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  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  1. 
  Trachyderma 
  serrata. 
  PI. 
  XV. 
  fig. 
  9. 
  

  

  Tube 
  cylindrical, 
  strongly 
  corrugated 
  by 
  irregular 
  transverse 
  

   ridges, 
  which 
  are 
  closely 
  set 
  in 
  some 
  portions 
  and 
  irregularly 
  remote 
  

   at 
  others 
  (see 
  fig. 
  9 
  a). 
  As 
  the 
  tube 
  grows 
  larger, 
  it 
  appears 
  (fig. 
  9 
  b) 
  

   to 
  lose 
  the 
  regular 
  transverse 
  ridges, 
  and 
  to 
  be 
  furnished 
  only 
  with 
  

   irregular 
  rugae 
  or 
  varices 
  of 
  growth, 
  but 
  rather 
  closely 
  set. 
  These 
  

   varices 
  are 
  roughly 
  trumpet-shaped 
  upwards, 
  and 
  where 
  the 
  tube 
  is 
  

   perfect 
  (fig. 
  9 
  a) 
  expand 
  into 
  wide-spreading 
  lamellae, 
  which 
  stand 
  

   out 
  at 
  right 
  angles 
  for 
  a 
  distance 
  equal 
  to 
  about 
  half 
  the 
  diameter 
  of 
  

   the 
  tube 
  itself; 
  they 
  are 
  of 
  various 
  sizes, 
  and 
  occur 
  at 
  intervals 
  

   corresponding 
  to 
  the 
  irregular 
  rings 
  or 
  varices 
  from 
  which 
  they 
  take 
  

   their 
  rise. 
  Only 
  the 
  two 
  specimens 
  here 
  figured 
  have 
  yet 
  been 
  

   observed; 
  but 
  it 
  is 
  probably 
  a 
  very 
  common 
  fossil. 
  It 
  is 
  nearly 
  

   half 
  an 
  inch 
  in 
  diameter. 
  

  

  I 
  do 
  not 
  attempt 
  to 
  identify 
  this 
  with 
  either 
  of 
  M. 
  Rouault's 
  

   species 
  of 
  Tigillites 
  (Bull. 
  Soc. 
  Geol. 
  Fr. 
  2nd 
  ser. 
  vol. 
  vii. 
  p. 
  741, 
  &c), 
  

   though 
  it 
  is 
  quite 
  possible 
  the 
  T. 
  Dufrenoyi 
  is 
  a 
  tube 
  formed 
  by 
  a 
  

   larger 
  but 
  closely 
  allied 
  species. 
  T. 
  Danielii 
  would 
  be 
  about 
  the 
  

   same 
  diameter 
  (^- 
  inch), 
  but 
  its 
  surface 
  is 
  not 
  described. 
  Nor 
  do 
  I 
  

   think 
  the 
  genus 
  Tigillites 
  necessary, 
  as, 
  if 
  not 
  referable 
  to 
  Trachy- 
  

   derma, 
  the 
  genus 
  Scolithus, 
  Hall, 
  would 
  receive 
  them. 
  

  

  I 
  think 
  M. 
  Rouault's 
  genus 
  Humilis 
  can 
  only 
  be 
  the 
  filled-up 
  

   crossing 
  and 
  anastomosing 
  burrows 
  of 
  marine 
  worms. 
  His 
  genus 
  

   Tigillites 
  is 
  the 
  vertical 
  burrow 
  ; 
  Foralites 
  comprises 
  the 
  less 
  regular 
  

   perforations 
  among 
  the 
  vegetable 
  masses 
  ; 
  and 
  Vermiculites, 
  as 
  its 
  

   name 
  implies, 
  are 
  the 
  irregular 
  surface-markings 
  produced 
  by 
  other 
  

   animals 
  of 
  the 
  same 
  order. 
  

  

  CRUSTACEA. 
  

  

  Of 
  Trilobites 
  we 
  have 
  only 
  four 
  species, 
  but 
  three 
  are 
  characteristic 
  

   of 
  the 
  May 
  Sandstone 
  group 
  of 
  Normandy. 
  The 
  well-known 
  Homalo- 
  

   notus 
  Brongniarti 
  and 
  Calymene 
  Tristani 
  occur 
  here, 
  with 
  the 
  

   Phacops 
  incertus. 
  I 
  need 
  hardly 
  describe 
  these, 
  but 
  offer 
  a 
  few 
  ex- 
  

   planatory 
  notes 
  on 
  each. 
  

  

  1. 
  Homalonotus 
  Brongniarti, 
  Deslongchamps. 
  PI. 
  XV. 
  fig. 
  1 
  (and 
  

   fig. 
  2?). 
  

  

  Asaplius 
  Brongniartii, 
  Deslongch. 
  Trans. 
  Linn. 
  Soc. 
  de 
  Calvados, 
  

   1825, 
  vol. 
  ii. 
  pis. 
  19, 
  20. 
  

  

  Homalonotus 
  Brongniartii, 
  Rouault, 
  Bull. 
  Soc. 
  Geol. 
  Fr. 
  2nd 
  ser. 
  

   vol. 
  vi., 
  1849 
  ; 
  vol. 
  viii. 
  p. 
  370, 
  1850. 
  

  

  Although 
  Deslongchamps's 
  figures 
  are 
  not 
  quite 
  so 
  perfect 
  as 
  they 
  

   would 
  be 
  in 
  these 
  critical 
  days, 
  there 
  is 
  no 
  difficulty 
  in 
  recognizing 
  

   the 
  species 
  so 
  carefully 
  illustrated 
  by 
  him. 
  He 
  gives 
  us 
  a 
  large 
  

   Trilobite, 
  fully 
  9 
  inches 
  long, 
  and 
  has 
  figured 
  every 
  portion 
  but 
  the 
  

   labrum. 
  The 
  parabolic 
  glabella, 
  convex 
  front 
  border 
  (" 
  chaperon 
  ") 
  

   separated 
  by 
  furrows 
  from 
  the 
  equally 
  convex 
  cheeks, 
  the 
  small 
  

   eye 
  placed 
  far 
  back, 
  the 
  body 
  strongly 
  trilobed 
  for 
  the 
  genus, 
  and 
  

   the 
  smooth 
  contour 
  of 
  the 
  rhomboidal 
  tail 
  are 
  all 
  well 
  shown. 
  In 
  

  

  