
  species 
  as 
  bearing 
  upon 
  distribution 
  

   under 
  physical 
  changes, 
  enables 
  us 
  to 
  state 
  confidently 
  the 
  lines 
  of 
  

   demarcation 
  between 
  large 
  divisions 
  of 
  the 
  stratified 
  rocks 
  where 
  a 
  

   physical 
  unconformity 
  does 
  not 
  exist 
  ; 
  yet 
  causes 
  existed 
  at 
  the 
  time 
  

   of 
  deposition 
  to 
  extensively 
  modify 
  the 
  then 
  existing 
  fauna. 
  Pive 
  

   genera 
  and 
  5 
  species 
  range 
  from 
  the 
  Lias 
  to 
  the 
  Euller's 
  Earth 
  ; 
  

   6 
  genera 
  and 
  6 
  species 
  to 
  the 
  Great 
  Oolite 
  ; 
  and 
  only 
  2 
  species 
  to 
  the 
  

   Cornbrash, 
  viz. 
  Homomya 
  crassiuscula 
  and 
  Leda 
  lacliryma, 
  both 
  

   moderately 
  deep-sea 
  forms. 
  Comparing 
  then 
  the 
  figures 
  which 
  

   numerically 
  represent 
  the 
  Dimyarian 
  fauna 
  of 
  the 
  Lias 
  with 
  those 
  

   of 
  the 
  immediately 
  succeeding 
  and 
  conformable 
  Oolitic 
  rocks, 
  the 
  

   result 
  is 
  remarkable. 
  It 
  will 
  stand 
  thus 
  : 
  — 
  

  

  In 
  the 
  Lias 
  45 
  genera 
  and 
  286 
  species 
  occur 
  ; 
  

  

  36 
  „ 
  „ 
  138 
  „ 
  arc 
  in 
  the 
  Lower 
  Lias, 
  

   34 
  „ 
  „ 
  108 
  „ 
  „ 
  Middle 
  „ 
  

  

  25 
  „ 
  „ 
  69 
  „ 
  „ 
  Upper 
  „ 
  

  

  of 
  which 
  only 
  11 
  genera 
  and 
  12 
  species 
  pass 
  to 
  the 
  Inferior 
  Oolite, 
  

   whose 
  Dimyarian 
  fauna 
  numbers 
  47 
  genera 
  and 
  236 
  species. 
  Thus 
  

   these 
  two 
  extensive 
  formations, 
  whose 
  united 
  Dimyarian 
  fauna 
  alone 
  

   equals 
  62 
  genera 
  and 
  522 
  species, 
  arc 
  linked 
  together 
  by 
  only 
  12 
  

   species 
  belonging 
  to 
  11 
  genera, 
  and 
  only 
  2 
  species 
  from 
  the 
  whole 
  of 
  

   the 
  Lias 
  pass 
  to 
  the 
  Cornbrash. 
  This 
  small 
  but 
  representative 
  

   series 
  of 
  species 
  which 
  passed 
  the 
  confines 
  of 
  the 
  Upper 
  Lias 
  and 
  

  

  