﻿VERTEBEATES. 
  249 
  

  

  the 
  pulp 
  cavity, 
  the 
  carinate 
  matrix 
  of 
  which 
  would 
  indicate, 
  per- 
  

   haps, 
  a 
  rather 
  prominent 
  median 
  angularity 
  in 
  the 
  contour 
  of 
  the 
  

   posterior 
  face 
  of 
  the 
  spine. 
  Although 
  we 
  have 
  no 
  evidence 
  of 
  the 
  

   denticles 
  arming 
  the 
  postero-lateral 
  angles, 
  and 
  even 
  the 
  wide 
  fur- 
  

   row 
  immediately 
  adjacent 
  the 
  anterior 
  keel 
  is 
  destitute 
  of 
  the 
  char- 
  

   acteristic 
  tubercles, 
  nevertheless 
  the 
  character 
  of 
  the 
  striato-punctate 
  

   intercostal 
  furrows, 
  as 
  also 
  the 
  general 
  facies 
  of 
  the 
  specimen, 
  leave 
  

   little 
  room 
  to 
  doubt 
  its 
  generic 
  identity 
  with 
  Asteroptychins. 
  It 
  is 
  at 
  

   the 
  same 
  time 
  readily 
  distinguished 
  specifically 
  by 
  its 
  extremely 
  

   compressed, 
  slender 
  form, 
  in 
  which 
  respects 
  it 
  presents 
  marked 
  con- 
  

   trast 
  with 
  the 
  congeneric 
  form 
  Asteroptychius 
  bellulus, 
  St. 
  J. 
  and 
  W., 
  

   from 
  the 
  Lower 
  Coal 
  Measures. 
  

  

  Geological 
  position 
  and 
  locality.— 
  Upper 
  Coal 
  Measures 
  ; 
  calcareous 
  

   shales 
  overlying 
  the 
  coal 
  at 
  Topeka, 
  Kansas. 
  

  

  Genus 
  GLYMM 
  AT 
  ACANTHUS, 
  St. 
  J. 
  and 
  W. 
  

  

  Glvmmatacanthus 
  rudis, 
  St. 
  J. 
  and 
  W. 
  

  

  PL 
  XXV. 
  Fig. 
  1. 
  

  

  Dorsal 
  spine 
  large, 
  slightly 
  curved 
  and 
  somewhat 
  rapidly 
  tapering. 
  

   Transverse 
  section 
  wedge-shaped, 
  lateral 
  surfaces 
  slightly 
  convex, 
  

   meeting 
  in 
  the 
  sharply 
  rounded 
  anterior 
  edge, 
  posterior 
  face 
  not 
  

   shown. 
  The 
  lateral 
  surfaces 
  diverge 
  at 
  an 
  angle 
  of 
  30° 
  to 
  35°, 
  oc- 
  

   cupied 
  by 
  widish, 
  rounded 
  costae, 
  bifurcating 
  below, 
  separated 
  by 
  

   sharp 
  impressed 
  lines, 
  and 
  bearing 
  along 
  their 
  crests 
  irregularly- 
  

   shaped, 
  compressed, 
  conical, 
  closely 
  arranged 
  tubercles, 
  which 
  pro- 
  

   duce 
  an 
  exceedingly 
  rough, 
  rudely 
  sculptured 
  effect. 
  The 
  anterior 
  

   angle 
  of 
  the 
  spine 
  is 
  flanked 
  by 
  a 
  pair 
  of 
  costal, 
  which 
  support 
  

   approximately 
  opposite 
  tubercles. 
  The 
  tuberculation 
  more 
  or 
  less 
  

   distinctly 
  ranged 
  in 
  slightly 
  oblique 
  rows, 
  ascending 
  from 
  the 
  pos- 
  

   tero-lateral 
  angle 
  to 
  the 
  anterior 
  border, 
  and 
  rudely 
  sculptured 
  by 
  

   radiating 
  carinas. 
  Pulp 
  cavity 
  large, 
  apparently 
  confined 
  within 
  the 
  

   posterior 
  half 
  of 
  the 
  spine, 
  lateral 
  walls 
  thick. 
  

  

  The 
  unique 
  example 
  described 
  above 
  represents 
  a 
  fragment 
  from 
  

   the 
  middle 
  of 
  a 
  large 
  spine, 
  both 
  extremities 
  and 
  the 
  posterior 
  face 
  

   being 
  broken 
  away. 
  The 
  superficial 
  costation 
  and 
  tuberculation, 
  as 
  

   also 
  the 
  general 
  form 
  of 
  the 
  spine, 
  accord 
  well 
  with 
  the 
  distinctive 
  

   characteristics 
  of 
  Glymmatacanthus. 
  The 
  specimen 
  further 
  shows 
  the 
  

  

  