﻿P. 
  E. 
  Raymond 
  — 
  Beecher^s 
  Classification 
  of 
  Trilobites. 
  205 
  

  

  segment, 
  but 
  it 
  is 
  possible 
  to 
  think 
  of 
  them 
  as 
  belonging 
  to 
  

   different 
  segments, 
  in 
  which 
  case 
  the 
  ventral 
  plate 
  of 
  the 
  

   Agnostidse 
  and 
  Trinucleidse 
  might 
  be 
  thought 
  of 
  as 
  simply 
  an 
  

   epistoma 
  and 
  not 
  as 
  undifferentiated 
  free 
  cheeks 
  and 
  epistoma. 
  

   Free 
  specimens 
  of 
  Lonchodomas 
  porilocki 
  (Barrande) 
  show 
  on 
  

   the 
  ventral 
  side 
  of 
  the 
  head 
  a 
  yoke-shaped 
  plate 
  like 
  that 
  of 
  

   Agnostus 
  nudus, 
  but 
  instead 
  of 
  being 
  confined 
  to 
  the 
  ventral 
  

   side, 
  it 
  laps 
  over 
  the 
  margins 
  up 
  onto 
  the 
  dorsal 
  side, 
  being 
  

   separated 
  from 
  the 
  cranidium 
  by 
  a 
  suture 
  which 
  has 
  the 
  course 
  

   of 
  the 
  ordinary 
  facial 
  suture. 
  The 
  absence 
  of 
  eyes 
  makes 
  the 
  

   analogy 
  with 
  the 
  ventral 
  plate 
  of 
  Agnostus 
  the 
  more 
  complete, 
  

   and 
  there 
  can 
  be 
  no 
  doubt 
  that 
  in 
  this 
  case 
  the 
  ventral 
  plate 
  

   has 
  encroached 
  upon 
  the 
  dorsal 
  side, 
  and 
  there 
  can 
  also 
  be 
  no 
  

   doubt 
  that 
  the 
  plate 
  represents 
  the 
  undifferentiated 
  free 
  cheeks 
  

   and 
  epistoma. 
  

  

  Fig. 
  2. 
  

  

  Fig. 
  2. 
  Lonchodomas 
  portlocki 
  (Barrande). 
  Figure, 
  somewhat 
  restored, 
  

   of 
  an 
  enrolled 
  specimen 
  in 
  the 
  Museum 
  of 
  Comparative 
  Zoology 
  to 
  show 
  the 
  

   continuous 
  ventral 
  plate 
  of 
  the 
  cephalon. 
  Enlarged. 
  

  

  All 
  the 
  families 
  of 
  the 
  Hypoparia 
  have 
  now 
  been 
  reviewed 
  

   and 
  it 
  hardly 
  seems 
  that 
  there 
  is 
  strong 
  evidence 
  at 
  the 
  present 
  

   time 
  for 
  removing 
  any 
  of 
  the 
  families 
  from 
  that 
  order. 
  Within 
  

   the 
  order 
  there 
  seems 
  to 
  be 
  a 
  tendency 
  in 
  two 
  directions, 
  in 
  the 
  

   Agnostidse.and 
  Eodiscidse 
  toward 
  the 
  Proparia, 
  and 
  in 
  the 
  

   Trinucleidse 
  and 
  Raphiophoridse 
  toward 
  the 
  Opisthoparia. 
  

   That 
  the 
  Eodiscidse 
  should 
  in 
  the 
  Middle 
  Cambrian 
  have 
  

   produced 
  a 
  true 
  Proparian, 
  Pagetia, 
  and 
  that 
  on 
  the 
  other 
  

   hand 
  the 
  Opisthoparian 
  Trinucleids 
  should 
  apparently 
  hark 
  

   back 
  to 
  another 
  branch 
  of 
  the 
  same 
  stock, 
  shows 
  that 
  we 
  can 
  

   not 
  dispense 
  with 
  the 
  order 
  and 
  relegate 
  its 
  families 
  to 
  the 
  

   Opisthoparia 
  and 
  Proparia. 
  The 
  attempt 
  to 
  show 
  that 
  the 
  

   Agnostidse, 
  Trinucleidae 
  and 
  Harpedidse 
  are 
  degenerate 
  Pro- 
  

   paria 
  and 
  Opisthoparia 
  seems 
  to 
  fall 
  from 
  lack 
  of 
  evidence, 
  

   while 
  the 
  evidence 
  for 
  their 
  primitive 
  position 
  seems 
  to 
  increase 
  

   with 
  new 
  discoveries. 
  

  

  