﻿210 
  PUOCEEDIiVGS 
  OF 
  THE 
  MALAC01,OGICAE 
  SOCIETY. 
  

  

  posterior 
  than 
  the 
  anterior 
  end. 
  The 
  anterior 
  part 
  is 
  rounded, 
  whilst 
  

   the 
  posterior 
  end 
  is 
  bluntly 
  triangular. 
  

  

  In 
  colour 
  tlie 
  mantle 
  is 
  slightly 
  a 
  greyish-white, 
  whilst 
  the 
  anterior 
  

   part 
  has 
  a 
  sulphur 
  tinge 
  and 
  the 
  posterior 
  part 
  near 
  the 
  margin 
  an 
  

   orange 
  one. 
  The 
  foot 
  is 
  white. 
  

  

  The 
  mantle 
  is 
  bordered 
  by 
  the 
  band 
  of 
  circumpallial 
  muscles 
  

   (PI. 
  XI, 
  Fig. 
  3, 
  CM.), 
  which, 
  are 
  deeper 
  at 
  the 
  posterior 
  than 
  along 
  

   the 
  anterior 
  and 
  ventral 
  edges. 
  

  

  The 
  inhalent 
  aperture 
  {In. 
  A.) 
  is 
  nearly 
  the 
  same 
  size 
  as 
  the 
  

   exhalent 
  one 
  {Ex. 
  A.). 
  Along 
  each 
  side 
  of 
  them 
  the 
  inner 
  

   longitudinal 
  fold 
  of 
  the 
  mantle 
  is 
  produced 
  in 
  a 
  pronounced 
  manner, 
  

   and 
  when 
  required 
  the 
  free 
  edges 
  come 
  together 
  and 
  close 
  tlie 
  

   apertures. 
  On 
  the 
  inner 
  surface 
  of 
  it, 
  bordering 
  the 
  inlialent 
  

   aperture, 
  is 
  a 
  number 
  of 
  tentacular 
  processes, 
  about 
  fifty 
  on 
  each 
  side, 
  

   arranged 
  in 
  four 
  irregular 
  rows. 
  The 
  row 
  nearest 
  the 
  outer 
  edge 
  

   })ossesses 
  the 
  smallest 
  in 
  size 
  but 
  the 
  largest 
  in 
  number. 
  In 
  the 
  next 
  

   two 
  rows 
  the 
  processes 
  are 
  larger 
  — 
  the 
  ones 
  in 
  the 
  rear 
  row 
  alternating 
  

   with 
  those 
  in 
  front. 
  In 
  the 
  last 
  row 
  are 
  to 
  be 
  found 
  the 
  largest 
  in 
  

   size 
  but 
  fewest 
  in 
  number. 
  

  

  The 
  exposed 
  terminal 
  parts 
  of 
  the 
  muscles 
  exhibit 
  the 
  following 
  

   features 
  : 
  — 
  

  

  The 
  anterior 
  adductor 
  muscle 
  {A. 
  A.) 
  situated 
  in 
  the 
  dorso-anterior 
  

   part 
  of 
  the 
  animal 
  is 
  nearly 
  twice 
  the 
  size 
  measured 
  dorso-ventrally 
  

   by 
  antero-posteriorly, 
  with 
  rounded 
  margins 
  except 
  on 
  tlie 
  posterior 
  

   side, 
  where 
  the 
  dorsal 
  part 
  curves 
  inwardly 
  and 
  in 
  the 
  recess 
  of 
  wliich 
  

   closely 
  lies 
  the 
  anterior 
  retractor 
  pedis 
  muscle. 
  Below 
  this 
  is 
  a 
  

   slight 
  contraction, 
  and 
  to 
  the 
  rear 
  of 
  the 
  posterior 
  part 
  is 
  situated 
  

   the 
  anterior 
  protractor 
  pedis 
  muscle. 
  

  

  The 
  posterior 
  adductor 
  muscle 
  {P. 
  A.) 
  is 
  large 
  and 
  somewhat 
  round 
  

   in 
  shape, 
  slightlj' 
  projecting 
  at 
  the 
  antero-ventral 
  part 
  and 
  flattened 
  

   at 
  the 
  antero-dorsal 
  edge. 
  On 
  the 
  latter 
  rest 
  the 
  retractor 
  pedis 
  

   posterior 
  muscles. 
  

  

  The 
  anterior 
  retractor 
  pedis 
  muscle 
  {R.P.A.) 
  is 
  triangular 
  in 
  

   shape 
  and 
  situated 
  close 
  to 
  the 
  dorso-posterior 
  edge 
  of 
  the 
  anterior 
  

   adductor. 
  

  

  The 
  anterior 
  protractor 
  pedis 
  muscle 
  {P. 
  P. 
  A.) 
  is 
  of 
  an 
  irregular 
  

   shape 
  and 
  lies 
  a 
  short 
  way 
  from 
  the 
  ventro-posterior 
  margin 
  of 
  the 
  

   anterior 
  adductor. 
  

  

  The 
  posterior 
  retractor 
  pedis 
  muscle 
  {R.P.P.) 
  is 
  of 
  a 
  triangular 
  

   shape, 
  with 
  tlie 
  base 
  resting 
  on 
  the 
  posterior 
  adductor. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XI. 
  

   Fig. 
  

  

  1. 
  A7iodonta 
  cygncea 
  {Linn.). 
  

  

  2. 
  A. 
  anatina 
  (Linn.). 
  

  

  3. 
  Pseudanodonta 
  rothomagensis, 
  Locard. 
  

  

  All 
  of 
  the 
  natural 
  size. 
  

   A. 
  A. 
  anterior 
  adductor 
  muscle. 
  P. 
  A. 
  posterior 
  adductor 
  muscle. 
  

  

  CM. 
  circumpallial 
  muscle. 
  P. 
  P. 
  A. 
  anterior 
  protractor 
  pedis 
  muscle. 
  

  

  Ex. 
  A. 
  exhalent 
  aperture. 
  R.P.A. 
  anterior 
  retractor 
  pedis 
  muscle. 
  

  

  F. 
  foot. 
  R.P.P. 
  posterior 
  retractor 
  pedis 
  muscle. 
  

  

  III. 
  A. 
  inhalent 
  aperture. 
  

  

  