﻿COOKE: 
  THE 
  RADULA 
  IN 
  THAIS, 
  ETC. 
  103 
  

  

  base 
  shaped 
  as 
  in 
  hulbosa, 
  but 
  not 
  sloping 
  in 
  quite 
  so 
  sharply 
  at 
  the 
  

   sides 
  ; 
  mass 
  of 
  the 
  tooth 
  decidedly 
  deeper 
  in 
  proportion 
  to 
  its 
  width. 
  

  

  Specimens 
  from 
  the 
  Persian 
  Gulf 
  and 
  Japan 
  agree 
  completely. 
  

   (Fig. 
  28.) 
  

  

  For 
  the 
  radula 
  of 
  Neohapana, 
  and 
  Aoanthina, 
  and 
  Acanthinu- 
  

   CELLA, 
  see 
  Froc. 
  Malac. 
  Soc, 
  xiii, 
  1918, 
  pp. 
  6-11. 
  

  

  NucELLA, 
  Bolten. 
  

  

  The 
  Nucella 
  group 
  is 
  characterised 
  by 
  a 
  rhachidian, 
  the 
  central 
  

   cusp 
  of 
  which 
  is 
  set 
  (as 
  in 
  MoruUi) 
  in 
  a 
  small 
  pit 
  or 
  excavation 
  on 
  

   the 
  upper 
  margin 
  of 
  the 
  tooth 
  ; 
  it 
  is 
  mounted 
  on 
  a 
  strong 
  root 
  or 
  

   pillar 
  which 
  runs 
  downward 
  tlirough 
  the 
  main 
  mass, 
  and 
  terminates 
  

   in 
  the 
  base, 
  usually 
  causing 
  a 
  more 
  or 
  less 
  prominent 
  projection. 
  

   The 
  side 
  cusps 
  are 
  mounted 
  on 
  buttresses, 
  and 
  are 
  denticled 
  inside 
  

   and 
  outside; 
  the 
  outer 
  denticles 
  descend 
  steeply, 
  far 
  below 
  the 
  upper 
  

   margin. 
  The 
  base, 
  instead 
  of 
  being 
  rounded, 
  is 
  produced 
  more 
  or 
  

   less 
  sharply, 
  at 
  the 
  two 
  outer 
  angles. 
  The 
  knobs 
  are 
  very 
  prominent, 
  

   and 
  a 
  portion 
  of 
  the 
  substructure 
  of 
  the 
  tooth 
  appears 
  to 
  run 
  from 
  

   one 
  to 
  tlie 
  other. 
  

  

  These 
  features 
  are 
  reproduced 
  in 
  all 
  the 
  forms 
  of 
  this 
  small 
  group 
  

   which 
  are 
  known 
  to 
  me, 
  and 
  afford 
  additional 
  evidence 
  of 
  the 
  close 
  

   connexion 
  of 
  the 
  West 
  American 
  Thaidae 
  {lima. 
  Mart., 
  jw//frt/rt. 
  Mart., 
  

   emarginata, 
  Desh., 
  and 
  their 
  varieties; 
  see 
  JProc. 
  Malac. 
  Soc, 
  xi, 
  

   1915, 
  pp. 
  203-4) 
  with 
  the 
  European 
  and 
  East 
  American 
  Wucella 
  

   lapillus. 
  Unfortunately 
  the 
  radula 
  of 
  Thais 
  freycineti, 
  Desh., 
  is 
  not 
  

   included 
  in 
  Professor 
  Gwatkin's 
  collections, 
  otherwise 
  it 
  would 
  have 
  

   been 
  interesting 
  to 
  determine 
  whether 
  that 
  species 
  has 
  radular 
  

   affinities 
  with 
  the 
  Nticella 
  group, 
  or 
  is 
  a 
  northern 
  representative 
  of 
  

   the 
  main 
  Thais 
  group. 
  The 
  form 
  of 
  shell 
  certainly 
  inclines 
  one 
  to 
  

   expect 
  the 
  former 
  to 
  be 
  the 
  case, 
  and 
  geographically 
  there 
  seems 
  

   no 
  reason 
  why 
  the 
  ancestors 
  of 
  the 
  West 
  American 
  Nucella, 
  when 
  

   thej^ 
  reached 
  that 
  district 
  from 
  the 
  north, 
  should 
  not 
  also 
  have 
  

   reached 
  North 
  Asiatic 
  shores. 
  

  

  The 
  following 
  species 
  have 
  been 
  examined: 
  — 
  

  

  lapillus, 
  L. 
  : 
  Torbay. 
  Central 
  cusp 
  thick, 
  one-third 
  longer 
  than 
  

   the 
  side 
  cusps, 
  deeply 
  set 
  in 
  a 
  pit 
  below 
  the 
  level 
  of 
  the 
  upper 
  margin, 
  

   root 
  carried 
  througli 
  to 
  the 
  base 
  and 
  sharply 
  projecting 
  ; 
  side 
  cusps 
  

   broad, 
  set 
  on 
  strong 
  buttresses, 
  which 
  descend 
  into 
  the 
  body 
  of 
  tlie 
  

   tooth, 
  bluntly 
  denticled 
  low 
  down 
  on 
  the 
  inside 
  and 
  outside 
  ; 
  two 
  

   more 
  small 
  denticles, 
  which 
  are 
  not 
  always 
  present 
  or 
  not 
  always 
  

   discernible, 
  beyond 
  and 
  below 
  the 
  exterior 
  base 
  of 
  the 
  side 
  cusps; 
  

   knob 
  strong, 
  much 
  elevated; 
  base 
  angles 
  well 
  produced. 
  

  

  Specimens 
  from 
  Oporto 
  and 
  Nahant, 
  Mass., 
  agree 
  in 
  essentials; 
  

   frequently 
  there 
  is 
  only 
  one 
  small 
  exterior 
  denticle. 
  

  

  lima. 
  Mart, 
  (as 
  canaliculata, 
  Duel.) 
  : 
  Vancouver 
  I. 
  Central 
  

   cusp 
  thick, 
  long, 
  nari'ow, 
  considerably 
  longer 
  than 
  the 
  side 
  cusps, 
  

   sunk 
  very 
  deeply 
  in 
  the 
  upper 
  margin, 
  root 
  carried 
  through 
  to 
  the 
  

   base, 
  but 
  not 
  causing 
  a 
  marked 
  projection 
  in 
  it 
  ; 
  side 
  cusps 
  Avith 
  a 
  

   conspicuous 
  bluntish 
  denticle 
  high 
  up 
  on 
  the 
  inside, 
  and 
  another, 
  

   also 
  blunt, 
  lower 
  down 
  on 
  the 
  outside 
  (this 
  latter 
  is 
  sometimes 
  not 
  

  

  