﻿358 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  los 
  

  

  The 
  family 
  Pleuroceridae, 
  fresh-water 
  representative 
  of 
  the 
  ancestral 
  

   cerithiid 
  stock, 
  is 
  now 
  known 
  to 
  include 
  species 
  living 
  in 
  Africa, 
  

   Asia, 
  and 
  the 
  Americas. 
  

  

  The 
  family 
  Thiaridae, 
  likewise, 
  is 
  known 
  from 
  Africa, 
  Asia, 
  and 
  

   America. 
  With 
  identical 
  reproductive 
  characters, 
  the 
  Thiaridae 
  are 
  

   only 
  too 
  obviously 
  the 
  fresh-water 
  relatives 
  of 
  the 
  Planaxidae. 
  It 
  is 
  

   only 
  when 
  the 
  Melanopsidae, 
  Pleuroceridae, 
  and 
  Thiaridae 
  are 
  

   separated 
  that 
  their 
  zoogeographic 
  story 
  can 
  be 
  read 
  without 
  confu- 
  

   sion. 
  Perfect 
  separation 
  of 
  these 
  three 
  fresh-water 
  families 
  can 
  only 
  

   be 
  accomplished 
  by 
  reference 
  to 
  characters 
  of 
  the 
  animals, 
  particularly 
  

   the 
  reproductive 
  characters. 
  Radular, 
  opercular, 
  or 
  shell 
  characters 
  

   that 
  will 
  completely 
  separate 
  these 
  families 
  are 
  nonexistent 
  because 
  of 
  

   their 
  concurrent 
  and 
  convergent 
  evolution. 
  

  

  The 
  following 
  key 
  to 
  the 
  major 
  groups 
  of 
  the 
  Melanian 
  complex 
  is 
  

   given 
  here 
  as 
  the 
  most 
  logical 
  one 
  possible. 
  In 
  the 
  author's 
  opinion, 
  

   it 
  represents 
  the 
  true 
  biological 
  relationship 
  of 
  these 
  groups. 
  

  

  c* 
  Reproduction 
  dioecious; 
  males 
  present 
  in 
  species. 
  

  

  6.1 
  Female 
  with 
  large 
  grooved 
  "ovipositor" 
  in 
  pit 
  on 
  right 
  side 
  of 
  foot; 
  few 
  eggs 
  

  

  of 
  proportionately 
  large 
  size. 
  

  

  c' 
  Marine 
  shells 
  Modulidae 
  

  

  C.2 
  Fresh-water 
  shells 
  Melanopsidae 
  

  

  6.2 
  Female 
  with 
  egg-laying 
  sinus 
  and 
  rudimentary 
  papilla, 
  or 
  no 
  special 
  struc- 
  

  

  ture 
  on 
  right 
  side 
  of 
  foot; 
  numerous 
  eggs 
  of 
  proportionately 
  smaller 
  size. 
  

  

  d.i 
  Marine 
  shells 
  Cerithiidae 
  

  

  d.^ 
  Fresh-water 
  shells 
  Pleuroceridae 
  

  

  c.i 
  Males 
  with 
  no 
  intromittent 
  structures. 
  

   /.I 
  Females 
  oviparous, 
  with 
  egg-laying 
  sinus 
  in 
  right 
  side 
  of 
  foot. 
  

  

  Pleurocerinae 
  

   /.2 
  Females 
  ovo 
  viviparous, 
  without 
  egg-laying 
  sinus; 
  brood 
  pouch 
  

  

  uterine, 
  the 
  enlarged 
  end 
  of 
  the 
  oviduct 
  Lavigeriinae 
  

  

  e.^ 
  Males 
  •with 
  eversible 
  "penis" 
  in 
  mantle 
  edge 
  near 
  end 
  of 
  vas 
  deferens; 
  

  

  females 
  ovo 
  viviparous; 
  brood 
  pouch 
  uterine 
  Tiphobiinae 
  

  

  a.2 
  Reproduction 
  parthenogenetic; 
  no 
  males 
  present 
  in 
  species; 
  brood 
  pouch 
  not 
  

   uterine, 
  but 
  adventitious 
  (subhaemocoelic) 
  in 
  the 
  neck 
  region, 
  with 
  opening 
  

   on 
  right 
  side 
  of 
  neck. 
  

  

  g.^ 
  Marine 
  shells 
  Planaxidae 
  

  

  0.2 
  Fresh- 
  water 
  shells 
  Thiaridae 
  

  

  Family 
  Melanopsidae 
  (Europe) 
  

  

  Two 
  genera 
  from 
  the 
  fresh 
  waters 
  of 
  Europe 
  have 
  been 
  studied 
  and 
  

   proven 
  to 
  belong 
  to 
  the 
  family 
  Melanopsidae. 
  They 
  are 
  more 
  special- 
  

   ized 
  than 
  the 
  Asiatic 
  and 
  American 
  Pleuroceridae, 
  possessing 
  a 
  much 
  

   larger 
  "ovipositor" 
  and 
  laying 
  a 
  much 
  smaller 
  number 
  of 
  proportion- 
  

   ately 
  much 
  larger 
  eggs. 
  

  

  