﻿Genera 
  of 
  Recent 
  Clypeastroids. 
  599 
  

  

  species 
  in 
  Arachnoides, 
  it 
  is 
  obviously 
  the 
  type. 
  There 
  is 
  

   room 
  for 
  difference 
  of 
  opinion 
  as 
  to 
  whether 
  Arachnoides 
  

   should 
  date 
  from 
  Leske 
  or 
  Agassiz 
  ; 
  but 
  as 
  I 
  have 
  no 
  doubt 
  

   that 
  the 
  " 
  Genus 
  1 
  " 
  of 
  the 
  former 
  is 
  Arachnoides, 
  Klein, 
  and 
  

   as 
  Leske 
  himself 
  uses 
  that 
  name 
  on 
  p. 
  8, 
  it 
  seems 
  to 
  me 
  right 
  

   to 
  date 
  the 
  genus 
  from 
  the 
  ' 
  Additamenta.' 
  Fourtau 
  (1904) 
  

   has 
  attempted 
  to 
  substitute 
  Echinodiscus 
  for 
  Arachnoides, 
  

   but 
  as 
  his 
  argument 
  is 
  based 
  on 
  the 
  acceptance 
  of 
  pre- 
  

   Linnean 
  names, 
  it 
  does 
  not 
  concern 
  us 
  here. 
  Ortmann 
  

   (1902) 
  believes 
  that 
  Echinarachnivs 
  is 
  not 
  distinguishable 
  

   from 
  Scutella; 
  but 
  I 
  cannot 
  agree 
  with 
  him, 
  for 
  the 
  differences 
  

   between 
  the 
  petals 
  of 
  a 
  typical 
  Scutella 
  (like 
  subrotunda) 
  and 
  

   those 
  of 
  Echinarachnius 
  are 
  sufficiently 
  important 
  from 
  the 
  

   phylogenetic 
  point 
  of 
  view 
  to 
  warrant 
  generic 
  separation, 
  in 
  

   spite 
  of 
  the 
  existence 
  of 
  perplexing 
  connecting 
  forms. 
  The 
  

   genus 
  Dendraster 
  was 
  proposed 
  by 
  Agassiz 
  and 
  Desor 
  (1847) 
  

   for 
  the 
  remarkable 
  sand-dollar 
  of 
  the 
  North 
  Pacific 
  called 
  

   Scutella 
  excentrica 
  by 
  Eschscholtz. 
  In 
  the 
  ' 
  Revision 
  ' 
  this 
  

   genus 
  is 
  considered 
  a 
  synonym 
  of 
  Echinarachnius 
  ; 
  but 
  I 
  

   cannot 
  believe 
  this 
  is 
  desirable, 
  for 
  excentrica 
  is 
  quite 
  unique 
  

   in 
  several 
  important 
  characters, 
  and 
  in 
  my 
  judgment 
  

   Dendraster 
  should 
  be 
  retained. 
  

  

  The 
  genera 
  Peronella, 
  Gray, 
  Anomclanthus, 
  Bell, 
  Alex- 
  

   andria, 
  Pfeffer, 
  and 
  Astriclypeus, 
  Verrill, 
  ware 
  all 
  monotypic 
  

   when 
  established, 
  so 
  there 
  is 
  no 
  room 
  for 
  doubt 
  as 
  to 
  their 
  

   types. 
  I 
  am 
  quite 
  unable 
  to 
  follow 
  Bell's 
  (1883, 
  Ann. 
  & 
  

   Mag. 
  Nat. 
  Hist., 
  February) 
  line 
  of 
  argument, 
  by 
  which 
  he 
  

   endeavours 
  to 
  dissociate 
  Peronella 
  from 
  Gray. 
  To 
  my 
  mind 
  

   it 
  is 
  perfectly 
  clear 
  that 
  Gray 
  established 
  Peronella 
  as 
  a 
  

   subgenus 
  for 
  Laganum 
  peronii, 
  Agass. 
  I 
  am 
  by 
  no 
  means 
  

   clear 
  as 
  to 
  the 
  exact 
  limits 
  of 
  Peronella 
  as 
  a 
  generic 
  term 
  at 
  

   the 
  present 
  day, 
  but 
  I 
  am 
  inclined 
  to 
  think 
  it 
  may 
  well 
  be 
  

   used 
  to 
  include 
  the 
  species, 
  otherwise 
  referred 
  to 
  Laganum, 
  

   which 
  have 
  only 
  four 
  genital 
  pores. 
  

  

  In 
  spite 
  of 
  their 
  long-continued 
  use, 
  the 
  genera 
  Eucope 
  

   and 
  Mellita, 
  so 
  far 
  as 
  I 
  can 
  discover, 
  have 
  never 
  had 
  any 
  

   types 
  designated. 
  For 
  the 
  former 
  I 
  would 
  choose 
  the 
  species 
  

   called 
  Echinodiscus 
  emarginatus, 
  Leske, 
  which 
  seems 
  to 
  have 
  

   been 
  the 
  longest 
  known 
  of 
  any 
  species. 
  For 
  Mellita 
  I 
  select 
  

   quinijuiesperforatus, 
  Leske, 
  both 
  because 
  it 
  has 
  page 
  prece- 
  

   dence 
  over 
  sexiesperforatus 
  and 
  because 
  it 
  seems 
  to 
  be 
  a 
  

   commoner 
  and 
  more 
  generally 
  known 
  species. 
  I 
  greatly 
  

   regret 
  that 
  the 
  shorter 
  and 
  much 
  more 
  euphonious 
  names 
  

   given 
  by 
  Gmelin 
  ten 
  years 
  later 
  to 
  these 
  two 
  species 
  may 
  not 
  

   be 
  used, 
  but 
  it 
  would 
  involve 
  a 
  deliberate 
  violation 
  of 
  the 
  

   Code. 
  The 
  fact 
  that 
  Leske 
  wrote 
  the 
  specific 
  name 
  in 
  two 
  

  

  