﻿Genera 
  of 
  Recent 
  Clypeastroids. 
  603 
  

  

  branched*. 
  This 
  group 
  has 
  long 
  been 
  known 
  as 
  the 
  

   Scutellidae, 
  and 
  while 
  there 
  are 
  obvious 
  reasons 
  why 
  it 
  is 
  

   preferable 
  that 
  the 
  type 
  genus 
  of 
  a 
  family 
  should, 
  if 
  possible, 
  

   be 
  one 
  with 
  Recent 
  species, 
  it 
  would 
  be 
  worse 
  than 
  absurd 
  to 
  

   abandon 
  this 
  ancient 
  and 
  euphonious 
  name 
  for 
  no 
  better 
  

   reason 
  than 
  that 
  all 
  known 
  Scutellas 
  are 
  fossil. 
  

  

  We 
  thus 
  find 
  it 
  desirable 
  to 
  recognize 
  five 
  families, 
  which 
  

   seems 
  like 
  an 
  excessive 
  number 
  for 
  only 
  fifteen 
  genera, 
  

   especially 
  since 
  eight 
  of 
  the 
  genera 
  clearly 
  belong 
  to 
  one 
  

   family. 
  But 
  I 
  do 
  not 
  see 
  how 
  the 
  number 
  can 
  be 
  lessened 
  

   without 
  obscuring 
  real 
  relationships. 
  The 
  Clypeastridse 
  are 
  

   almost 
  certainly 
  the 
  nearest 
  of 
  the 
  families 
  to 
  the 
  original 
  

   stock, 
  and 
  it 
  is 
  not 
  hard 
  to 
  believe 
  that 
  the 
  Laganidse 
  have 
  

   had 
  a 
  common 
  ancestry 
  with 
  them. 
  The 
  Fibulariidae 
  seem 
  

   to 
  have 
  been 
  derived 
  from 
  the 
  Laganidse, 
  or 
  from 
  its 
  near 
  

   ancestor, 
  by 
  a 
  process 
  of 
  simplification. 
  The 
  Arachnoididse 
  are 
  

   certainly 
  an 
  old 
  stock 
  beginning 
  on 
  or 
  near 
  the 
  Clypeastrid 
  

   branch 
  and 
  with 
  no 
  near 
  relatives 
  at 
  the 
  present 
  day. 
  The 
  

   Scutellidse 
  are 
  quite 
  a 
  distinct 
  branch, 
  though 
  their 
  origin 
  is 
  

   probably 
  very 
  near 
  that 
  of 
  the 
  Laganidae, 
  if 
  not 
  identical 
  

   with 
  it. 
  

  

  The 
  five 
  families 
  and 
  their 
  constituent 
  genera 
  may 
  be 
  

   distinguished 
  by 
  the 
  following 
  key. 
  For 
  convenience 
  I 
  have 
  

   included 
  Scutella, 
  the 
  type 
  genus 
  of 
  the 
  Scutellidse, 
  although 
  

   it 
  contains 
  no 
  Recent 
  species. 
  

  

  Auricles 
  separate, 
  each 
  placed 
  more 
  or 
  less 
  clearly 
  on 
  

   the 
  ambulacrum. 
  

   Test 
  uot 
  discoidal 
  and 
  seldom 
  very 
  flat 
  ; 
  anus 
  not 
  

   supra-marginal 
  ; 
  genital 
  pores 
  5. 
  (Clype- 
  

  

  ASTKIDiE.) 
  

  

  Poriferous 
  areas 
  of 
  petals 
  divergent, 
  not 
  incurved 
  

  

  distally 
  ; 
  anus 
  marginal 
  Anomolanthus. 
  

  

  Poriferous 
  areas 
  of 
  petals 
  more 
  or 
  less 
  incurved 
  

  

  distally 
  ; 
  anus 
  submarginal 
  Clypeaster. 
  

  

  Test 
  exceedingly 
  flat, 
  discoidal 
  ; 
  anus 
  supra- 
  

   marginal 
  ; 
  genital 
  pores 
  4. 
  (Arachnoidid^;.) 
  

  

  With 
  characters 
  of 
  the 
  family 
  Arachnoides. 
  

  

  Auricles 
  more 
  or 
  less 
  fully 
  fused 
  into 
  a 
  single 
  piece, 
  

   situated 
  on 
  the 
  interambulacrum. 
  

   Actinal 
  ambulacral 
  furrows 
  short 
  and 
  indistinct 
  or 
  

  

  * 
  They 
  are 
  not 
  branched 
  in 
  Alexandria, 
  and 
  often 
  only 
  indistinctly 
  so 
  

   in 
  Echinarachnius. 
  Duncan's 
  suggestion 
  that 
  Alexandria 
  " 
  appears 
  to 
  

   be 
  an 
  Arachnoides 
  with 
  a 
  posterior 
  notch 
  " 
  indicates 
  that 
  he 
  neither 
  read 
  

   Pfeffer's 
  description 
  nor 
  examined 
  carefully 
  the 
  photograph 
  given, 
  in 
  

   which 
  the 
  interambulacra 
  may 
  be 
  seen 
  to 
  be 
  continuous. 
  

  

  40* 
  

  

  