﻿ANATOMY 
  AND 
  AFFINITIES 
  OF 
  TYIK 
  TnOOHID^. 
  39 
  

  

  entirely 
  unrepresented, 
  but 
  takes 
  the 
  form 
  of 
  a 
  number 
  of 
  

   large 
  unicellular 
  gland-cells 
  on 
  the 
  under 
  surface 
  of 
  the 
  

   foot, 
  aggregated 
  more 
  especially 
  round 
  its 
  anterior 
  margin. 
  

   Although 
  Pleurotomaria 
  has 
  the 
  transverse 
  groove 
  on 
  

   the 
  anterior 
  margin 
  of 
  the 
  foot 
  very 
  well 
  developed, 
  thei-e 
  

   is 
  no 
  longitudinal 
  canal 
  or 
  pedal 
  gland 
  connected 
  with 
  it, 
  such 
  

   as 
  exists 
  in 
  T. 
  zizyphinus, 
  etc 
  , 
  but 
  it 
  is 
  more 
  than 
  probable 
  

   that 
  tlie 
  groove 
  coiitains 
  numerous 
  gland-cells. 
  

  

  On 
  the 
  dorsal 
  surface 
  of 
  the 
  foot 
  there 
  is 
  invariably 
  present 
  

   a 
  specialised 
  area 
  running 
  from 
  the 
  opercular 
  lobe 
  to 
  the 
  

   posterior 
  extremity. 
  The 
  exact 
  appearance 
  of 
  this 
  differs 
  

   somewhat 
  in 
  the 
  different 
  species. 
  In 
  T. 
  gi-anulatus 
  (fig. 
  8) 
  

   and 
  T. 
  zizyphinus 
  it 
  is 
  well 
  defined 
  and 
  V-shaped, 
  bounded 
  

   by 
  two 
  lateral 
  converging 
  furrows. 
  A 
  shallow 
  median 
  furrow, 
  

   together 
  with 
  the 
  two 
  lateral 
  fuirow^s, 
  arise 
  from 
  under 
  the 
  

   free 
  border 
  of 
  the 
  opercular 
  lobe 
  and 
  run 
  down 
  the 
  dorsal 
  

   surface 
  of 
  the 
  foot 
  for 
  a 
  short 
  distance 
  ; 
  the 
  median 
  furrow 
  

   then 
  terminates, 
  and 
  numerous 
  transverse 
  grooves 
  make 
  tlieir 
  

   appearance 
  and 
  are 
  continued 
  to 
  the 
  end 
  of 
  the 
  foot, 
  the 
  

   posterior 
  grooves 
  being- 
  deeper 
  than 
  those 
  moi-e 
  anterior. 
  

   These 
  grooves 
  are 
  not 
  continued 
  right 
  across 
  the 
  foot 
  from 
  

   side 
  to 
  side, 
  but 
  are 
  bounded 
  by 
  the 
  two 
  converging 
  lateral 
  

   furrows. 
  In 
  addition 
  to 
  these 
  deep 
  transverse 
  grooves 
  there 
  

   are 
  numerous 
  smaller 
  branching 
  furrows 
  which 
  run 
  in 
  a 
  

   transverse 
  direction 
  across 
  the 
  dorsal 
  surface 
  of 
  the 
  foot 
  from 
  

   side 
  to 
  side 
  ; 
  these 
  are 
  not 
  interrupted 
  by 
  the 
  lateral 
  furrows. 
  

   In 
  the 
  remaining 
  species 
  there 
  is 
  a 
  slight 
  difference 
  in 
  the 
  

   arrangement 
  of 
  this 
  specialised 
  portion 
  of 
  the 
  foot. 
  The 
  

   lateral 
  furrows 
  are 
  only 
  continued 
  for 
  a 
  short 
  distance 
  beyond 
  

   the 
  opercular 
  lobe 
  and 
  do 
  not 
  limit 
  the 
  transverse 
  furrows 
  to 
  

   a 
  marked!}" 
  V-shaped 
  area. 
  

  

  These 
  transverse 
  furrows 
  run 
  right 
  across 
  the 
  foot 
  to 
  the 
  

   epipodial 
  lobes 
  and 
  frequently 
  branch. 
  In 
  Trochus 
  magus 
  

   (fig. 
  9) 
  this 
  condition 
  is 
  well 
  exhibited 
  ; 
  at 
  the 
  posterior 
  

   extremity 
  of 
  the 
  foot 
  a 
  clearly 
  defined 
  median 
  groove 
  is 
  

   present; 
  in 
  T. 
  cinerarius 
  this 
  median 
  groove 
  is 
  continued 
  

   from 
  the 
  opercular 
  lobe 
  to 
  the 
  exti-eme 
  tip 
  of 
  the 
  foot. 
  

  

  