﻿2J0 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  Fam. 
  III. 
  Lytoceratid^s. 
  

  

  Contains 
  5 
  genera, 
  all 
  of 
  which 
  are 
  British, 
  and 
  as 
  such 
  I 
  must 
  

   notice 
  them. 
  

  

  The 
  genera 
  of 
  the 
  Lytoceratidce 
  differ 
  greatly 
  from 
  each 
  other 
  in 
  

   external 
  form, 
  but 
  have 
  close 
  relations 
  in 
  their 
  internal 
  structure. 
  

   The 
  body-chamber 
  is 
  short 
  (f 
  of 
  whorl), 
  with 
  simple 
  mouth-border, 
  

   produced 
  on 
  the 
  columellar 
  side. 
  

  

  This 
  family 
  includes 
  the 
  typical 
  genera 
  Lytoceras 
  and 
  Phylloceras, 
  

   the 
  former 
  represented 
  by 
  L. 
  fimbriatum, 
  Sow., 
  from 
  the 
  Middle 
  

   and 
  Upper 
  Lias, 
  and 
  the 
  latter 
  by 
  Phylloceras 
  heterophyllum 
  from 
  

   the 
  Upper 
  Lias. 
  The 
  remaining 
  3 
  genera 
  are 
  Hamites, 
  Turrilites, 
  

   and 
  B 
  acuities, 
  all 
  Cretaceous, 
  and 
  differing 
  essentially 
  in 
  external 
  

   form. 
  

  

  Lytoceras 
  commences 
  in 
  the 
  Trias 
  with 
  Lyt. 
  Maloti 
  and 
  Lyt. 
  patens. 
  

   It 
  is 
  represented 
  in 
  the 
  Lias 
  by 
  Lyt. 
  fimbriatum, 
  Sow., 
  Lyt. 
  cornu- 
  

   copia, 
  Lyt. 
  jurense, 
  Ziet., 
  Lyt. 
  lineatum, 
  Schloth., 
  Lyt. 
  hircinum, 
  

   Schloth., 
  and 
  Lyt. 
  tondosum, 
  and 
  by 
  Lyt. 
  Eudesianum, 
  D'Orb., 
  in 
  

   the 
  Inferior 
  Oolite. 
  In 
  the 
  Lower 
  Cretaceous 
  rocks 
  this 
  genus 
  is 
  

   represented 
  by 
  Lyt. 
  (Crioceras) 
  Duvalianum 
  and 
  Lyt. 
  subfimbriatum, 
  

   D'Orb. 
  

  

  Genus 
  Hamites. 
  — 
  Prof. 
  Neumayer 
  does 
  not 
  believe 
  that 
  " 
  a 
  spiral 
  

   curve 
  of 
  a 
  particular 
  form 
  gives 
  sufficient 
  warrant 
  for 
  the 
  establish- 
  

   ment 
  of 
  a 
  distinct 
  genus. 
  Adopting 
  this 
  view, 
  the 
  7 
  old 
  and 
  recognized 
  

   genera 
  (Anisoceras, 
  Ancyloceras, 
  Baculina, 
  Hamulina, 
  Helicoceras, 
  

   Ptychoceras, 
  and 
  Tocvoceras), 
  in 
  which 
  the 
  curvature 
  receives 
  many 
  

   modifications, 
  and 
  exists 
  in 
  some 
  in 
  more 
  than 
  one 
  plane, 
  are 
  now 
  

   suppressed, 
  and 
  the 
  whole 
  scries 
  reduced 
  to 
  the 
  single 
  genus 
  Ha- 
  

   mites, 
  which 
  is 
  a 
  conical 
  straight 
  shell 
  (ex. 
  II. 
  elegans, 
  D'Orb.) 
  bent 
  

   in 
  one 
  plane, 
  the 
  bends 
  or 
  curves 
  not 
  in 
  contact. 
  The 
  suture-line 
  

   is 
  divided 
  into 
  six 
  lobes, 
  and 
  the 
  chief 
  or 
  under 
  lateral 
  lobe 
  is 
  divided 
  

   into 
  pairs 
  of 
  branches. 
  

  

  Genus 
  Turrilites. 
  — 
  Neumayer 
  under 
  this 
  genus 
  classes 
  Helicoceras 
  

   with 
  an 
  open 
  spiral, 
  not 
  on 
  one 
  plane. 
  In 
  Turrilites 
  the 
  suture- 
  

   line 
  is 
  divided 
  into 
  six 
  lobes, 
  each 
  lobe 
  possessing 
  a 
  single 
  pair 
  of 
  

   digitations, 
  and 
  the 
  mouth 
  is 
  simple 
  and 
  the 
  shell 
  sinistral. 
  

  

  Genus 
  Baculites. 
  — 
  Neumayer 
  connects 
  this 
  genus 
  with 
  Lytoceras 
  

   and 
  Hamites 
  by 
  the 
  structure 
  of 
  the 
  principal 
  lateral 
  lobe. 
  The 
  

   septa 
  are 
  symmetrical, 
  divided 
  into 
  four 
  or 
  six 
  lobes, 
  each 
  having 
  

   a 
  pair 
  of 
  digitations 
  (type 
  B. 
  anceps). 
  

  

  Genus 
  Phylloceras. 
  — 
  In 
  this 
  fine 
  genus 
  the 
  body-chamber 
  is 
  

   short, 
  and 
  the 
  mouth-border 
  with 
  lateral 
  forwardly 
  directed 
  lappets. 
  

   Lobes 
  numerous, 
  eight 
  or 
  nine 
  on 
  each 
  side, 
  very 
  complicated. 
  

   Phylloceras 
  heterophyllum, 
  Sow., 
  from 
  the 
  Upper 
  Lias, 
  is 
  the 
  type. 
  

   Neumayer 
  distinguishes 
  4 
  groups 
  in 
  this 
  genus 
  ; 
  the 
  following 
  are 
  

   his 
  types 
  : 
  — 
  

  

  1. 
  Phylloceras 
  heterophyllum, 
  Sow. 
  

  

  2. 
  P. 
  tatricum, 
  Pusch. 
  

  

  3. 
  P. 
  Capitanei, 
  Catullo. 
  

  

  4. 
  P. 
  ultramontanum, 
  Zittel. 
  

  

  