﻿154 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  species, 
  171 
  Monomyarian 
  and 
  286 
  Dimyarian 
  forms. 
  They 
  are 
  

   thus 
  distributed 
  : 
  — 
  

  

  Monomyaria. 
  — 
  18 
  genera 
  and 
  114 
  species 
  occur 
  in 
  the 
  Lower 
  Lias. 
  

   16 
  „ 
  60 
  „ 
  „ 
  Middle 
  Lias. 
  

  

  13 
  „ 
  32 
  „ 
  „ 
  Upper 
  Lias. 
  

  

  Only 
  5 
  genera 
  and 
  8 
  species 
  pass 
  up 
  to 
  the 
  Oolitic 
  rocks, 
  and 
  thus 
  

   unite 
  the 
  two 
  formations, 
  clearly 
  showing 
  that 
  considerable 
  change 
  

   must 
  have 
  taken 
  place 
  in 
  the 
  physical 
  conditions 
  of 
  the 
  sea 
  on 
  

   the 
  introduction 
  of 
  the 
  more 
  calcareous 
  deposits 
  of 
  the 
  Oolitic 
  rocks. 
  

   10 
  of 
  the 
  18 
  genera 
  and 
  23 
  of 
  the 
  114 
  species 
  in 
  the 
  Lower 
  Lias 
  

   pass 
  to 
  the 
  Middle 
  Lias 
  : 
  but 
  only 
  2 
  genera 
  and 
  2 
  species 
  are 
  common 
  

   to 
  the 
  Lower, 
  Middle, 
  and 
  Upper 
  divisions, 
  viz. 
  Lima 
  punctata 
  and 
  

   Pecten 
  textorius 
  ; 
  and 
  Lima 
  punctata 
  ranges 
  to 
  the 
  Inferior 
  Oolite. 
  

   This 
  clearly 
  shows 
  the 
  restricted 
  range 
  of 
  the 
  species 
  of 
  the 
  Lower 
  

   and 
  Middle 
  Lias. 
  Of 
  the 
  16 
  genera 
  and 
  60 
  species 
  that 
  occur 
  in 
  

   the 
  Middle 
  Lias, 
  6 
  genera 
  and 
  8 
  species 
  pass 
  to 
  the 
  Upper 
  Lias, 
  and 
  

   5 
  genera 
  and 
  8 
  species 
  to 
  the 
  Inferior 
  Oolite. 
  In 
  the 
  Upper 
  Lias 
  

   22 
  of 
  the 
  32 
  species 
  are 
  confined 
  to 
  it. 
  The 
  number 
  of 
  Mono- 
  

   myarian 
  species 
  that 
  pass 
  from 
  the 
  Lias 
  to 
  the 
  Oolitic 
  rocks 
  is 
  13, 
  

   the 
  connexion 
  occurring 
  through 
  Lima 
  bellula, 
  Perna 
  rugosa, 
  Avicula 
  

   incBquivalvis, 
  Hi 
  unites 
  abjectus, 
  H.velatus, 
  Lima 
  electra, 
  L. 
  punctata, 
  

   Pecten 
  demissus, 
  P. 
  articulatus, 
  P. 
  comatus, 
  Pinna 
  Jissa, 
  P. 
  Hart- 
  

   manni, 
  and 
  Gervillia 
  Hartmanni. 
  So 
  restricted 
  arc 
  the 
  species 
  that 
  

   only 
  of 
  the 
  above 
  13 
  range 
  higher 
  into 
  the 
  Oolitic 
  rocks 
  than 
  

   the 
  Inferior 
  Oolite, 
  viz. 
  Hinnites 
  abjectus, 
  H. 
  velatus, 
  Lima 
  bellula, 
  

   Pecten 
  demissus, 
  P. 
  articulatus, 
  and 
  Perna 
  rugosa. 
  

  

  In 
  Yorkshire 
  Messrs. 
  Tate 
  and 
  Blake 
  have 
  exhaustively 
  studied 
  

   the 
  whole 
  Lias 
  series, 
  placing 
  in 
  the 
  several 
  Ammonite-zones 
  their 
  

   associated 
  Molluscan 
  contents. 
  The 
  following 
  Table 
  exhibits, 
  as 
  

   near 
  as 
  can 
  be, 
  the 
  result 
  of 
  their 
  Yorkshire 
  labours 
  in 
  the 
  single 
  

   group 
  Monomyaria 
  : 
  — 
  

  

  The 
  zone 
  of 
  

  

  ( 
  Mgoceras 
  planorhis 
  contains 
  4 
  genera 
  and 
  6 
  species. 
  

  

  Lower 
  " 
  angulation 
  „ 
  9 
  „ 
  20 
  „ 
  

  

  jjower 
  J 
  Arietites 
  Bucklandi 
  „ 
  12 
  „ 
  23 
  „ 
  *? 
  

  

  | 
  Amaltheus 
  oxynotus 
  „ 
  7 
  „ 
  11 
  ,, 
  

  

  [JEgoceras 
  Jamesoni 
  „ 
  11 
  „ 
  17 
  „ 
  

  

  Middle 
  j 
  fffoaeras 
  aapncornm 
  „ 
  9 
  „ 
  15 
  „ 
  

  

  T 
  \ 
  Amalthcusmargaritatus. 
  „ 
  10 
  „ 
  17 
  „ 
  %% 
  

  

  1J,AS 
  * 
  „ 
  spinatus 
  „ 
  11 
  „ 
  22 
  „ 
  

  

  {Stephanoceras 
  annulatum 
  „ 
  5 
  „ 
  7 
  ,, 
  

  

  Harpoceras 
  serpentinwm 
  „ 
  4 
  „ 
  5 
  „ 
  j 
  T 
  

  

  Stephanoceras 
  commune 
  . 
  „ 
  4 
  ,, 
  6 
  „ 
  24 
  

  

  Lytoceras 
  jurense 
  ,, 
  4 
  „ 
  6 
  ,, 
  

  

  DO 
  „ 
  155 
  „ 
  

  

  These 
  twelve 
  zones 
  are 
  clearly 
  defined 
  in 
  Yorkshire, 
  and 
  may 
  be 
  

   studied 
  along 
  the 
  coast, 
  from 
  the 
  Peak 
  to 
  Iiedcar, 
  in 
  many 
  of 
  the 
  

   deep 
  valleys, 
  and 
  on 
  the 
  tableland 
  of 
  Lofthouse, 
  Easington, 
  and 
  the 
  

  

  