﻿VEETEBEATES. 
  255 
  

  

  Genus 
  OEACANTHUS, 
  Agassiz. 
  

   Oeacanthus 
  vetustus, 
  Leidy. 
  

  

  PL 
  XXIV, 
  Fig. 
  a. 
  

  

  Oracanthus 
  vetustus, 
  Leidy, 
  1856. 
  Jour. 
  Acad. 
  Nat. 
  Sei., 
  Phlla., 
  2d 
  series, 
  iii. 
  p. 
  161, 
  PL 
  16, 
  

  

  f. 
  1, 
  2, 
  3. 
  

   Oracanthus 
  consimilis, 
  St.';J. 
  and 
  W., 
  1875. 
  111. 
  Geol, 
  Surv. 
  VI, 
  p. 
  476, 
  PL 
  XXII, 
  1. 
  15. 
  

  

  The 
  cabinet 
  of 
  Washington 
  University, 
  of 
  St. 
  Louis, 
  contains 
  a 
  

   fine 
  large 
  spine, 
  which, 
  we 
  have 
  no 
  doubt, 
  is 
  specifically 
  identical 
  with 
  

   the 
  form 
  originally 
  described 
  by 
  Dr. 
  Leidy 
  under 
  the 
  above 
  desig- 
  

   nation, 
  and 
  which 
  was 
  subsequently 
  noticed 
  by 
  the 
  authors 
  under 
  the 
  

   name 
  Oracanthus 
  consimilis. 
  This 
  specimen, 
  however, 
  affords 
  a 
  much 
  

   more 
  satisfactory 
  idea 
  of 
  the 
  superficial 
  characteristics 
  of 
  the 
  spine 
  

   than 
  it 
  was 
  possible 
  to 
  gain 
  from 
  the 
  fragmentary 
  material 
  acces- 
  

   sible 
  to 
  us 
  at 
  the 
  time 
  the 
  latter 
  notice 
  was 
  prepared, 
  and 
  we 
  are 
  

   thankful 
  for 
  the 
  opportunity 
  of 
  correcting 
  and 
  extending 
  the 
  notice 
  

   of 
  the 
  species, 
  which 
  we 
  owe 
  to 
  Dr. 
  Hambach, 
  of 
  that 
  institution, 
  

   and 
  to 
  Dr. 
  Leidy, 
  who 
  kindly 
  secured 
  the 
  loan 
  of 
  the 
  type 
  specimen 
  

   from 
  the 
  museum 
  of 
  the 
  Academy 
  of 
  Natural 
  Science. 
  

  

  The 
  above 
  mentioned 
  specimen 
  preserves 
  a 
  length 
  of 
  15 
  centimetres, 
  

   and 
  a 
  width 
  of 
  above 
  6 
  c. 
  m., 
  the 
  basal 
  margin 
  and 
  a 
  portion 
  of 
  the 
  

   left 
  side 
  being 
  broken 
  away, 
  exposing 
  the 
  large 
  pulp 
  cavity. 
  The 
  

   outline 
  is 
  that 
  of 
  a 
  moderately 
  backward-curved, 
  rapidly-tapering, 
  

   laterally-compressed 
  cone, 
  terminating 
  in 
  a 
  sharp 
  point 
  ; 
  the 
  anterior 
  

   edge 
  broadly 
  and 
  regularly 
  rounded 
  into 
  the 
  gently-convex 
  lateral 
  

   surfaces 
  ; 
  the 
  concave 
  posterior 
  border 
  somewhat 
  flattened 
  and 
  more 
  

   sharply 
  rounded, 
  but 
  without 
  defined 
  postero-lateral 
  angles. 
  The 
  

   walls 
  of 
  the 
  pulp 
  cavity 
  are 
  moderately 
  thick, 
  presenting 
  the 
  great- 
  

   est 
  thickness 
  along 
  the 
  convex 
  anterior 
  border, 
  the 
  lateral 
  walls 
  more 
  

   or 
  less 
  crushed 
  in 
  by 
  pressure. 
  The 
  exposed 
  surfaces 
  of 
  the 
  spine 
  

   show 
  obscure, 
  irregular 
  longitudinal 
  costae, 
  and 
  are 
  thickly 
  studded 
  

   with 
  tubercles, 
  which 
  assume 
  a 
  variety 
  of 
  shapes, 
  according 
  to 
  their 
  

   position, 
  and 
  ranged 
  in 
  distinct, 
  though 
  interrupted 
  obliquely 
  trans- 
  

   verse 
  rows, 
  which, 
  in 
  the 
  right 
  side, 
  rise 
  from 
  the 
  anterior 
  edge 
  up- 
  

   ward 
  and 
  backward 
  to 
  a 
  point 
  near 
  the 
  middle, 
  where 
  they 
  meet 
  

   similar 
  rows 
  rising 
  obliquely 
  from 
  the 
  concave 
  border 
  in 
  the 
  opposite 
  

   direction 
  ; 
  but 
  toward 
  the 
  base, 
  where 
  the 
  tubercles 
  are 
  more 
  crowded 
  

   and 
  larger, 
  this 
  oblique 
  course 
  is 
  less 
  conspicuous, 
  while 
  their 
  longi- 
  

   tudinal 
  disposition 
  is 
  more 
  or 
  less 
  distinctly 
  marked 
  throughout. 
  Over 
  

  

  