﻿Mr. 
  J. 
  W. 
  Gregory 
  on 
  Zeuglopleurus. 
  497 
  

  

  1840. 
  Echinopsis 
  pusilla, 
  Bronn, 
  not 
  E. 
  pusilla, 
  Rcem., 
  of 
  Forbes, 
  

  

  Desor, 
  &c. 
  

   1883. 
  Echinocyphus 
  pisum, 
  Schliiter, 
  " 
  Die 
  regularen 
  Echinideri 
  der 
  

  

  norddeutschen 
  Kreide," 
  Abhandl. 
  geol. 
  Specialkarte 
  v. 
  Preussen 
  und 
  

  

  den 
  Thviringischen 
  Staaten, 
  Bd. 
  iv. 
  Heft. 
  1 
  (Berlin, 
  1883), 
  pp. 
  41), 
  

  

  50. 
  

  

  Rcemer 
  defined* 
  Agassiz's 
  genus 
  Echinopsis 
  as 
  " 
  Wie 
  Ar- 
  

   bacia, 
  aber 
  die 
  Zwischenfehlerfelder 
  mit 
  einer 
  Langsfiirche;" 
  

   and 
  of 
  this 
  he 
  described 
  a 
  new 
  species, 
  E. 
  pusilla. 
  Only 
  four 
  

   lines 
  above 
  this 
  he 
  described 
  E. 
  radiatus, 
  Kon., 
  which 
  he 
  

   referred 
  to 
  a 
  different 
  genus 
  and 
  group 
  of 
  genera, 
  and 
  recog- 
  

   nizing 
  such 
  structural 
  differences 
  between 
  them 
  as 
  to 
  pre- 
  

   clude 
  the 
  necessity 
  for 
  closer 
  comparison. 
  Bronn, 
  in 
  the 
  

   same 
  year 
  f 
  , 
  adopted 
  Rcemer's 
  decision 
  and 
  kept 
  Arbacia 
  ra- 
  

   diata 
  (Kon.) 
  and 
  Echinopsis 
  pusilla, 
  Rcem., 
  as 
  quite 
  sepa- 
  

   rate. 
  Geinitz 
  in 
  1850 
  took 
  J 
  exactly 
  the 
  same 
  position. 
  

   Forbes 
  in 
  1850 
  § 
  described 
  the 
  abactinal 
  figure 
  of 
  his 
  so- 
  

   called 
  Glypticus 
  Konincki 
  (really 
  a 
  Lower 
  Oolite 
  species) 
  as 
  

   E. 
  pusilla, 
  Rcem., 
  though 
  the 
  structure 
  of 
  the 
  abactinal 
  sur- 
  

   face 
  is 
  quite 
  different 
  ; 
  his 
  specimen, 
  now 
  in 
  the 
  British 
  

   Museum, 
  is 
  a 
  true 
  Ghjphocyphus 
  radiatus. 
  Bronn 
  in 
  1852 
  |j, 
  

   possibly 
  trusting 
  to 
  the 
  accuracy 
  of 
  Forbes's 
  identifica- 
  

   tion, 
  gave 
  a 
  figure 
  resembling 
  that 
  of 
  Forbes 
  which 
  he 
  also 
  

   referred 
  to 
  E. 
  pusilla, 
  Rcem. 
  ; 
  but 
  in 
  both 
  these 
  cases 
  all 
  the 
  

   radials 
  enter 
  the 
  anal 
  ring, 
  and 
  thus 
  are 
  true 
  Glyphocyphus. 
  

   Desor 
  followed 
  these 
  authors, 
  and 
  henceforth 
  E. 
  pusilla, 
  Rcem., 
  

   appears 
  in 
  all 
  lists 
  of 
  the 
  synonyms 
  of 
  G. 
  radiatus. 
  Unsatis- 
  

   factory 
  though 
  Rcemer's 
  figure 
  may 
  be 
  as 
  to 
  general 
  details, 
  

   it 
  clearly 
  shows 
  the 
  structure 
  of 
  the 
  apical 
  disk, 
  in 
  which 
  only 
  

   two 
  radials 
  enter 
  the 
  anal 
  ring, 
  the 
  others 
  being 
  excluded 
  by 
  

   the 
  ingrowth 
  of 
  the 
  paired 
  basals, 
  as 
  in 
  Zeuglopleurus. 
  

  

  We 
  must 
  therefore 
  conclude 
  that 
  Rcemer 
  was 
  fully 
  justified 
  

   in 
  separating 
  his 
  species 
  from 
  E. 
  radiatus, 
  and 
  it 
  only 
  remains 
  

   to 
  consider 
  its 
  differences 
  from 
  Z. 
  costulatus. 
  It 
  differs 
  from 
  

   this, 
  so 
  far 
  as 
  Rcemer's 
  figure 
  and 
  description 
  enable 
  us 
  to 
  

   compare 
  them, 
  in 
  several 
  important 
  points 
  : 
  thus 
  the 
  base 
  is 
  

   much 
  flatter 
  and 
  the 
  abactinal 
  side 
  more 
  conical 
  ; 
  the 
  central 
  

   part 
  of 
  the 
  apical 
  disk 
  is 
  raised, 
  so 
  that 
  on 
  a 
  posterior 
  eleva- 
  

  

  * 
  ' 
  Die 
  Versteinerungen 
  des 
  norddeutschen 
  Kreidegebirges 
  ' 
  (Han- 
  

   over, 
  1840), 
  p. 
  30, 
  pi. 
  vi. 
  tig. 
  10. 
  

  

  t 
  ' 
  Index 
  palseontologicus, 
  A. 
  Nomenclator 
  paleeontologicus,' 
  Heft 
  i. 
  

   pp. 
  91 
  and 
  447 
  (Stuttgart, 
  1848). 
  

  

  % 
  ' 
  Das 
  Quadersandsteingebirge 
  oder 
  Kreidegebirge 
  in 
  Deutschland 
  ' 
  

   (Freiburg, 
  1850), 
  pp. 
  222, 
  223. 
  

  

  § 
  Forbes, 
  loc. 
  cit. 
  p. 
  340, 
  pi. 
  xxv. 
  fig. 
  31. 
  

  

  || 
  ' 
  Lethsea 
  geognostica,' 
  Bd. 
  ii. 
  Th. 
  v. 
  (Stuttgart, 
  1852), 
  p. 
  187, 
  

   pi. 
  xxix. 
  7 
  tigs. 
  1) 
  a, 
  b. 
  

  

  