﻿34 
  W, 
  B. 
  HANDLES. 
  

  

  the 
  greater 
  part 
  of 
  them 
  having 
  been 
  obtained 
  from 
  Plymouth 
  

   during 
  the 
  months 
  of 
  July 
  and 
  August, 
  1901. 
  

  

  For 
  specimens 
  of 
  Trochus 
  exasperatus 
  and 
  T. 
  Mon- 
  

   tacuti 
  I 
  am 
  indebted 
  to 
  Mr. 
  E. 
  R. 
  Sykes, 
  and 
  of 
  T. 
  magus 
  

   to 
  Mr. 
  E. 
  W. 
  Holt. 
  

  

  I 
  wish 
  here 
  to 
  express 
  my 
  best 
  thanks 
  to 
  the 
  Committee 
  of 
  

   the 
  Royal 
  Society 
  for 
  a 
  grant 
  which 
  enabled 
  me 
  to 
  carry 
  on 
  my 
  

   researches 
  at 
  Plymouth, 
  also 
  to 
  the 
  British 
  Association 
  and 
  

   Zoological 
  Society 
  for 
  the 
  use 
  of 
  their 
  tables 
  at 
  the 
  Marine 
  

   Biological 
  Laboratory 
  during 
  July 
  and 
  August, 
  1901. 
  

  

  The 
  various 
  species 
  of 
  the 
  genus 
  Trochus 
  of 
  which 
  there 
  

   are 
  a 
  considerable 
  number, 
  have 
  been 
  grouped 
  into 
  numerous 
  

   subgenera. 
  These 
  sub-divisions 
  have 
  been 
  founded 
  upon 
  

   conchological 
  differences 
  without 
  regard 
  to 
  the 
  anatomical 
  

   organisation 
  of 
  the 
  animal. 
  It 
  is 
  highly 
  probable 
  that 
  if 
  

   anatomical 
  characteristics 
  are 
  taken 
  into 
  account 
  the 
  number 
  

   of 
  sub-genera 
  can 
  be 
  considerably 
  reduced. 
  

  

  The 
  following 
  species 
  of 
  Trochus 
  are 
  those 
  which 
  I 
  have 
  

   examined 
  : 
  

  

  1. 
  T. 
  magus 
  (Linn.). 
  

  

  2. 
  T. 
  cinerarius 
  (Linn.). 
  

  

  3. 
  T. 
  umbilicatus 
  (Montagu). 
  

  

  4. 
  T. 
  tumid 
  us 
  (Montagu). 
  

  

  5. 
  T. 
  lineatus 
  (Da 
  Costa). 
  

  

  6. 
  T. 
  zizyphinus 
  (Linn.). 
  

  

  7. 
  T. 
  granulatus 
  (Born). 
  

  

  8. 
  T. 
  striatus 
  (Linn.). 
  

  

  9. 
  T. 
  exasperatus 
  (Pennant). 
  

   10. 
  T. 
  Montagui 
  (Gray). 
  

  

  These 
  species 
  are, 
  according 
  to 
  Forbes 
  and 
  Hanley 
  (17), 
  

   grouped 
  into 
  two 
  sub-genera, 
  viz. 
  1 
  — 
  5 
  under 
  the 
  sub-genus 
  

   Gibbula 
  and 
  6 
  — 
  10 
  under 
  the 
  sub-genus 
  Trochus. 
  

  

  If 
  we 
  folloAv 
  the 
  classification 
  given 
  either 
  by 
  Gwyn 
  

   Jeffries 
  (24) 
  or 
  Tyron 
  (43), 
  we 
  must 
  group 
  the 
  above 
  species 
  

   into 
  three 
  subgeneric 
  divisions, 
  viz. 
  1 
  — 
  4 
  under 
  the 
  sub- 
  

   genus 
  Gibbula 
  (Leach), 
  5 
  under 
  the 
  sub-genus 
  Mono- 
  

   donta 
  (Lamarck), 
  or 
  Trochocochlea 
  (Klein), 
  and 
  6 
  — 
  10 
  

  

  