﻿ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  1 
  83 
  

  

  Gyrena, 
  Gastrochcena, 
  Hippopodium, 
  Macrodon, 
  Myopsis, 
  Pacliy- 
  

   rhisma, 
  Thracia, 
  &c. 
  &o. 
  among 
  the 
  Dimyaria, 
  are 
  feebly 
  repre- 
  

   sented 
  by 
  species, 
  but 
  nevertheless, 
  bathy 
  metrically 
  considered, 
  and 
  

   with 
  reference 
  to 
  temperature 
  and 
  sedimentation, 
  are 
  of 
  great 
  

   classificatory 
  value. 
  I 
  compare 
  the 
  class 
  Gasteropoda 
  under 
  its 
  

   own 
  division 
  ; 
  for 
  no 
  less 
  than 
  76 
  genera 
  and 
  1015 
  species 
  are 
  

   known 
  in 
  the 
  Jurassic 
  group 
  ; 
  they 
  culminate 
  in 
  the 
  Lower 
  Jurassic 
  

   rocks, 
  the 
  Lower 
  Lias 
  with 
  226 
  species, 
  the 
  Inferior 
  Oolite 
  with 
  240 
  

   species, 
  and 
  the 
  Great 
  Oolite 
  with 
  247 
  species. 
  In 
  higher 
  Jurassic 
  

   strata 
  they 
  die 
  away 
  to 
  a 
  few 
  species. 
  

  

  Monomyaria. 
  — 
  25 
  genera 
  and 
  444 
  species 
  of 
  this 
  group 
  are 
  known 
  

   in 
  the 
  Jurassic 
  rocks. 
  Of 
  these, 
  15 
  genera 
  and 
  106 
  species 
  belong 
  

   to 
  the 
  Inferior 
  Oolite, 
  connected 
  only 
  by 
  13 
  species 
  with 
  the 
  entire 
  

   Lias. 
  It 
  is 
  important 
  to 
  know 
  those 
  forms 
  which 
  unite 
  the 
  two 
  

   horizons, 
  especially 
  as 
  so 
  complete 
  a 
  change 
  in 
  the 
  fauna 
  occurred 
  

   at 
  the 
  close 
  of 
  the 
  Lias 
  and 
  commencement 
  of 
  the 
  Inferior 
  Oolite. 
  

   This 
  group, 
  as 
  we 
  have 
  seen, 
  was 
  represented 
  in 
  the 
  Lias 
  strata 
  by 
  

   jW 
  in 
  the 
  Lower, 
  J 
  § 
  in 
  the 
  Middle, 
  and 
  \ 
  f 
  in 
  the 
  Upper 
  Lias, 
  and 
  

   through 
  13 
  of 
  these 
  latter 
  passed 
  into 
  the 
  more 
  calcareous 
  waters 
  of 
  

   the 
  so-called 
  Inferior 
  Oolite. 
  The 
  connecting 
  species 
  are 
  Avicula 
  

   incequivalvis, 
  Gervillia 
  Hartmanni, 
  Hinnites 
  abjectus, 
  H. 
  velatus, 
  Lima 
  

   bellula, 
  L. 
  electra, 
  L. 
  punctata, 
  Pecten 
  articidatus, 
  P. 
  comatus, 
  P. 
  

   demissus, 
  Perna 
  rugosa, 
  Pinna 
  jissa, 
  and 
  P. 
  Hartmanni. 
  6 
  genera 
  

   and 
  8 
  species 
  pass 
  up 
  into 
  the 
  Puller's 
  Earth, 
  where 
  this 
  latter, 
  in 
  

   its 
  argillaceous 
  character, 
  is 
  fairly 
  developed, 
  in 
  the 
  Stroud 
  valley, 
  

   the 
  Bath 
  area, 
  and 
  parts 
  of 
  Somerset 
  : 
  12 
  genera 
  and 
  33 
  species 
  

   connect 
  the 
  Inferior 
  and 
  Great 
  Oolite 
  ; 
  and 
  no 
  less 
  than 
  11 
  genera 
  

   and 
  18 
  species 
  range 
  to 
  the 
  Cornbrash, 
  10 
  species 
  avoiding 
  the 
  

   Forest 
  Marble 
  shallow-water 
  deposits. 
  The 
  faunal 
  recurrence 
  

   between 
  the 
  Inferior 
  Oolite 
  and 
  Cornbrash 
  is 
  smaller 
  than 
  might 
  be 
  

   expected, 
  both 
  for 
  this 
  group 
  and 
  the 
  Dimyaria, 
  it 
  being 
  only 
  \ 
  g 
  

   out 
  of 
  2 
  4 
  3 
  7 
  6 
  in 
  that 
  division 
  ; 
  in 
  the 
  Gasteropoda 
  it 
  is 
  only 
  \ 
  out 
  

   of 
  gVo* 
  1^ 
  has 
  been 
  often 
  stated 
  that 
  the 
  two 
  horizons 
  were 
  

   zoologically 
  closely 
  allied 
  through 
  recurrence. 
  This 
  could 
  only 
  apply 
  

   to 
  certain 
  areas 
  where 
  the 
  conditions 
  of 
  the 
  Great 
  and 
  Inferior 
  Oolite 
  

   during 
  deposition 
  were 
  little 
  changed 
  and 
  gradually 
  merged 
  into 
  the 
  

   locally 
  developed 
  Cornbrash. 
  Community 
  of 
  species 
  between 
  the 
  

   Inferior 
  Oolite 
  and 
  Cornbrash 
  could 
  hardly 
  have 
  occurred 
  in 
  the 
  

   Yorkshire 
  basin. 
  The 
  great 
  series 
  of 
  Estuarine 
  sandstones, 
  shales, 
  

   and 
  iron-stones 
  is 
  broken 
  in 
  sequence 
  between 
  the 
  Dogger 
  and 
  the 
  

   Cornbrash 
  only 
  by 
  the 
  Grey 
  or 
  Scarboro 
  Limestone 
  and 
  the 
  Millepore- 
  

   beds, 
  which 
  last, 
  although 
  the 
  lowest 
  of 
  the 
  two, 
  are 
  most 
  nearly 
  allied 
  

   palseontologically. 
  The 
  long-range 
  species 
  are 
  Avicula 
  braambu- 
  

   riensis, 
  A. 
  Munsteri, 
  Gervillia 
  acuta, 
  Hinnites 
  abjectus 
  (Middle 
  Lias 
  

   to 
  Cornbrash), 
  Lima 
  duplicata, 
  L. 
  pectiniformis, 
  Ostrea 
  acuminata, 
  0. 
  

   Jtabelloides, 
  Pecten 
  annulatus, 
  P. 
  crenatus, 
  P. 
  demissus 
  (Middle 
  Lias 
  

   to 
  Kimmeridge 
  Clay), 
  P. 
  lens, 
  P. 
  personatus, 
  Perna 
  rugosa, 
  Pinna 
  

   cuneata, 
  and 
  Placunopsis 
  incequalis. 
  These 
  16 
  species, 
  if 
  not 
  as 
  

   good 
  witnesses 
  as 
  the 
  rarer 
  forms, 
  show 
  that 
  the 
  conditions 
  

   were 
  such 
  that 
  only 
  minor 
  physical 
  changes 
  affected 
  the 
  fauna 
  

  

  