﻿196 
  Beecher 
  — 
  Natural 
  Classification 
  of 
  the 
  Trilobites. 
  

  

  lobes, 
  and 
  then 
  diverging 
  and 
  cutting 
  the 
  anterolateral 
  mar- 
  

   gins 
  separately. 
  Eyes 
  crescentic. 
  Thorax 
  of 
  ten 
  segments, 
  

   with 
  ridged 
  pleura. 
  Pygidium 
  longer 
  than 
  cephalon 
  or 
  

   thorax 
  ; 
  axis 
  very 
  short, 
  with 
  radiating 
  furrows 
  extending 
  

   from 
  it 
  across 
  the 
  broad 
  limb 
  toward 
  the 
  margin 
  ; 
  doublure 
  

   very 
  wide 
  ; 
  margin 
  generally 
  entire. 
  Ordovician 
  to 
  Devonian. 
  

   Including 
  the 
  single 
  genus 
  Bronteus 
  Goldfuss 
  ( 
  = 
  Goldius 
  

   de 
  Koninck). 
  

  

  Many 
  of 
  the 
  species 
  of 
  Bronteus 
  (as 
  B. 
  angusticeps 
  Barr., 
  

   B. 
  palifer 
  Bey.) 
  show 
  a 
  breaking 
  up 
  of 
  the 
  glabella 
  into 
  sym- 
  

   metrically 
  disposed 
  separate 
  lobes, 
  as 
  in 
  Conoliohas 
  and 
  Acid- 
  

   aspis. 
  The 
  frontal 
  lobe 
  is 
  transverse 
  and 
  much 
  larger 
  than 
  the 
  

   others. 
  Back 
  of 
  it 
  may 
  be 
  simple 
  grooves 
  marking 
  the 
  ele- 
  

   ments 
  (B. 
  campamfer 
  Bey.), 
  or 
  there 
  may 
  be 
  one 
  or 
  two 
  cir- 
  

   cular 
  or 
  elliptical 
  swellings 
  on 
  each 
  side 
  of 
  the 
  axis 
  {B. 
  angus- 
  

   ticeps 
  Barr.), 
  or 
  in 
  addition, 
  the 
  axial 
  portion 
  may 
  consist 
  of 
  

   several 
  lobes. 
  The 
  reduction 
  of 
  the 
  axis 
  of 
  the 
  pygidium 
  and 
  

   the 
  expansion 
  of 
  the 
  limb 
  meet 
  with 
  their 
  greatest 
  expression 
  

   in 
  this 
  genus. 
  Lichas 
  shows 
  the 
  decline 
  of 
  these 
  characters, 
  

   the 
  pygidial 
  limb 
  becoming 
  more 
  or 
  less 
  deeply 
  lobed, 
  and 
  

   finally 
  the 
  lobes 
  are 
  represented 
  by 
  spines 
  (Arges, 
  Terataspis). 
  

   Further 
  progression 
  of 
  these 
  changes 
  is 
  shown 
  in 
  Acidaspis. 
  

  

  Family 
  IX. 
  Lichadim; 
  Barrande. 
  

  

  Dorsal 
  shield 
  generally 
  large 
  and 
  flat, 
  with 
  granulated 
  test. 
  

   Cephalon 
  small, 
  not 
  more 
  than 
  one-fourth 
  the 
  entire 
  length 
  ; 
  

   genal 
  angles 
  spiniform. 
  Free 
  cheeks 
  separate 
  ; 
  sutures 
  extend- 
  

   ing 
  from 
  the 
  posterior 
  margin 
  obliquely 
  inward 
  to 
  the 
  eyes, 
  

   and 
  then 
  almost 
  directly 
  forward, 
  cutting 
  the 
  margin 
  separately. 
  

   Glabella 
  broad, 
  with 
  a 
  large, 
  often 
  tumid, 
  central 
  lobe 
  and 
  from 
  

   one 
  to 
  three 
  side 
  lobes. 
  Eyes 
  not 
  large. 
  Thorax 
  with 
  nine 
  or 
  

   ten 
  segments 
  and 
  grooved 
  and 
  falcate 
  pleura. 
  Pygidium 
  large, 
  

   flat, 
  commonly 
  with 
  toothed 
  or 
  notched 
  margin 
  corresponding 
  

   to 
  the 
  pleural 
  grooves 
  ; 
  doublure 
  very 
  broad. 
  

  

  Ordovician 
  to 
  Devonian. 
  

  

  Including 
  the 
  genera 
  and 
  subgenera 
  Lichas 
  Dal 
  man, 
  Arcti- 
  

   nurus 
  Castelnau, 
  Arges 
  Goldfuss, 
  Ceratolichas 
  Hall 
  and 
  Clarke, 
  

   Conolichas 
  Dames, 
  Dicranogmus 
  Corda, 
  Sornolichas 
  Schmidt, 
  

   Hoplolichas 
  Dames, 
  Leiolichas 
  Schmidt, 
  Metopias 
  Eichwald, 
  

   Oncholichas 
  Schmidt, 
  Platymetopus 
  Angelin, 
  Terataspis 
  Hall, 
  

   Trochurus 
  Beyrich, 
  and 
  Uralichas 
  Delgado. 
  

  

  

  