﻿2 
  20 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  Gasteropoda. 
  — 
  The 
  distinctiveness 
  of 
  the 
  Gasteropod 
  fauna 
  in 
  

   the 
  Corallian 
  beds 
  is 
  equally 
  complete 
  and 
  definite 
  ; 
  in 
  the 
  Kira- 
  

   meridgian 
  23 
  species 
  occur, 
  and 
  with 
  two 
  exceptions, 
  Pleurotomaria 
  

   reticulata 
  and 
  Turritella 
  minuta, 
  all 
  are 
  restricted. 
  Pleuroto- 
  

   maria 
  reticulata 
  occurs 
  in 
  the 
  Corallian 
  beds, 
  and 
  the 
  Turritella 
  

   passes 
  to 
  the 
  Portland. 
  This 
  concise 
  history 
  of 
  the 
  Kimmeridge 
  

   Gasteropoda, 
  like 
  that 
  of 
  the 
  Corallian, 
  has 
  scarcely 
  any 
  parallel 
  in 
  

   any 
  other 
  member 
  of 
  the 
  British 
  strata. 
  8 
  of 
  the 
  12 
  genera 
  that 
  

   occur 
  have 
  only 
  one 
  species 
  in 
  each 
  ; 
  they 
  are 
  Alaria, 
  CJiemnitzia, 
  

   Dentalium, 
  Neritopsis, 
  Pleurotomaria, 
  Pseudo 
  melanin, 
  liissoina, 
  and 
  

   Turritella. 
  Cerithium, 
  the 
  only 
  genus 
  at 
  all 
  largely 
  represented, 
  in- 
  

   cludes 
  6 
  species, 
  and 
  Natica 
  has 
  4. 
  

  

  Many 
  of 
  the 
  genera 
  with 
  only 
  one 
  known 
  species 
  each 
  in 
  the 
  

   Kimmeridge 
  Clay 
  are 
  extremely 
  rich 
  in 
  species 
  in 
  their 
  range 
  

   through 
  the 
  Jurassic 
  rocks. 
  Thus 
  Alaria 
  possesses 
  39 
  species, 
  

   but 
  A. 
  rasanensis 
  is 
  the 
  only 
  Kimmeridgian 
  form 
  : 
  CJiemnitzia 
  

   58 
  species 
  — 
  C. 
  infiata 
  is 
  known 
  only 
  ; 
  Weritopsis, 
  14 
  known, 
  but 
  

   iV. 
  delpJiinula 
  is 
  its 
  only 
  representative 
  here 
  ; 
  Pleurotomaria 
  num- 
  

   bers 
  no 
  less 
  than 
  110 
  species, 
  53 
  of 
  which 
  occur 
  in 
  the 
  Inferior 
  

   Oolite, 
  1(5 
  in 
  the 
  Great 
  Oolite, 
  and 
  38 
  in 
  the 
  Lias, 
  but 
  P. 
  reticulata 
  

   is 
  the 
  only 
  known 
  Kimmeridgian 
  form 
  ; 
  Bissoina 
  11, 
  chiefly 
  Great 
  

   Oolite 
  — 
  R. 
  mossensis 
  is 
  the 
  only 
  one 
  here 
  ; 
  and 
  Turritella 
  numbers 
  

   17 
  species, 
  11 
  of 
  them 
  Lias, 
  but 
  only 
  T. 
  minuta 
  and 
  T. 
  concava 
  

   occur 
  in 
  the 
  Upper 
  Oolite, 
  and 
  the 
  latter 
  is 
  a 
  Portlandian 
  spe- 
  

   cies. 
  Thus 
  of 
  the 
  above 
  8 
  genera 
  so 
  largely 
  represented 
  through 
  

   the 
  Jurassic 
  rocks 
  (and 
  known 
  in 
  the 
  Kimmeridge 
  beds) 
  with 
  

   Dentalium 
  and 
  i%< 
  udomdania, 
  as 
  before 
  stated, 
  exhibit 
  only 
  one 
  spe- 
  

   cies. 
  I 
  commend 
  those 
  genera, 
  both 
  of 
  the 
  Lamellibranchiata 
  and 
  

   the 
  Gasteropoda, 
  which 
  have 
  only 
  one 
  or 
  two 
  species 
  in 
  each, 
  to 
  the 
  

   special 
  attention 
  of 
  those 
  studying 
  the 
  Jurassic 
  rocks 
  ; 
  they 
  offer 
  

   promising 
  material 
  for 
  future 
  research. 
  

  

  Cephalopoda. 
  Ammonites. 
  — 
  31 
  species 
  occur 
  in, 
  and 
  22 
  of 
  these 
  

   are 
  strictly 
  confined 
  to, 
  the 
  Kimmeridgian 
  strata. 
  Of 
  the 
  re- 
  

   maining 
  9 
  species 
  only 
  4 
  pass 
  to 
  the 
  Portlandian 
  beds 
  ; 
  they 
  are 
  

   Am. 
  triplicatus, 
  Am. 
  triplex, 
  Am. 
  biplex, 
  and 
  Am. 
  hector. 
  6 
  species 
  

   oscillate 
  between 
  the 
  Oxford 
  Clay, 
  Corallian, 
  and 
  Kimmeridgian 
  

   horizons. 
  The 
  importance 
  of 
  the 
  Ammonites, 
  stratigraphically 
  as 
  well 
  

   as 
  zoologically, 
  induces 
  me 
  to 
  name 
  those 
  species 
  that 
  are 
  essentially 
  

   of 
  this 
  age 
  ; 
  and 
  as 
  only 
  7 
  of 
  the 
  11 
  Portlandian 
  species 
  are 
  confined 
  

   to 
  that 
  horizon, 
  and 
  all 
  the 
  Jurassic 
  forms 
  become 
  extinct 
  with 
  

   the 
  close 
  of 
  the 
  Portland, 
  this 
  may 
  be 
  of 
  importance. 
  The 
  22 
  

   Kimmeridge 
  species 
  are 
  Am. 
  accipitris, 
  Am. 
  autissiodorensis, 
  Am. 
  

   Benyeri, 
  Am. 
  Beaugrandi, 
  Am. 
  calisto, 
  Am. 
  ccecilia, 
  Am. 
  cymodoce, 
  

   Am. 
  decipiens, 
  Am. 
  eudoxus, 
  Am. 
  eumelus, 
  Am. 
  eupalus, 
  Am. 
  flexu- 
  

   osus, 
  Am. 
  Kapffi, 
  Am. 
  Lallerianus, 
  Am. 
  mutabilis, 
  Am. 
  orthocera, 
  Am. 
  

   ■polyploeus, 
  Am. 
  pseudo-mutabilis, 
  Am. 
  rotundas, 
  Am. 
  superstes, 
  Am. 
  

   Thurmanni, 
  and 
  Am. 
  yo. 
  The 
  genera 
  Perisphinctes, 
  Aspidoceras, 
  

   Cosmoceras, 
  &c. 
  are 
  represented 
  amongst 
  this 
  series 
  of 
  Ammonites. 
  

  

  Nautili. 
  — 
  None 
  known. 
  

  

  Belemnites. 
  — 
  8 
  species 
  occur, 
  and 
  7 
  of 
  them 
  are 
  peculiar. 
  

  

  