﻿PROCEEDINGS 
  OF 
  THE 
  UNITED 
  STATES 
  NATIONAL 
  MUSEUM 
  

  

  issued 
  

  

  SMITHSONIAN 
  INSTITUTION 
  

   U. 
  S. 
  NATIONAL 
  MUSEUM 
  

  

  Vol. 
  103 
  Washington 
  : 
  1954 
  No. 
  3325 
  

  

  THE 
  RELATIONSHIPS 
  OF 
  OLD 
  AND 
  NEW 
  WORLD 
  

   MELANIANS 
  

  

  By 
  J. 
  P. 
  E. 
  Morrison 
  

  

  Recent 
  anatomical 
  observations 
  on 
  the 
  reproductive 
  systems 
  of 
  

   certain 
  so-called 
  "melanian" 
  fresh-water 
  snails 
  and 
  their 
  marine 
  rela- 
  

   tives 
  have 
  clarified 
  to 
  a 
  remarkable 
  degree 
  the 
  supergeneric 
  relation- 
  

   ships 
  of 
  these 
  fresh-water 
  forms. 
  

  

  The 
  family 
  of 
  Melanians, 
  in 
  the 
  broad 
  sense, 
  is 
  a 
  biological 
  ab- 
  

   surdity. 
  We 
  have 
  the 
  anomaly 
  of 
  one 
  fresh-water 
  "family" 
  of 
  snails 
  

   derived 
  from 
  or 
  at 
  least 
  structurally 
  identical 
  in 
  peculiar 
  animal 
  

   characters 
  to 
  and 
  ancestrally 
  related 
  to 
  three 
  separate 
  and 
  distinct 
  

   marine 
  famiHes. 
  On 
  the 
  other 
  hand, 
  the 
  biological 
  picture 
  has 
  been 
  

   previously 
  misunderstood 
  largely 
  because 
  of 
  the 
  concurrent 
  and 
  

   convergent 
  evolution 
  of 
  the 
  three 
  fresh-water 
  groups, 
  Pleuroceridae, 
  

   Melanopsidae, 
  and 
  Thiaridae, 
  from 
  ancestors 
  common 
  to 
  the 
  marine 
  

   families 
  Cerithiidae, 
  Modulidae, 
  and 
  Planaxidae, 
  respectively. 
  

  

  The 
  family 
  Melanopsidae 
  is 
  definitely 
  known 
  living 
  only 
  in 
  Europe. 
  

   At 
  present, 
  the 
  exact 
  placement 
  of 
  the 
  genus 
  Zemelanopsis 
  Uving 
  in 
  

   fresh 
  waters 
  of 
  New 
  Zealand 
  is 
  uncertain, 
  since 
  its 
  reproductive 
  

   characters 
  are 
  as 
  yet 
  unknown. 
  In 
  spite 
  of 
  obvious 
  differences 
  in 
  

   shape, 
  the 
  shells 
  of 
  the 
  marine 
  genus 
  Modulus 
  possess 
  at 
  least 
  a 
  well- 
  

   indicated 
  columellar 
  notch 
  of 
  the 
  aperture, 
  to 
  corroborate 
  the 
  biologi- 
  

   cal 
  relationship 
  indicated 
  by 
  the 
  almost 
  identical 
  female 
  egg-laying 
  

   structure 
  in 
  the 
  right 
  side 
  of 
  the 
  foot 
  of 
  Modulus 
  and 
  Melanopsis. 
  

  

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