﻿DR. 
  COOKE 
  : 
  OPKRCULUM 
  OF 
  THE 
  GENUS 
  BURSA. 
  1 
  1 
  

  

  The 
  evidence 
  of 
  the 
  radula, 
  as 
  kindly 
  given 
  to 
  me 
  by 
  Professor 
  

   H. 
  ^I. 
  Gwatkin, 
  may 
  be 
  stated 
  thus 
  : 
  — 
  

  

  An 
  examination 
  of 
  twenty-six 
  sj^ecies 
  and 
  varieties 
  shows 
  three 
  

   types 
  of 
  radula. 
  

  

  1. 
  A 
  Bursa 
  ty^Q^ 
  which 
  includes 
  all 
  the 
  typical 
  Bursce, 
  viz. 
  bufonia, 
  

   ccelata, 
  cruetitata, 
  crumena, 
  gramolaris 
  and 
  varieties, 
  pustnlosa, 
  rana, 
  

   rhodostoma, 
  semigranosa, 
  siplionata, 
  spinosa, 
  thoime. 
  

  

  Under 
  this 
  type 
  also, 
  but 
  somewhat 
  distinct 
  from 
  it, 
  come 
  

   («) 
  marginata, 
  with 
  radula 
  of 
  so 
  delicate 
  proportions 
  that 
  it 
  stands 
  

   somewhat 
  apart 
  from 
  the 
  others, 
  and 
  {b) 
  rulela, 
  of 
  the 
  typical 
  form, 
  

   but 
  much 
  stronger 
  and 
  stouter. 
  

  

  2. 
  A 
  Triton 
  [Lotorimn) 
  type 
  (i.e. 
  a 
  median 
  tooth 
  with 
  strong 
  

   central 
  denticle 
  and 
  several 
  small 
  side 
  denticles) 
  including 
  jjerca, 
  

   pusilla, 
  tuherculata, 
  vexillum, 
  and 
  orgus, 
  but 
  wot 
  gig 
  ante 
  a 
  or 
  leucostonia. 
  

   (jS'.B. 
  Tliese 
  radulae 
  of 
  tlie 
  " 
  Triton" 
  type 
  are 
  by 
  no 
  means 
  tvpical 
  

   "Tritons".) 
  

  

  3. 
  A 
  type 
  unlike 
  both 
  Bursa 
  and 
  " 
  Triton 
  " 
  proper, 
  and 
  including 
  

   californica, 
  ventricosa, 
  gigantea, 
  and 
  leucostonia. 
  The 
  median 
  exhibits 
  

   one 
  great 
  central 
  denticle, 
  aTid 
  is 
  almost 
  bare 
  of 
  side 
  denticles 
  in 
  

   californica 
  and 
  gigantea 
  : 
  ventricosa 
  combines 
  the 
  big 
  central 
  denticle 
  

   with 
  the 
  lateral 
  prolongations 
  of 
  a 
  Bursa 
  (Fig. 
  1). 
  

  

  I 
  have 
  to 
  express 
  mj^ 
  thanks 
  to 
  'Mv. 
  R. 
  Standen, 
  of 
  the 
  Manchester 
  

   Museum, 
  to 
  the 
  authorities 
  of 
  tlie 
  Museum 
  of 
  Zoology 
  at 
  Cambridge, 
  

   to 
  Dr. 
  J. 
  C. 
  Melvill, 
  and 
  Mr. 
  J. 
  E-. 
  Le 
  B. 
  Tomlin 
  for 
  the 
  kind 
  loan 
  of 
  

   specimens, 
  now 
  exhibited, 
  and 
  also 
  to 
  M. 
  Ph. 
  Dautzenberg 
  for 
  valuable 
  

   information. 
  

  

  