﻿Genera 
  of 
  Recent 
  Clypeastroids. 
  G01 
  

  

  Ecliinocyamus 
  and 
  Fibularia 
  is 
  mainly 
  in 
  this 
  character, 
  and 
  

   in 
  these 
  genera 
  there 
  is 
  no 
  reason 
  to 
  question 
  the 
  constancy 
  

   and 
  systematic 
  value 
  of 
  the 
  difference. 
  But 
  having 
  satisfied 
  

   myself 
  that 
  <c 
  Mellita 
  stokesii 
  " 
  is 
  only 
  the 
  young 
  of 
  Eucope 
  

   micropora, 
  I 
  am 
  bound 
  to 
  say 
  that 
  I 
  consider 
  the 
  internal 
  

   structure 
  of 
  the 
  test 
  of 
  little 
  taxonomic 
  importance 
  in 
  the 
  

   Eucopes 
  and 
  their 
  allies 
  ; 
  and 
  having 
  found 
  the 
  greatest 
  

   difficulty 
  in 
  making 
  use 
  of 
  the 
  character 
  in 
  Clypeaster 
  and 
  

   Laganum, 
  I 
  have 
  practically 
  ignored 
  it. 
  

  

  The 
  development 
  of 
  lunules 
  in 
  the 
  more 
  specialized 
  clypc- 
  

   astroids 
  affords 
  an 
  obvious, 
  constant, 
  and 
  most 
  interesting 
  

   character 
  ; 
  but 
  how 
  much 
  weight 
  is 
  to 
  be 
  attached 
  to 
  their 
  

   manner 
  of 
  formation 
  we 
  do 
  not 
  know. 
  Is 
  Mellita 
  sexies- 
  

   perforatus 
  unique 
  in 
  the 
  process 
  of 
  formation 
  of 
  its 
  ambu- 
  

   lacral 
  lunules? 
  What 
  significance 
  does 
  its 
  characteristic 
  

   method 
  have 
  ? 
  Is 
  it 
  of 
  taxonomic 
  importance 
  ? 
  Not 
  being- 
  

   able 
  to 
  answer 
  these 
  questions, 
  I 
  suggest 
  them 
  as 
  worthy 
  of 
  

   further 
  investigation. 
  The 
  form 
  of 
  the 
  petals 
  is 
  of 
  course 
  

   a 
  good 
  character, 
  but 
  it 
  is 
  well 
  known 
  that 
  even 
  a 
  single 
  

   species 
  may 
  show 
  great 
  diversity 
  not 
  only 
  in 
  the 
  relative 
  

   length 
  and 
  width, 
  but 
  in 
  the 
  degree 
  of 
  closure 
  at 
  the 
  distal 
  

   end. 
  The 
  position 
  of 
  the 
  anus 
  is 
  an 
  important 
  character, 
  

   but 
  as 
  it 
  shows 
  relatively 
  little 
  difference 
  in 
  adults 
  it 
  is 
  only 
  

   occasionally 
  of 
  practical 
  value. 
  The 
  form 
  of 
  the 
  test 
  seems 
  

   to 
  be 
  the 
  most 
  easily 
  modified 
  character, 
  and 
  little 
  weight 
  

   can 
  be 
  placed 
  on 
  it 
  in 
  determining 
  relationships. 
  Attention 
  

   has 
  been 
  called 
  by 
  De 
  Meijere 
  to 
  some 
  interesting 
  differences 
  

   between 
  the 
  spines 
  of 
  Laganum 
  and 
  Clypeaster; 
  but 
  as 
  I 
  

   have 
  not 
  found 
  it 
  necessary 
  to 
  use 
  this 
  character 
  and 
  have 
  

   not 
  yet 
  examined 
  all 
  the 
  genera 
  in 
  this 
  particular, 
  I 
  have 
  

   nothing 
  to 
  add 
  to 
  his 
  valuable 
  account 
  (1904, 
  'Siboga' 
  Ech. 
  

   pp. 
  103 
  et 
  seq.). 
  The 
  pedicellarise 
  also 
  show 
  characters 
  

   which 
  may 
  be 
  useful 
  for 
  help 
  in 
  distinguishing 
  species 
  and 
  

   genera, 
  but 
  they 
  have 
  not 
  seemed 
  to 
  me 
  of 
  sufficient 
  im- 
  

   portance 
  to 
  take 
  them 
  into 
  account 
  here. 
  

  

  There 
  can 
  be 
  little 
  question 
  that 
  Ecliinocyamus 
  and 
  Fibu- 
  

   laria 
  belong 
  in 
  a 
  family 
  by 
  themselves, 
  but 
  I 
  do 
  not 
  think 
  

   this 
  can 
  be 
  considered 
  a 
  primitive 
  group. 
  Such 
  simplicity 
  

   of 
  structure 
  as 
  they 
  show 
  is 
  probably 
  associated 
  with 
  their 
  

   small 
  size, 
  while 
  their 
  fused 
  auricles 
  and 
  the 
  structure 
  of 
  the 
  

   interambulacra 
  strongly 
  suggest 
  relationship 
  to 
  Laganum. 
  

  

  In 
  my 
  judgment 
  the 
  most 
  primitive 
  of 
  the 
  Recent 
  Clype- 
  

  

  astroidais 
  probably 
  Anomolanthus 
  or 
  those 
  species 
  of 
  Clypeaster 
  

  

  with 
  wide 
  open 
  petals 
  such 
  as 
  C. 
  ravenellii, 
  A. 
  Ag. 
  In 
  these 
  

  

  forms 
  the 
  auricles 
  are 
  paired, 
  well 
  separated, 
  and 
  ambulaeral 
  

  

  Ann. 
  iSo 
  Mag. 
  N. 
  Hist. 
  Ser. 
  8. 
  Vol. 
  vii. 
  10 
  

  

  