﻿SUBDIVISIONS 
  OF 
  THE 
  SPEETON 
  CLAY. 
  615 
  

  

  become 
  suddenly 
  plentiful 
  ; 
  and 
  from 
  this 
  horizon 
  the 
  genus 
  ranges 
  

   upwards, 
  varying 
  from 
  time 
  to 
  time 
  in 
  form 
  and 
  abundance, 
  to 
  the 
  

   upper 
  part 
  of 
  the 
  zone 
  of 
  Bel. 
  semicanaliculatus 
  i 
  { 
  The 
  species 
  in 
  

   the 
  higher 
  part 
  of 
  the 
  clay, 
  above 
  the 
  " 
  Cement-beds," 
  are 
  certainly 
  

   different 
  from 
  those 
  at 
  lower 
  horizons. 
  A 
  form 
  which 
  I 
  think 
  is 
  

   Crioceras 
  Puzosianum, 
  D'Orb., 
  is 
  particularly 
  abundant 
  between 
  the 
  

   Noricus- 
  and 
  Sjpeetonensis-be&s. 
  

  

  Teoches 
  pulcheeeimes, 
  Phil., 
  and 
  Ceeithiem 
  aceleatum, 
  Forbes, 
  

   MS. 
  

   These 
  delicate 
  and 
  beautiful 
  shells 
  abound 
  in 
  the 
  upper 
  Noricus- 
  

   beds, 
  and 
  pass 
  upwards 
  into 
  the 
  " 
  main 
  Speetonensi&-\>GdL? 
  and 
  the 
  

   first-mentioned 
  persists 
  in 
  a 
  dwarfed 
  variety 
  as 
  high 
  as 
  the 
  Echino- 
  

   sj.uttangus-'bed, 
  but 
  I 
  have 
  not 
  found 
  them 
  elsewhere 
  in 
  the 
  

   section. 
  

  

  ExOGYEA 
  SINEATA, 
  Sow. 
  

  

  This 
  is 
  one 
  of 
  the 
  commonest 
  fossils 
  of 
  the 
  Speeton 
  Clay 
  ; 
  but 
  

   though 
  a 
  strong 
  shell 
  it 
  is 
  generally 
  much 
  crushed, 
  and 
  is 
  difficult 
  

   to 
  obtain 
  even 
  in 
  fair 
  condition. 
  Judd 
  notes 
  several 
  distinct 
  sub- 
  

   species 
  or 
  varieties 
  occurring 
  at 
  different 
  horizons. 
  I 
  have 
  found 
  

   the 
  shell 
  as 
  low 
  as 
  the 
  " 
  Lingula-bed" 
  of 
  the 
  zone 
  of 
  Bel. 
  lateralis 
  

   (1)5), 
  and 
  upwards 
  as 
  high 
  as 
  the 
  clays 
  just 
  below 
  the 
  " 
  Cement- 
  

   beds." 
  

  

  Pecten 
  lens, 
  Sow., 
  var. 
  Moeini, 
  De 
  Lor. 
  

  

  The 
  shell 
  referred 
  to 
  this 
  species 
  occurs 
  in 
  the 
  " 
  Astarte-loed 
  " 
  of 
  

   the 
  Later 
  alis-zone, 
  and 
  is 
  plentiful 
  in 
  the 
  neighbourhood 
  of 
  the 
  

   Compound 
  Nodular 
  Band, 
  and 
  particularly 
  in 
  a 
  shelly 
  layer 
  about 
  a 
  

   foot 
  above 
  that 
  stratum. 
  It 
  is 
  said 
  not 
  to 
  be 
  separable 
  from 
  the 
  

   Jurassic 
  species. 
  

  

  AVICULA 
  IN^lQUIVALVIS, 
  Sow. 
  

  

  Another 
  Jurassic 
  species 
  of 
  wide 
  range, 
  to 
  which 
  has 
  been 
  re- 
  

   ferred 
  a 
  shell 
  which 
  occurs 
  rather 
  abundantly 
  in 
  the 
  Compound 
  

   Nodular 
  Band, 
  and 
  in 
  the 
  clay 
  just 
  above 
  and 
  below 
  that 
  stratum, 
  

   and 
  possibly 
  also 
  higher. 
  Its 
  resemblance 
  to 
  the 
  original 
  figure 
  of 
  

   Sowerby 
  is 
  not 
  so 
  great 
  as 
  to 
  the 
  figure 
  given 
  in 
  Goldfuss 
  (Petrefact. 
  

   pi. 
  118. 
  fig. 
  1), 
  with 
  which 
  it 
  agrees 
  very 
  closely. 
  In 
  the 
  different 
  

   public 
  collections 
  of 
  Speeton-Clay 
  fossils 
  this 
  shell 
  has 
  received 
  various 
  

   names, 
  as 
  A. 
  macroptera, 
  Pom., 
  A. 
  multicostata 
  (Leckenby), 
  &c. 
  

   The 
  wide 
  range 
  in 
  time 
  of 
  this 
  species 
  makes 
  its 
  reappearance 
  in 
  

   these 
  beds 
  less 
  remarkable. 
  

  

  Inoceeamus 
  yenesteles, 
  Bean, 
  MS., 
  and 
  I. 
  imeeicates, 
  Bean, 
  MS. 
  

  

  These 
  shells 
  occur 
  plentifully 
  in 
  the 
  upper 
  part 
  of 
  the 
  zone 
  of 
  

   Amm. 
  noricus, 
  and 
  are, 
  I 
  believe, 
  confined 
  to 
  this 
  part 
  of 
  the 
  section. 
  

   I 
  am 
  inclined 
  to 
  think 
  that 
  there 
  is 
  only 
  one 
  species 
  — 
  the 
  coarsely- 
  

   striated 
  /. 
  imbricatus 
  being 
  the 
  adult 
  form, 
  and 
  the 
  smooth 
  polished 
  

   I. 
  venustulus 
  the 
  young 
  form 
  of 
  the 
  same 
  species. 
  

  

  