﻿Vol. 
  53-] 
  OF 
  THE 
  CHALK 
  ROCK. 
  387 
  

  

  near 
  the 
  middle 
  of 
  the 
  valve 
  is 
  about 
  three 
  times 
  the 
  thickness 
  of 
  

   the 
  outer 
  layer 
  ; 
  it 
  possesses 
  an 
  indistinct 
  and 
  irregular 
  prismatic 
  

   structure, 
  but 
  a 
  high 
  power 
  shows 
  two 
  sets 
  of 
  fibres 
  crossing 
  each 
  

   other 
  obliquely 
  ; 
  this 
  layer 
  is 
  traversed 
  by 
  numerous 
  parallel 
  tubes 
  

   placed 
  at 
  right 
  angles 
  to 
  the 
  surface, 
  but 
  at 
  the 
  umbo, 
  where 
  the 
  

   shell 
  is 
  thicker, 
  they 
  radiate 
  outward 
  so 
  as 
  to 
  become 
  perpendicular 
  

   to 
  the 
  outside 
  of 
  the 
  shell. 
  This 
  layer 
  thins 
  out 
  on 
  the 
  area 
  towards 
  

   the 
  hinge-line. 
  The 
  teeth 
  and 
  the 
  main 
  part 
  of 
  the 
  area 
  are 
  formed 
  

   of 
  large 
  distinct 
  prisms 
  placed 
  more 
  or 
  less 
  parallel 
  to 
  the 
  surface, 
  

   but 
  bending 
  inward, 
  and 
  they 
  are 
  crossed 
  obliquely 
  by 
  tubules. 
  

   On 
  the 
  outer 
  surface 
  of 
  the 
  area 
  is 
  a 
  thin 
  layer 
  which 
  tapers 
  in 
  

   passing 
  from 
  the 
  hinge-line, 
  and 
  is 
  absent 
  in 
  the 
  neighbourhood 
  

   of 
  the 
  umbo 
  ; 
  this 
  layer 
  has 
  a 
  finer 
  structure, 
  and 
  under 
  a 
  high 
  

   power 
  appears 
  to 
  be 
  fibrous 
  ; 
  it 
  is 
  not 
  traversed 
  by 
  tubules. 
  

  

  Distribution. 
  — 
  England 
  : 
  in 
  the 
  upper 
  part 
  of 
  the 
  Middle 
  Chalk 
  

   (namely 
  : 
  zones 
  of 
  Terebratulina 
  gracilis, 
  Holaster 
  planus, 
  & 
  Hetero- 
  

   ceras 
  Reussianum), 
  and 
  throughout 
  the 
  Upper 
  Chalk. 
  Chalk 
  Rock 
  

   (Reussianwn-zone) 
  of 
  Shalcombe 
  and 
  Brixton 
  (Isle 
  of 
  Wight), 
  Win- 
  

   chester, 
  Cuckhamsley, 
  Bledlow, 
  Wycombe, 
  Princes 
  Eisborough, 
  Box- 
  

   moor, 
  Luton, 
  Reed, 
  Barkway, 
  Great 
  Chesterford, 
  Westley 
  Waterless, 
  

   and 
  Underwood 
  Hall 
  near 
  Dullingham. 
  Ireland 
  : 
  Hibernian 
  Green- 
  

   sand 
  (Chloritic 
  Sandstone 
  division) 
  and 
  White 
  Limestone. 
  France 
  : 
  

   zone 
  of 
  Inoceramus 
  labiatus 
  at 
  Joigny 
  (Yonne), 
  etc. 
  ; 
  zone 
  of 
  Tere- 
  

   bratulina 
  gracilis 
  at 
  Hauteville, 
  Cyosing, 
  in 
  theYonne 
  and 
  Aube, 
  etc. 
  

   zone 
  of 
  Micraster 
  breviporus 
  of 
  Cambrai, 
  and 
  at 
  Partout 
  (Yonne) 
  , 
  

   zone 
  of 
  Holaster 
  planus, 
  east 
  of 
  the 
  Paris 
  basin 
  ; 
  zone 
  of 
  Epiaster 
  

   brevis 
  at 
  Guise, 
  etc. 
  ; 
  zones 
  of 
  Spondylus 
  spinosus 
  and 
  Sp. 
  truncatus 
  

   in 
  Loir-et-Cher 
  ; 
  zone 
  of 
  Micraster 
  cor-anguinum 
  at 
  Lezennes. 
  

   Belgium 
  : 
  Hervien 
  of 
  Limbourg. 
  North-ivestern 
  Germany 
  : 
  zone 
  of 
  

   Heteroccras 
  Reussianum 
  in 
  Westphalia. 
  Saxony 
  : 
  Planer-Kalk 
  of 
  

   Strehlen, 
  Weinbohla, 
  etc. 
  ; 
  ^ron^nmr^'-Planer 
  of 
  Cottauer 
  Berge 
  ; 
  

   and 
  the 
  Glauconitic 
  Marl 
  and 
  Planer. 
  Silesia 
  : 
  Scaphites-be&s 
  of 
  

   Oppeln. 
  Bohemia 
  : 
  Weissenberg, 
  Malnitz, 
  and 
  Teplitz 
  Beds. 
  

   Bavaria: 
  Kagerhoh 
  Beds. 
  

  

  SroNDYLus 
  latus 
  (Sowerby), 
  1815. 
  

  

  1815. 
  BiancJwra 
  lata, 
  J. 
  Sowerby, 
  ' 
  Min. 
  Conch.' 
  vol. 
  i. 
  p. 
  184, 
  pi. 
  lxxx. 
  f. 
  2 
  ; 
  

   1822. 
  G. 
  A. 
  Mantell, 
  ' 
  Foss. 
  S. 
  Downs,' 
  p. 
  205, 
  pi. 
  xxvi. 
  f. 
  21. 
  

  

  1822. 
  ? 
  DiancJwra 
  obliqua, 
  G. 
  A. 
  Mantell, 
  'Foss. 
  S. 
  Downs,' 
  p. 
  206, 
  pi. 
  xxv. 
  f 
  . 
  1 
  & 
  

   pi. 
  xxvi. 
  f. 
  12. 
  

  

  1836. 
  Spondylus 
  lineatus, 
  A. 
  Goldfuss, 
  ' 
  Petref. 
  Germ.' 
  vol. 
  ii. 
  pi. 
  cvi. 
  £. 
  3, 
  p. 
  97 
  ; 
  

   1839. 
  H. 
  B. 
  Geinitz, 
  ' 
  Cliar. 
  d. 
  Schichten 
  u. 
  Petref. 
  des 
  sachs. 
  Kreidegeb.' 
  pt. 
  i. 
  p. 
  25 
  

   (pi. 
  xx. 
  f. 
  39?); 
  1841. 
  F. 
  A. 
  Romer, 
  ' 
  Die 
  Verstein. 
  des 
  norddeutsch. 
  Kreidegeb.' 
  

   p. 
  59 
  ; 
  1846. 
  A. 
  E. 
  Reuss, 
  ' 
  Die 
  Verstein. 
  der 
  bohm. 
  Kreideformat.' 
  pt. 
  ii. 
  p. 
  36, 
  pi. 
  xl. 
  

   f. 
  7-9 
  ; 
  1847. 
  J. 
  Muller, 
  ' 
  Petref. 
  der 
  Aachener 
  Kreideformat.' 
  pt. 
  i. 
  p. 
  34; 
  1850. 
  H. 
  

   B. 
  Geinitz, 
  ' 
  Das 
  Quadersandsteingeb. 
  in 
  Deutschl.' 
  p. 
  194 
  (partim) 
  ; 
  1850. 
  A. 
  

   d'Orbigny, 
  ' 
  Prodr. 
  de 
  Pal.' 
  vol. 
  ii. 
  p. 
  254 
  ; 
  1850? 
  A. 
  Alth, 
  ' 
  Geogn.-pal. 
  Beschreib. 
  

   der 
  nachst. 
  Umgeb. 
  von 
  Lemberg,' 
  Haidinger's 
  Naturwiss. 
  Abbandl. 
  vol. 
  iii. 
  pt. 
  ii. 
  

   p. 
  250; 
  1869? 
  E. 
  Favre, 
  ' 
  Moll. 
  Foss. 
  de 
  la 
  Craie 
  des 
  Envir. 
  de 
  Lemberg,' 
  p. 
  158. 
  

  

  1841. 
  Spondylus 
  latus, 
  F. 
  A. 
  Komer, 
  ' 
  Die 
  Verstein. 
  des 
  norddeutsch. 
  Kreidegeb. 
  

   p. 
  59 
  ; 
  1842. 
  H. 
  B. 
  Geinitz, 
  ' 
  Char. 
  d. 
  Schichten 
  u. 
  Petref. 
  des 
  sachs. 
  -bohm. 
  Kreidegeb. 
  

   pt. 
  iii. 
  p. 
  82 
  ; 
  1850. 
  J. 
  de 
  C. 
  Sowerby 
  in 
  F. 
  Dixon's 
  ' 
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  p. 
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  pi. 
  xxviii; 
  

   f 
  . 
  30 
  & 
  31 
  ; 
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  ed. 
  p. 
  182 
  ; 
  1872. 
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  B. 
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   'Das 
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  in 
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  Paheontographica, 
  vol. 
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  pt. 
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  p. 
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  pi. 
  xlii. 
  f.4-6 
  

  

  2d2 
  

  

  