﻿376 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  io3 
  

  

  unnecessary 
  and 
  invalid 
  under 
  present 
  international 
  rules 
  of 
  nomen- 
  

   clature. 
  Basistoma 
  Lea 
  (1852, 
  p. 
  295) 
  is 
  exactly 
  equivalent 
  biologi- 
  

   cally 
  to 
  Aylacostoma, 
  being 
  based 
  on 
  the 
  same 
  type 
  of 
  shell 
  from 
  

   South 
  America. 
  Verena 
  H. 
  and 
  A. 
  Adams 
  (1854, 
  p. 
  308) 
  differs 
  from 
  

   the 
  typical 
  Aylacostoma 
  group 
  in 
  shorter 
  shell 
  outline 
  and 
  in 
  sculpture. 
  

  

  Genu8 
  Cubaedomus 
  Thiele, 
  1928 
  

  

  This 
  genus 
  (Thiele, 
  1928, 
  p. 
  401), 
  based 
  on 
  the 
  species 
  hrevis 
  Orbigny 
  

   from 
  Cuba, 
  is 
  the 
  only 
  American 
  group 
  clearly 
  and 
  generically 
  distinct 
  

   from 
  Aylacostoma 
  on 
  shell 
  characters. 
  The 
  shell 
  is 
  ovate-conic, 
  with 
  

   a 
  trace 
  of 
  nodulous 
  coronate 
  sculpture 
  on 
  the 
  upper 
  slope 
  or 
  shoulder 
  

   of 
  the 
  body 
  whorl. 
  There 
  is 
  no 
  columellar 
  notch 
  or 
  sinus 
  in 
  the 
  

   aperture, 
  which 
  is 
  evenly 
  rounded 
  below 
  (anteriorly). 
  The 
  operculum 
  

   is 
  paucispiral. 
  Animals 
  of 
  this 
  species, 
  dried 
  in 
  the 
  shells, 
  were 
  

   recently 
  boiled 
  up 
  in 
  water 
  (softened) 
  and 
  personally 
  examined. 
  

   These 
  specimens 
  (USNM 
  407991) 
  were 
  collected 
  by 
  Jaume 
  from 
  Eio 
  

   "Los 
  Cayos", 
  Bahia 
  Hondo, 
  Pinar 
  del 
  Rio, 
  Cuba. 
  The 
  mantle 
  is 
  

   fringed. 
  The 
  embryonic 
  young 
  are 
  relatively 
  large, 
  and 
  there 
  were 
  

   only 
  two 
  in 
  the 
  subhaemocoelic 
  brood 
  pouch 
  in 
  the 
  neck 
  region 
  at 
  one 
  

   time 
  in 
  the 
  material 
  examined 
  (pi. 
  11, 
  fig. 
  19). 
  Proof 
  that 
  this 
  

   genus 
  belongs 
  to 
  the 
  family 
  Thiaridae 
  gives 
  us 
  another 
  excellent 
  

   example 
  of 
  concurrent 
  and 
  convergent 
  evolution. 
  Both 
  PUsbry 
  (1893) 
  

   and 
  Aguayo 
  (1944, 
  p. 
  69) 
  have 
  previously 
  considered 
  the 
  species 
  

   hrevis 
  Orbigny 
  of 
  Cuba 
  congeneric 
  with 
  {" 
  Potamanax" 
  = 
  ) 
  Pachychilus 
  

   (Oxymelania) 
  pilsbryi 
  (Martens) 
  of 
  the 
  Guatemala 
  region, 
  a 
  member 
  

   of 
  the 
  Pleuroceridae, 
  because 
  of 
  the 
  almost 
  identical 
  shell 
  character- 
  

   istics 
  of 
  the 
  two 
  species. 
  

  

  Genus 
  Aylacostoma 
  Spix, 
  1827 
  

  

  Subgenus 
  Hemisinus 
  Swaiason, 
  1840 
  

  

  Genotype: 
  {Melania 
  lineolata 
  Gray 
  =) 
  Aylacostoma 
  (Hemisinus) 
  

   lineolatum 
  (Gray) 
  1828. 
  

  

  This 
  group 
  of 
  elongate-ovate 
  or 
  ovate-conic 
  shells, 
  almost 
  completely 
  

   lacking 
  macroscopic 
  spiral 
  sculpture, 
  includes 
  one 
  or 
  two 
  species 
  from 
  

   Cuba, 
  the 
  genotype 
  from 
  Jamaica, 
  and 
  a 
  few 
  other 
  species 
  of 
  Central 
  

   and 
  South 
  America 
  from 
  Panam^ 
  to 
  Ecuador 
  and 
  Peril. 
  

  

  Subgenus 
  Aylacostoma 
  Spix, 
  1827, 
  sensu 
  stricto 
  

  

  Genotype: 
  (Aylacostoma 
  glahrum 
  Spix=) 
  Aylacostoma 
  (Aylacostoma) 
  

   scalare 
  (Wagner) 
  1827. 
  

  

  This 
  typical 
  group 
  includes 
  one 
  species 
  from 
  the 
  Atlantic 
  side 
  of 
  

   Central 
  America, 
  one 
  species 
  from 
  the 
  Pacific 
  drainage 
  in 
  the 
  Dari6n 
  

   region 
  of 
  Panamd, 
  and 
  numerous 
  species 
  from 
  the 
  Magdalena, 
  

   Orinoco, 
  Amazon, 
  and 
  southern 
  Brazil 
  regions 
  of 
  South 
  America. 
  

  

  