﻿190 
  Twenty-eighth 
  Keport 
  on 
  the 
  State 
  Museum. 
  

  

  Ceraurus 
  bimucronatus 
  ? 
  (Murchison) 
  Roemer. 
  Silur. 
  Fauna 
  Westl. 
  Tenn., 
  

  

  S. 
  80, 
  T. 
  V. 
  fig. 
  19; 
  not 
  Cheirurus 
  bimucronatus 
  Murchison. 
  SiluriaFoss. 
  64; 
  

  

  fig. 
  4, 
  pi. 
  3, 
  fig. 
  5; 
  and 
  pi. 
  19, 
  figs. 
  10, 
  11. 
  

   Compare 
  Cheirurus 
  pauper 
  Barrande. 
  Syst. 
  Sil. 
  Cent. 
  Boherne, 
  p. 
  800, 
  pi. 
  41, 
  fig. 
  

  

  41. 
  

   Compare 
  Cheirurus 
  obtusatus 
  (Cord 
  a) 
  Barrande. 
  Syst. 
  Sil. 
  Cent. 
  Boheme, 
  p. 
  

  

  786, 
  pi. 
  41, 
  figs. 
  14-16. 
  

  

  This 
  species, 
  so 
  far 
  as 
  known, 
  is 
  only 
  represented 
  by 
  frag- 
  

   ments 
  of 
  the 
  cephalic 
  shields 
  found 
  in 
  JN~ew 
  York, 
  Wisconsin, 
  

   Tennessee 
  and 
  Indiana, 
  and 
  nearly 
  perfect 
  specimens 
  of 
  the 
  

   pygidia, 
  also 
  found 
  at 
  Waldron, 
  Indiana. 
  With 
  the 
  material 
  

   now 
  at 
  hand, 
  a 
  more 
  exact 
  and 
  satisfactory 
  comparison 
  can 
  be 
  

   made 
  with 
  various 
  European 
  species. 
  

  

  The 
  only 
  European 
  species 
  with 
  a 
  single 
  obtuse 
  node 
  at 
  

   the 
  extremity 
  of 
  the 
  pygidium 
  are 
  C. 
  insignis 
  Beyrich, 
  C. 
  

   pauper 
  Barr., 
  and 
  C. 
  obtusatus 
  Corda 
  ; 
  the 
  other 
  allied 
  

   species 
  have 
  the 
  extremity 
  variously 
  mucronate 
  or 
  emargin- 
  

   ate. 
  These 
  species 
  also 
  all 
  agree 
  in 
  the 
  comparatively 
  slender 
  

   sharp 
  spines 
  on 
  the 
  lateral 
  margins. 
  

  

  The 
  pygidia 
  found 
  at 
  Waldron 
  may 
  be 
  described 
  as 
  follows 
  : 
  

  

  i 
  Pygidium 
  longitudinally 
  subelliptical, 
  very 
  slightly 
  convex, 
  

   axis 
  prominent 
  in 
  front, 
  diminishing 
  very 
  rapidly 
  in 
  size 
  and 
  

   elevation 
  toward 
  the 
  posterior 
  end^coxaposed 
  of 
  three 
  promi- 
  

   nent 
  annulations, 
  and 
  a 
  flat, 
  rounded 
  node 
  extending 
  beyond 
  

   the 
  margin, 
  with 
  two 
  small 
  circular 
  depressions 
  at 
  the 
  base 
  

   near 
  the 
  third 
  segment, 
  probably 
  indicating 
  a 
  rudimentary 
  

   fourth 
  segment. 
  Lateral 
  lobes 
  composed 
  of 
  three 
  pairs 
  of 
  

   segments, 
  having 
  a 
  very 
  short, 
  deep 
  furrow 
  at 
  the 
  base 
  of 
  

   each 
  segment 
  ; 
  produced 
  into 
  three 
  broad, 
  flat, 
  subtriangular 
  

   curved 
  spines, 
  notched 
  at 
  the 
  base 
  on 
  the 
  anterior 
  margin, 
  ex- 
  

   tending 
  outward 
  and 
  curving 
  abruptly 
  backward, 
  concave 
  

   to 
  the 
  axis. 
  Surface 
  granulose. 
  

  

  Surface 
  of 
  the 
  glabella 
  covered 
  with 
  small 
  crateriform 
  pus- 
  

   tules. 
  The 
  fixed 
  cheek 
  is 
  finely 
  granulose, 
  with 
  small, 
  irregu 
  - 
  

   lar 
  circular 
  depressions. 
  

  

  From 
  the 
  above 
  it 
  will 
  be 
  seen 
  that 
  the 
  separation 
  first 
  

   made 
  in 
  the 
  revised 
  edition 
  of 
  the 
  20th 
  Rept. 
  St. 
  Cab., 
  was 
  

   necessary, 
  and 
  that 
  it 
  constitutes 
  a 
  distinct 
  species. 
  

  

  