﻿OLD 
  AND 
  NEW 
  WORLD 
  MELANIANS 
  — 
  MORRISON 
  387 
  

  

  As 
  mentioned 
  above 
  in 
  the 
  discussion 
  of 
  tlie 
  genus 
  Potadoma, 
  all 
  

   species 
  of 
  Melanoides 
  are 
  ovoviviparous 
  and 
  parthenogenetic. 
  They 
  

   must 
  also 
  agree 
  with 
  the 
  genotype 
  in 
  the 
  paucispiral 
  character 
  of 
  the 
  

   operculum. 
  The 
  species 
  that 
  differ 
  from 
  this 
  pattern 
  and 
  are 
  incor- 
  

   rectly'- 
  placed 
  in 
  the 
  genus 
  must 
  be 
  placed 
  elsewhere 
  when 
  their 
  

   anatomic 
  characters 
  become 
  known. 
  

  

  Genus 
  Tanganyicia 
  Crosse, 
  1881 
  

  

  Genotype: 
  (Lithoglyphus 
  rufqfilosus 
  E. 
  A. 
  Smith 
  =) 
  Tanganyicia 
  

   rufofilosa 
  (E. 
  A. 
  Smith) 
  1880. 
  

  

  With 
  a 
  shell 
  similar 
  to 
  that 
  of 
  the 
  American 
  genus 
  Cuhaedomus, 
  

   Tanganyicia 
  from 
  the 
  shores 
  of 
  Lake 
  Tanganjdka 
  differs 
  most 
  notably 
  

   in 
  possessing 
  an 
  operculum 
  that 
  is 
  secondarily 
  concentric 
  around 
  a 
  

   paucispiral 
  center. 
  This 
  African 
  genus 
  Tanganyicia 
  (Crosse, 
  1881, 
  

   p. 
  123) 
  has 
  a 
  brood 
  pouch 
  similar 
  if 
  not 
  identical 
  in 
  origin 
  to 
  that 
  

   of 
  all 
  other 
  known 
  genera 
  of 
  the 
  family 
  Thiaridae. 
  The 
  species 
  

   rufofilosa 
  (E. 
  A. 
  Smith 
  1880, 
  p. 
  426) 
  has 
  been 
  anatomically 
  described 
  

   by 
  Moore 
  (1898c, 
  p. 
  457). 
  The 
  primary 
  reproductive 
  organs 
  are 
  

   identical 
  in 
  their 
  simphcity. 
  The 
  genital 
  groove 
  from 
  the 
  oviduct 
  

   opening 
  to 
  the 
  opening 
  of 
  the 
  brood 
  pouch 
  is 
  of 
  exactly 
  the 
  same 
  type 
  

   (structurally 
  demarcated) 
  as 
  that 
  observed 
  by 
  me 
  in 
  the 
  genus 
  Brotia. 
  

   The 
  brood-pouch 
  pore 
  is 
  on 
  the 
  right 
  side, 
  as 
  in 
  all 
  the 
  other 
  genera. 
  

   Moore 
  (1898c, 
  fig. 
  3), 
  in 
  his 
  ''semidiagrammatic 
  representation," 
  

   depicts 
  the 
  brood 
  pouch 
  passing 
  under 
  the 
  oesophageal 
  canal. 
  The 
  

   extensively 
  developed 
  brood 
  pouches 
  of 
  many 
  genera 
  of 
  this 
  family 
  

   may 
  effectively 
  almost 
  surround 
  the 
  pharyngeal 
  or 
  buccal 
  mass, 
  but 
  

   I 
  believe 
  the 
  brood 
  pouch 
  is 
  ordinarily 
  dorsal 
  thereto. 
  Even 
  if 
  the 
  

   brood 
  pouch 
  proves 
  upon 
  complete 
  reexamination 
  only 
  to 
  be 
  beneath 
  

   and 
  expanded 
  to 
  the 
  left 
  of 
  the 
  buccal 
  mass, 
  these 
  differences 
  in 
  

   the 
  subhaemocoelic 
  extent 
  of 
  an 
  identically 
  originating 
  invagination 
  

   can 
  only 
  be 
  further 
  proof 
  of 
  the 
  distinction 
  of 
  the 
  genus 
  Tanganyicia 
  

   from 
  the 
  other 
  members 
  of 
  the 
  family. 
  

  

  Moore 
  (1898b, 
  p. 
  307) 
  listed 
  Tanganyicia 
  as 
  a 
  member 
  of 
  the 
  

   Planaxidae, 
  and 
  again 
  (1898c, 
  p. 
  456) 
  stated 
  that 
  rufofilosa, 
  in 
  the 
  

   characters 
  of 
  the 
  radula 
  and 
  alimentary 
  canal, 
  approximates 
  the 
  

   Planaxidae. 
  This 
  statement 
  constitutes 
  unbiased 
  corroboration 
  of 
  

   the 
  present 
  studies 
  which 
  show 
  that 
  the 
  Thiaridae 
  and 
  the 
  Planaxidae 
  

   are 
  relatives 
  from 
  the 
  same 
  stock, 
  since 
  Moore 
  was 
  completely 
  

   unaware 
  of 
  the 
  identical 
  type 
  of 
  reproductive 
  characters 
  possessed 
  

   by 
  the 
  Planaxidae 
  (see 
  Thorson, 
  1940). 
  

  

  The 
  statement 
  of 
  Moore 
  that 
  the 
  genital 
  groove 
  is 
  present 
  "in 
  

   both 
  sexes" 
  may 
  be 
  easily 
  explained 
  by 
  the 
  assumption 
  that 
  he 
  had 
  

   before 
  him 
  nongravid 
  females 
  and 
  gravid 
  females 
  at 
  the 
  beginning 
  

   of 
  a 
  seasonal 
  reproductive 
  period. 
  He 
  mentions 
  only 
  eggs 
  in 
  

  

  