﻿114 
  

  

  ON 
  AN 
  UNDESCRIBED 
  ANOBONTA 
  FEOM 
  THE 
  ENGLISH 
  

   WEALDEN 
  FORMATION, 
  WITH 
  REMARKS 
  ON 
  THE 
  OTHER 
  

   UNIONID^ 
  OF 
  THE 
  SAME 
  PERIOD. 
  

  

  By 
  R. 
  BuLLEN 
  Newton, 
  F.G.S. 
  

  

  Read 
  Wth 
  February, 
  1910. 
  

  

  (Published 
  by 
  permission 
  of 
  tlie 
  Trustees 
  of 
  the 
  British 
  Museum.) 
  

  

  PLATE 
  I. 
  

  

  The 
  typical 
  "Wealdea 
  deposits 
  of 
  the 
  South 
  of 
  England 
  occupy 
  

   a 
  large 
  tract 
  of 
  Sussex, 
  Kent, 
  and 
  Surrey, 
  which 
  is 
  enclosed 
  by 
  

   the 
  Chalk 
  escarpments 
  of 
  the 
  J^orth 
  and 
  South 
  Downs. 
  Extensions 
  

   of 
  the 
  same 
  formation 
  occur 
  beyond 
  this 
  region, 
  more 
  especially 
  

   in 
  the 
  Isle 
  of 
  AVight 
  and 
  Dorsetshire. 
  These 
  strata 
  have 
  yielded 
  

   a 
  remarkable 
  fauna 
  and 
  flora, 
  such 
  as 
  minute 
  Ostracoda, 
  delicate 
  

   insect 
  remains, 
  mollusoa, 
  fishes, 
  reptiles 
  of 
  great 
  size 
  like 
  the 
  

   Igiianodon, 
  ferns, 
  cycads, 
  and 
  other 
  plants. 
  All 
  these 
  organisms 
  

   serve 
  to 
  indicate 
  that 
  the 
  deposits 
  containing 
  them 
  were 
  of 
  an 
  

   estuarine 
  or 
  lacustrine 
  character, 
  and 
  that 
  freshwater 
  conditions 
  

   prevailed 
  during 
  their 
  period 
  of 
  sedimentation. 
  A 
  considerable 
  

   literature 
  exists 
  on 
  the 
  Wealden 
  fossils, 
  the 
  basis 
  of 
  which 
  is 
  to 
  

   be 
  found 
  in 
  the 
  works 
  of 
  Gideon 
  Algernon 
  Mantell, 
  mostly 
  published 
  

   between 
  1822 
  and 
  1851. 
  For 
  our 
  knowledge 
  of 
  the 
  Unioniform 
  

   mollusca 
  of 
  this 
  period 
  we 
  are, 
  however, 
  almost 
  entirely 
  dependent 
  

   on 
  the 
  writings 
  of 
  James 
  de 
  Carle 
  Sowerby,^ 
  who 
  described, 
  as 
  early 
  

   as 
  1828, 
  several 
  forms 
  of 
  JJnio 
  collected 
  by 
  Mantell 
  from 
  quarries 
  

   in 
  the 
  Til 
  gate 
  Forest 
  area 
  of 
  Sussex, 
  as 
  well 
  as 
  some 
  further 
  species 
  

   in 
  1836-7 
  from 
  Sussex 
  localities, 
  also 
  collected 
  by 
  Mantell, 
  which 
  

   were 
  in 
  illustration 
  of 
  W. 
  H. 
  Eitton's 
  memoir 
  " 
  On 
  some 
  of 
  the 
  

   Strata 
  between 
  the 
  Chalk 
  and 
  the 
  Oxford 
  Oolite 
  ". 
  In 
  1844 
  MantelP 
  

   described 
  and 
  figured 
  in 
  outline 
  the 
  now 
  well-known 
  TJ. 
  Valdensis 
  

   which 
  he 
  had 
  discovered 
  in 
  the 
  Wealden 
  beds 
  of 
  the 
  Isle 
  of 
  Wight 
  

   (near 
  Brook), 
  comparing 
  it 
  with 
  some 
  of 
  the 
  recent 
  massive 
  forms 
  

   of 
  that 
  genus 
  found 
  in 
  jS^orth 
  American 
  waters, 
  such 
  as 
  U. 
  furpuratus. 
  

   Further 
  figures 
  of 
  this 
  species 
  were 
  published 
  in 
  1846 
  by 
  James 
  de 
  

   Carle 
  Sowerby,^ 
  but 
  without 
  text, 
  Mantell 
  ^ 
  also 
  issuing 
  in 
  the 
  

   following 
  year 
  some 
  excellent 
  illustrations 
  of 
  the 
  same 
  shell, 
  with 
  

   an 
  extended 
  notice 
  of 
  its 
  history. 
  

  

  The 
  species 
  of 
  TJnio 
  thus 
  referred 
  to 
  comprise 
  aduncus, 
  antiquus, 
  

   compressus, 
  cordiformis, 
  porrectus, 
  Mantelli, 
  Martini, 
  Gualteri, 
  and 
  

   suhtruncatiis, 
  all 
  of 
  Sowerby, 
  whilst 
  the 
  history 
  of 
  Valdetisis, 
  as 
  

   stated, 
  is 
  entirely 
  due 
  to 
  Mantell. 
  It 
  is 
  of 
  interest 
  to 
  mention 
  that 
  

   with 
  the 
  exception 
  of 
  two 
  of 
  these 
  species 
  ( 
  Gualteri 
  and 
  suhtruncatus) 
  

  

  1 
  J. 
  de 
  C. 
  Sowerby, 
  Mineral 
  Conchology, 
  1828, 
  voL 
  vi, 
  pp. 
  189-92, 
  pis. 
  594-5, 
  

   and 
  Trans. 
  Geol. 
  Soc. 
  London, 
  1836-7, 
  ser. 
  ii, 
  vol. 
  iv, 
  p. 
  346, 
  pi. 
  xxi, 
  

   figs. 
  14-17. 
  

  

  - 
  Mantell, 
  Amer. 
  Journ. 
  Sci. 
  (Silliman), 
  1844, 
  vol. 
  xlvii, 
  pp. 
  403-6, 
  figs. 
  1-3. 
  

  

  ' 
  J. 
  de 
  C. 
  Sowerby, 
  Mineral 
  Conchology, 
  1846, 
  vol. 
  vii, 
  pi. 
  646. 
  

  

  * 
  Mantell, 
  London 
  Geological 
  Journ., 
  1847, 
  No. 
  2, 
  pp. 
  41-4, 
  pi. 
  xiv. 
  

  

  