﻿90 
  Beecher 
  — 
  Natural 
  Classification 
  of 
  the 
  Trilobites. 
  

  

  writer, 
  5 
  where 
  from 
  the 
  facts 
  presented, 
  their 
  intimate 
  relation- 
  

   ships 
  with 
  the 
  Crustacea 
  follow 
  as 
  a 
  necessary 
  corollary. 
  

  

  Previous 
  Classifications. 
  

  

  The 
  various 
  schemes 
  of 
  classification 
  that 
  have 
  been 
  applied 
  

   to 
  the 
  trilobites 
  since 
  that 
  of 
  Brongniart, 
  11 
  in 
  1822, 
  have 
  been 
  

   enlarged 
  and 
  revised 
  by 
  various 
  authors, 
  until, 
  at 
  the 
  present 
  

   time, 
  no 
  particular 
  arrangement 
  of 
  the 
  families 
  or 
  genera 
  can 
  

   be 
  said 
  to 
  be 
  endorsed. 
  The 
  one 
  which 
  is 
  generally 
  recognized 
  

   as 
  manifestly 
  faulty, 
  that 
  of 
  Barrande, 
  3 
  is 
  the 
  one 
  most 
  com- 
  

   monly 
  found 
  in 
  text-books 
  and 
  special 
  memoirs. 
  Barrande's 
  

   definitions 
  and 
  limitations 
  of 
  the 
  generic 
  and 
  family 
  groups 
  

   were 
  natural 
  and 
  accurate, 
  showing 
  a 
  most 
  complete 
  knowledge 
  

   of 
  generic 
  and 
  specific 
  values, 
  but 
  in 
  the 
  grouping 
  and 
  arrange- 
  

   ment 
  of 
  the 
  families, 
  he 
  selected 
  characters 
  of 
  secondary 
  rank. 
  

  

  Of 
  all 
  the 
  investigators 
  who 
  have 
  attempted 
  any 
  classifica- 
  

   tion 
  of 
  the 
  families, 
  J. 
  W. 
  Salter 
  32 
  seems 
  to 
  have 
  had 
  the 
  

   clearest 
  insight 
  into 
  the 
  important 
  value 
  of 
  certain 
  characters, 
  

   and 
  to 
  have 
  approached 
  nearest 
  to 
  a 
  natural 
  system. 
  In 
  zoo- 
  

   logical 
  research, 
  the 
  study 
  of 
  ontogeny 
  and 
  the 
  principles 
  of 
  

   morphogenesis 
  were 
  then 
  scarcely 
  recognized 
  as 
  having 
  any 
  

   direct 
  application. 
  It 
  is 
  quite 
  remarkable, 
  therefore, 
  that 
  

   Salter, 
  as 
  early 
  as 
  1864, 
  should 
  have 
  singled 
  out, 
  as 
  the 
  basis 
  of 
  

   his 
  subdivisions, 
  the 
  characters 
  which 
  are 
  the 
  dominant 
  variants 
  

   in 
  ontogeny. 
  

  

  It 
  is 
  not 
  necessary 
  in 
  this 
  place 
  to 
  discuss 
  all 
  the 
  classifica- 
  

   tions 
  which 
  have 
  been 
  proposed. 
  Barrande 
  3 
  gives 
  a 
  complete 
  

   resume 
  down, 
  to 
  1850, 
  and 
  shows 
  in 
  a 
  very 
  satisfactory 
  manner 
  

   the 
  weak 
  points 
  of 
  each, 
  furnishing 
  strong 
  reasons 
  as 
  to 
  why 
  

   they 
  are 
  unnatural 
  and 
  therefore 
  untenable. 
  The 
  underlying 
  

   principles 
  of 
  these 
  early 
  attempts 
  at 
  a 
  classification 
  are 
  here 
  

   briefly 
  summarized. 
  (1) 
  The 
  first 
  classification 
  of 
  trilobites 
  

   was 
  advanced 
  by 
  Brongniart 
  11 
  in 
  182:4, 
  in 
  which 
  all 
  the 
  forms 
  

   previously 
  known 
  as 
  Eatomolithus 
  paradoxus 
  were 
  shown 
  to 
  

   belong 
  to 
  five 
  distinct 
  genera. 
  (2) 
  Dalman, 
  16 
  in 
  1826, 
  made 
  

   two 
  groups 
  based 
  upon 
  the 
  presence 
  or 
  absence 
  of 
  eyes. 
  (3) 
  

   Quenstedt, 
  30 
  in 
  1837, 
  recognized 
  the 
  number 
  of 
  thoracic 
  seg- 
  

   ments 
  and 
  the 
  structure 
  of 
  the 
  eyes 
  as 
  of 
  the 
  greatest 
  impor- 
  

   tance. 
  (4) 
  Milne-Edwards, 
  28 
  in 
  1840, 
  considered 
  the 
  power 
  of 
  

   enrollment 
  as 
  of 
  prime 
  value. 
  (5) 
  Goldfuss, 
  20 
  in 
  1843, 
  made 
  

   three 
  groups, 
  depending 
  on 
  the 
  presence 
  or 
  absence 
  of 
  eyes 
  

   and 
  their 
  structure. 
  (6) 
  Burmeister, 
  12 
  in 
  1843, 
  accepted 
  the 
  

   two 
  divisions 
  of 
  Milne-Edwards, 
  and 
  laid 
  stress 
  on 
  the 
  nature 
  

   of 
  the 
  pleura 
  and 
  the 
  size 
  of 
  the 
  pygidium. 
  (7) 
  Emmrich's 
  

   first 
  scheme, 
  17 
  in 
  1839, 
  was 
  founded 
  on 
  the 
  shape 
  of 
  the 
  pleura, 
  

   the 
  presence 
  or 
  absence 
  of 
  eyes 
  and 
  their 
  structure. 
  (8) 
  The 
  

   later 
  classification 
  of 
  the 
  same 
  author, 
  18 
  published 
  in 
  1844, 
  was 
  

  

  