﻿360 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  103 
  

  

  Rafinesque 
  originally 
  described 
  Oxytrema 
  (1819, 
  p. 
  423), 
  including 
  

   young 
  specimens 
  of 
  both, 
  his 
  genus 
  Pleurocera 
  and 
  this 
  one. 
  There 
  

   were 
  no 
  specific 
  names 
  included, 
  Blainville, 
  in 
  1824 
  and 
  again 
  in 
  

   1825 
  (p. 
  442), 
  placed 
  one 
  species 
  of 
  Rafinesque 
  under 
  this 
  generic 
  

   name. 
  He 
  gave 
  as 
  the 
  sole 
  example 
  of 
  the 
  subgenus 
  Pleurocerus 
  

   (Oxytrema) 
  acutus 
  (Rafinesque), 
  validating 
  the 
  specific 
  name 
  in 
  1824. 
  

   Rafinesque 
  (1831, 
  p. 
  3) 
  again 
  described 
  his 
  Pleurocera 
  acuta, 
  and 
  at 
  

   the 
  same 
  time 
  declared 
  he 
  had 
  given 
  the 
  name 
  in 
  1818. 
  From 
  1824 
  

   on, 
  Oxytrema 
  has 
  been 
  the 
  earliest 
  available 
  name 
  for 
  the 
  group 
  be- 
  

   cause 
  the 
  genotype 
  was 
  fixed 
  at 
  that 
  time 
  as 
  Pleurocera 
  (Oxytrema) 
  

   acuta 
  Blainville 
  by 
  monotypy. 
  With 
  no 
  serious 
  question 
  ever 
  raised 
  

   about 
  the 
  identity 
  of 
  acuta, 
  the 
  genotype, 
  doubts 
  about 
  the 
  identity 
  

   of 
  the 
  genus 
  Oxytrema 
  vanish. 
  

  

  The 
  eastern 
  American 
  (Appalachian) 
  species 
  of 
  Oxytrema 
  include 
  

   some 
  whose 
  shells 
  are 
  almost 
  completely 
  smooth 
  as 
  adults, 
  such 
  as 
  

   0. 
  symmetrica 
  (Haldeman) 
  ; 
  some 
  with 
  spiral 
  sculpture 
  predominant, 
  

   such 
  as 
  0. 
  drginica 
  multilineata 
  (Say); 
  others 
  with 
  axial 
  sculpture 
  

   strong, 
  such 
  as 
  0. 
  laqueata 
  (Say); 
  and 
  still 
  others 
  with 
  both 
  axial 
  

   and 
  spiral 
  lirae 
  to 
  produce 
  reticulate 
  or 
  nodose 
  sculpture, 
  such 
  as 
  

   0. 
  catenana 
  (Say). 
  

  

  In 
  exactly 
  parallel 
  fashion, 
  as 
  should 
  be 
  expected 
  of 
  congeneric 
  

   stocfe, 
  the 
  western 
  American 
  species 
  now 
  laiown 
  to 
  belong 
  to 
  Oxytrema 
  

   show 
  the 
  same 
  rather 
  complete 
  range 
  of 
  sculpture 
  from 
  smooth 
  to 
  

   axially 
  and 
  spu-ally 
  sculptured 
  adult 
  shells. 
  The 
  easternmost 
  living 
  

   representative 
  of 
  the 
  Rocky 
  Mountain 
  group 
  of 
  species 
  is 
  0. 
  comalensis 
  

   (Pilsbry). 
  This 
  species 
  from 
  Texas 
  belongs 
  to 
  this 
  minor 
  group 
  

   within 
  the 
  genus, 
  possessing 
  the 
  same 
  minutae 
  of 
  female 
  reproductive 
  

   characters 
  as 
  does 
  0. 
  plicifera 
  (Lea) 
  from 
  Oregon 
  and 
  Washington. 
  

   Most 
  if 
  not 
  all 
  the 
  western 
  America 
  Tertiary 
  fossil 
  species 
  described 
  

   as 
  "Melania," 
  "Goniobasis," 
  and 
  ''Pachychilus," 
  from 
  Texas 
  to 
  

   Washington, 
  were 
  members 
  of 
  this 
  genus 
  Oxytrema 
  Rafinesque. 
  For 
  

   example, 
  ''Amhloxus'' 
  olequaensis 
  Arnold 
  and 
  Haiuiibal 
  (Hannibal, 
  

   1912, 
  p. 
  178, 
  pi. 
  8, 
  fig. 
  27) 
  closely 
  resembles 
  the 
  smoother 
  phase 
  of 
  

   the 
  living 
  Oxytrema 
  silicula 
  (Gould) 
  from 
  the 
  same 
  region, 
  while 
  

   "Pachychilus" 
  drakei 
  Arnold 
  and 
  Hannibal 
  (Hannibal, 
  1912, 
  p. 
  183, 
  

   pi. 
  8, 
  fig. 
  26) 
  is 
  close 
  to 
  the 
  living 
  species 
  Oxytrema 
  plicifera 
  (Lea). 
  

   Certain 
  other 
  fossil 
  species 
  from 
  the 
  Rocky 
  Mountain 
  region 
  parallel 
  

   eastern 
  forms 
  in 
  the 
  possession 
  of 
  cancellate 
  or 
  reticulate 
  sculpture. 
  

   Species 
  known 
  from 
  the 
  fossil 
  record 
  indicate 
  the 
  previous 
  continuity 
  

   of 
  geographic 
  distribution 
  from 
  Washington 
  to 
  Texas, 
  now 
  noncon- 
  

   tinuous 
  since 
  much 
  of 
  the 
  intervening 
  area 
  (progressively 
  desiccated 
  

   since 
  the 
  Miocene) 
  is 
  now 
  unsuited 
  to 
  survival 
  of 
  pleurocerine 
  fresh- 
  

   water 
  snails. 
  

  

  Female 
  animals 
  of 
  Oxytrema 
  canaliculatum 
  undulatum 
  (Say) 
  from 
  

  

  