﻿2l6 
  PROCEEDINGS 
  OP 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  Cetjstacea. 
  — 
  Glyphea 
  ferruginea 
  and 
  G. 
  rostrata 
  are 
  the 
  only 
  2 
  

   species 
  known 
  ; 
  the 
  latter 
  ranges 
  from 
  the 
  Inferior 
  Oolite. 
  The 
  

   Oxford 
  Clay 
  below 
  holds 
  6 
  species, 
  and 
  the 
  Kimmeridge 
  above 
  7. 
  

   Glyphea 
  ferruginea 
  is 
  the 
  only 
  species 
  confined 
  to 
  the 
  Corallian 
  

   rocks. 
  

  

  Bryozoa. 
  — 
  Two 
  doubtful 
  species, 
  Heteropora 
  conifera 
  aud 
  Terebel- 
  

   laria 
  ramosissima 
  occur, 
  but 
  they 
  are 
  also 
  found 
  in 
  the 
  Inferior 
  and 
  

   Great 
  Oolite. 
  

  

  Eeachiopoda. 
  — 
  21 
  species 
  occur 
  in 
  the 
  Corallian 
  beds, 
  repre- 
  

   senting 
  7 
  genera 
  — 
  Terebratula 
  7 
  species, 
  Waldlieimia 
  6, 
  BJiynchoneTla 
  

   3, 
  Lingula, 
  Piscina, 
  and 
  Zelania 
  one 
  each, 
  and 
  Thecidium 
  2. 
  Discina 
  

   Humphresiana 
  ranges 
  into 
  the 
  Kiniineridge 
  Clay, 
  and 
  is 
  the 
  only 
  

   species 
  connecting 
  the 
  two 
  horizons. 
  

  

  Lamelllbraxchiata. 
  Monomyaria. 
  — 
  14 
  genera 
  and 
  58 
  species 
  

   are 
  known 
  to 
  occur 
  ; 
  of 
  these 
  16 
  are 
  Corallian 
  forms 
  only. 
  7 
  genera 
  

   and 
  15 
  species 
  pass 
  to 
  the 
  Kimmeridge 
  Clay, 
  9 
  genera 
  and 
  13 
  

   species 
  unite 
  the 
  Oxford 
  Clay 
  below 
  with 
  the 
  Corallian. 
  The 
  

   genera 
  most 
  largely 
  represented 
  are 
  Avicula 
  with 
  7 
  species, 
  Lima 
  8, 
  

   Pecten 
  5, 
  and 
  Ostrea 
  9. 
  Plicatula, 
  Pteroperna, 
  Trichites, 
  and 
  Ger- 
  

   villia 
  each 
  possess 
  but 
  one 
  species. 
  Perna, 
  Pinna, 
  Hinnites, 
  and 
  

   Placunopsis 
  have 
  2 
  species 
  each. 
  We 
  should 
  expect 
  to 
  find 
  these 
  

   genera 
  more 
  largely 
  represented 
  on 
  comparing 
  them 
  numerically 
  

   with 
  the 
  Inferior 
  Oolite, 
  in 
  which 
  the 
  four 
  first-named 
  genera 
  yield 
  

   17 
  species, 
  and 
  the 
  four 
  last 
  17 
  species. 
  The 
  Monomyarian 
  fauna 
  

   in 
  the 
  Inferior 
  Oolite 
  is 
  Afj 
  species, 
  in 
  the 
  Great 
  Oolite 
  \%, 
  the 
  

   Cornbrash 
  \\, 
  and 
  the 
  Corallian 
  under 
  examination 
  J 
  j. 
  The 
  con- 
  

   ditions 
  of 
  deposition 
  and 
  accumulation 
  are 
  most 
  nearly 
  allied 
  to 
  

   those 
  of 
  the 
  Great 
  Oolite. 
  Space 
  will 
  not 
  allow 
  me 
  to 
  name 
  the 
  

   species 
  constituting 
  the 
  fauna 
  of 
  this 
  horizon 
  ; 
  my 
  only 
  resource 
  is 
  

   to 
  treat 
  them 
  numerically. 
  Exogyra 
  nana, 
  E. 
  spiralis, 
  Lima 
  rustica, 
  

   Ostrea 
  solitaria, 
  and 
  Perna 
  mytiloides 
  range 
  to 
  the 
  Portland 
  beds. 
  

  

  Dimyaria. 
  — 
  29 
  genera 
  and 
  93 
  species 
  occur 
  in 
  this 
  group 
  of 
  

   the 
  Bivalvia; 
  no 
  less 
  than 
  47 
  of 
  the 
  93 
  species 
  are 
  peculiar 
  to 
  

   it, 
  and 
  they 
  belong 
  to 
  22 
  of 
  the 
  29 
  genera. 
  9 
  genera 
  and 
  14 
  

   species 
  occur 
  in 
  the 
  Oxford 
  Clay 
  below, 
  and 
  10 
  genera 
  and 
  12 
  

   species 
  pass 
  to 
  the 
  Kimmeridge 
  Clay 
  ; 
  but 
  Thracia 
  depressa 
  and 
  

   Modidla 
  pallida 
  are 
  the 
  only 
  2 
  species 
  that 
  pass 
  to 
  the 
  Portland 
  

   beds. 
  Astarte, 
  Area, 
  Modiola, 
  Lucina, 
  Pholadomya, 
  and 
  Trigonia 
  

   are 
  the 
  genera 
  most 
  largely 
  represented. 
  United 
  their 
  species 
  number 
  

   46, 
  or 
  50 
  per 
  cent, 
  of 
  the 
  whole. 
  10 
  genera 
  possess 
  only 
  1 
  species 
  

   each 
  ; 
  this 
  tends 
  to 
  show 
  the 
  importance 
  of 
  correctly 
  determining 
  

   the 
  genera 
  in 
  an 
  extensive 
  fauna, 
  so 
  that 
  undue 
  value 
  may 
  not 
  be 
  

   assigned 
  to 
  those 
  having 
  only 
  a 
  single 
  species. 
  In 
  the 
  present, 
  as 
  

   in 
  many 
  other 
  formations, 
  nearly 
  one 
  half 
  are 
  thus 
  poorly 
  repre- 
  

   sented. 
  In 
  the 
  present 
  instance 
  we 
  have 
  little 
  doubt 
  of 
  correct 
  

   determination 
  ; 
  such 
  genera 
  as 
  Gastrochama, 
  Homomya, 
  Myoconcha, 
  

   Mytilus, 
  Pholas, 
  Taneredia, 
  and 
  Protocardium 
  can 
  hardly 
  be 
  mis- 
  

   taken 
  ; 
  it 
  is 
  the 
  single 
  representative 
  that 
  causes 
  anxiety 
  when 
  

   examining 
  extensive 
  catalogues 
  cf 
  species 
  or 
  specimens 
  in 
  col- 
  

   ections. 
  

  

  