﻿106 
  

  

  ON 
  VNIO, 
  MARGARITANA, 
  PSEUDANOBONTA, 
  AND 
  THEIK 
  

   OCCURRENCE 
  IN 
  THE 
  THAMES 
  VALLEY.' 
  

  

  By 
  Feitz 
  Haas, 
  Frankfurt. 
  

  

  Read 
  Wth 
  Februarij, 
  1910. 
  

  

  In 
  the 
  Journal 
  of 
  Concliology, 
  1909, 
  voL 
  xii, 
  p. 
  321, 
  Mr. 
  J. 
  W. 
  Jackson 
  

   and 
  Mr. 
  A. 
  S. 
  Kennard 
  mention 
  the 
  occurrence 
  of 
  Unio 
  margaritifer 
  in 
  

   the 
  Pleistocene 
  strata 
  of 
  the 
  Thames. 
  

  

  As 
  a 
  special 
  feature 
  of 
  the 
  shells, 
  which 
  according 
  to 
  the 
  description 
  

   are 
  exceedingly 
  well 
  preserved, 
  they 
  mention 
  the 
  so-called 
  " 
  Tliames 
  

   mark" 
  — 
  an 
  incrustation 
  of 
  carbonate 
  of 
  lime. 
  This 
  fact 
  puzzled 
  me 
  

   considerably, 
  since, 
  according 
  to 
  my 
  own 
  experience, 
  the 
  pearl 
  mussel 
  

   lives 
  only 
  in 
  water 
  completely 
  or 
  almost 
  free 
  from 
  lime. 
  Such 
  water 
  

   always 
  contains 
  large 
  quantities 
  of 
  carbonic 
  acid 
  in 
  solution, 
  which, 
  

   after 
  the 
  death 
  of 
  the 
  mussel, 
  dissolves 
  the 
  lime 
  of 
  the 
  shell, 
  and 
  only 
  

   the 
  conchyolin. 
  layer 
  remains. 
  This 
  fact, 
  so 
  well 
  known 
  to 
  all 
  

   zoologists 
  and 
  biologists, 
  cannot 
  be 
  reconciled 
  with 
  the 
  presence 
  of 
  an 
  

   incrustation 
  on 
  U. 
  margaritifer 
  from 
  the 
  Thames 
  strata. 
  A 
  fortunate 
  

   circumstance 
  materially 
  assisted 
  in 
  explaining 
  this 
  apparent 
  contra- 
  

   diction. 
  

  

  About 
  two 
  years 
  ago 
  shells 
  of 
  TJ. 
  sinuatus, 
  Lam., 
  a 
  species 
  not 
  known 
  

   to 
  occur 
  in 
  the 
  Ehine 
  in 
  a 
  living 
  state, 
  were 
  discovered 
  in 
  Uoloeene 
  

   strata 
  of 
  the 
  Ehine, 
  near 
  Ludwigshafen. 
  I 
  was 
  aware 
  that 
  this 
  shell, 
  

   which 
  bears 
  some 
  superficial 
  resemblance 
  to 
  the 
  pearl 
  mussel, 
  had 
  

   long 
  been 
  confounded 
  with 
  it, 
  and 
  that 
  llossmassler 
  - 
  was 
  the 
  first 
  

   to 
  separate 
  the 
  two 
  forms. 
  It 
  appeared 
  to 
  me 
  not 
  impossible 
  that 
  

   English 
  naturalists 
  had 
  made 
  the 
  same 
  mistake 
  as 
  Rossmassler's 
  

   predecessors. 
  Mr. 
  A. 
  S. 
  Kennai'd 
  had 
  the 
  great 
  kindness 
  to 
  send 
  me 
  

   a 
  specimen 
  of 
  the 
  Thames 
  mussel 
  in 
  question, 
  and 
  it 
  proved 
  to 
  be, 
  in 
  

   fact, 
  U. 
  sinuatus. 
  

  

  I 
  was 
  struck 
  by 
  the 
  coincidence 
  that 
  both 
  in 
  Jackson 
  & 
  Kennard's 
  

   above-mentioned 
  article 
  and 
  in 
  the 
  Census 
  of 
  the 
  British 
  Land 
  and 
  

   Freshwater 
  Mollusca 
  issued 
  by 
  the 
  Conchological 
  Society 
  of 
  Great 
  

   Britain 
  and 
  Ireland, 
  the 
  pearl 
  mussel 
  — 
  Linne's 
  Mya 
  margaritifer 
  a 
  — 
  is 
  

   given 
  under 
  the 
  name 
  of 
  Unio 
  margaritifer, 
  although 
  Schumacher,^ 
  as 
  

   far 
  back 
  as 
  1817, 
  removed 
  this 
  species 
  from 
  the 
  genus 
  Z7?^^o, 
  to 
  which 
  it 
  

   had 
  been 
  referred 
  by 
  Ketzius, 
  and 
  created 
  for 
  it 
  the 
  genus 
  Ilargaritana. 
  

   This 
  separation 
  was 
  based 
  on 
  the 
  diflterence 
  in 
  structure 
  of 
  the 
  hinge 
  

   between 
  Unio 
  and 
  the 
  pearl 
  mussel, 
  which 
  possesses 
  only 
  cardinal 
  

   teeth 
  and 
  no 
  laterals, 
  and 
  was 
  universally 
  recognized 
  especially 
  since 
  

   in 
  the 
  anatomy 
  of 
  the 
  soft 
  parts 
  important 
  distinctions 
  between 
  the 
  

   two 
  were 
  observed. 
  Those 
  who 
  consider 
  the 
  absence 
  of 
  laterals 
  

   insufficient 
  reason 
  for 
  generic 
  separation 
  of 
  the 
  pearl 
  mussel 
  from 
  

   Unio 
  will 
  probably 
  find 
  conclusive 
  proof 
  in 
  the 
  following 
  comparative 
  

  

  ' 
  Translated 
  from 
  the 
  German 
  text 
  by 
  G. 
  K. 
  Gude. 
  

  

  2 
  Rossmassler, 
  Iconographie, 
  1836, 
  Heftiii, 
  p. 
  22, 
  pi. 
  xiii, 
  fig. 
  195. 
  

  

  2 
  Schumacher, 
  Nouveau 
  systeme 
  vers 
  test., 
  1817, 
  p. 
  137. 
  

  

  