﻿640 
  MB. 
  J. 
  W. 
  GREGORY 
  02* 
  C 
  YSTEC 
  EXNTTS 
  CRASSTJS 
  

  

  40. 
  Cystechixtts 
  crassus, 
  a 
  new 
  Species 
  from 
  the 
  Badioiarlot 
  Marls 
  

   of 
  Barbados, 
  and 
  the 
  Evidence 
  it 
  affords 
  as 
  to 
  the 
  Age 
  and 
  

   Origin 
  of 
  those 
  Deposits. 
  By 
  J. 
  W. 
  Gregory, 
  Esq., 
  E.G.S., 
  

   E.Z.S., 
  of 
  the 
  British 
  Museum 
  (Natural 
  History). 
  (Bead 
  

   June 
  19, 
  1889.) 
  

  

  The 
  most 
  important 
  addition 
  made 
  by 
  the 
  ' 
  Challenger 
  ' 
  to 
  our 
  

   knowledge 
  of 
  the 
  living 
  Echinoidea 
  was 
  unquestionably 
  the 
  dis- 
  

   covery 
  of 
  those 
  abyssal 
  Spatangoids 
  which 
  are 
  Ethmophract, 
  Meri- 
  

   dosternous, 
  and 
  Adete 
  ; 
  it 
  was 
  the 
  close 
  resemblance 
  of 
  these 
  to 
  

   the 
  Cretaceous 
  Ananchytidse 
  that 
  led 
  to 
  the 
  well-known 
  and 
  oft- 
  

   refuted 
  generalization 
  that 
  we 
  are 
  still 
  living 
  in 
  the 
  age 
  of 
  the 
  

   Chalk. 
  The 
  discovery 
  of 
  a 
  new 
  species 
  of 
  Oystechinus, 
  one 
  of 
  the 
  

   most 
  typical 
  of 
  these 
  genera, 
  in 
  the 
  Badiolarian 
  beds 
  of 
  Barbados 
  

   is 
  therefore 
  of 
  interest 
  ; 
  and 
  this 
  is 
  enhanced 
  by 
  the 
  light 
  it 
  throws 
  

   on 
  the 
  age 
  and 
  horizon 
  of 
  those 
  well-known 
  deposits. 
  

  

  Of 
  the 
  genus 
  Oystechinus 
  Prof. 
  A. 
  Agassiz 
  has 
  only 
  given 
  a 
  com- 
  

   parative 
  diagnosis 
  ; 
  in 
  the 
  original 
  description 
  * 
  he 
  simply 
  states 
  

   that 
  it 
  has 
  the 
  general 
  appearance 
  of 
  Ananchytes, 
  the 
  simple 
  am- 
  

   bulacra! 
  system 
  of 
  the 
  Pourtalesiadas, 
  and 
  an 
  actinostome 
  less 
  

   labiate 
  than 
  in 
  that 
  group. 
  He 
  points 
  out 
  that 
  it 
  serves, 
  with 
  

   the 
  genera 
  Homolampus 
  and 
  Pala?otropus, 
  as 
  a 
  transition 
  from 
  the 
  

   Spatangidse 
  to 
  the 
  Nucleolidae 
  and 
  Echinolampidae. 
  

  

  In 
  the 
  'Challenger' 
  Beport 
  this 
  notice 
  has 
  been 
  somewhat 
  ex- 
  

   panded 
  f. 
  Here 
  the 
  Galeritic 
  features 
  of 
  the 
  subcentral 
  actinostome 
  

   and 
  the 
  position 
  of 
  the 
  anal 
  system, 
  the 
  Ananchytid 
  apical 
  disc, 
  the 
  

   simple 
  pores, 
  the 
  rudimentary 
  auricles, 
  and 
  the 
  proportions 
  of 
  the 
  

   coronal 
  plates 
  in 
  the 
  ambulacra! 
  and 
  interambulacral 
  areas 
  are 
  all 
  

   noticed. 
  But 
  a 
  positive 
  diagnosis 
  is 
  necessary 
  to 
  the 
  worker, 
  as 
  Prof. 
  

   Duncan 
  recently 
  insisted 
  when 
  introducing 
  his 
  Bevision 
  of 
  the 
  Genera 
  

   of 
  Echinoidea 
  to 
  the 
  Linnean 
  Society 
  ; 
  it 
  may 
  therefore 
  be 
  of 
  use 
  to' 
  

   summarize 
  the 
  characters 
  of 
  the 
  genus. 
  I 
  must 
  here 
  express 
  my 
  

   thanks 
  to 
  Prof. 
  Duncan 
  for 
  much 
  kind 
  advice 
  ; 
  to 
  E. 
  A. 
  Bather, 
  Esq., 
  

   for 
  drawing 
  the 
  figures 
  which 
  illustrate 
  the 
  present 
  paper 
  ; 
  and 
  

   to 
  Prof. 
  Jeffrey 
  Bell 
  for 
  his 
  assistance 
  during 
  my 
  examination 
  

   of 
  the 
  ' 
  Challenger 
  ' 
  specimens, 
  without 
  seeing 
  which 
  I 
  should 
  not 
  

   have 
  ventured 
  on 
  this 
  diagnosis. 
  

  

  Cystechintjs, 
  A. 
  Ag., 
  1879. 
  

  

  Test 
  attaining 
  a 
  considerable 
  size, 
  Shape 
  normally 
  oval, 
  depressed 
  

   or 
  subcorneal 
  above, 
  and 
  flat 
  below, 
  but 
  variable, 
  owing 
  to 
  the 
  

   more 
  or 
  less 
  flexible 
  nature 
  of 
  the 
  test. 
  The 
  plates 
  vary 
  in 
  thickness 
  

   from 
  that 
  of 
  ordinary 
  writing-paper 
  to 
  1*5 
  mm. 
  

  

  * 
  A. 
  Agassiz, 
  "' 
  Preliminary 
  Report 
  on 
  the 
  Echini 
  of 
  the 
  Exploring 
  Expe- 
  

   dition 
  of 
  H.M.S. 
  ' 
  Challenger,' 
  " 
  Proc. 
  Anier. 
  Acad. 
  vol. 
  xiv. 
  (Boston, 
  1879), 
  

   pp. 
  207-8. 
  

  

  t 
  A. 
  Agassiz, 
  " 
  Eeport 
  on 
  the 
  Echinoidea 
  dredged 
  by 
  H.M.S. 
  ' 
  Challenger 
  r 
  

   during 
  the 
  years 
  1873-6," 
  ' 
  Challenger 
  ' 
  Reports, 
  Zool. 
  vol. 
  iii. 
  No 
  1 
  (London,. 
  

   1881), 
  p. 
  148. 
  

  

  