﻿232 
  PROCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  the 
  apposed 
  mantle-edges 
  nowhere 
  coalesce, 
  but 
  near 
  the 
  latter 
  

   muscle 
  the 
  inner 
  longitudinal 
  fold, 
  or 
  velum, 
  of 
  the 
  one 
  mantle-lobe 
  

   becomes 
  fused 
  with 
  that 
  of 
  the 
  other 
  lobe. 
  The 
  united 
  part 
  then 
  

   diverges 
  from 
  its 
  relative 
  position 
  to 
  the 
  pallial 
  edge, 
  and, 
  proceeding 
  

   dorsally, 
  separates 
  only 
  to 
  become 
  connected 
  on 
  each, 
  side 
  witli 
  the 
  

   lateral 
  walls 
  of 
  the 
  siphon. 
  The 
  apposed 
  folds 
  again 
  become 
  fused, 
  

   and 
  afterwards 
  pass 
  around 
  the 
  posterior 
  and 
  dorsal 
  parts 
  of 
  the 
  

   posterior 
  adductor 
  muscle. 
  Thus 
  the 
  posterior 
  portion 
  of 
  the 
  pallial 
  

   cavity 
  is 
  completely 
  enclosed 
  with 
  the 
  exception 
  of 
  the 
  siphonal 
  

   apertures. 
  The 
  inner 
  longitudinal 
  folds 
  are 
  also 
  fused 
  over 
  the 
  

   anterior 
  (Fig. 
  5) 
  as 
  well 
  as 
  the 
  posterior 
  adductor 
  muscle, 
  and 
  con- 
  

   sequently 
  form 
  the 
  covering 
  of 
  these 
  muscles. 
  Fig. 
  6 
  presents 
  

   typical 
  mucus 
  glands 
  of 
  this 
  portion 
  of 
  the 
  pallium, 
  and 
  their 
  ducts 
  

   will 
  be 
  seen 
  passing 
  between 
  the 
  e{)ithelial 
  cells 
  to 
  the 
  outer 
  surface. 
  

   Mucus 
  glands, 
  cells, 
  or 
  masses 
  are 
  present 
  all 
  round 
  the 
  inner 
  surface 
  

   of 
  the 
  mantle-lobes 
  just 
  above 
  or 
  below 
  the 
  velum. 
  The 
  pallium 
  is 
  

   apparently 
  perforated 
  by 
  both 
  the 
  large 
  adductor 
  muscles, 
  and 
  its 
  

   line 
  of 
  attachment 
  passes 
  on 
  each 
  side 
  from 
  the 
  anterior 
  adductor 
  to 
  

   the 
  body 
  of 
  the 
  animal, 
  ascending 
  as 
  it 
  goes 
  rearwardly 
  until 
  over 
  

   the 
  branchia, 
  where 
  it 
  is 
  near 
  the 
  dorsal 
  surface, 
  then, 
  descending, 
  

   it 
  skirts 
  the 
  edge 
  of 
  the 
  posterior 
  adductor 
  muscle. 
  Each 
  mantle- 
  

   lobe 
  carries 
  a 
  tentacular 
  fringe 
  at 
  the 
  distal 
  edge 
  of 
  the 
  middle 
  

   longitudinal 
  fold. 
  

  

  Underneath 
  the 
  posterior 
  adductor 
  muscle 
  is 
  situated 
  the 
  siphon. 
  

   It 
  consists 
  of 
  two 
  long 
  tubes 
  (Fig. 
  2, 
  JEx.S. 
  and/w./S.) 
  capable 
  of 
  great 
  

   elongation 
  and 
  contraction. 
  The 
  lower 
  or 
  inhalent 
  is 
  longer 
  than 
  the 
  

   upper 
  or 
  exhalent 
  one, 
  and, 
  in 
  an 
  extended 
  condition, 
  both, 
  at 
  the 
  free 
  

   end, 
  usually 
  curve 
  upwards. 
  The 
  lower 
  portion 
  of 
  the 
  proximal 
  part 
  

   of 
  the 
  exhalent 
  tube 
  is 
  united 
  with 
  the 
  upper 
  portion 
  of 
  the 
  inhalent 
  

   one, 
  and 
  the 
  combined 
  part 
  (Fig. 
  2, 
  S.R.M.) 
  projects 
  some 
  distance 
  

   into 
  the 
  pallial 
  cavity. 
  On 
  each 
  side 
  of 
  the 
  animal 
  the 
  siphonal 
  

   muscles 
  are 
  continued 
  as 
  a 
  short 
  thick 
  muscle 
  which 
  penetrates 
  the 
  

   thin 
  membranous 
  pallial 
  wall, 
  and 
  spreads 
  out 
  into 
  a 
  large 
  flat 
  ovate- 
  

   shaped 
  disc, 
  with 
  its 
  external 
  surface 
  attached 
  to 
  the 
  shell. 
  Each 
  

   tube 
  generally 
  carries 
  at 
  its 
  extreme 
  free 
  edge 
  six 
  papillae, 
  whilst 
  

   along 
  the 
  external 
  surface 
  is 
  a 
  corresponding 
  number 
  of 
  rows 
  ot 
  

   them, 
  each 
  row 
  being 
  in 
  alignment 
  with 
  one 
  of 
  the 
  papillae 
  at 
  the 
  

   free 
  end. 
  The 
  position 
  of 
  each 
  row 
  is 
  radially 
  in 
  a 
  line 
  with 
  one 
  of 
  the 
  

   internally 
  arched 
  muscle-masses 
  mentioned 
  farther 
  on. 
  It 
  is 
  further 
  

   to 
  be 
  observed 
  that 
  the 
  pallial 
  lobes 
  extend 
  some 
  distance 
  posteriorly 
  

   beyond 
  the 
  proximal 
  portion 
  of 
  the 
  siphon, 
  and 
  the 
  siphonal 
  tubes 
  can 
  

   be 
  quite 
  withdrawn 
  between 
  them 
  (Fig. 
  2, 
  P.L.P.). 
  In 
  this 
  state 
  

   the 
  posterior 
  portion 
  of 
  the 
  branchia 
  is 
  forced 
  into 
  a 
  folded 
  position. 
  

  

  Pallial 
  Muscles. 
  — 
  The 
  muscles 
  of 
  the 
  pallial 
  edge 
  form 
  a 
  band, 
  

   diminishing 
  in 
  depth 
  as 
  it 
  proceeds 
  posteriorly. 
  They 
  consist 
  

   principally 
  of 
  transverse 
  muscle-fibres, 
  radiating 
  as 
  from 
  the 
  umbonal 
  

   region 
  to 
  the 
  edge 
  of 
  the 
  pallium, 
  and 
  longitudinal 
  ones 
  running 
  

   chiefly 
  near 
  and 
  parallel 
  to 
  the 
  circumpallial 
  edge. 
  

  

  The 
  siphonal 
  tubes 
  proximally 
  become 
  somewhat 
  flattened. 
  Their 
  

   muscular 
  wall 
  is 
  composed 
  of 
  five 
  coats, 
  alternately 
  circular 
  and 
  

  

  