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  COLLECTIONS 
  FEOM 
  MELANESIA. 
  

  

  any 
  one 
  of 
  the 
  three 
  collected 
  by 
  the 
  officials 
  of 
  that 
  great 
  circum- 
  

   navigating 
  expedition. 
  

  

  Though 
  the 
  term 
  Plturechhins 
  is 
  due 
  to 
  L. 
  Agassiz, 
  and 
  the 
  specific 
  

   name 
  hothryoides 
  to 
  his 
  incomplete 
  comprehension 
  of 
  the 
  Cidaris 
  

   hotlinjoides 
  of 
  Klein 
  and 
  Leske, 
  I 
  have 
  confined 
  my 
  " 
  synonymy 
  " 
  

   to 
  Alexander 
  Agassiz's 
  Report 
  on 
  the 
  ' 
  Challenger 
  ' 
  specimens, 
  as 
  

   it 
  is 
  there 
  only 
  that 
  any 
  such 
  definite 
  information 
  is 
  given 
  as 
  would 
  

   enable 
  a 
  zoologist 
  to 
  recognize 
  examples 
  of 
  the 
  species. 
  The 
  result 
  

   to 
  which 
  my 
  own 
  study 
  of 
  the 
  specimens 
  and 
  of 
  the 
  definitions 
  has 
  

   led 
  me 
  has, 
  I 
  think, 
  been 
  essentially 
  confirmed 
  by 
  the 
  investigation 
  

   into 
  the 
  structure 
  of 
  the 
  test 
  which, 
  at 
  my 
  suggestion, 
  Prof. 
  Martin 
  

   Duncan 
  was 
  allowed 
  to 
  make 
  *. 
  

  

  Looking, 
  first 
  of 
  all, 
  at 
  the 
  general 
  form 
  of 
  the 
  test, 
  the 
  observer 
  

   is 
  struck 
  by 
  its 
  greater 
  proportional 
  height 
  ; 
  thus 
  we 
  find 
  speci- 
  

   mens 
  with 
  an 
  absolute 
  diam(!ter 
  of 
  20, 
  18, 
  or 
  17 
  millim. 
  respec- 
  

   tively 
  having 
  a 
  proportional 
  height 
  of 
  58-5, 
  66-6, 
  and 
  60. 
  In 
  

   no 
  known 
  examples 
  of 
  any 
  other 
  species 
  of 
  Temnopleurus 
  is 
  the 
  

   proportional 
  height 
  more 
  than 
  03-63 
  millim. 
  f, 
  and 
  this 
  is 
  a 
  rare 
  

   case, 
  which 
  obtains 
  with 
  a 
  specimen 
  only 
  11 
  millim. 
  wide. 
  The 
  

   examination 
  of 
  the 
  dental 
  apparatus 
  did 
  not 
  shov/ 
  any 
  real 
  point 
  of 
  

   difference 
  between 
  this 
  species 
  and 
  T. 
  hardwicl-ii. 
  As 
  in 
  other 
  

   species 
  of 
  this 
  genus, 
  the 
  abactinal 
  area 
  is 
  much 
  more 
  prominent 
  

   in 
  younger 
  than 
  in 
  older 
  specimens, 
  while 
  the 
  characters 
  of 
  the 
  

   furrows 
  between 
  the 
  plates 
  is 
  only 
  intermediate 
  between 
  the 
  ex- 
  

   treme 
  condition 
  presented 
  by 
  T. 
  toreumaticus 
  and 
  that 
  which 
  is 
  

   Been 
  in 
  the 
  species 
  just 
  mentioned. 
  

  

  As 
  to 
  the 
  minute 
  construction 
  of 
  the 
  test. 
  Dr. 
  Duncan 
  finds 
  that 
  

   " 
  there 
  is 
  a 
  generic 
  relation 
  between 
  Temnopleurus 
  and 
  Pleurechmns, 
  

   and 
  the 
  only 
  important 
  distinction 
  is 
  the 
  absence 
  of 
  crenulation 
  in 
  

   the 
  last-named 
  type." 
  To 
  this 
  crenulation 
  or 
  its 
  absence 
  Dr. 
  Duncan 
  

   attaches 
  more 
  importance 
  than 
  do 
  many 
  naturalists 
  who 
  have 
  devoted 
  

   themselves 
  to 
  this 
  group, 
  and 
  he 
  finds 
  in 
  consequence 
  that 
  " 
  the 
  

   classificatory 
  position 
  assigned 
  by 
  A. 
  Agassiz 
  to 
  Plmrechinus 
  in 
  the 
  

   ' 
  Eevision 
  ' 
  must 
  be 
  conceded, 
  and 
  it 
  is 
  a 
  subgenus 
  or 
  section 
  of 
  

   Temnopleurus 
  r 
  Notwithstanding 
  the 
  weight 
  of 
  the 
  authority 
  of 
  

   Agassiz 
  and 
  Dimcan, 
  I 
  am 
  bound 
  to 
  say 
  that 
  I 
  feel 
  still 
  the 
  im- 
  

   portance 
  of 
  the 
  objections 
  long 
  ago 
  urged 
  by 
  D'Archiac 
  and 
  HaimeJ, 
  

   " 
  Quant 
  aux 
  crenelures 
  des 
  tubcrcules, 
  on 
  sait 
  que 
  cette 
  particularite 
  

   n'a 
  cgalement 
  qu'une 
  valeur 
  tres-secondaire, 
  puisqu'on 
  la 
  voit 
  deja 
  

   disparaitre 
  dans 
  une 
  certaine 
  portion 
  du 
  genre 
  Cidaris, 
  sans 
  qu'on 
  

   puisse 
  decouvrir 
  chez 
  les 
  especes 
  a 
  tubercules 
  lisses 
  aucune 
  autre 
  

   difference 
  concomitante; 
  " 
  and 
  that 
  being 
  so, 
  I 
  can 
  find 
  no 
  reason 
  

   which 
  will 
  justify 
  the 
  retention 
  of 
  a 
  genus 
  never 
  very 
  accurately 
  

   defined. 
  

  

  The 
  largest 
  specimen 
  in 
  the 
  ' 
  Alert 
  ' 
  collection 
  has 
  a 
  diameter 
  

  

  * 
  Journ. 
  Linn. 
  Soc. 
  (Zool.) 
  xvi. 
  p. 
  447. 
  

   t 
  P. 
  Z. 
  S. 
  1880, 
  p. 
  424. 
  

  

  X 
  Anim. 
  f■o^s. 
  de 
  I'lnde, 
  p. 
  202 
  (ISr^S). 
  The 
  student 
  should 
  be 
  reminded 
  

   that 
  Prof. 
  Martin 
  (Notes 
  Leyd. 
  Mus. 
  ii. 
  p. 
  75) 
  accepts 
  the 
  genus 
  Plcurcchinus. 
  

  

  