﻿OLD 
  AND 
  NEW 
  WORLD 
  MELANIANS 
  — 
  MORRISON 
  367 
  

  

  solely 
  on 
  shell 
  characters. 
  The 
  genotype 
  by 
  original 
  designation 
  is 
  

   Pachychilus 
  {Pilsbrychihs) 
  dalli 
  Pilsbry, 
  which 
  was 
  first 
  validly 
  

   published 
  April 
  17, 
  1896, 
  in 
  Science 
  (vol. 
  3, 
  p. 
  608) 
  ahead 
  of 
  the 
  com- 
  

   plete 
  description 
  by 
  Pilsbry 
  in 
  Proceedings 
  of 
  the 
  Academy 
  of 
  Natural 
  

   Sciences 
  of 
  Philadelphia, 
  June 
  16, 
  1896 
  (p. 
  269). 
  Fortunately, 
  this 
  

   earliest 
  validation 
  preceded 
  the 
  typographical 
  error 
  "walli," 
  which 
  

   appeared 
  in 
  Zoologischer 
  Anzeiger 
  in 
  May 
  1896. 
  

  

  Genus 
  Doryssa 
  H. 
  and 
  A. 
  Adams, 
  1854 
  

  

  Doryssa 
  H. 
  and 
  A. 
  Adams 
  (1854, 
  p. 
  304), 
  whose 
  genotype 
  is 
  D. 
  

   atra 
  (Bruguiere) 
  from 
  Suriname, 
  ecologically 
  and 
  geographically 
  

   replaces 
  Pachychilus 
  in 
  northern 
  South 
  America 
  from 
  Venezuela 
  to 
  

   the 
  Guianas 
  and 
  Brazil. 
  In 
  both 
  these 
  genera 
  the 
  females 
  have 
  a 
  

   well-developed 
  genital 
  groove 
  ending 
  in 
  the 
  characteristic 
  pleurocerine 
  

   glandular 
  egg-laying 
  sinus 
  near 
  the 
  right 
  edge 
  of 
  the 
  foot. 
  The 
  

   males 
  lack 
  this 
  groove. 
  Doryssa 
  consolidata 
  (Bruguiere) 
  was 
  per- 
  

   sonally 
  collected 
  by 
  the 
  hundreds 
  from 
  rocks 
  in 
  the 
  Mazaruni 
  and 
  

   Cuyuni 
  Rivers 
  of 
  the 
  Essiquibo 
  system, 
  British 
  Guiana, 
  in 
  the 
  

   summer 
  of 
  1925. 
  At 
  that 
  time 
  the 
  shells 
  were 
  cleaned 
  and 
  the 
  

   radulae 
  (see 
  Baker, 
  1930, 
  p. 
  30) 
  extracted 
  from 
  the 
  animals 
  for 
  future 
  

   study 
  of 
  variation. 
  Although 
  at 
  that 
  time 
  I 
  did 
  not 
  know 
  what 
  char- 
  

   acters 
  were 
  critical 
  for 
  subfamily 
  classification, 
  no 
  difference 
  of 
  gross 
  

   anatomy 
  was 
  observed 
  between 
  this 
  British 
  Guiana 
  Doryssa 
  and 
  the 
  

   North 
  American 
  species 
  Oxytrema 
  semicarinata 
  (Say), 
  already 
  crit- 
  

   ically 
  and 
  completely 
  personally 
  studied 
  near 
  Lexington, 
  Ky., 
  in 
  

   1924. 
  The 
  egg-laying 
  season 
  of 
  Doryssa 
  is 
  apparently 
  still 
  unrecorded. 
  

   It 
  was 
  not 
  observed 
  during 
  June, 
  July, 
  or 
  August 
  in 
  the 
  Kartabo 
  

   region. 
  Sheppardiconcha 
  Marshall 
  and 
  Bowles 
  (1932, 
  p. 
  3), 
  described 
  

   as 
  a 
  new 
  genus 
  from 
  the 
  (Miocene?) 
  fossil 
  deposits 
  of 
  the 
  Upper 
  

   Amazon 
  region 
  of 
  Ecuador, 
  is 
  not 
  a 
  subgenus 
  of 
  Aylacostoma. 
  Refer- 
  

   ence 
  of 
  the 
  group 
  by 
  later 
  authors 
  to 
  Aylacostoma 
  (=Hemisinus) 
  is 
  

   primarily 
  due 
  to 
  the 
  difficulty 
  of 
  complete 
  separation 
  of 
  the 
  genus 
  

   Doryssa 
  of 
  the 
  Pleuroceridae 
  from 
  Aylacostoma 
  of 
  the 
  Thiaridae 
  by 
  

   shell 
  characters 
  alone. 
  According 
  to 
  the 
  shell 
  characters 
  of 
  the 
  

   original 
  material, 
  Sheppardiconcha 
  is 
  a 
  synonym 
  of 
  Doryssa, 
  

  

  Family 
  Pleuroceridae 
  (in 
  Asia) 
  

  

  Subfamily 
  pleurocerinae 
  

  

  Genus 
  Oxytrema 
  Rafinesque, 
  1819 
  

  

  In 
  the 
  present 
  state 
  of 
  our 
  knowledge 
  it 
  is 
  no 
  longer 
  possible 
  to 
  

   maintain 
  the 
  generic 
  distinction 
  of 
  certain 
  eastern 
  Asiatic 
  species 
  

   from 
  the 
  genus 
  Oxytrema, 
  which 
  has 
  previously 
  been 
  considered 
  

  

  