﻿ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  l8l 
  

  

  Thecidium, 
  Spiriferina, 
  JRhynchonella, 
  and 
  Distinct, 
  through 
  the 
  

   whole 
  Jurassic 
  series, 
  is 
  significant. 
  I 
  give 
  their 
  value 
  — 
  

  

  Terebratula 
  has 
  yielded 
  67 
  species. 
  

  

  Waldheimia 
  44 
  „ 
  

  

  Rhynchonella 
  64 
  „ 
  

  

  Spiriferina 
  18 
  ,, 
  

  

  Discina 
  18 
  „ 
  

  

  Thecidium 
  15 
  „ 
  

  

  These 
  6 
  genera 
  thus 
  yield 
  226 
  species. 
  The 
  whole 
  class 
  in 
  the 
  

   Jurassic 
  rocks 
  numbers 
  275 
  species, 
  the 
  16 
  known 
  genera 
  being 
  thus 
  

   represented. 
  The 
  Inferior 
  Oolite 
  possesses 
  90 
  species, 
  the 
  largest 
  

   number 
  known 
  to 
  occur 
  ; 
  the 
  Middle 
  Lias 
  74 
  ; 
  and 
  the 
  Lower 
  Lias 
  

   36. 
  Suessia 
  and 
  Kingena 
  have 
  but 
  one 
  species 
  each, 
  and 
  Megerlia 
  2, 
  

   through 
  all 
  the 
  Jurassic 
  rocks. 
  The 
  tabular 
  distribution 
  I 
  have 
  

   given 
  at 
  the 
  end 
  of 
  the 
  Jurassic 
  group 
  (Table 
  XLIV.) 
  tells 
  its 
  own 
  

   tale. 
  The 
  total 
  appearances 
  of 
  the 
  genera 
  and 
  species 
  through 
  time 
  

   are 
  thus 
  expressed, 
  .^ 
  1 
  8 
  l 
  . 
  

  

  Lamellibranchiata. 
  — 
  The 
  Lamellibranchiate 
  or 
  Bivalve 
  fauna 
  of 
  

   the 
  whole 
  of 
  the 
  Jurassic 
  rocks 
  of 
  Britain 
  now 
  numbers 
  95 
  genera 
  

   and 
  1368 
  species. 
  The 
  group 
  Dimyaria 
  possesses 
  70 
  genera 
  and 
  

   924 
  species, 
  and 
  the 
  Monomyaria 
  25 
  genera 
  and 
  444 
  species. 
  The 
  

   Inferior 
  Oolite, 
  which 
  contains 
  by 
  far 
  the 
  richest 
  fauna 
  in 
  the 
  13 
  

   divisions, 
  has 
  yielded 
  342 
  species 
  in 
  both 
  groups 
  (106 
  Monomyaria 
  

   and 
  236 
  Dimyaria). 
  Possibly 
  no 
  horizon 
  in 
  Britain 
  or 
  on 
  the 
  con- 
  

   tinent 
  has 
  received 
  so 
  much 
  investigation 
  and 
  scrutiny. 
  The 
  im- 
  

   portance 
  of 
  a 
  knowledge 
  of 
  the 
  Mollusca 
  as 
  an 
  aid 
  to 
  stratigraphical 
  

   geology, 
  the 
  value 
  of 
  species 
  (regard 
  them 
  how 
  we 
  may) 
  as 
  factors 
  

   in 
  the 
  identification 
  of 
  strata, 
  however 
  different 
  petrologically, 
  and 
  

   however 
  distant, 
  is 
  familiar 
  to 
  all 
  students. 
  In 
  no 
  group 
  of 
  rocks 
  

   is 
  more 
  critical 
  knowledge 
  required 
  for 
  the 
  discrimination 
  of 
  con- 
  

   temporaneous 
  or 
  homotaxial 
  strata 
  than 
  in 
  the 
  Jurassic 
  series. 
  In 
  

   Europe 
  the 
  Molluscan 
  fauna 
  of 
  the 
  Jurassic 
  group 
  is 
  one 
  and 
  the 
  same 
  

   through 
  each 
  of 
  its 
  subdivisions. 
  The 
  fauna 
  of 
  the 
  Lias 
  of 
  England, 
  

   Scotland, 
  Ireland, 
  France, 
  and 
  Germany, 
  is 
  almost 
  identical, 
  zone 
  for 
  

   zone 
  ; 
  when 
  the 
  species 
  in 
  the 
  larger 
  genera 
  are 
  critically 
  examined 
  

   their 
  universality 
  and 
  continuity 
  are 
  remarkable 
  and 
  striking 
  ; 
  and 
  

   the 
  two 
  great 
  palaeontological 
  breaks, 
  one 
  at 
  the 
  close 
  of 
  the 
  

   Lias 
  and 
  the 
  next 
  at 
  the 
  close 
  of 
  the 
  Inferior 
  Oolite, 
  where 
  so 
  great 
  

   a 
  change 
  took 
  place 
  in 
  the 
  Molluscan 
  fauna, 
  are 
  readily 
  seen 
  in 
  

   Tables 
  XXYL, 
  XXXI., 
  and 
  XXXIII. 
  The 
  numerical 
  value 
  of 
  the 
  

   species 
  in 
  certain 
  genera 
  is 
  still 
  more 
  forcibly 
  shown 
  in 
  the 
  accom- 
  

   panying 
  table 
  (XXX.), 
  where 
  34 
  of 
  the 
  larger 
  genera 
  are 
  noticed. 
  

   I 
  append 
  the 
  Lias, 
  as 
  it 
  is 
  the 
  base 
  of 
  the 
  Jurassic 
  system, 
  but 
  will 
  

   not 
  extend 
  the 
  table 
  here 
  beyond 
  the 
  Cornbrash, 
  where 
  community 
  

   is 
  greatest, 
  and 
  which 
  completes 
  the 
  Lower 
  Oolite 
  or 
  Lower 
  Jurassic 
  

   series. 
  Eew 
  species 
  pass 
  to 
  the 
  higher 
  members 
  of 
  the 
  Jurassic 
  

   group. 
  

  

  