﻿21 
  

  

  ON 
  THE 
  NOETH 
  AMERICAN 
  GENUS 
  OBEOHELIX. 
  

   Ey 
  Junius 
  Hendeuson. 
  

  

  Read 
  14th 
  December, 
  1917. 
  

   [Condensed. 
  '\ 
  

   The 
  most 
  important 
  Itind-snail 
  genus 
  in 
  North 
  Americn, 
  north 
  of 
  

   Mexico, 
  is 
  Polygyra, 
  including 
  more 
  tlian 
  125 
  species 
  and 
  subspecies. 
  

   A 
  lurge 
  majority 
  of 
  these 
  inhabits 
  the 
  region 
  east 
  of 
  the 
  Mississippi 
  

   and 
  Missouri 
  llivers. 
  The 
  genus 
  is 
  also 
  well 
  represented 
  west 
  of 
  

   those 
  rivers 
  in 
  Texas, 
  Indian 
  Territory, 
  Oklahoma, 
  Louisiana, 
  

   Arkansas, 
  Southern 
  Missouri, 
  and 
  Eastern 
  Kansas. 
  A 
  few 
  species 
  

   are 
  found 
  through 
  British 
  America 
  and 
  the 
  northern 
  tier 
  of 
  the 
  

   United 
  States 
  to 
  the 
  Pacific 
  coast, 
  thence 
  southward 
  to 
  California. 
  

   They 
  are 
  exceedingly 
  rare 
  in 
  New 
  Mexico, 
  and, 
  so 
  far 
  as 
  I 
  recollect, 
  

   unknown 
  in 
  Arizona, 
  most 
  of 
  the 
  material 
  formerly 
  reported 
  under 
  

   that 
  name 
  from 
  those 
  states 
  being 
  now 
  assigned 
  to 
  the 
  south-western 
  

   semi-desert 
  genus 
  Ashmmella. 
  In 
  the 
  lower 
  portions 
  of 
  Arizona 
  and 
  

   New 
  Mexico 
  the 
  true 
  desert 
  genus 
  Sonorella 
  occurs, 
  the 
  species 
  of 
  

   which 
  were 
  formerly 
  included 
  in 
  the 
  genus 
  Epiphragmophora. 
  The 
  

   most 
  important 
  genus 
  of 
  Helicoid 
  snails 
  in 
  California 
  is 
  that 
  com- 
  

   prising 
  the 
  species 
  usually 
  assigned 
  to 
  Epiphragmophora, 
  but 
  perhaps 
  

   referable, 
  on 
  anatomical 
  characters, 
  to 
  Micrarionta. 
  Thus 
  tliese 
  four 
  

   genera 
  complete 
  a 
  circuit 
  enclosing 
  a 
  vast 
  "island" 
  comprising 
  

   Colorado, 
  Utah, 
  Wyoming, 
  Western 
  Kansas, 
  Western 
  Nebraska, 
  

   Southern 
  Idaho, 
  and 
  the 
  greater 
  piirt 
  of 
  Nevada, 
  aggregating 
  more 
  

   than 
  500,000 
  square 
  miles, 
  from 
  which 
  those 
  genera 
  appear 
  to 
  be 
  

   entirely 
  absent. 
  The 
  only 
  genus 
  of 
  large 
  land-snails 
  thus 
  far 
  found 
  

   in 
  that 
  area 
  is 
  the 
  viviparous, 
  herbivorous 
  Oreohelix,^ 
  though 
  smaller 
  

   snails, 
  such 
  as 
  Vallonia, 
  Papilla, 
  Zonitoides, 
  Vitrina, 
  and 
  many 
  others, 
  

   are 
  abundant 
  and 
  generally 
  distril)uted 
  in 
  favourable 
  stations 
  

   tliroughout 
  the 
  mountainous 
  portions. 
  The 
  present 
  range 
  of 
  

   Oreohelix 
  overlaps 
  that 
  of 
  Polygi/ra 
  in 
  Montana, 
  Northern 
  Idaho, 
  

   Washington, 
  California, 
  and 
  perhaps 
  Oregon. 
  It 
  ot*erlaps 
  that 
  of 
  

   Epiphragmophora 
  in 
  California, 
  owing 
  to 
  the 
  occurrence 
  of 
  a 
  small 
  

   form 
  on 
  Cataliiia 
  Island, 
  off 
  the 
  coast, 
  and 
  possibly 
  also 
  in 
  Oregon, 
  

   most 
  of 
  which 
  is 
  concliologically 
  unexplored. 
  It 
  nearly 
  meets 
  the 
  

   range 
  of 
  Poh/gyra 
  in 
  New 
  Mexico, 
  and 
  is 
  abundant 
  within 
  the 
  range 
  

   of 
  Ashmmella 
  and 
  Sonorella 
  in 
  New 
  Mexico 
  and 
  Arizona. 
  The 
  

   almost 
  treeless 
  and 
  shrubless 
  plains 
  of 
  Eastern 
  Colorado, 
  Wyoming 
  

   and 
  New 
  Mexico, 
  and 
  Western 
  Kansas 
  and 
  Nebraska, 
  are 
  wholly 
  

   unfavourable 
  to 
  large 
  land- 
  snails, 
  so 
  the 
  genus 
  does 
  not, 
  along 
  its 
  

   eastern 
  limit, 
  touch 
  the 
  range 
  of 
  Polygyra, 
  though 
  a 
  fossil 
  form 
  from 
  

   the 
  loess 
  of 
  Iowa 
  tells 
  of 
  a 
  former 
  connexion. 
  

  

  The 
  few 
  who 
  have 
  critically 
  studied 
  Oreohelix 
  now 
  recognize 
  

   approximately 
  sixty 
  species 
  and 
  subspecies, 
  besides 
  which 
  there 
  are 
  

   more 
  than 
  twenty-five 
  named 
  forms 
  of 
  doubtful 
  value. 
  Undoubtedly 
  

  

  ^ 
  Cf. 
  H. 
  A. 
  Pilsbry, 
  "Notes 
  on 
  the 
  Anatomy 
  of 
  Oreohelix, 
  with 
  a 
  Catalogue 
  of 
  

   the 
  species 
  " 
  : 
  Proc. 
  Acad. 
  Nat. 
  Sci. 
  Philad., 
  1916, 
  pp. 
  340 
  et 
  seqq. 
  

  

  