﻿198 
  P. 
  E. 
  Raymond 
  — 
  Beecher's 
  Classification 
  of 
  Trilobites. 
  

  

  Fig. 
  1. 
  

  

  have 
  gone 
  over 
  the 
  specimens 
  in 
  the 
  Museum 
  of 
  Comparative 
  

   Zoology, 
  and 
  I 
  find 
  that 
  the 
  facial 
  suture 
  and 
  free 
  cheeks 
  are 
  

   very 
  well 
  shown 
  on 
  many 
  specimens 
  of 
  Agnostus 
  nudus, 
  can 
  

   be 
  plainly 
  seen 
  on 
  a 
  few 
  specimens 
  of 
  A. 
  integer* 
  and 
  A. 
  

   bibidlatus, 
  and 
  rather 
  imperfectly 
  made 
  out 
  on 
  a 
  number 
  of 
  

   A. 
  rex. 
  Curiously 
  enough, 
  these 
  free 
  cheeks 
  and 
  sutures 
  occur 
  

  

  on 
  that 
  portion 
  of 
  the 
  animal 
  which 
  

   Angelin, 
  Barrande, 
  Jaekel 
  and 
  others 
  

   have 
  designated 
  the 
  pygidium, 
  a 
  fact 
  

   which 
  may 
  have 
  caused 
  some 
  investi- 
  

   gators 
  to 
  overlook 
  them. 
  The 
  speci- 
  

   mens 
  in 
  which 
  these 
  features 
  can 
  be 
  

   seen 
  are 
  all 
  casts 
  in 
  a 
  very 
  fine-grained 
  

   shale 
  and 
  are, 
  of 
  course, 
  all 
  from 
  

   Bohemia. 
  I 
  think 
  the 
  structures 
  can 
  

   be 
  seen 
  by 
  anyone 
  who 
  has 
  access 
  to 
  a 
  

   large 
  collection 
  of 
  these 
  species, 
  the 
  

   only 
  preparation 
  necessary 
  being 
  the 
  

   flaking 
  off 
  with 
  a 
  h'ne 
  needle 
  of 
  the 
  

   cast 
  of 
  the 
  doublure 
  around 
  the 
  mar- 
  

   gin 
  of 
  the 
  cephalon. 
  Full 
  grown 
  

   specimens 
  of 
  Agnostus 
  nudus 
  are 
  of 
  

   fair 
  size, 
  and 
  so 
  permit 
  this 
  develop- 
  

   ment. 
  Other 
  species 
  would 
  probably 
  

   show 
  the 
  features 
  as 
  well 
  under 
  favor- 
  

   able 
  conditions 
  of 
  preservation, 
  but 
  I 
  

   have 
  looked 
  through 
  our 
  extensive 
  set 
  

   of 
  Swedish 
  and 
  American 
  specimens 
  

   without 
  finding 
  any 
  examples 
  showing 
  

   the 
  sutures. 
  Agnostus 
  nudus 
  has 
  

   one 
  shield 
  evenly 
  convex, 
  and 
  the 
  other 
  with 
  a 
  depressed 
  

   brim. 
  All 
  authors 
  seem 
  to 
  have 
  considered 
  the 
  evenly 
  convex 
  

   shield 
  the 
  cephalon, 
  because 
  of 
  the 
  way 
  in 
  which 
  the 
  segments 
  

   overlap 
  one 
  another. 
  The 
  facial 
  sutures 
  are 
  not 
  marginal, 
  but 
  

   intra-marginal. 
  They 
  meet 
  in 
  an 
  obtuse 
  angle 
  at 
  the 
  front, 
  

   and 
  run 
  backward 
  just 
  inside 
  the 
  margin, 
  reminding 
  one 
  much 
  

   of 
  the 
  course 
  of 
  the 
  pre-ocular 
  portion 
  of 
  the 
  suture 
  in 
  an 
  

   Homalonotus. 
  The 
  sutures 
  keep 
  within 
  the 
  angles, 
  so 
  that 
  the 
  

   fixed 
  cheeks 
  bear 
  the 
  genal 
  angles, 
  a 
  Proparian 
  characteristic. 
  

   The 
  sutures 
  in 
  this 
  manner 
  cut 
  off 
  a 
  yoke-shaped 
  area, 
  bounded 
  

   outside 
  by 
  the 
  facial 
  sutures 
  and 
  inside 
  by 
  a 
  natural 
  edge 
  which 
  

   follows 
  the 
  outline 
  of 
  the 
  base 
  of 
  the 
  elevated 
  portion 
  of 
  the 
  

   cranidium 
  (the 
  glabella). 
  Both 
  limbs 
  of 
  the 
  yoke 
  taper 
  back- 
  

   ward 
  to 
  a 
  point, 
  and 
  it 
  forms 
  a 
  continuous 
  plate, 
  with 
  no 
  ver- 
  

   tical 
  or 
  epistomal 
  sutures. 
  The 
  plate 
  has 
  the 
  position 
  and 
  aspect 
  

   of 
  a 
  large 
  epistomal 
  plate, 
  but 
  whether 
  called 
  an 
  epistoma 
  or 
  free 
  

   cheeks, 
  the 
  sutures 
  which 
  separate 
  it 
  from 
  the 
  cranidium 
  must 
  

  

  * 
  It 
  is 
  shown 
  in 
  one 
  of 
  Barrande's 
  figures 
  of 
  this 
  species, 
  on 
  what 
  he 
  

   believed 
  to 
  be 
  the 
  pygidium. 
  System 
  Silur. 
  Boheme, 
  I, 
  pi. 
  49, 
  fig. 
  56. 
  

  

  Fig. 
  1. 
  Agnostus 
  nudus 
  

   (Beyrich). 
  Figure 
  after 
  

   Barrande, 
  with 
  the 
  sutures 
  

   and 
  ventral 
  plate 
  added 
  

   from 
  a 
  specimen 
  in 
  the 
  

   Museum 
  of 
  Comparative 
  

   Zoology. 
  Enlarged. 
  

  

  