﻿112 
  DK. 
  J. 
  W. 
  GREGORY 
  ON 
  THE 
  [Feb. 
  1 
  897, 
  

  

  8. 
  On 
  the 
  Affinities 
  of 
  the 
  Echinothtjkid^: 
  ; 
  and 
  on 
  Pedinothuria. 
  

   and 
  Hellkodiadema, 
  two 
  new 
  Genera 
  of 
  Echinoidea. 
  By 
  

   J. 
  W. 
  Gregory, 
  D.Sc, 
  E.G.S., 
  E.Z.S., 
  Assistant 
  in 
  the 
  Geological 
  

   Department, 
  British 
  Museum. 
  (Read 
  December 
  2nd, 
  1896.) 
  

  

  [Plate 
  VII.] 
  

  

  The 
  genus 
  Echinothuria 
  was 
  founded 
  by 
  S. 
  P. 
  Woodward 
  1 
  in 
  1863 
  

   to 
  include 
  two 
  Chalk 
  fossils 
  in 
  the 
  British 
  Museum 
  (Nat. 
  Hist.). 
  The 
  

   specimen 
  first 
  discovered 
  was 
  found 
  at 
  Rochester, 
  and 
  it 
  was 
  regarded 
  

   as 
  a 
  fossil 
  cirripede 
  until 
  Darwin 
  refused 
  to 
  accept 
  it 
  as 
  a 
  member 
  

   of 
  that 
  class. 
  Ed. 
  Eorbes 
  then 
  proposed 
  to 
  describe 
  it 
  as 
  an 
  holo- 
  

   thurian, 
  but 
  finally 
  declined 
  this 
  responsibility. 
  It 
  was 
  not 
  till 
  the 
  

   second 
  specimen 
  was 
  found 
  at 
  Charlton 
  by 
  the 
  Rev. 
  J. 
  N". 
  Glass 
  that 
  

   the 
  two 
  fossils 
  were 
  recognized 
  as 
  probably 
  fragments 
  of 
  an 
  abnormal 
  

   echinid. 
  S. 
  P. 
  Woodward 
  discussed 
  the 
  possibility 
  of 
  the 
  fossils 
  

   being 
  holothurians 
  or 
  allied 
  to 
  Palaeozoic 
  echinids, 
  such 
  as 
  Proto- 
  

   echinus; 
  but 
  he 
  rejected 
  both 
  ideas, 
  and 
  cautiously 
  described 
  the 
  

   specimens 
  as 
  belonging 
  to 
  a 
  uew 
  genus 
  of 
  echinoderm, 
  of 
  which 
  the 
  

   affinities 
  ' 
  are 
  still 
  matter 
  for 
  conjecture.' 
  He 
  remarked 
  that 
  ' 
  the 
  

   disciples 
  of 
  von 
  Baer 
  may 
  regard 
  it 
  it 
  as 
  a 
  " 
  generalized 
  form 
  " 
  of 
  

   echinoderm 
  ' 
  ; 
  but 
  he 
  shows 
  that 
  he 
  realized 
  one 
  strong 
  objection 
  

   to 
  this 
  view, 
  by 
  pointing 
  out 
  the 
  fact 
  of 
  the 
  fossil 
  ' 
  coming, 
  how- 
  

   ever, 
  rather 
  late 
  in 
  the 
  geological 
  day.' 
  

  

  The 
  importance 
  of 
  the 
  genus 
  Echinothuria 
  was 
  not 
  fully 
  appre- 
  

   ciated 
  until 
  1873. 
  In 
  that 
  year 
  Sir 
  Wyville 
  Thomson 
  2 
  published 
  

   an 
  account 
  of 
  some 
  recent 
  echinids 
  with 
  flexible 
  tests 
  : 
  for 
  one 
  

   series 
  of 
  these 
  he 
  proposed 
  the 
  name 
  Calveria, 
  but 
  this 
  has 
  since 
  

   made 
  way 
  for 
  that 
  of 
  Asthenosoma, 
  which 
  had 
  been 
  given 
  by 
  Grube 
  3 
  

   in 
  1868. 
  Thomson 
  recognized 
  the 
  affinity 
  of 
  the 
  deep-sea 
  species 
  

   with 
  the 
  Chalk 
  fossil, 
  and 
  included 
  both, 
  with 
  a 
  third 
  genus 
  Phor- 
  

   mosoma, 
  in 
  a 
  new 
  family 
  — 
  Echinothuridse. 
  

  

  The 
  possible 
  affinity 
  of 
  these 
  flexible 
  echinids 
  with 
  the 
  Palaeozoic 
  

   genera 
  at 
  once 
  aroused 
  the 
  interest 
  of 
  palaeontologists. 
  Prof. 
  J. 
  

   Young, 
  4 
  in 
  1873, 
  and 
  Mr. 
  R. 
  Etheridge, 
  Jun., 
  in 
  1874, 
  promptly 
  

   called 
  attention 
  to 
  the 
  resemblances 
  between 
  them. 
  The 
  latter 
  

   author 
  welcomed 
  the 
  new 
  genera 
  as 
  throwing 
  light 
  on 
  the 
  relation- 
  

   ship 
  between 
  Palaeozoic 
  and 
  recent 
  Echini, 
  and 
  as 
  serving 
  ' 
  to 
  unite 
  

  

  1 
  ' 
  On 
  Echinothuria 
  floris, 
  a 
  New 
  and 
  Anomalous 
  Echinoderm 
  from 
  the 
  

   Chalk 
  of 
  Kent,' 
  Geologist, 
  vol. 
  vi. 
  (1863) 
  pp. 
  327-330, 
  & 
  pi. 
  xviii. 
  

  

  2 
  ' 
  The 
  Depths 
  of 
  the 
  Sea,' 
  1873, 
  pp. 
  155-159 
  ; 
  ' 
  On 
  the 
  Echinoidea 
  of 
  the 
  

   Porcupine 
  Deep-Sea 
  Dredging 
  Expedition,' 
  Phil. 
  Trans. 
  Boy. 
  Soc. 
  vol. 
  clxiv. 
  

   (1874) 
  pp. 
  730-737. 
  

  

  3 
  ' 
  Asthenosoma 
  varium,n. 
  sp.,' 
  Jahresber. 
  Schles. 
  Gesellsch. 
  Breslau, 
  vol. 
  xlv. 
  

   (1868) 
  pp. 
  42-44. 
  

  

  4 
  ' 
  On 
  a 
  Carboniferous 
  Genus 
  of 
  Echinoderms 
  with 
  Overlapping 
  Plates,' 
  

   Geol. 
  Mag. 
  1873, 
  pp. 
  301-303. 
  

  

  