﻿^°1- 
  53'] 
  AFFINITIES 
  OF 
  THE 
  ECHI3T0THURID.E. 
  113 
  

  

  the 
  echini 
  of 
  the 
  present 
  seas 
  with 
  certain 
  of 
  those 
  genera 
  which 
  

   existed 
  during 
  Palaeozoic 
  times.' 
  x 
  

  

  The 
  view 
  of 
  the 
  close 
  affinity 
  of 
  the 
  Echinothuridae 
  with 
  the 
  

   Palaeozoic 
  ' 
  Perischoechinidae' 
  was 
  not 
  allowed 
  to 
  pass 
  unchallenged. 
  

   It 
  was 
  denied 
  by 
  the 
  late 
  W. 
  Keeping, 
  2 
  from 
  a 
  study 
  of 
  the 
  fossil 
  

   forms, 
  and 
  by 
  Prof. 
  E. 
  J. 
  Bell 
  3 
  in 
  his 
  classification 
  of 
  the 
  recent 
  

   families. 
  Pell, 
  however, 
  still 
  regarded 
  the 
  gap 
  between 
  the 
  Echino- 
  

   thuridae 
  and 
  other 
  ectobranchiate 
  echinids 
  as 
  very 
  marked. 
  He 
  

   included 
  the 
  family 
  in 
  his 
  Ectobranchiata, 
  which 
  he 
  divided 
  into 
  

   two 
  series 
  : 
  one 
  of 
  these, 
  the 
  Neoproctous, 
  included 
  all 
  regular 
  

   echinids 
  except 
  the 
  Cidaridae 
  and 
  Saleniidae 
  ; 
  it 
  was 
  subdivided 
  

   into 
  two 
  subseries, 
  the 
  ' 
  polylepid,' 
  including 
  only 
  the 
  Echino- 
  

   thuridae, 
  and 
  the 
  ' 
  decalepid,' 
  containing 
  all 
  the 
  rest. 
  

  

  Prof. 
  A. 
  Agassiz, 
  about 
  the 
  same 
  time, 
  also 
  clearly 
  recognized 
  

   the 
  affinity 
  of 
  the 
  Echinothuridae 
  with 
  the 
  typical 
  families 
  of 
  living 
  

   ectobranchiate 
  echinids. 
  He 
  even 
  remarked 
  4 
  that 
  ' 
  it 
  is 
  difficult 
  

   to 
  separate 
  this 
  group 
  of 
  echinids 
  as 
  a 
  distinct 
  family 
  from 
  the 
  

   Diadematidae.' 
  But 
  he 
  counteracted 
  this 
  advanced 
  view 
  and 
  gave 
  

   great 
  encouragement 
  to 
  the 
  older 
  hypothesis 
  by 
  the 
  remark 
  ' 
  that 
  

   the 
  Palaechinidae 
  are 
  far 
  more 
  closely 
  allied 
  to 
  the 
  recent 
  echinids 
  

   than 
  is 
  usually 
  supposed, 
  and 
  that 
  we 
  have 
  in 
  the 
  recent 
  Echino- 
  

   thuridae 
  structural 
  features 
  combining 
  the 
  characteristics 
  of 
  the 
  

   normal 
  Desmosticha 
  and 
  of 
  the 
  Palaechinidae.' 
  5 
  

  

  This 
  view 
  received 
  its 
  most 
  definite 
  exposition 
  in 
  an 
  important 
  

   memoir 
  by 
  the 
  cousins 
  P. 
  & 
  F. 
  Sarasin, 
  6 
  published 
  in 
  1888. 
  

   These 
  authors, 
  impressed 
  by 
  many 
  remarkable 
  features 
  in 
  the 
  

   anatomy 
  of 
  a 
  new 
  species 
  of 
  Asthenosoma 
  (A. 
  urens), 
  claimed 
  that 
  

   the 
  Echinothuridae 
  are 
  the 
  most 
  primitive 
  of 
  living 
  Echinoidea, 
  and 
  

   established 
  the 
  origin 
  of 
  this 
  class 
  from 
  an 
  holotburoid 
  ancestor. 
  

   They 
  laid 
  especial 
  stress 
  on 
  the 
  great 
  size 
  of 
  the 
  ' 
  Stewart's 
  organs,' 
  

   on 
  the 
  presence 
  of 
  a 
  series 
  of 
  powerful 
  radial 
  muscles, 
  and 
  on 
  the 
  

   absence 
  of 
  the 
  supposed 
  calycinal 
  system 
  of 
  plates. 
  Bell, 
  7 
  however, 
  

   showed 
  in 
  1889 
  that 
  both 
  the 
  ' 
  Stewart's 
  organs 
  ' 
  and 
  radial 
  muscles 
  

   are 
  absent 
  or 
  rudimentary 
  in 
  the 
  genus 
  Phormosoma, 
  and 
  that 
  these 
  

   organs 
  therefore 
  do 
  not 
  possess 
  the 
  importance 
  attached 
  to 
  them 
  

   by 
  the 
  Sarasins. 
  

  

  1 
  ' 
  On 
  the 
  Eelationship 
  existing 
  between 
  the 
  Echinothuridas, 
  Wyv. 
  Thorns., 
  

   and 
  the 
  Perischoechinidge, 
  M'Coy,' 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxx. 
  (1874) 
  

   pp. 
  307-315, 
  & 
  pi. 
  xxiv. 
  

  

  2 
  ' 
  Notes 
  on 
  the 
  Paleeozoic 
  Echini/ 
  ibid. 
  vol. 
  xxxii. 
  (1876) 
  p. 
  40. 
  

  

  3 
  ' 
  Observations 
  on 
  the 
  Characters 
  of 
  the 
  Echinoidea. 
  pt. 
  iv. 
  : 
  The 
  Echino- 
  

   metridae; 
  their 
  Affinities 
  and 
  Systematic 
  Position,' 
  Proc. 
  Zool. 
  Soc. 
  1881, 
  

   p. 
  417. 
  

  

  4 
  'Report 
  on 
  the 
  Echinoidea,' 
  Challenger 
  Exped., 
  Zool. 
  vol. 
  iii. 
  (1881) 
  

   p. 
  71. 
  

  

  5 
  Ibid. 
  p. 
  81. 
  

  

  6 
  ' 
  Ueber 
  die 
  Anatomie 
  der 
  Echinothuriden 
  u. 
  die 
  Phylogenie 
  der 
  Echino- 
  

   dermen,' 
  Ergebn. 
  naturw. 
  Forsch. 
  auf 
  Ceylon, 
  vol. 
  i. 
  (1888) 
  pp. 
  83-151. 
  

  

  7 
  ' 
  Report 
  of 
  a 
  Deep-Sea 
  Trawling 
  Cruise 
  off 
  the 
  S.W. 
  Coast 
  of 
  Ireland 
  

   under 
  the 
  direction 
  of 
  Rev. 
  W. 
  Spotswood 
  Green. 
  Echinodermata,' 
  by 
  F. 
  J. 
  

   Bell, 
  Ann. 
  Mag. 
  Nat. 
  Hist. 
  ser. 
  6, 
  vol. 
  iv. 
  (1889) 
  pp. 
  436-438. 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  209. 
  t 
  

  

  