﻿COOKK 
  : 
  THE 
  llADULA 
  IN 
  THAIS, 
  ETC, 
  99 
  

  

  The 
  occurrence 
  of 
  a 
  group 
  of 
  Thaidte 
  possessing 
  a 
  peculiar 
  type 
  of 
  

   radula, 
  and 
  so 
  restricted 
  in 
  its 
  distribution, 
  is 
  remarkable. 
  It 
  may 
  

   be 
  paralleled 
  by 
  the 
  restriction 
  of 
  the 
  Nucella 
  group 
  to 
  northern 
  

   waters, 
  l^ot 
  all 
  Kew 
  Zealand 
  Thaidoe 
  possess 
  a 
  radula 
  of 
  tliis 
  type. 
  

   The 
  exceptions 
  are 
  2\ 
  succincta, 
  Lam., 
  and 
  T. 
  smithi, 
  Braz. 
  

   Evidently, 
  however, 
  succincta 
  is 
  an 
  immigrant 
  from 
  Australian 
  

   Avaters, 
  which 
  smithi, 
  in 
  view 
  of 
  its 
  general 
  form 
  and 
  restricted 
  

   geographical 
  distribution, 
  may 
  be 
  confidently 
  regarded 
  as 
  a 
  derivative 
  

   from 
  the 
  same 
  stock. 
  Tiie 
  fact 
  that 
  the 
  only 
  remaining 
  New 
  

   Zealand 
  Thais 
  {Agneivia 
  tritoniformis, 
  Blainv., 
  see 
  p. 
  100) 
  is 
  also 
  found 
  

   in 
  Australia, 
  is 
  noteworthy 
  on 
  other 
  grounds, 
  and 
  the 
  species 
  is 
  

   probably 
  a 
  recent 
  immigrant 
  to 
  Neozealanian 
  waters. 
  

  

  Patellipurpuka, 
  Dall. 
  

  

  P. 
  patula, 
  L. 
  Central 
  cusp 
  very 
  long, 
  thick, 
  and 
  sharp, 
  set 
  witli 
  

   a 
  guard 
  at 
  the 
  sides, 
  broadening 
  considerably 
  at 
  its 
  junction 
  with 
  

   the 
  upper 
  margin, 
  penetrated 
  down 
  the 
  centre 
  by 
  a 
  long 
  hollow 
  tube, 
  

   which 
  broadens 
  from 
  the 
  apex 
  and 
  almost 
  appears 
  to 
  cut 
  the 
  cusp 
  

   in 
  halves; 
  at 
  the 
  bottom 
  of 
  this 
  cusp, 
  where 
  it 
  is 
  imbedded 
  in 
  

   the 
  mass 
  of 
  the 
  tooth, 
  there 
  appears 
  to 
  be 
  a 
  kind 
  of 
  hollow 
  chamber, 
  

   in 
  which 
  may 
  be 
  stored 
  the 
  poison 
  emitted 
  through 
  the 
  tube 
  ; 
  this 
  

   chamber 
  can 
  only 
  be 
  seen 
  by 
  careful 
  examination 
  of 
  the 
  worn 
  end 
  of 
  

   the 
  radula, 
  where 
  it 
  is 
  disclosed. 
  The 
  side 
  cusps 
  are 
  much 
  shorter, 
  

   narrow, 
  and 
  sharp; 
  there 
  is 
  a 
  prominent 
  sharp 
  and 
  narrow 
  denticle 
  

   very 
  low 
  down, 
  equidistant 
  from 
  the 
  central 
  and 
  side 
  cusps, 
  and 
  not 
  

   connected 
  witli 
  the 
  one 
  more 
  than 
  with 
  the 
  other 
  ; 
  no 
  denticles 
  

   outside, 
  knob 
  broadly 
  blunt. 
  The 
  base 
  is 
  broadly 
  but 
  not 
  prominently 
  

   waved 
  in 
  the 
  centre 
  by 
  the 
  root 
  of 
  the 
  central 
  cusp; 
  angles 
  of 
  the 
  

   base 
  produced 
  into 
  short 
  " 
  wings 
  ". 
  The 
  whole 
  tooth 
  is 
  very 
  solid, 
  

   and 
  the 
  upper 
  margin 
  appears 
  to 
  be 
  remarkably 
  thickened. 
  

   Troschel's 
  figure 
  is 
  inadequate. 
  

  

  These 
  features 
  of 
  the 
  radula 
  afford, 
  on 
  all 
  grounds, 
  abundant 
  

   reason 
  for 
  separating 
  patula 
  from 
  the 
  mass 
  of 
  species 
  referable 
  to 
  

   Thais 
  proper. 
  The 
  position 
  of 
  the 
  intermediate 
  denticle, 
  the 
  winged 
  

   base, 
  and 
  above 
  all 
  the 
  unique 
  form 
  of 
  the 
  central 
  cusp 
  constitute 
  

   points 
  of 
  difference 
  which 
  are 
  decisive. 
  The 
  type 
  of 
  rhachidian 
  

   appears 
  to 
  be 
  primitive, 
  a 
  view 
  which 
  is 
  perhaps 
  supported 
  by 
  the 
  

   occurrence 
  of 
  the 
  species 
  on 
  both 
  sides 
  of 
  the 
  Isthmus 
  of 
  Panama, 
  

   a 
  distribution 
  shared 
  by 
  no 
  other 
  member 
  of 
  the 
  family. 
  The 
  

   locality 
  "Philippines" 
  is 
  an 
  old 
  error, 
  which 
  has 
  already 
  been 
  

   pointed 
  out 
  (Journ. 
  de 
  Conch., 
  1887, 
  pp. 
  228-38), 
  but 
  is 
  still 
  

   repeated. 
  

  

  Chorus, 
  Gray. 
  

  

  C. 
  giganteiis, 
  Less. 
  : 
  Chili. 
  Central 
  and 
  side 
  cusps 
  long 
  and 
  

   broad, 
  sharply 
  triangular, 
  almost 
  equal 
  in 
  length, 
  somewhat 
  removed 
  

   from 
  one 
  another, 
  central 
  not 
  deeply 
  rooted, 
  no 
  denticles 
  or 
  

   wrinkles 
  on 
  the 
  inside 
  or 
  the 
  outside; 
  angle 
  of 
  upper 
  margin 
  

   slightly 
  elevated; 
  base 
  straight 
  or 
  gently 
  curved 
  upward, 
  sides 
  

   scarcely 
  curved. 
  Laterals 
  with 
  a 
  very 
  broad 
  and 
  strong 
  base. 
  

  

  