﻿110 
  

  

  PKOCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  As, 
  however, 
  many, 
  and 
  to 
  my 
  mind 
  important, 
  differences 
  exist 
  in 
  

   the 
  structure 
  of 
  the 
  shells 
  and 
  in 
  the 
  anatomy 
  of 
  the 
  soft 
  parts, 
  

   I 
  consider 
  the 
  retention 
  of 
  the 
  genus 
  Pseudanodonta, 
  as 
  defined 
  by 
  

   Bourguigriat, 
  quite 
  justified. 
  As 
  living 
  Pseudanodontas 
  from 
  the 
  

   llhine, 
  the 
  Neckar, 
  and 
  the 
  Danube 
  were 
  at 
  my 
  disposal 
  for 
  anatomical 
  

   investigation, 
  I 
  am 
  enabled 
  to 
  subjoin 
  a 
  diagnosis 
  based 
  on 
  shell 
  and 
  

   anatomical 
  characters 
  as 
  compared 
  with 
  those 
  of 
  Anodonta. 
  

  

  PSEUDANODONTA. 
  

  

  Shell 
  rhombic, 
  more 
  or 
  less 
  

   elongated, 
  thin, 
  much 
  coijipressed, 
  

   almost 
  toithout 
  wings, 
  gaping 
  

   behind 
  ; 
  leak 
  scidptiire 
  consisting 
  

   of 
  feiv 
  isolated, 
  rather 
  elevated 
  

   tubercles 
  ; 
  surface 
  usuallj- 
  smooth, 
  

   shining 
  ; 
  hinge 
  edentulous, 
  re- 
  

   duced 
  to 
  a 
  mere 
  line, 
  never 
  curved 
  ; 
  

   muscle- 
  scars 
  rather 
  faint. 
  

  

  Animal 
  having 
  the 
  gills 
  free 
  

   about 
  half 
  the 
  length 
  from 
  the 
  

   abdominal 
  sac 
  ; 
  palpi 
  rather 
  long 
  ; 
  

   branchial 
  orifice 
  papillose, 
  darkly 
  

   coloured 
  ; 
  anal 
  orifice 
  ivith 
  small 
  

   hut 
  true 
  papillce, 
  darkly 
  coloured 
  ; 
  

   superanal 
  orifice 
  closed 
  behind. 
  

   Gills 
  very 
  soft 
  ; 
  the 
  eggs 
  develop 
  

   in 
  the 
  outer 
  gills 
  of 
  the 
  female 
  

   into 
  a 
  glochidium 
  0-33 
  mm. 
  in 
  

   length. 
  It 
  is 
  very 
  convex, 
  rounded 
  

   triangular 
  in 
  form, 
  provided 
  with 
  

   rather 
  short 
  blunt 
  hooks, 
  and 
  is 
  

   without 
  a 
  larval 
  thread. 
  

  

  Anodonta. 
  

  

  Shell 
  elliptical, 
  thin, 
  inflated, 
  

   mostly 
  loinged 
  posteriorly 
  ; 
  lealc 
  

   sculpture 
  consisting 
  of 
  rather 
  

   numerous 
  parallel 
  ridges, 
  lasually 
  

   somewhat 
  doubly 
  looped 
  ; 
  surface 
  

   generally 
  smooth, 
  shining; 
  hinge 
  

   edentulous, 
  reduced 
  to 
  a 
  mere 
  

   line, 
  seldom 
  curved 
  ; 
  muscle-scars 
  

   rather 
  faint. 
  

  

  Animal 
  with 
  the 
  gills 
  free 
  from 
  

   the 
  abdominal 
  sac 
  from 
  one-half 
  

   to 
  their 
  entire 
  length 
  ; 
  palpi 
  

   generally 
  large 
  ; 
  branchial 
  open- 
  

   ing 
  papillose, 
  darkly 
  pigmented; 
  

   anal 
  opening 
  ivithout 
  papillce, 
  but 
  

   sotnetitnes 
  very 
  slightly 
  crenulate, 
  

   darkly 
  pigmented 
  ; 
  superanal 
  

   opening 
  small, 
  widely 
  separated 
  

   from 
  the 
  anal.^ 
  

  

  Gill 
  rather 
  solid 
  ; 
  the 
  eggs 
  

   develop 
  in 
  the 
  outer 
  gills 
  of 
  the 
  

   female 
  into 
  a 
  glochidium 
  0'35 
  mm. 
  

   long. 
  It 
  is 
  rather 
  flat, 
  rounded 
  

   triangular 
  in 
  form, 
  provided 
  with 
  

   large 
  narrow 
  hooks, 
  and 
  has 
  a 
  

   larval 
  thread. 
  

  

  To 
  my 
  knowledge 
  a 
  more 
  correct 
  anatomical 
  and 
  embryological 
  

   description 
  of 
  Pseudanodonta 
  has 
  not 
  hitherto 
  been 
  published. 
  The 
  

   distinctive 
  characters 
  of 
  this 
  genus 
  may 
  be 
  further 
  multiplied; 
  the 
  

   formation 
  of 
  the 
  ova 
  differs 
  considerably 
  from 
  that 
  of 
  Anodonta,^ 
  

   the 
  nearest 
  approach 
  being 
  observed 
  in 
  Unio. 
  According 
  to 
  Schierholz^ 
  

   the 
  bundles 
  of 
  sensory 
  threads 
  peculiar 
  to 
  glochidia 
  are 
  differently 
  

   arranged 
  in 
  the 
  glochidium 
  of 
  Pseudanodonta 
  from 
  those 
  of 
  Aiiodonta. 
  

   In 
  this 
  respect 
  the 
  conditions 
  remind 
  us 
  of 
  those 
  obtaining 
  in 
  the 
  

   glochidium 
  of 
  Vfiio. 
  I 
  will 
  not 
  here 
  refer 
  to 
  the 
  histological 
  structure 
  

   of 
  the 
  gills, 
  although 
  this 
  exhibits 
  important 
  differences 
  in 
  the 
  two 
  

  

  1 
  After 
  Simpson, 
  Synopsis 
  of 
  the 
  Naiades, 
  1900, 
  p. 
  620. 
  

  

  2 
  Flemming, 
  Archir 
  f 
  . 
  Mikro. 
  Anat., 
  1874; 
  Sitz. 
  Ber. 
  Math. 
  Nat. 
  Akad. 
  "Wien, 
  

  

  1875, 
  vol. 
  Ixxi. 
  

  

  3 
  Schierholz, 
  Denkschr. 
  Kais. 
  vVkad. 
  Wiss. 
  Wien, 
  Math. 
  Nat. 
  CI., 
  1888. 
  

  

  