﻿500 
  H. 
  ALLEYNE 
  NICHOLSON 
  ON 
  SPECIES 
  OE 
  CHiETETES 
  

  

  examples 
  are 
  concerned, 
  though 
  the 
  occurrence 
  of 
  Stenopora 
  fibrosa 
  

   has 
  been 
  often 
  quoted, 
  I 
  have 
  vainly 
  sought 
  for 
  any 
  specimens 
  

   which 
  I 
  could 
  refer 
  to 
  this 
  genus. 
  The 
  periodically 
  constricted 
  

   tubes, 
  contracted 
  in 
  planes 
  parallel 
  with 
  the 
  surface, 
  do 
  not 
  form 
  a 
  

   feature 
  in 
  any 
  of 
  our 
  specimens. 
  The 
  existence 
  of 
  tubercles 
  and 
  

   granules 
  on 
  the 
  bounding-ridges 
  of 
  the 
  calices 
  can 
  be 
  observed 
  in 
  

   undoubted 
  species 
  of 
  Chcetetes 
  (Monticulipora), 
  such 
  as 
  C. 
  Jamesi, 
  

   Nich., 
  and 
  C. 
  Ortoni, 
  Nich. 
  A 
  Devonian 
  species, 
  0. 
  monilifera, 
  

   Nich., 
  though 
  in 
  other 
  respects 
  agreeing 
  entirely 
  with 
  Chcetetes, 
  

   carries 
  a 
  series 
  of 
  vertical 
  spines 
  which 
  project 
  above 
  the 
  surface 
  

   from 
  all 
  the 
  angles 
  of 
  the 
  calices 
  ; 
  and 
  I 
  have 
  observed 
  the 
  same 
  

   feature 
  in 
  an 
  undescribed 
  species 
  from 
  the 
  Trenton 
  Limestone. 
  

   Lastly, 
  all 
  the 
  forms 
  which 
  I 
  have 
  examined 
  from 
  the 
  Silurian 
  and 
  

   Devonian 
  rocks 
  of 
  America, 
  with 
  the 
  single 
  exception 
  of 
  a 
  large 
  

   lobate 
  form 
  from 
  the 
  Trenton 
  Limestone, 
  have 
  the 
  outer 
  walls 
  of 
  

   the 
  corallites 
  exposed 
  by 
  a 
  rough 
  fracture, 
  and 
  may 
  thus 
  be 
  sup- 
  

   posed 
  to 
  increase 
  by 
  lateral 
  budding. 
  Taking 
  this 
  character 
  alone, 
  

   therefore, 
  they 
  would 
  all 
  have 
  to 
  be 
  referred 
  to 
  the 
  genus 
  Stenopora, 
  

   though 
  in 
  other 
  respects 
  not 
  agreeing 
  with 
  it, 
  but 
  with 
  Chcetetes 
  

   or 
  Monticulipora. 
  

  

  The 
  genera 
  Chcetetes, 
  Fischer, 
  and 
  Monticulipora, 
  D'Orbigny, 
  save 
  

   in 
  one 
  point 
  to 
  be 
  discussed 
  immediately, 
  are 
  identical 
  with 
  one 
  

   another, 
  and 
  may 
  be 
  briefly 
  defined 
  as 
  including 
  ramose, 
  frondescent, 
  

   massive, 
  or 
  incrusting 
  corals, 
  composed 
  of 
  closely 
  aggregated, 
  poly- 
  

   gonal, 
  circular 
  or 
  subcircular 
  corallites, 
  which 
  are 
  traversed 
  by 
  well- 
  

   developed 
  tabulae, 
  and 
  which 
  may 
  or 
  may 
  not 
  be 
  separated 
  by 
  very 
  

   minute 
  intermediate 
  tubuli. 
  No 
  mural 
  pores. 
  Septa 
  absent 
  or 
  

   quite 
  rudimentary. 
  

  

  The 
  point 
  by 
  which 
  it 
  has 
  been 
  attempted 
  to 
  separate 
  Chaztetes 
  

   and 
  Monticulipora 
  is 
  the 
  mode 
  of 
  increase 
  of 
  the 
  coral, 
  which 
  is 
  

   stated 
  to 
  be 
  by 
  fission 
  in 
  Chcetetes 
  and 
  by 
  lateral 
  gemmation 
  in 
  

   Monticulipora, 
  the 
  corallum 
  in 
  the 
  two 
  genera 
  being 
  in 
  other 
  respects 
  

   precisely 
  similar. 
  It 
  seems 
  to 
  me, 
  however, 
  that 
  it 
  is 
  a 
  pity 
  to 
  

   attempt 
  to 
  found 
  a 
  generic 
  distinction 
  upon 
  this 
  point 
  alone, 
  and 
  for 
  

   the 
  following 
  reasons 
  : 
  — 
  In 
  the 
  first 
  place, 
  even 
  if 
  other 
  objections 
  

   were 
  removed, 
  and 
  the 
  distinction 
  could 
  be 
  shown 
  to 
  be 
  constant, 
  it 
  

   might 
  be 
  doubted 
  if 
  this 
  character 
  alone 
  should 
  be 
  regarded 
  as 
  of 
  

   more 
  than 
  subgeneric 
  value. 
  Secondly, 
  the 
  character 
  is 
  one 
  under 
  

   the 
  best 
  of 
  circumstances 
  difficult 
  of 
  determination, 
  as 
  shown 
  by 
  the 
  

   fact 
  that 
  very 
  eminent 
  palaeontologists 
  have 
  come 
  to 
  precisely 
  oppo- 
  

   site 
  conclusions 
  as 
  to 
  the 
  mode 
  of 
  growth 
  of 
  the 
  corallum 
  of 
  the 
  

   same 
  species. 
  Thus 
  Lonsdale 
  regards 
  Chcetetes 
  petropolitanus 
  as 
  

   increasing 
  fissiparously, 
  and 
  places 
  it 
  accordingly 
  ; 
  whereas 
  Milne 
  - 
  

   Edwards 
  and 
  Haime 
  regard 
  the 
  same 
  species 
  as 
  increasing 
  by 
  gem- 
  

   mation, 
  and 
  refer 
  it 
  to 
  Monticulipora. 
  Thirdly, 
  in 
  a 
  great 
  many 
  

   specimens 
  of 
  all 
  the 
  species 
  the 
  distinction 
  in 
  question 
  is 
  one 
  which 
  

   it 
  is 
  impossible 
  to 
  apply 
  ; 
  and 
  in 
  some 
  cases 
  this 
  is 
  true 
  of 
  all 
  the 
  

   examples. 
  Thus, 
  in 
  the 
  exceedingly 
  thin 
  incrusting 
  species 
  the 
  

   mode 
  of 
  growth 
  cannot 
  be 
  satisfactorily 
  determined 
  ; 
  and 
  one 
  meets 
  

   with 
  numerous 
  examples 
  of 
  the 
  ramose, 
  frondescent, 
  or 
  massive 
  

  

  