﻿COOKK 
  : 
  THE 
  IIADULA 
  IN 
  THAIS, 
  ETC. 
  109 
  

  

  two 
  side 
  denticles 
  are 
  mucli 
  smaller, 
  set 
  below 
  the 
  upper 
  margin, 
  

   and 
  not 
  deeply 
  rooted, 
  base 
  somewhat 
  more 
  broadly 
  oblong, 
  little 
  

   arched, 
  laterals 
  much 
  shorter, 
  blunted 
  at 
  top, 
  and 
  not 
  serrated 
  

   (Fig. 
  37.) 
  

  

  Specimen 
  3: 
  Durban 
  (H. 
  C. 
  Burnup). 
  Ehachidian 
  consisting 
  of 
  

   a 
  single 
  long, 
  broad, 
  sharply 
  triangular 
  tooth, 
  whose 
  sides 
  abut 
  on 
  

   the 
  upper 
  angles 
  of 
  the 
  margin, 
  and 
  are 
  broken 
  by 
  a 
  single 
  sharp 
  

   denticle 
  low 
  down 
  ; 
  base 
  narrow, 
  arched 
  below 
  ; 
  laterals 
  very 
  

   slender, 
  serrated. 
  (Fig. 
  38.) 
  

  

  The 
  shell 
  of 
  specimen 
  1, 
  with 
  others 
  from 
  the 
  same 
  source, 
  is 
  in 
  

   my 
  possession, 
  and 
  is 
  undoubtedly 
  vexillum, 
  Cliem. 
  Mr. 
  Burnup 
  

   used 
  to 
  send 
  Professor 
  Gwatkin 
  the 
  soft 
  parts 
  only, 
  so 
  that 
  for 
  

   specimens 
  2 
  and 
  3 
  no 
  shell 
  is 
  present 
  for 
  verification. 
  But 
  the 
  

   probability 
  is 
  that 
  on 
  the 
  Natal 
  coast 
  there 
  are 
  two 
  more 
  species 
  of 
  

   Fexilla, 
  distinct 
  from 
  one 
  another 
  and 
  from 
  vexillum, 
  Chem. 
  Further 
  

   investigation 
  must 
  settle 
  the 
  point. 
  

  

  Subg. 
  UsiLLA, 
  H. 
  Adams. 
  

  

  Usilla 
  fusconigra, 
  Pease 
  : 
  Hilo. 
  Tlie 
  single 
  specimen 
  lias 
  the 
  

   radula 
  of 
  a 
  typical 
  Morula, 
  and 
  is 
  probably 
  wrongly 
  labelled. 
  

  

  Summing 
  up 
  the 
  general 
  relationships 
  of 
  the 
  group, 
  so 
  far 
  as 
  the 
  

   radula 
  is 
  concerned, 
  I 
  should 
  be 
  inclined 
  to 
  regard 
  both 
  Uaustrum 
  

   and 
  Patellipurpura 
  as 
  decidedly 
  primitive 
  forms, 
  widely 
  separated 
  

   from 
  one 
  another, 
  not 
  necessarily 
  the 
  immediate 
  ancestors 
  of 
  our 
  

   present 
  generation 
  of 
  Thaidae, 
  and 
  possibly 
  survivors 
  of 
  groups 
  once 
  

   more 
  widely 
  spread. 
  

  

  Closely 
  related 
  to 
  TJiais 
  proper 
  are 
  a 
  number 
  of 
  genera 
  whose 
  shell 
  

   has 
  become 
  modified 
  in 
  various 
  ways 
  ; 
  these 
  are 
  Concholepas, 
  Chorus, 
  

   Agnetvia, 
  Brupa, 
  Rapana, 
  and 
  Neorapana. 
  In 
  all 
  these 
  the 
  radula 
  is 
  

   of 
  a 
  similar 
  type, 
  and 
  exhibits, 
  in 
  the 
  different 
  groups, 
  divergencies 
  

   which 
  are 
  not 
  of 
  a 
  fundamental 
  character. 
  

  

  Not 
  far 
  removed 
  from 
  these 
  is 
  Acanthina, 
  as 
  restricted 
  by 
  the 
  

   views 
  expressed 
  in 
  Proc. 
  Malac. 
  Soc, 
  xiii, 
  pp. 
  6-11, 
  1918. 
  

  

  Nuctlla, 
  widely 
  distributed 
  in 
  the 
  northern 
  hemisphere, 
  but 
  

   restricted 
  in 
  species, 
  exhibits 
  a 
  type 
  of 
  radula 
  which 
  stands 
  apart 
  

   from 
  all 
  those 
  hitherto 
  mentioned, 
  and 
  is 
  separated 
  by 
  a 
  wide 
  gap 
  of 
  

   structure 
  from 
  Thais 
  and 
  its 
  congeners. 
  

  

  Morula 
  is 
  a 
  group 
  of 
  marked 
  individuality, 
  and, 
  while 
  displaying 
  

   in 
  the 
  sunken 
  central 
  cusp 
  and 
  waved 
  base, 
  some 
  affinitj' 
  to 
  Nucella, 
  

   has 
  other 
  points, 
  noted 
  above, 
  which 
  are 
  markedly 
  its 
  own. 
  Crania 
  

   is, 
  in 
  essence, 
  an 
  offshoot 
  of 
  Nucella, 
  while 
  Cijviia 
  appears 
  to 
  link 
  

   Morula 
  with 
  Thais, 
  possessing 
  as 
  it 
  does 
  characteristics 
  of 
  both 
  

   genera. 
  

  

  lopas 
  possesses 
  a 
  radula 
  so 
  entirely 
  peculiar 
  that 
  I 
  hesitate 
  to 
  

   approximate 
  it 
  to 
  any 
  group, 
  while 
  Vexillum, 
  xmtil 
  our 
  knowledge 
  of 
  

   its 
  radula 
  is 
  finally 
  cleared 
  up, 
  must 
  remain 
  in 
  a 
  similar 
  position, 
  

   though 
  it 
  certainly 
  stands 
  in 
  a 
  relation 
  more 
  or 
  less 
  close 
  to 
  lopas. 
  

  

  