﻿■1 
  ii 
  PALEONTOLOGY 
  OF 
  ILL 
  IV 
  

  

  in 
  front 
  bearing 
  two 
  rows 
  of 
  minute 
  punctures 
  and 
  a 
  faint 
  me 
  dia 
  n 
  

   tiiiforru 
  line, 
  the 
  costae 
  enveloped 
  in 
  a 
  smooth 
  coating 
  of 
  enamel 
  

   without 
  transverse 
  or 
  tubercular 
  elevation. 
  Near 
  the 
  middle 
  of 
  the 
  ^ 
  

   exposed 
  right 
  side 
  of 
  the 
  type 
  specimen, 
  one 
  of 
  the 
  cost;i 
  attai 
  

   double 
  the 
  breadth 
  of 
  those 
  in 
  front, 
  and 
  immediately 
  along 
  the 
  

   beveled 
  posterior 
  edges 
  occurs 
  a 
  plain 
  space 
  apparently 
  destitute 
  of 
  

   longitudinal 
  ridges. 
  Pulp 
  cavity 
  compressed 
  ovate 
  in 
  outline, 
  con- 
  

   fined 
  within 
  the 
  posterior 
  half, 
  and 
  inoloaed 
  between 
  thick 
  wall 
  

   A 
  specimen 
  preserving 
  a 
  length 
  of 
  65 
  millimetres 
  has 
  a 
  breadth 
  at 
  

   base 
  of 
  6.5 
  mm., 
  and 
  a 
  thickness 
  of 
  8 
  mm. 
  

  

  \V. 
  have 
  met 
  with 
  only 
  a 
  single 
  example 
  of 
  the 
  above 
  described 
  

   iolithyodorolite, 
  which 
  presents 
  the 
  greater 
  portion 
  of 
  a 
  6mall 
  spine 
  

   ■ 
  ading 
  from 
  the 
  acute 
  distal 
  extremity 
  to 
  a 
  point 
  near 
  the 
  dorsal 
  

   line, 
  above 
  which 
  it 
  is 
  broken 
  off. 
  The 
  specimen 
  is 
  embedded 
  in 
  a 
  

   limestone 
  matrix 
  in 
  such 
  manner 
  as 
  to 
  allow 
  of 
  the 
  exposure 
  of 
  the 
  

   right 
  side 
  and 
  the 
  posterior 
  face; 
  it 
  is 
  slightly 
  distorted 
  and 
  fn 
  

   tured 
  across 
  at 
  several 
  places, 
  revealing 
  the 
  small 
  pulp-cavity, 
  and 
  

   somewhat 
  worn 
  especially 
  along 
  the 
  posterior 
  half 
  of 
  the 
  lateral 
  

   surfaces. 
  The 
  anterior 
  costse, 
  however, 
  are 
  uninjured, 
  and 
  their 
  

   condition 
  is 
  as 
  noted 
  above. 
  The 
  striking 
  oharaofc 
  of 
  the 
  

  

  spine 
  are 
  its 
  slight 
  curvature, 
  rigid 
  outline, 
  and 
  the 
  deeply 
  channeled 
  

   posterior 
  face 
  and 
  closely 
  set 
  large 
  denticles. 
  Thi 
  men 
  basno 
  

  

  Dear 
  ally 
  in 
  the 
  Coal 
  Measure 
  strata, 
  and 
  so 
  far 
  as 
  it 
  is 
  possible 
  to 
  

  

  determine 
  to 
  the 
  contrary, 
  it 
  presents 
  all 
  the 
  charaol 
  ib- 
  

  

  able 
  to 
  Acondylacanthiu. 
  

  

  logical 
  position 
  and 
  locality: 
  Upper 
  Coal 
  M 
  . 
  above 
  coal 
  

  

  No, 
  9, 
  111. 
  Gen'l 
  Sec; 
  the 
  upper 
  limestone 
  at 
  f. 
  a 
  Salle. 
  Qlim 
  

  

  AcoM'viAt'w 
  i 
  n: 
  ji 
  Si. 
  .1. 
  and 
  VY. 
  

  

  PL 
  WVI, 
  1 
  u: 
  

  

  Dorsal 
  Bpine 
  of 
  medium 
  sue, 
  rather 
  Btrongrj 
  the 
  

  

  anterior 
  edge 
  and 
  somewhal 
  rapidly 
  tapering, 
  laterally 
  compressed, 
  

   transvi 
  ion 
  ouneate; 
  posterior 
  face 
  narrow, 
  deeply 
  channeled 
  ; 
  

  

  palp 
  cavity 
  relatively 
  small, 
  BoblentieoJar 
  or 
  compressed 
  ovoid 
  in 
  

   trai 
  oatline. 
  Lateral 
  surfaces 
  n 
  lyoonvexti 
  ely; 
  

  

  sharpl] 
  rounded 
  into 
  the 
  anterior 
  keel, 
  also 
  gentlj 
  rounded 
  and 
  

   compressed 
  posteriorly 
  to 
  the 
  postero-latera] 
  angles, 
  winch 
  bear 
  • 
  

  

  n 
  of 
  lateralis 
  oompi 
  downward-booked 
  dent 
  

  

  oiroled 
  al 
  the 
  a 
  oinotnre, 
  more 
  or 
  less 
  regularl] 
  by 
  

  

  than 
  their 
  ow 
  ■ 
  ler 
  diameter, 
  and 
  extending 
  two-thirds 
  or 
  

  

  h 
  of 
  tli. 
  d 
  portion 
  of 
  tl 
  

  

  