﻿90 
  TWEXTY-EIGHTH 
  KePORT 
  OX 
  THE 
  STATE 
  MUSEUM. 
  

  

  this 
  species 
  appear 
  to 
  be 
  attacked 
  to 
  the 
  ventral 
  surface 
  of 
  

   the 
  visceral 
  cavity, 
  while 
  in 
  Ceraurus 
  pleurexantliemus 
  they 
  

   are 
  either 
  attached 
  to 
  the 
  axial 
  processes, 
  or 
  were 
  attached 
  to 
  

   the 
  thin 
  membrane 
  which 
  must 
  have 
  extended 
  outward 
  from 
  

   the 
  axial 
  lobe 
  beneath 
  the 
  pleural 
  lobes. 
  Sections 
  of 
  forty- 
  

   one 
  trilobites 
  of 
  the 
  above 
  species 
  show 
  two 
  hundred 
  and 
  

   eighty- 
  eight 
  axial 
  appendages. 
  

  

  In 
  sections 
  of 
  fifteen 
  individuals 
  of 
  the 
  species 
  Ceraurus 
  

   pleur 
  exanthemus 
  , 
  remains 
  of 
  the 
  branchial 
  appendages 
  have 
  

   been 
  found. 
  They 
  occur 
  beneath 
  the 
  pleura] 
  lobes 
  near 
  the 
  

   union 
  with 
  the 
  free 
  pleurae. 
  In 
  nine 
  sections 
  of 
  the 
  fifteen 
  

   trilobites, 
  in 
  which 
  these 
  appendages 
  have 
  been 
  discovered, 
  

   forty-three 
  distinct 
  appendages 
  are 
  to 
  be 
  seen. 
  Transverse 
  

   sections 
  of 
  the 
  trilobite 
  show 
  the 
  appendage 
  to 
  be 
  a 
  row 
  of 
  

   obliquely 
  inclined 
  bars, 
  arranged 
  one 
  beneath 
  the 
  other, 
  

   under 
  the 
  pleurae. 
  Three 
  sections 
  show 
  the 
  support 
  to 
  which 
  

   the 
  bars 
  were 
  attached. 
  This 
  support 
  must 
  have 
  been 
  of 
  a 
  

   fleshy 
  character, 
  probably 
  muscular, 
  as 
  in 
  most 
  of 
  the 
  sections 
  

   where 
  the 
  bars 
  are 
  in 
  position, 
  the 
  support 
  is 
  not 
  to 
  be 
  seen. 
  

   The 
  greatest 
  number 
  of 
  bars 
  seen 
  in 
  position, 
  belonging 
  to 
  

   one 
  appendage, 
  is 
  fourteen. 
  It 
  is 
  very 
  rare 
  to 
  find 
  them 
  in 
  

   position 
  at 
  all. 
  Longitudinal 
  sections 
  at 
  the 
  union 
  of 
  the 
  

   pleural 
  lobes 
  and 
  free 
  pleurae, 
  show 
  the 
  branchial 
  appendages 
  

   as 
  rows 
  of 
  dots, 
  varying 
  from 
  square 
  to 
  oblong 
  in 
  shape. 
  

   One 
  section 
  shows 
  forty-eight 
  such 
  dots. 
  The 
  branchial 
  

   appendages 
  were 
  longer, 
  by 
  one-half, 
  than 
  the 
  axial 
  append- 
  

   ages. 
  A 
  section 
  of 
  Calymene 
  senaria 
  shows 
  the 
  branchial 
  

   appendages 
  in 
  position. 
  They 
  appear 
  to 
  be 
  the 
  same 
  as 
  those 
  

   of 
  Ceraurus 
  pleurexantliemus. 
  Numerous 
  central 
  longitudi- 
  

   nal 
  sections 
  of 
  C 
  pleurexantliemus 
  ; 
  show 
  the 
  membrane 
  

   covering 
  the 
  visceral 
  cavity 
  beneath 
  the 
  axial 
  lobe. 
  In 
  

   coiled 
  specimens 
  it 
  is 
  corrugated 
  by 
  the 
  folding. 
  Several 
  

   sections 
  show 
  that 
  there 
  was 
  a 
  thickening 
  of 
  the 
  membrane 
  

   opposite 
  each 
  thoracic 
  segment. 
  One 
  section 
  has 
  eight 
  such 
  

   thickenings, 
  or 
  membraneous 
  arches. 
  Sections 
  cut 
  through 
  

   the 
  pleural 
  lobes, 
  have 
  not, 
  as 
  yet, 
  given 
  evidence 
  of 
  the 
  

   presence 
  of 
  a 
  ventral 
  membrane. 
  

  

  Sections 
  of 
  Acidaspis 
  Trentonensis 
  show 
  it 
  to 
  be 
  closely 
  

   related 
  to 
  Ceraurus 
  pleur 
  exanthemus, 
  in 
  the 
  structure 
  of 
  its 
  

   ventral 
  surface. 
  

  

  From 
  the 
  evidence 
  obtained 
  from 
  sections 
  of 
  Asaphus 
  

   [gigas) 
  platycephalus, 
  and 
  the 
  paper 
  published 
  by 
  Prof. 
  E. 
  

  

  