﻿Appendages 
  of 
  Trilobites. 
  91 
  

  

  Billings,* 
  it 
  appears 
  that 
  'the 
  ventral 
  surface 
  in 
  this 
  species 
  

   was 
  strengthened 
  by 
  arches, 
  to 
  which 
  the 
  double 
  row 
  of 
  

   appendages 
  were 
  attached, 
  f 
  From 
  the 
  evidence 
  thus 
  far 
  

   obtained, 
  the 
  conclusions 
  are, 
  that 
  trilobites 
  swam 
  on 
  their 
  

   backs 
  (see 
  notes 
  on 
  Qeraurus 
  pleurexanthemus, 
  Ann. 
  Lye. 
  

   Nat. 
  Hist., 
  1ST. 
  Y., 
  Yol. 
  XI, 
  p. 
  155, 
  November, 
  1875), 
  and 
  that 
  

   they 
  had 
  a 
  double 
  row 
  of 
  appendages 
  on 
  each 
  side 
  of 
  the 
  

   central 
  axis. 
  

  

  The 
  central 
  or 
  axial 
  series 
  were 
  either 
  the 
  attachments 
  of 
  

   swimming 
  lobes, 
  or 
  rudimentary, 
  ambulatory, 
  legs. 
  The 
  

   lateral 
  series 
  were 
  branchial 
  in 
  their 
  structure, 
  the 
  bars 
  serv- 
  

   ing 
  as 
  points 
  of 
  attachment 
  for 
  their 
  lamellse. 
  It 
  is 
  probable 
  

   that 
  they 
  were 
  also 
  used 
  in 
  swimming. 
  Many 
  sections 
  show 
  

   appendages 
  beneath 
  the 
  head, 
  but 
  nothing 
  satisfactory 
  can 
  be 
  

   established 
  from 
  them. 
  As 
  the 
  writer 
  has 
  a 
  large 
  amount 
  of 
  

   material 
  from 
  the 
  same 
  locality, 
  which 
  is 
  unworked, 
  he 
  hopes 
  

   to 
  present 
  in 
  a 
  future 
  article 
  a 
  series 
  of 
  descriptions 
  and 
  

   illustrations, 
  giving 
  the 
  structure 
  of 
  the 
  ventral 
  surface 
  and 
  

   appendages 
  of 
  the 
  trilobite. 
  

  

  Trenton 
  Falls, 
  May 
  26, 
  1876. 
  

  

  Note 
  of 
  Additional 
  Evidence 
  Obtained 
  since 
  the 
  above 
  was 
  

  

  Written. 
  

  

  Additional 
  evidence, 
  obtained 
  from 
  sections 
  of 
  Calymene 
  

   senaria, 
  proves 
  that 
  the 
  central, 
  or 
  axial, 
  appendages, 
  were 
  

   articulated 
  to 
  the 
  thickened 
  arches 
  of 
  the 
  ventral 
  membrane, 
  

   on 
  a 
  line 
  with 
  the 
  outer 
  edges 
  of 
  the 
  alimentary 
  canal. 
  The 
  

   structure 
  of 
  the 
  appendages, 
  as 
  shown 
  in 
  numerous 
  micro- 
  

   scopic, 
  transparent 
  and 
  opaque 
  sections, 
  leads 
  me 
  to 
  the 
  con- 
  

   clusion 
  that 
  they 
  were 
  the 
  support 
  of 
  swimming 
  lobes. 
  What 
  

   may 
  have 
  been 
  a 
  portion 
  of 
  the 
  swimming 
  lobe 
  has 
  been 
  seen 
  

   in 
  several 
  sections 
  near 
  the 
  end 
  of 
  the 
  appendage. 
  These 
  

   appendages 
  terminate 
  either 
  in 
  a 
  round 
  blunt 
  point 
  or 
  else 
  

   appear 
  as 
  if 
  crushed. 
  The 
  form 
  and 
  outline 
  of 
  the 
  swimming 
  

   lobe 
  could 
  not 
  well 
  be 
  preserved. 
  Transverse 
  sections 
  show 
  

   the 
  ventral 
  membrane 
  between 
  the 
  axial 
  appendages, 
  the 
  space 
  

   occupied 
  by 
  the 
  alimentary 
  canal, 
  and 
  the 
  axial 
  and 
  bran- 
  

   chial 
  appendages. 
  The 
  branchial 
  appendages 
  were 
  attached 
  

  

  * 
  Notes 
  on 
  some 
  specimens 
  of 
  Lower 
  Silurian 
  Trilobites, 
  by 
  E. 
  Billings, 
  Quarterly 
  Jour- 
  

   nal 
  Geological 
  Society, 
  November, 
  1870. 
  

  

  t 
  A 
  conclusion 
  also 
  given 
  by 
  Messrs. 
  Dana, 
  Verrill 
  and 
  Smith, 
  after 
  examining 
  Prof. 
  

   Billings' 
  specimen. 
  Am. 
  Jour. 
  S. 
  & 
  A., 
  M 
  series, 
  I, 
  p. 
  320. 
  

  

  