﻿SUBUVISIONS 
  OF 
  THE 
  SPEETON 
  CLAY. 
  613 
  

  

  Ammonites 
  nortcus, 
  Schloth., 
  = 
  A. 
  neocomiensis, 
  D'Orb. 
  

  

  This 
  is 
  decidedly 
  the 
  most 
  abundant 
  of 
  the 
  Speeton 
  Ammonites, 
  

   but 
  appears 
  to 
  be 
  strictly 
  confined 
  within 
  the 
  limits 
  of 
  its 
  zone 
  

   (beds 
  C8 
  to 
  D 
  1 
  of 
  sections). 
  It 
  shows 
  several 
  distinct 
  varieties, 
  

   which 
  received 
  specific 
  recognition 
  from 
  the 
  early 
  collectors, 
  and 
  

   probably 
  also 
  from 
  many 
  foreign 
  palaeontologists; 
  but, 
  as 
  noted 
  by 
  

   Judd, 
  a 
  moderate 
  collection 
  will 
  show 
  that 
  these 
  pass 
  insensibly 
  into 
  

   one 
  another. 
  Leckenby 
  records 
  an 
  allied 
  form, 
  A. 
  evalidus, 
  Bean, 
  

   from 
  beds 
  low 
  down 
  in 
  the 
  bituminous 
  shales 
  (Upper 
  Kimeridge) 
  

   (see 
  diagram 
  fig. 
  2), 
  which 
  Judd 
  states 
  (Q. 
  J. 
  G. 
  S. 
  xxiv. 
  p. 
  246) 
  to 
  

   be 
  Amm. 
  consobrinus, 
  D'Orb. 
  ; 
  but 
  in 
  a 
  later 
  paper, 
  referring 
  to 
  

   the 
  same 
  species 
  as 
  found 
  at 
  Knapton, 
  Judd 
  places 
  it 
  under 
  Amm. 
  

   fascicularis, 
  D'Orb., 
  a 
  different 
  shell 
  (Q. 
  J. 
  G. 
  S. 
  vol. 
  xxvi. 
  p. 
  328), 
  

   thus 
  illustrating 
  the 
  uncertainty 
  which 
  surrounds 
  these 
  species. 
  

  

  There 
  is, 
  however, 
  one 
  very 
  distinct, 
  though 
  allied 
  species, 
  possibly 
  

   the 
  Amm. 
  liystrix, 
  Phil., 
  in 
  which 
  the 
  costaa 
  develop 
  tubercles 
  and 
  

   spines 
  ; 
  but 
  it 
  is 
  a 
  shell 
  of 
  rare 
  occurrence. 
  

  

  Ammonites 
  speetonensis, 
  Young 
  and 
  Bird; 
  var. 
  concinnes, 
  Phil., 
  

   and 
  var, 
  venustus, 
  Phil. 
  

  

  The 
  variability 
  of 
  this 
  species 
  is 
  so 
  great 
  that 
  it 
  is 
  difficult 
  to 
  

   mark 
  out 
  its 
  limits. 
  On 
  the 
  one 
  hand, 
  the 
  coarse-ribbed 
  variety 
  

   (concinmis, 
  Phil.) 
  approaches 
  so 
  closely 
  to 
  the 
  Upper 
  Jurassic 
  species 
  

   Amm. 
  biplex, 
  Sow., 
  that 
  it 
  has 
  sometimes 
  been 
  wrongly 
  identified 
  as 
  

   belonging 
  to 
  that 
  species 
  : 
  and, 
  on 
  the 
  other 
  hand, 
  the 
  fine-lined 
  

   form 
  (yenustu.% 
  Phil.) 
  merges 
  almost 
  insensibly, 
  especially 
  in 
  young 
  

   specimens, 
  into 
  Amm. 
  Astierianus, 
  D'Orb. 
  ; 
  and 
  between 
  these 
  two 
  

   extremes 
  there 
  is 
  every 
  gradation. 
  The 
  shell 
  is 
  not 
  abundant 
  except 
  

   in 
  the 
  "main 
  SpeetoyieRsis-hed" 
  (C 
  6), 
  but 
  it 
  undoubtedly 
  occurs 
  in 
  

   the 
  " 
  Echinospatahgus-hed" 
  (0 
  3), 
  and 
  probably 
  ranges 
  quite 
  to 
  

   the 
  top 
  of 
  the 
  zone 
  of 
  Bel. 
  jaculum. 
  I 
  know 
  of 
  no 
  really 
  satisfactory 
  

   figures 
  of 
  this 
  species 
  or 
  of 
  its 
  varieties 
  * 
  ; 
  it 
  is 
  a 
  form 
  which 
  stands 
  

   in 
  great 
  need 
  of 
  elucidation. 
  

  

  Ammonites 
  Astieeianus, 
  D'Orb. 
  

  

  Touching 
  Amm. 
  speetonenis, 
  var. 
  venustus, 
  on 
  the 
  one 
  hand, 
  this 
  

   species 
  on 
  the 
  other 
  approaches 
  closely 
  to 
  Amm. 
  marginatus, 
  Phil., 
  

   the 
  line 
  of 
  demarcation 
  between 
  the 
  three 
  in 
  a 
  large 
  collection 
  being 
  

   difficult 
  to 
  draw, 
  although 
  the 
  extreme 
  forms 
  are 
  very 
  distinct. 
  

  

  The 
  species 
  is 
  not 
  very 
  easy 
  to 
  localize 
  in 
  the 
  section, 
  as 
  it 
  is 
  no- 
  

   where 
  plentiful. 
  It 
  certainly 
  occurs 
  in 
  the 
  " 
  Noricus 
  -beds" 
  but 
  

   not, 
  I 
  think, 
  lower 
  ; 
  and 
  ranges 
  upwards 
  as 
  high 
  as 
  the 
  " 
  Ecliino- 
  

   spatangus-bed" 
  though 
  I 
  have 
  not 
  yet 
  detected 
  it 
  at 
  some 
  of 
  the 
  

   intermediate 
  horizons. 
  Its 
  distribution 
  may, 
  perhaps, 
  be 
  said 
  to 
  

   coincide 
  roughly 
  with 
  that 
  of 
  Bel. 
  jaculum. 
  I 
  have 
  not 
  found 
  any 
  

   undoubted 
  specimens 
  of 
  it 
  within 
  the 
  zone 
  of 
  Bel. 
  lateralis, 
  the 
  

   nearest 
  approach 
  to 
  it 
  being 
  the 
  small 
  fine-lined 
  Ammonite 
  which 
  

  

  * 
  Written 
  before 
  the 
  appearance 
  of 
  Prof. 
  Pavlow's 
  paper, 
  in 
  which 
  young 
  

   specimens 
  of 
  this 
  species 
  are 
  figured. 
  He 
  recognizes 
  in 
  them 
  Oleostephanus 
  

   fasciatofalcatus, 
  Lah., 
  and 
  Olc. 
  subvkversus, 
  Pavl. 
  

  

  