﻿THE 
  

  

  AMERICAN 
  JOURNAL 
  OF 
  SCIENCE 
  

  

  [FOURTH 
  SERIES. 
  ] 
  

  

  Art. 
  YIII. 
  — 
  Outline 
  of 
  a 
  NaUiral 
  Classification 
  of 
  the 
  

   Trilobites 
  ; 
  by 
  Charles 
  E. 
  Beecher. 
  (With 
  Plate 
  III.) 
  

  

  Introduction. 
  

  

  With 
  the 
  possible 
  exception 
  of 
  the 
  barnacles, 
  no 
  group 
  of 
  

   arthropods 
  has 
  received 
  more 
  varied 
  treatment 
  by 
  specialists 
  

   than 
  the 
  trilobites. 
  This 
  taxonomic 
  uncertainty 
  has 
  been 
  due 
  

   mainly 
  to 
  a 
  lack 
  of 
  knowledge 
  of 
  the 
  structure, 
  and 
  to 
  certain 
  

   real 
  or 
  fancied 
  resemblances 
  to 
  Limulus. 
  

  

  The 
  early 
  references 
  of 
  trilobites 
  to 
  the 
  mollusks, 
  insects, 
  

   and 
  fishes 
  need 
  not 
  be 
  noticed, 
  for 
  since 
  they 
  have 
  been 
  made 
  

   the 
  subject 
  of 
  special 
  study, 
  they 
  have 
  been 
  commonly 
  classed 
  

   with 
  the 
  Crustacea, 
  and 
  placed 
  near 
  the 
  phyllopods 
  by 
  most 
  

   observers. 
  Quite 
  a 
  number 
  of 
  naturalists, 
  however, 
  still 
  divorce 
  

   the 
  trilobites 
  and 
  limuloids 
  from 
  the 
  Crustacea 
  and 
  ally 
  them 
  

   with 
  the 
  arachnids. 
  It 
  is 
  not 
  proposed 
  at 
  this 
  time 
  to 
  discuss 
  

   the 
  homologies 
  of 
  Limulus, 
  but 
  the 
  trilobites 
  show 
  the 
  clearest 
  

   evidence 
  of 
  primitive 
  crustacean 
  affinities, 
  in 
  their 
  protonau- 
  

   plius 
  larval 
  form, 
  their 
  hypostoma 
  and 
  metastoma, 
  the 
  live 
  pairs 
  

   of 
  cephalic 
  appendages, 
  the 
  slender 
  jointed 
  antennules, 
  the 
  

   biramous 
  character 
  of 
  all 
  the 
  other 
  limbs 
  and 
  their 
  original 
  

   phyllopodiform 
  structure. 
  They 
  differ 
  from 
  Limulus, 
  not 
  

   only 
  in 
  most 
  of 
  these 
  regards, 
  but 
  also 
  -in 
  not 
  haviug 
  an 
  oper- 
  

   culum. 
  From 
  this 
  and 
  all 
  other 
  arthropods, 
  they 
  are 
  distin- 
  

   guished 
  by 
  having 
  compound 
  eyes 
  on 
  free 
  cheek 
  pieces 
  which 
  

   apparently 
  represent 
  the 
  pleura 
  of 
  a 
  head 
  segment 
  that 
  is 
  other- 
  

   wise 
  lost, 
  except 
  possibly 
  in 
  some 
  forms 
  of 
  stalked 
  eyes 
  and 
  in 
  

   the 
  cephalic 
  neuromeres 
  of 
  later 
  forms. 
  The 
  most 
  recent 
  dis- 
  

   cussions 
  as 
  to 
  the 
  affinities 
  of 
  trilobites 
  are 
  to 
  be 
  found 
  in 
  the 
  

   papers 
  by 
  Bernard, 
  7 
  ' 
  8 
  - 
  9 
  ' 
  10 
  Kingsley, 
  23 
  Woodward, 
  34 
  and 
  the 
  

  

  Am. 
  Jour. 
  Scl— 
  Fourth 
  Series, 
  Vol. 
  HI, 
  No. 
  14.— 
  February, 
  1897. 
  

  

  7 
  

  

  