﻿116 
  PROCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  examination 
  of 
  the 
  types 
  these 
  have 
  been 
  considered 
  by 
  Mr. 
  Wheelton 
  

   Hind 
  ^ 
  as 
  belonging 
  to 
  the 
  genus 
  Carlonicola. 
  

  

  Some 
  few 
  forms 
  of 
  Anodonta 
  are 
  foimd 
  in 
  Tertiary 
  formations, 
  

   although 
  the 
  evidence 
  seems 
  to 
  prove 
  that 
  probably 
  from 
  a 
  generally 
  

   thin 
  and 
  delicate 
  shell-structure, 
  the 
  genus 
  is 
  sparingly 
  distributed 
  

   geologically, 
  and 
  that 
  so 
  far 
  as 
  can 
  be 
  ascertained 
  no 
  true 
  examples 
  

   appear 
  to 
  be 
  known 
  below 
  the 
  Wealden 
  formation. 
  

  

  Anodonta 
  Becklesi, 
  n.sp. 
  

   " 
  A 
  large 
  Anodon 
  (?)," 
  S. 
  H. 
  Beckles, 
  " 
  On 
  the 
  Lowest 
  Strata 
  of 
  the 
  

  

  Cliffs 
  at 
  Hastings": 
  Quart. 
  Journ. 
  Geol. 
  Soc, 
  1856, 
  vol. 
  xii, 
  

  

  pp. 
  291, 
  292. 
  

   Description. 
  — 
  Yalves 
  oblong, 
  suboval, 
  sometimes 
  sub-quadrangular, 
  

   thin-tested, 
  length 
  usually 
  about 
  1^^ 
  times 
  in 
  excess 
  of 
  the 
  height, 
  

   widely 
  inflated 
  over 
  the 
  umbonal 
  region, 
  afterwards 
  compressed 
  to 
  the 
  

   margins 
  ; 
  dorsal 
  line 
  well 
  below 
  umbonal 
  region, 
  straight, 
  nearly 
  

   parallel 
  with 
  ventral 
  margin, 
  angulated 
  at 
  both 
  ends 
  ; 
  anterior 
  side 
  

   short, 
  well 
  rounded 
  ; 
  posterior 
  surface 
  oblique, 
  wide, 
  much 
  depressed, 
  

   produced, 
  obliquelj^ 
  margined, 
  subangulate 
  at 
  ventral 
  corner, 
  furnished 
  

   with 
  a 
  prominent, 
  more 
  or 
  less 
  concave, 
  obtuse 
  ridge 
  extending 
  from 
  

   the 
  umbones 
  to 
  the 
  postero-ventral 
  angle, 
  followed 
  by 
  one 
  or 
  two 
  

   obscure 
  oblique 
  costse, 
  which, 
  like 
  the 
  ridge, 
  originate 
  at 
  the 
  umbones 
  ; 
  

   ventral 
  margin 
  extensive 
  and 
  curved 
  ; 
  umbones 
  anterior, 
  more 
  or 
  less 
  

   polished, 
  bending 
  inwards, 
  having 
  the 
  dorsal 
  margins 
  of 
  umbonal 
  region 
  

   elongate, 
  flattened, 
  and 
  nearly 
  parallel 
  with 
  each 
  other 
  ; 
  sculpture 
  

   consisting 
  of 
  periodical, 
  nearly 
  equidistant, 
  concentric 
  growth-lines, 
  

   with 
  finer 
  striations 
  within, 
  which 
  become 
  subangulate 
  at 
  the 
  postero- 
  

   ventral 
  corner, 
  and 
  then 
  assume 
  an 
  upward 
  oblique 
  direction 
  to 
  meet 
  

   the 
  dorsal 
  margin. 
  Crossing 
  the 
  concentric 
  lines 
  is 
  a 
  series 
  of 
  

   extremely 
  fine 
  and 
  elevated, 
  mostly 
  equidistant, 
  radial 
  striations 
  which 
  

   extend 
  from 
  the 
  umbones 
  to 
  the 
  margins, 
  occurring 
  occasionally 
  in 
  

   pairs, 
  and 
  frequently 
  interrupted, 
  when 
  the 
  broken 
  lines 
  exhibit 
  fine 
  

   tapering 
  ends 
  which 
  are 
  laterally 
  disposed 
  without 
  touching. 
  Between 
  

   the 
  main 
  radial 
  striations 
  are 
  numerous 
  finer 
  lines 
  taking 
  the 
  same 
  

   direction. 
  Hinge 
  characters 
  unknown. 
  

  

  Dimensions 
  of 
  two 
  examples 
  in 
  millimetres. 
  

  

  A 
  B 
  

  

  Height 
  92 
  . 
  78 
  

  

  Length 
  144 
  . 
  100 
  

  

  Umbonal 
  diameter 
  of 
  both 
  valves 
  when 
  closed 
  . 
  30 
  . 
  20 
  

  

  Remarlcs. 
  — 
  This 
  description 
  applies 
  to 
  a 
  generally 
  large 
  form 
  of 
  

   Anodonta, 
  examples 
  of 
  which 
  in 
  the 
  British 
  Museum 
  were 
  collected 
  

   by 
  Mantell, 
  Samuel 
  Beckles, 
  and 
  in 
  more 
  recent 
  years 
  by 
  the 
  late 
  

   Philip 
  Rufford. 
  Beckles, 
  as 
  far 
  back 
  as 
  1856, 
  referred 
  "to 
  a 
  large 
  

   Anodon 
  (?) 
  "• 
  being 
  found 
  in 
  the 
  Hastings 
  deposits, 
  which 
  probably 
  

   included 
  the 
  form 
  now 
  described, 
  although 
  his 
  statement 
  might 
  also 
  

   have 
  had 
  reference 
  to 
  a 
  much 
  larger 
  freshwater 
  bivalve 
  commonly 
  

   found 
  in 
  this 
  formation, 
  but 
  which, 
  from 
  a 
  recent 
  examination 
  of 
  

  

  1 
  W. 
  H. 
  Hind, 
  Mon. 
  Pal. 
  Soc, 
  1894, 
  p. 
  24. 
  

  

  