﻿ACADEMY 
  OF 
  SCIENCES. 
  121 
  

  

  Mr. 
  Stearns 
  submitted 
  the 
  following 
  communication 
  for 
  Dr. 
  

   Cooper 
  : 
  

  

  On 
  the 
  Law 
  of 
  Variation 
  in 
  the 
  banded 
  California 
  Land 
  Shells. 
  

  

  BY 
  J. 
  G. 
  COOPER, 
  M. 
  D. 
  

  

  1. 
  ARIONTA 
  Leach. 
  

  

  In 
  studying 
  further 
  the 
  species 
  referable 
  to 
  this 
  genus 
  in 
  California, 
  together 
  

   with 
  their 
  geographical 
  distribution, 
  some 
  curious 
  generalizations 
  are 
  arrived 
  

   at, 
  hinted 
  at 
  in 
  a 
  former 
  article 
  by 
  me 
  in 
  the 
  American 
  Journal 
  of 
  Cuuchology, 
  

   Vol. 
  IV, 
  p. 
  211, 
  but 
  not 
  then 
  so 
  fully 
  understood. 
  

  

  The 
  close 
  relationship 
  and 
  probable 
  identity 
  of 
  some 
  assumed 
  species 
  has 
  

   been 
  long 
  apparent 
  to 
  all 
  who 
  have 
  examined 
  them, 
  but 
  from 
  paucity 
  of 
  speci- 
  

   mens, 
  or 
  reasons 
  by 
  which 
  to 
  account 
  for 
  their 
  differences, 
  they 
  have 
  been 
  

   allowed 
  to 
  retain 
  their 
  rank 
  as 
  species 
  until 
  more 
  numerous 
  intermediate 
  forms 
  

   should 
  establish 
  their 
  position 
  as 
  varieties.* 
  

  

  Though 
  these 
  connecting 
  links 
  are 
  very 
  few, 
  and 
  from 
  the 
  peculiarly 
  local 
  

   distribution 
  of 
  the 
  chief 
  forms 
  are 
  not 
  likely 
  to 
  be 
  found 
  numerous, 
  yet 
  I 
  think 
  

   it 
  can 
  be 
  shown 
  that 
  these 
  local 
  forms 
  are 
  not 
  entitled 
  to 
  higher 
  rank 
  than 
  that 
  

   of 
  sub-species 
  which 
  have 
  had 
  a 
  common 
  origin. 
  By 
  gradual 
  divergence 
  from 
  

   one 
  or 
  a 
  few 
  centers 
  of 
  distribution, 
  and 
  being 
  brought 
  under 
  the 
  influence 
  of 
  

   different 
  climates, 
  they 
  have 
  assumed 
  their 
  present 
  conditions, 
  which 
  are 
  still 
  

   subject 
  to 
  many 
  variations, 
  showing 
  a 
  tendency 
  to 
  the 
  production 
  of 
  other 
  

   forms. 
  The 
  systematic 
  arrangement 
  of 
  these 
  species 
  and 
  varieties, 
  or 
  sub-spe- 
  

   cies, 
  in 
  connection 
  with 
  their 
  distribution, 
  can 
  be 
  best 
  shown 
  by 
  a 
  diagram. 
  

   See 
  Plate 
  VII. 
  

  

  The 
  plan 
  here 
  given 
  shows 
  the 
  position 
  and 
  extent 
  of 
  range 
  of 
  each 
  form 
  

   allied 
  to 
  Ariovta, 
  the 
  range 
  north 
  and 
  south 
  being 
  shown 
  by 
  the 
  parallels 
  of 
  

   latitude, 
  and 
  that 
  east 
  and 
  west 
  by 
  the 
  length 
  of 
  the 
  brackets 
  enclosing 
  or 
  ad- 
  

   joining 
  the 
  names, 
  which 
  may 
  be 
  compared 
  with 
  the 
  scale 
  given. 
  It 
  will 
  be 
  

   observed 
  that 
  the 
  additions 
  to 
  our 
  knowledge 
  of 
  their 
  range 
  has 
  n( 
  t 
  much 
  in- 
  

   creased 
  since 
  the 
  publication 
  of 
  the 
  map 
  given 
  in 
  the 
  Amer. 
  Jour, 
  of 
  Conch., 
  

   Vol. 
  IV, 
  p. 
  211, 
  though 
  some 
  doubtful 
  points 
  have 
  been 
  settled. 
  

  

  The 
  chief 
  centers 
  of 
  distribution 
  are 
  around 
  San 
  Francisco 
  Bay, 
  on 
  the 
  Santa 
  

   Barbara 
  islands, 
  and 
  near 
  San 
  Diego, 
  whence 
  one 
  species 
  follows 
  up 
  the 
  Sierra 
  

   Nevada 
  to 
  near 
  lat. 
  40°. 
  As 
  this 
  species 
  has 
  so 
  wide 
  a 
  range, 
  and 
  presents 
  

   nearly 
  as 
  many 
  varieties 
  as 
  are 
  found 
  in 
  the 
  other 
  groups, 
  it 
  becomes 
  a 
  question 
  

   whether 
  it 
  is 
  not 
  the 
  (Darwinian) 
  progenitor 
  of 
  those 
  along 
  the 
  coast 
  which 
  

   occupy 
  regions 
  of 
  later 
  geological 
  age. 
  Though 
  the 
  group 
  around 
  San 
  Fran- 
  

   cisco 
  Bay 
  is 
  one 
  hundred 
  miles 
  distant 
  from 
  the 
  nearest 
  of 
  that 
  species, 
  it 
  must 
  be 
  

   remembered 
  that 
  the 
  rivers 
  all 
  converge 
  toward 
  the 
  bay, 
  and 
  that 
  the 
  floods 
  

  

  *Most 
  of 
  the 
  names 
  in 
  use 
  wiU 
  no 
  doubt 
  be 
  always 
  retained 
  for 
  convenience 
  in 
  distin- 
  

   guishing 
  between 
  the 
  various 
  races, 
  etc. 
  

  

  