﻿VEETEBEATES. 
  253 
  

  

  Genus 
  DKEPA^ACANTHUS, 
  N. 
  and 
  W. 
  

   Dbepanacanthus 
  beversus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XXIV, 
  Fig. 
  5. 
  

  

  Drepanacantlius 
  reversus, 
  St. 
  John 
  and 
  Worthen, 
  1875. 
  111. 
  Geol. 
  Surv., 
  VI, 
  p. 
  45(i, 
  PI. 
  

   XIX., 
  f. 
  5, 
  6. 
  

  

  A 
  nearly 
  perfect 
  specimen 
  of 
  the 
  above 
  named 
  species 
  has 
  lately- 
  

   been 
  obtained 
  at 
  Alton. 
  The 
  specimen 
  shows 
  nearly 
  the 
  complete 
  

   outline, 
  but 
  it 
  is, 
  unfortunately, 
  too 
  abraded 
  to 
  distinctly 
  display 
  

   the 
  ornamentation, 
  which 
  was 
  very 
  clearly 
  made 
  out 
  from 
  the 
  frag- 
  

   ments 
  upon 
  which 
  the 
  original 
  description 
  was 
  based. 
  The 
  speci- 
  

   men 
  here 
  referred 
  to 
  is 
  reproduced 
  in 
  the 
  illustrations. 
  "With 
  the 
  

   exception 
  of 
  the 
  tip 
  and 
  the 
  extreme 
  end 
  of 
  the 
  base, 
  it 
  is 
  perfect, 
  

   and 
  is 
  readily 
  distinguished 
  from 
  the 
  Keokuk 
  species 
  previously 
  

   described 
  by 
  its 
  stronger 
  curvature, 
  while 
  the 
  tuberculation 
  is 
  quite 
  

   different, 
  as 
  has 
  been 
  already 
  pointed 
  out. 
  

  

  Geological 
  position 
  and 
  localities: 
  St. 
  Louis 
  limestone 
  ; 
  Alton, 
  Illi- 
  

   nois, 
  and 
  St. 
  Louis, 
  Missouri. 
  

  

  Genus 
  BAT 
  ACANTHUS, 
  St. 
  John 
  and 
  Worthen. 
  

   Batacanthus 
  ? 
  neois, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XXV, 
  Fig. 
  4. 
  

  

  The 
  collection 
  of 
  Mr. 
  Cox 
  from 
  the 
  Keokuk 
  limestone 
  affords 
  an 
  

   example 
  showing 
  a 
  length 
  of 
  some 
  7 
  centimetres 
  from 
  the 
  distal 
  

   extremity 
  of 
  a 
  medium-size 
  spine, 
  the 
  uncertain 
  relations 
  of 
  which 
  

   suggested 
  the 
  above 
  specific 
  designation. 
  In 
  size 
  and 
  general 
  form, 
  

   as 
  displayed 
  bedded 
  in 
  the 
  limestone 
  matrix, 
  the 
  spirie 
  is 
  not 
  unlike 
  

   Drepanacantlius 
  gemmatus, 
  N. 
  and 
  W., 
  of 
  the 
  same 
  formation. 
  It 
  

   gradually 
  tapers 
  and 
  is 
  moderately 
  curved 
  to 
  a 
  point 
  within 
  a 
  short 
  

   distance 
  of 
  the 
  extremity, 
  where 
  it 
  is 
  more 
  rapidly 
  narrowed 
  and 
  

   suddenly 
  bent 
  forward. 
  But 
  here 
  the 
  resemblance 
  to 
  Drepanacan- 
  

   tlius 
  ceases; 
  instead 
  of 
  the 
  wedge-shaped 
  transverse 
  section 
  and 
  de- 
  

   fined 
  posterior 
  face, 
  the 
  present 
  spine 
  is 
  elliptic 
  or 
  lenticular 
  in 
  

   section, 
  anterior 
  and 
  posterior 
  angles 
  sharply 
  rounded, 
  the 
  pulp 
  

   cavity 
  occupying 
  the 
  entire 
  posterior 
  half 
  of 
  the 
  antero-posterior 
  di- 
  

   ameter 
  of 
  the 
  spine, 
  as 
  indicated 
  by 
  the 
  crushed-in 
  thin 
  lateral 
  

  

  