﻿Beecher 
  — 
  Natural 
  Glussification 
  of 
  the 
  Trilobites. 
  1S9 
  

  

  oj?Jeura. 
  Liostracus, 
  Piychqparia 
  7 
  and 
  Sao. 
  Otenocephalus 
  

  

  and 
  Eryx 
  are 
  slightly 
  more 
  advanced, 
  as 
  the 
  glabella 
  no 
  longer 
  

   marks 
  the 
  edge 
  of 
  the 
  cephalon. 
  In 
  Ataps 
  9 
  * 
  Avalonia, 
  

  

  Bathynotv.s. 
  and 
  Carmon. 
  the 
  glabella 
  is 
  cylindrical, 
  distinctly 
  

   defined, 
  and 
  limited 
  within 
  the 
  margin, 
  and 
  in 
  CononQryphe, 
  

   Harttia, 
  and 
  Bailiella, 
  it 
  narrows 
  anteriorly, 
  and 
  only 
  extends 
  

   about 
  two-thirds 
  the 
  length 
  of 
  the 
  head. 
  Generally 
  in 
  this 
  

   family, 
  the 
  glabella 
  displays 
  its 
  primitive 
  pentamerous 
  origin. 
  

   In 
  Bailiella 
  and 
  Carausia. 
  two 
  basal 
  lobes 
  are 
  marked 
  off 
  

   from 
  the 
  fourth 
  segment 
  by 
  oblique 
  furrows, 
  as 
  in 
  Proetus 
  and 
  

   Oyphaspis. 
  

  

  from 
  a 
  phylogenetic 
  standpoint, 
  the 
  family 
  Conocoryphidae 
  

   is 
  at 
  the 
  base 
  of 
  this 
  extensive 
  order. 
  As 
  far 
  as 
  known, 
  all 
  

   the 
  larval 
  forms 
  in 
  the 
  other 
  families 
  of 
  the 
  Opisthoparia 
  agree 
  

   in 
  having 
  the 
  narrow 
  marginal 
  free 
  cheeks, 
  bearing 
  the 
  genal 
  

   angles. 
  The 
  eye 
  line 
  is 
  present 
  in 
  most 
  of 
  the 
  adult 
  Olenidas, 
  

   and 
  in 
  the 
  early 
  stages 
  of 
  all 
  as 
  far 
  as 
  known, 
  so 
  that 
  the 
  gen- 
  

   eral 
  average 
  of 
  the 
  characters 
  in 
  the 
  Conocoryphida? 
  represents 
  

   the 
  main 
  larval 
  features 
  throughout 
  the 
  other 
  families. 
  They 
  

   show. 
  too. 
  that 
  although 
  primitive 
  in 
  essential 
  structure, 
  differ- 
  

   entiation 
  through 
  time 
  has 
  developed 
  secondary 
  features 
  

   belonging 
  to 
  genera 
  in 
  higher 
  families, 
  as. 
  for 
  example, 
  the 
  

   basal 
  glabellar 
  lobes 
  in 
  BailUV.a. 
  

  

  Family 
  V. 
  Olexid_e 
  Salter. 
  

  

  Cephalon 
  larger 
  than 
  the 
  pygidium. 
  usually 
  wider 
  than 
  long 
  ; 
  

   genal 
  angles 
  commonly 
  produced 
  into 
  spines. 
  Free 
  cheeks 
  

   separate. 
  Facial 
  sutures 
  extending 
  forward 
  from 
  the 
  posterior 
  

   margin 
  of 
  the 
  cephalon 
  along 
  the 
  eye 
  lobes, 
  and 
  either 
  cutting 
  

   the 
  anterior 
  margin 
  separately 
  or 
  meeting 
  on 
  the 
  median 
  line. 
  

   Eyes 
  crescentic, 
  reniform. 
  or 
  semicircular, 
  situated 
  at 
  the 
  ends 
  

   of 
  eye 
  lines 
  in 
  all 
  but 
  highest 
  genera. 
  Trunk 
  long, 
  composed 
  

   of 
  from 
  eight 
  (?) 
  to 
  twenty-six 
  free 
  segments 
  : 
  rarely 
  capable 
  

   of 
  rolling 
  up. 
  Pygidium 
  frequently 
  small 
  : 
  margin 
  entire 
  or 
  

   spinose. 
  

  

  Principally 
  Cambrian, 
  but 
  extending 
  into 
  the 
  Ordovician. 
  

  

  Including 
  the 
  genus 
  Olenus 
  Dalman 
  as 
  the 
  type, 
  and 
  the 
  

   following 
  genera 
  and 
  subgenera, 
  which 
  should 
  doubtless 
  fall 
  

   into 
  several 
  subfamily 
  or 
  even 
  family 
  groups 
  : 
  Acerocare 
  

   Angelin, 
  Acroeephalites 
  Wallerius, 
  Agraulus 
  Corda, 
  Ange- 
  

   lina 
  Salter. 
  Anomocare 
  Angelin. 
  Anopolenus 
  Salter. 
  Asaphe- 
  

  

  * 
  Atops 
  (type 
  A. 
  frilineatus 
  Emmons) 
  seems 
  10 
  be 
  a 
  valid 
  genus, 
  and 
  differs 
  

   from 
  Gonocoryphe 
  (type 
  G. 
  Sulzeri 
  Schlotheim^ 
  in 
  its 
  glabellar 
  characters, 
  greater 
  

  

  number 
  of 
  thoracic 
  segments,, 
  and 
  much 
  smaller 
  pygidium 
  with 
  fewer 
  segments. 
  

  

  