﻿WALKEE 
  : 
  ON 
  MARGAIilTANA 
  JIABGABIIIFEBA. 
  127 
  

  

  agaiu 
  by 
  Trask 
  in 
  1855 
  as 
  A. 
  Yubaensis. 
  Dr. 
  Dall 
  has 
  recently 
  

   (1905) 
  considered 
  the 
  western 
  form 
  worthy 
  of 
  varietal 
  recognition 
  

   under 
  Gould's 
  name. 
  The 
  deep 
  purple 
  nacre, 
  however, 
  is 
  not 
  

   invariably 
  present, 
  and 
  specimens 
  not 
  infrequently 
  occur 
  with 
  the 
  

   nacre 
  quite 
  as 
  light-coloured 
  as 
  in 
  the 
  typical 
  form. 
  Individual 
  

   specimens 
  from 
  the 
  eastern 
  states 
  are 
  occasionally 
  quite 
  deeply 
  tinted 
  

   with 
  purple 
  and 
  salmon 
  colour. 
  

  

  On 
  the 
  Atlantic 
  coast, 
  the 
  most 
  northern 
  record 
  is 
  from 
  Labrador 
  

   (Packard), 
  but 
  this 
  is 
  questioned 
  by 
  AVhiteaves. 
  It 
  is 
  found 
  in 
  

   j!^ewfoundland 
  (Johnson 
  and 
  Marshall) 
  ; 
  Anticosti 
  (Johnson) 
  ; 
  New 
  

   Brunswick 
  (Matthew 
  and 
  AValker) 
  ; 
  JS'ova 
  Scotia 
  (Jones) 
  ; 
  in 
  the 
  

   northerly 
  tributaries 
  of 
  the 
  St. 
  Lawrence 
  west 
  to 
  the 
  St. 
  Charles 
  

   River 
  at 
  Quebec 
  (Latchford); 
  in 
  Maine 
  (Lermond); 
  Vermont 
  (Adams, 
  

   Davis, 
  and 
  AValker) 
  ; 
  Massachusetts 
  (Call, 
  Davis, 
  and 
  Walker) 
  ; 
  Con- 
  

   necticut 
  (Davis 
  and 
  Walker); 
  Ehode 
  Island 
  (Carpenter); 
  Eastern 
  

   New 
  York 
  (Lewis, 
  De 
  Kay, 
  Marshall, 
  and 
  Walker) 
  ; 
  and 
  in 
  Chester 
  Co. 
  

   (Hartman 
  and 
  ilinchner), 
  Delaware 
  Co. 
  (Lea), 
  and 
  Schuylkill 
  Co., 
  

   Pennsylvania 
  (Connor 
  and 
  Ortmann). 
  

  

  The 
  Delaware 
  Co., 
  Pa., 
  locality 
  is 
  the 
  most 
  southern 
  yet 
  recorded 
  

   on 
  the 
  Atlantic 
  coast. 
  It 
  has 
  not 
  been 
  listed 
  from 
  New 
  Jersey 
  or 
  

   Delaware 
  so 
  far 
  as 
  I 
  have 
  been 
  able 
  to 
  ascertain. 
  

  

  In 
  New 
  York, 
  where 
  it 
  attains 
  its 
  extreme 
  eastern 
  range, 
  it 
  is 
  

   recorded 
  from 
  Oneida 
  Co. 
  (De 
  Kay 
  and 
  Marshall), 
  and 
  Fox 
  Creek, 
  

   Lewis 
  Co., 
  a 
  tributary 
  of 
  Oneida 
  Lake 
  (Walker). 
  

  

  In 
  general, 
  therefore, 
  it 
  may 
  be 
  said 
  that 
  on 
  the 
  Pacific 
  coast 
  its 
  

   range 
  is 
  limited 
  on 
  the 
  east 
  by 
  the 
  Rocky 
  Mountains, 
  and 
  on 
  the 
  

   Atlantic 
  coast 
  it 
  is 
  confined 
  to 
  the 
  region 
  east 
  of 
  the 
  Appalachian 
  

   Mountains. 
  In 
  both 
  instances, 
  however, 
  it 
  has, 
  in 
  occasional 
  instances, 
  

   obtained 
  a 
  foothold 
  in 
  the 
  interior 
  beyond 
  the 
  mountains, 
  but 
  in 
  such 
  

   cases 
  its 
  range 
  is 
  extremely 
  limited. 
  In 
  the 
  United 
  States, 
  there 
  is 
  

   no 
  authentic 
  record 
  of 
  its 
  occurrence 
  between 
  Lewis 
  and 
  Oneida 
  

   Counties, 
  N.Y., 
  and 
  the 
  Falls 
  of 
  the 
  Missouri 
  in 
  Montana. 
  In 
  British 
  

   America, 
  with 
  a 
  single 
  exception, 
  it 
  has 
  not 
  been 
  recorded 
  at 
  all 
  from 
  

   the 
  vast 
  region 
  extending 
  from 
  the 
  Rocky 
  Mountains 
  east 
  to 
  Quebec. 
  

   The 
  single 
  exception 
  above 
  mentioned 
  from 
  Central 
  British 
  America 
  

   is 
  that 
  of 
  Dall 
  (1905), 
  who 
  records 
  the 
  typical 
  (eastern) 
  form 
  from 
  the 
  

   lower 
  Saskatchewan 
  near 
  Lake 
  Winnipeg. 
  

  

  In 
  considering 
  the 
  possible 
  causes 
  of 
  this 
  peculiar 
  distribution 
  of 
  

   the 
  species, 
  it 
  is 
  necessary 
  to 
  take 
  into 
  consideration 
  not 
  only 
  its 
  

   general 
  distribution 
  at 
  the 
  present 
  time, 
  but 
  also 
  the 
  geologic 
  changes, 
  

   which 
  in 
  past 
  ages 
  have 
  affected 
  the 
  configuration 
  of 
  the 
  continents 
  

   as 
  they 
  now 
  exist, 
  and 
  which 
  may 
  have 
  played 
  an 
  important 
  part 
  in 
  

   permitting 
  or 
  preventing 
  the 
  migration 
  of 
  the 
  species 
  in 
  different 
  

   directions 
  from 
  the 
  primitive 
  place 
  of 
  origination. 
  In 
  the 
  first 
  j^lace, 
  

   the 
  genus 
  JUarfjaritana, 
  as 
  limited 
  by 
  Simpson, 
  is 
  evidently 
  a 
  very 
  

   ancient 
  one. 
  This 
  is 
  shown 
  not 
  only 
  by 
  the 
  enormous 
  range 
  of 
  the 
  

   typical 
  species 
  {margaritifera), 
  but 
  also 
  by 
  the 
  equally 
  remarkable 
  

   discontinuity 
  of 
  the 
  ranges 
  of 
  the 
  six 
  species 
  included 
  in 
  the 
  genus. 
  

  

  As 
  already 
  stated, 
  i/". 
  margarUifera 
  is 
  circumpolar, 
  with 
  the 
  

   apparent 
  exception 
  of 
  the 
  central 
  region 
  of 
  British 
  North 
  America. 
  

  

  