﻿Vol. 
  53-] 
  

  

  OF 
  THE 
  CHALK 
  ROCK. 
  

  

  397 
  

  

  One 
  of 
  the 
  most 
  noteworthy 
  points 
  in 
  the 
  mollusca 
  of 
  the 
  Reussia- 
  

   num-zone, 
  as 
  compared 
  with 
  those 
  of 
  the 
  Cenomanian, 
  is 
  the 
  rarity 
  in 
  

   the 
  former, 
  of 
  the 
  three 
  families 
  Ostreidas, 
  Pectinidae, 
  and 
  Limidse. 
  

   All 
  three 
  are 
  very 
  important 
  in 
  the 
  Lower 
  Chalk. 
  

  

  Whether 
  the 
  Reussianum-zone 
  should 
  be 
  regarded 
  as 
  the 
  lowest 
  

   zone 
  of 
  the 
  Senonian 
  or 
  the 
  highest 
  of 
  the 
  Turonian 
  appears 
  to 
  me 
  

   to 
  be 
  a 
  point 
  of 
  no 
  great 
  importance. 
  The 
  forms 
  which 
  seem 
  to 
  

   show 
  that 
  its 
  relations 
  are 
  with 
  the 
  lower 
  rather 
  than 
  the 
  higher 
  

   division 
  are 
  Pachy 
  discus 
  peramplus, 
  Crioceras 
  ellipticum, 
  Turbo 
  

   gemmatus, 
  Arctica 
  quadrata, 
  and 
  Holaster 
  planus. 
  Others, 
  however 
  

   — 
  such 
  as 
  Spondylus 
  spinosus, 
  Lima 
  (Plagiostoma) 
  Hoperi, 
  and 
  the 
  

   species 
  of 
  Micr 
  aster, 
  Cardiaster, 
  and 
  Echinocorys, 
  — 
  link 
  it 
  to 
  the 
  

   Senonian. 
  Probably 
  the 
  species 
  of 
  Inoceramus, 
  when 
  fully 
  worked 
  

   out, 
  may 
  furnish 
  some 
  evidence 
  of 
  importance 
  on 
  this 
  point. 
  On 
  

   the 
  whole, 
  I 
  am 
  inclined 
  to 
  think 
  that 
  the 
  affinities 
  of 
  the 
  fauna 
  are 
  

   closer 
  to 
  the 
  Turonian 
  than 
  to 
  the 
  Senonian. 
  

  

  The 
  absence 
  of 
  Crustacea 
  in 
  the 
  Chalk 
  Rock, 
  with 
  the 
  exception 
  

   of 
  a 
  few 
  specimens 
  of 
  Pollicipes, 
  is 
  somewhat 
  remarkable, 
  but 
  the 
  

   rarity 
  of 
  this 
  class 
  of 
  animals 
  in 
  deposits 
  now 
  forming 
  was 
  noticed 
  

   by 
  the 
  Challenger 
  Expedition, 
  1 
  and 
  is 
  attributed 
  to 
  the 
  areolar 
  

   structure 
  of 
  the 
  exoskeleton, 
  ' 
  which 
  admits 
  of 
  relatively 
  rapid 
  

   solution 
  after 
  the 
  death 
  of 
  the 
  animal.' 
  

  

  It 
  may 
  be 
  convenient 
  for 
  reference 
  to 
  give 
  here 
  a 
  list 
  of 
  the 
  

   fossils, 
  other 
  than 
  the 
  mollusca, 
  which 
  are 
  found 
  in 
  the 
  Chalk 
  

   Rock 
  : 
  — 
  

  

  Brachiopoda 
  (cont.). 
  

  

  Terebratula 
  carnea. 
  Sow. 
  

  

  ,, 
  semiglobosa. 
  Sow. 
  

  

  Terebratulina 
  striata 
  (Wahl.). 
  

   Trigonosemus 
  incerta, 
  ? 
  Da 
  v. 
  (? 
  young 
  

   specimen). 
  3 
  

  

  Pisces. 
  

  

  Oxyrhina 
  Mantelli, 
  Ag. 
  2 
  

   Corax 
  falcatus, 
  Ag. 
  

   Ptychodus 
  latissimus, 
  Ag. 
  

   „ 
  manirnillaris, 
  1 
  

  

  ClRRIPEDIA. 
  

  

  Pollicipes 
  sp. 
  

  

  ClI^ETOPODA. 
  

  

  Serpula 
  ampullacea, 
  Sow. 
  

   ,, 
  plexus, 
  Sow. 
  

   ., 
  sp. 
  

  

  Brachiopoda. 
  

  

  Bhynchonella 
  Cuvieri, 
  d'Orb. 
  3 
  

   „ 
  plicatilis 
  (Sow.). 
  

   ,, 
  „ 
  var. 
  Woodwardi, 
  

  

  Dav. 
  

   ,, 
  „ 
  var. 
  octoplicata 
  

  

  (Sow.). 
  

   : 
  s, 
  Eth. 
  

  

  Crinoidea. 
  

   Pentacrinus 
  Agassizi, 
  v. 
  Hagen. 
  

  

  EciIINOIDEA. 
  

  

  Cardiaster 
  ananchytis 
  (Leske) 
  ; 
  ele- 
  

   vated 
  variety. 
  

  

  Cidaris 
  sp. 
  

  

  Cyphosoma 
  radiatum, 
  Sorig. 
  

  

  ,, 
  spatuliferum 
  ?, 
  Forbes. 
  

  

  Echinoconus 
  conicus, 
  Breyn. 
  

  

  Echinocorys 
  vulgaris, 
  Breyn., 
  var. 
  

   gibbus 
  (Lam.). 
  

  

  Holaster 
  planus 
  (Mant.). 
  

  

  Micraster 
  breviporus, 
  Ag. 
  

   ., 
  cor-bovis, 
  Forbes. 
  

  

  1 
  Murray 
  & 
  Renard, 
  Challenger 
  Rep. 
  'Deep-Sea 
  Deposits' 
  (1891), 
  p. 
  264. 
  

  

  2 
  For 
  the 
  determination 
  of 
  this 
  species 
  I 
  am 
  indebted 
  to 
  Mr. 
  A. 
  Smith 
  

   Woodward, 
  F.G.S. 
  

  

  3 
  I 
  am 
  indebted 
  to 
  Mr. 
  J. 
  F. 
  Walker 
  for 
  the 
  determination 
  of 
  these 
  species. 
  

  

  