﻿COOKR 
  : 
  ON 
  KADULA 
  OF 
  ACANTHJXA. 
  7 
  

  

  It 
  will 
  be 
  convenient 
  to 
  take 
  first 
  the 
  representatives 
  of 
  — 
  

   I. 
  The 
  Ckntral 
  Gkoup. 
  

  

  1. 
  A. 
  brevtdetitaia, 
  Wood. 
  The 
  rhachidian 
  has 
  a 
  strong, 
  pointed 
  

   central 
  cusp, 
  the 
  two 
  side 
  cusps 
  are 
  strongly 
  singly 
  denticled 
  on 
  the 
  

   inside, 
  three 
  or 
  four 
  small 
  denticles, 
  scarcely 
  climbing,^ 
  intervene 
  

   between 
  the 
  side 
  cusps 
  and 
  the 
  external 
  projection 
  (the 
  "knob"); 
  

   the 
  base 
  is 
  simply 
  curved 
  below. 
  In 
  other 
  words, 
  tlie 
  radula 
  is 
  of 
  

   the 
  normal 
  Thais 
  type, 
  hardly 
  to 
  be 
  distinguished 
  from 
  that 
  of 
  

   many 
  species 
  of 
  that 
  genus. 
  

  

  The 
  spine 
  or 
  spines, 
  for 
  there 
  are 
  sometimes 
  traces 
  of 
  more 
  than 
  

   one, 
  seem 
  scarcely 
  analogous 
  with 
  the 
  corresponding 
  formation 
  in 
  

   other 
  Acanthinse. 
  In 
  hrevidentata 
  the 
  spine 
  is 
  a 
  continuation 
  of 
  the 
  

   external 
  layer 
  of 
  the 
  shell 
  surface, 
  and 
  projects 
  from 
  it, 
  Avhile 
  in 
  

   certain 
  of 
  the 
  other 
  species 
  its 
  shape 
  and 
  position 
  suggest 
  an 
  origin 
  

   from 
  one 
  of 
  the 
  internal 
  denticulations 
  within 
  the 
  mouth. 
  In 
  

   hrevidentata, 
  as 
  well 
  as 
  in 
  the 
  other 
  species, 
  the 
  characteristic 
  groove 
  

   is 
  present, 
  marking 
  the 
  line 
  of 
  growth 
  of 
  the 
  spine. 
  

  

  I 
  propose 
  to 
  relegate 
  hrevidentata 
  to 
  the 
  genus 
  T/iais. 
  Both 
  the 
  

   shell 
  and 
  the 
  radula 
  are 
  in 
  close 
  agreement 
  with 
  that 
  group, 
  and 
  the 
  

   presence 
  of 
  tlie 
  spine 
  on 
  the 
  outer 
  lip 
  is 
  too 
  common 
  a 
  feature 
  in 
  

   other 
  genera 
  to 
  warrant 
  a 
  separation. 
  

  

  2. 
  A. 
  muricata, 
  Brod. 
  This 
  specifs 
  shows 
  a 
  different 
  and 
  very 
  

   striking 
  type 
  of 
  radula. 
  The 
  rhachidian 
  tooth 
  is 
  very 
  thick, 
  

   tricuspid 
  on 
  a 
  broad 
  base; 
  the. 
  central 
  cusp 
  is 
  long, 
  sharp, 
  and 
  

   flanked 
  by 
  two 
  small 
  similarly 
  shaped 
  side 
  cusps, 
  which 
  are 
  only 
  

   one-fourth 
  the 
  length 
  of 
  the 
  central 
  cusp, 
  and 
  are 
  closely 
  adjacent 
  to 
  

  

  'it. 
  There 
  are 
  no 
  denticles, 
  either 
  on 
  the 
  side 
  cusps 
  or 
  beyond 
  them, 
  

   while 
  the 
  knob 
  does 
  not 
  exist. 
  The 
  base 
  is 
  simple, 
  slightly 
  arched 
  

   below. 
  The 
  laterals 
  are 
  broad-bladed, 
  widening 
  rapidly 
  from 
  a 
  

   sharply 
  curved 
  apex, 
  with 
  a 
  greatly 
  produced 
  base. 
  

  

  In 
  general 
  facies 
  this 
  radula 
  (see 
  Fig. 
  1) 
  bears 
  not 
  the 
  remotest 
  

   resemblance 
  to 
  that 
  of 
  any 
  other 
  form 
  of 
  Acatithina. 
  The 
  type 
  to 
  

   which 
  it 
  is 
  most 
  closely 
  allied 
  appears 
  to 
  be 
  that 
  of 
  Rapana, 
  and 
  I 
  

   am 
  inclined 
  to 
  think 
  that, 
  both 
  conchologically, 
  and 
  from 
  the 
  point 
  

   of 
  view 
  of 
  the 
  radula, 
  A. 
  nmricata, 
  whose 
  position 
  among 
  the 
  other 
  

   west 
  coast 
  AcanthinaB 
  must 
  surely 
  have 
  puzzled 
  many 
  conchologists, 
  

   must 
  be 
  separated 
  fi'om 
  them 
  and 
  placed, 
  with 
  grandis, 
  Gray 
  

   (whose 
  radula 
  is 
  not 
  yet 
  known), 
  in 
  a 
  new 
  subgenus 
  of 
  its 
  own, 
  close 
  

   to 
  Rapana 
  of 
  the 
  Old 
  "World. 
  Neither 
  from 
  the 
  point 
  of 
  view 
  of 
  the 
  

   shell 
  nor 
  from 
  that 
  of 
  the 
  radula 
  (so 
  far 
  as 
  it 
  is 
  known) 
  can 
  these 
  

   two 
  species 
  any 
  longer 
  be 
  associated 
  with 
  the 
  west 
  coast 
  Acanthinse, 
  

   in 
  spite 
  of 
  R. 
  E. 
  C. 
  Stearns' 
  remark 
  that 
  "the 
  projecting 
  wave 
  is, 
  

   in 
  his 
  specimens, 
  developed 
  into 
  a 
  lioru 
  of 
  sufficient 
  prominence 
  to 
  

   enable 
  the 
  shell 
  to 
  enter 
  the 
  genus 
  on 
  its 
  own 
  hook". 
  It 
  has 
  been 
  

   abundantly 
  shown 
  that 
  the 
  possession 
  of 
  a 
  "horn" 
  is 
  often 
  an 
  

   accident 
  of 
  development, 
  especially 
  in 
  west 
  coast 
  genera. 
  . 
  

  

  Neobapana, 
  n.subgen., 
  is 
  therefore 
  here 
  proposed 
  by 
  me, 
  having 
  

  

  ^ 
  By 
  a 
  denticle 
  ' 
  ' 
  climbing 
  ' 
  ' 
  I 
  mean 
  ascending 
  the 
  external 
  edge 
  of 
  the 
  

   side 
  cusps. 
  

  

  