﻿32 
  PROCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  majority 
  of 
  zoologists 
  would 
  be 
  inclined 
  to 
  derive 
  the 
  Pulmonata 
  

   from 
  the 
  Neritidae 
  in 
  accordance 
  with 
  the 
  common 
  view 
  that 
  the 
  

   marine 
  forms 
  were 
  the 
  precursors 
  of 
  the 
  terrestrial. 
  M.y 
  opinion 
  is 
  

   the 
  reverse 
  with 
  regard 
  to 
  most 
  cases, 
  and 
  chiefly 
  to 
  the 
  present 
  one. 
  

   The 
  formation 
  of 
  spermatophores 
  is 
  only 
  the 
  exception 
  among 
  the 
  

   Prosobranchia, 
  it 
  is 
  the 
  rule 
  among 
  the 
  Pulmonata. 
  Therefore 
  ^ 
  the 
  

   probability 
  is 
  that 
  the 
  Pulmonata 
  are 
  the 
  older 
  stock. 
  The 
  same 
  is 
  

   proved 
  by 
  the 
  single 
  spermatophore 
  and 
  the 
  typical 
  bursa 
  copulatrix 
  in 
  

   the 
  Pulmonata, 
  whereas 
  the 
  several 
  spermatophores 
  and 
  the 
  secondary 
  

   bursa 
  testify 
  the 
  derived 
  character 
  of 
  the 
  Neritidae. 
  

  

  All 
  this 
  is 
  in 
  accordance 
  with 
  the 
  geographical 
  distribution 
  in 
  

   connexion 
  with 
  the 
  pendulation 
  theory.- 
  Professor 
  Bourne 
  regards 
  

   the 
  tropical 
  marine 
  Neritce. 
  as 
  the 
  oldest 
  stock. 
  But 
  he 
  cannot 
  find 
  

   its 
  ancestors. 
  He 
  considers 
  the 
  Helicinidse, 
  the 
  nearest 
  allies 
  of 
  the 
  

   Neritidse, 
  as 
  a 
  young 
  group, 
  because 
  they 
  are 
  not 
  found 
  in 
  a 
  fossil 
  

   state. 
  Therefore 
  he 
  thinks 
  that 
  the 
  similarity 
  of 
  the 
  Palaeozoic 
  

   Baivsonella 
  with 
  the 
  Helicinidse 
  is 
  founded 
  only 
  upon 
  convergence, 
  

   and 
  not 
  upon 
  true 
  affinity. 
  Why 
  not 
  ? 
  I 
  do 
  not 
  think 
  the 
  palseonto- 
  

   logical 
  argument 
  can 
  demonstrate 
  the 
  contrary. 
  If 
  I 
  am 
  right, 
  

   between 
  the 
  Palaeozoic 
  Pupse 
  and 
  the 
  modern 
  living 
  forms 
  we 
  

   have 
  the 
  same 
  gap. 
  And 
  this 
  is 
  not 
  surprising, 
  as 
  terrestrial 
  animals 
  

   have 
  not 
  so 
  good 
  a 
  prospect 
  of 
  being 
  preserved 
  in 
  a 
  fossil 
  state 
  

   as 
  aquatic 
  ones. 
  The 
  geographical 
  distribution 
  of 
  the 
  Helicinidse 
  is 
  

   a 
  most 
  striking 
  argument 
  for 
  their 
  age. 
  They 
  inhabit 
  two 
  separated 
  

   areas, 
  in 
  the 
  east 
  and 
  in 
  the 
  west. 
  Daiosonella 
  demonstrates 
  that 
  

   they 
  once 
  lived 
  in 
  our 
  European 
  -North 
  American 
  quadrant, 
  when 
  we 
  

   were 
  in 
  a 
  more 
  southern 
  position. 
  By 
  the 
  pendulating 
  movement 
  

   directed 
  northward, 
  they 
  were 
  obliged 
  to 
  retire 
  into 
  the 
  areas 
  of 
  the 
  

   cast 
  and 
  west 
  poles 
  with 
  a 
  constant 
  tropical 
  climate, 
  where 
  we 
  find 
  

   them 
  to-day. 
  The 
  old 
  Neritidse 
  were 
  also 
  originally 
  tropical 
  terrestrial 
  

   forms, 
  but 
  during 
  the 
  same 
  pendulating 
  movement 
  they 
  retired 
  into 
  

   the 
  sea 
  with 
  its 
  more 
  equal 
  temperature, 
  and 
  acquired 
  one 
  or 
  two 
  

   gills, 
  or 
  they 
  retired 
  into 
  fresh 
  water, 
  the 
  freshwater 
  forms 
  being 
  those 
  

   which 
  were 
  more 
  able 
  to 
  adapt 
  themselves 
  to 
  diminishing 
  temperature 
  

   during 
  the 
  northward 
  movement 
  under 
  the 
  swinging 
  circle, 
  as 
  the 
  

   conditions 
  of 
  fresh 
  water 
  conform 
  more 
  to 
  those 
  of 
  the 
  soil. 
  The 
  

   old 
  freshwater 
  stock 
  was 
  changed 
  to 
  Paranerita, 
  and 
  in 
  the 
  torrents 
  

   to 
  Septaria. 
  When 
  the 
  pendulating 
  movement 
  transferred 
  their 
  area 
  

   further 
  northward, 
  they 
  retired 
  into 
  the 
  warmer 
  parts 
  of 
  the 
  globe. 
  

   One 
  part 
  became 
  submerged 
  under 
  sea-level, 
  another 
  stayed 
  in 
  fresh 
  

   water, 
  Septaria 
  retiring 
  into 
  the 
  east 
  pole 
  area 
  occupying 
  the 
  former 
  

   under-ridges 
  from 
  Ceylon 
  to 
  Mauritius, 
  and 
  through 
  the 
  Pacific 
  to 
  the 
  

   coral 
  islands. 
  The 
  allied 
  Pileoliis 
  of 
  the 
  Secondary 
  age 
  seems 
  to 
  prove 
  

   that 
  even 
  this 
  stock 
  originated 
  in 
  Europe. 
  Finally, 
  that 
  part 
  which 
  

   persisted 
  for 
  the 
  longest 
  time 
  in 
  fresh 
  water, 
  and 
  became 
  adapted 
  

   to 
  the 
  lowest 
  temperature, 
  losing 
  in 
  the 
  meantime 
  the 
  faculty 
  of 
  

  

  1 
  H. 
  Siraroth, 
  " 
  Die 
  Entsteliung 
  der 
  Landtiere" 
  ; 
  Leipzig, 
  1891. 
  

  

  2 
  H. 
  Simroth, 
  ' 
  * 
  Die 
  Pendulationstlieorie 
  " 
  ; 
  Leipzig, 
  1907. 
  

  

  