﻿COOKE: 
  ON 
  KADULA. 
  OF 
  ACANTUINA. 
  

  

  respects 
  good 
  figures 
  of 
  the 
  two 
  forms. 
  In 
  fig. 
  8 
  {crasstlahum) 
  the 
  

   roots 
  of 
  the 
  central 
  cusps 
  are 
  not 
  carried 
  through 
  to 
  the 
  hase, 
  as 
  they 
  

   should 
  be, 
  while 
  in 
  fig. 
  7 
  (calcar) 
  I 
  am 
  not 
  able 
  to 
  recognize 
  the 
  two 
  

   prominent 
  denticles 
  whicli 
  he 
  figures 
  between 
  the 
  side 
  cusps 
  and 
  tlie 
  

   knob. 
  Again, 
  the 
  central 
  cusp 
  of 
  calcar 
  should 
  not 
  be 
  so 
  bluntly 
  

   bullet-shaped, 
  but 
  should 
  approximate 
  closely 
  in 
  form 
  to 
  that 
  of 
  

   crassilabrum. 
  

  

  m]4 
  

  

  $ 
  

  

  Fig. 
  1. 
  Neorapana 
  miiricata, 
  Brod. 
  Panama. 
  

  

  ,, 
  2. 
  Thais 
  hrevidentata 
  , 
  Wood. 
  Panama. 
  

  

  ,, 
  3. 
  Acanthinucella 
  punctulata, 
  Sowb. 
  California. 
  

  

  ,, 
  4. 
  A. 
  unicarinata, 
  Sowb. 
  California. 
  

  

  ,, 
  5. 
  Nucella 
  lapillus, 
  L. 
  Torquay. 
  

  

  ,, 
  6. 
  Acanthina 
  calcar 
  , 
  'M&xi. 
  Chili. 
  

  

  ,, 
  7. 
  A. 
  lugubr 
  is, 
  ^Q-fih. 
  Lower 
  California. 
  

  

  In 
  crassilahrum 
  tlie 
  central 
  cusp 
  is 
  somewhat 
  more 
  broadly 
  

   triangular 
  than 
  in 
  calcar; 
  the 
  denticle 
  on 
  the 
  inside 
  of 
  the 
  side 
  cusps 
  

   is 
  strong, 
  and 
  points 
  slightly 
  towards 
  the 
  central 
  cusp; 
  that 
  on 
  the 
  

   outside 
  is 
  weak. 
  In 
  calcar 
  (Fig. 
  6) 
  the 
  outside 
  denticle 
  is 
  somewhat 
  

   more 
  prominent, 
  while 
  what 
  may 
  be 
  called 
  the 
  false 
  (or 
  underneath) 
  

   knob 
  is 
  sharp 
  and 
  very 
  long. 
  In 
  both 
  forms 
  the 
  central 
  cusp 
  is 
  not 
  

   greatly 
  longer 
  than 
  the 
  side 
  cusps. 
  

  

  These 
  differences 
  in 
  structure 
  on 
  the 
  whole 
  are 
  small, 
  and 
  offer 
  no 
  

   obstacle 
  to 
  the 
  view 
  that 
  the 
  two 
  forms 
  are 
  conspecific; 
  one 
  would 
  

   expect 
  the 
  causes 
  which 
  have 
  made 
  the 
  shell 
  to 
  vary 
  to 
  produce 
  some 
  

   variation 
  in 
  the 
  radula. 
  

  

  IV. 
  

  

  Finally, 
  the 
  radula 
  of 
  A. 
  lugubris, 
  Sowb. 
  (Fig. 
  7), 
  appears 
  to 
  be 
  of 
  

   a 
  foi-m 
  intermediate 
  between 
  that 
  of 
  the 
  northern 
  and 
  the 
  southern 
  

   groups, 
  but 
  more 
  akin 
  to 
  the 
  latter. 
  

  

  The 
  central 
  cusp 
  is 
  long 
  and 
  narrow, 
  set 
  on 
  a 
  pillar 
  which 
  is 
  

   faintly 
  carried 
  through 
  to 
  the 
  base, 
  and 
  forms 
  a 
  slight 
  projection 
  on 
  

   the 
  under-side. 
  The 
  side 
  cusps, 
  which 
  are 
  sharp, 
  are 
  not 
  set 
  on 
  a 
  

   buttress, 
  they 
  carry 
  a 
  strong 
  sharp 
  denticle 
  both 
  on 
  the 
  inside 
  and 
  

   outside, 
  then 
  comes 
  a 
  single 
  toothlet, 
  sharp, 
  prominent, 
  quite 
  

   detached; 
  at 
  the 
  base 
  of 
  the 
  knob 
  is 
  another 
  smaller 
  toothlet 
  or 
  

   denticle 
  ; 
  knob 
  strong, 
  prominent. 
  

  

  