﻿ANATOMY 
  AND 
  AFFINITIES 
  OF 
  THI<] 
  TROOHID.'E. 
  67 
  

  

  and 
  runs 
  some 
  little 
  distance 
  into 
  the 
  nerve. 
  This 
  diver- 
  

   ticulum, 
  though 
  destitute 
  of 
  specialised 
  sensory 
  cells, 
  con- 
  

   tains 
  several 
  ol 
  the 
  numerous 
  otoconia 
  that 
  are 
  present 
  in 
  

   the 
  auditory 
  sac. 
  

  

  Lacaze 
  Duthiers, 
  in 
  his 
  memoir 
  on 
  the 
  otocysts 
  of 
  Mollnscs 
  

   (27), 
  has 
  described 
  a 
  somewhat 
  similar 
  condition 
  in 
  Patella. 
  

  

  The 
  ospli 
  radium 
  (tigs. 
  41 
  — 
  48, 
  o.y.) 
  is 
  a 
  snuill 
  patch 
  of 
  

   specialised 
  sensory 
  epithelium 
  of 
  a 
  yellowish 
  colour 
  situated 
  

   under 
  the 
  branchial 
  ganglion, 
  and 
  extending 
  for 
  a 
  short 
  

   distance 
  along 
  that 
  portion 
  of 
  the 
  gill-base 
  which 
  lies 
  free 
  

   in 
  the 
  mantle-cavity. 
  Bernard 
  (2, 
  pp. 
  167 
  — 
  173) 
  has 
  given 
  

   a 
  detailed 
  account 
  of 
  the 
  histological 
  structure 
  of 
  the 
  osphra- 
  

   diuni. 
  

  

  Other 
  sense-organs 
  are 
  the 
  cephalic 
  and 
  epipodial 
  tentacles, 
  

   which 
  are 
  undoubtedly 
  tactile. 
  I'he 
  epipotlial 
  papilho 
  have 
  

   proljably 
  a 
  similar 
  function. 
  

  

  Sensory 
  cells 
  occur 
  in 
  the 
  buccal 
  cavity 
  of 
  Trochus, 
  

   simihir 
  to 
  those 
  described 
  by 
  Haller 
  (19, 
  pi. 
  vii, 
  tig. 
  28) 
  as 
  

   occuri'ing 
  in 
  the 
  buccal 
  cavity 
  of 
  Fissurella, 
  anH 
  may 
  be 
  

   gustatory 
  in 
  function. 
  

  

  In 
  addition 
  a 
  peculiar 
  series 
  of 
  sensory 
  organs, 
  first 
  men- 
  

   tioned 
  by 
  Thiele 
  (41), 
  is 
  found 
  occurring 
  in 
  the 
  mantle-cavity 
  

   on 
  the 
  right 
  side, 
  in 
  the 
  angle 
  between 
  the 
  mantle 
  and 
  body- 
  

   wall. 
  

  

  Conclusions. 
  — 
  It 
  will 
  be 
  seen 
  from 
  the 
  foregoing 
  account 
  

   that 
  the 
  various 
  species 
  of 
  Trochus 
  examined 
  present 
  very 
  

   few 
  anatomical 
  differences 
  ; 
  it 
  is, 
  however, 
  possible 
  to 
  dis- 
  

   tinguish 
  between 
  two 
  slightly 
  diverse 
  types 
  of 
  organisation, 
  

   the 
  characters 
  of 
  which 
  are 
  sutKcieut 
  to 
  constitute 
  different 
  

   sub-genera. 
  Retaining 
  the 
  existing 
  nomenclature, 
  we 
  have 
  

   the 
  one 
  sub-genus 
  Calliostoma, 
  in 
  which 
  the 
  shell 
  is 
  pyra- 
  

   midal, 
  and 
  into 
  which 
  the 
  following 
  species 
  can 
  be 
  placed 
  : 
  — 
  

   T, 
  zizyphinus, 
  T. 
  granitlatus, 
  T. 
  striatus, 
  T. 
  exaspe- 
  

   ratus, 
  and 
  T. 
  Montagui. 
  In 
  another 
  sub-genus, 
  Gibbula, 
  

   we 
  can 
  include 
  the 
  remaining 
  forms, 
  viz. 
  T. 
  magus, 
  T. 
  cine- 
  

   rarius, 
  T. 
  umbi 
  Meatus, 
  T. 
  tumid 
  us, 
  and 
  T. 
  lineatus. 
  

   The 
  sub-genus 
  Trochocochlea, 
  in 
  which 
  this 
  latter 
  species 
  

  

  