﻿269 
  PAL^SONTOLOGI 
  OF 
  ILLINOIS. 
  

  

  where, 
  ae 
  already 
  noted, 
  th< 
  y 
  appear 
  to 
  have 
  the 
  oblique 
  arrange* 
  

   in. 
  nt 
  oommon 
  to 
  the 
  genus 
  to 
  which 
  the 
  erpeeies 
  represented 
  l»y 
  

   the 
  above 
  specimen 
  is 
  provisionally 
  referred, 
  and 
  "f 
  which 
  it 
  is, 
  at 
  

   the 
  present 
  time, 
  the 
  Hole 
  representative 
  from 
  the 
  Carboniferous 
  

   formations 
  of 
  the 
  Qpper 
  Mississippi 
  region. 
  Principal 
  Dawson 
  has 
  

   notice 
  I 
  representatives 
  of 
  the 
  grains 
  from 
  the 
  Carboniferous 
  <>f 
  

   Scotia, 
  and 
  Dr. 
  Newberry 
  has 
  described 
  Borne 
  interesting 
  sp< 
  

   from 
  the 
  Lower 
  Carboniferous 
  of 
  Ohio. 
  

  

  logical 
  'position 
  and 
  locality: 
  Keokuk 
  limestone; 
  Keokuk, 
  [owa. 
  

  

  GrENUS 
  PIIYSOXKMLS. 
  Agassiz. 
  

   Phybohxhus 
  falcati>. 
  St. 
  .1. 
  and 
  W. 
  

   pi. 
  xxiv. 
  nit. 
  ... 
  

   Dorsal 
  spine 
  of 
  small 
  size, 
  comparatively 
  narrow, 
  gradually 
  taper- 
  

   ing, 
  and 
  very 
  strongly 
  arched 
  along 
  the 
  posterior 
  face, 
  the 
  tip 
  reach- 
  

   ing 
  a 
  point 
  nearly 
  vertical 
  to 
  the 
  inferior 
  extremity. 
  Transwr-t 
  

   section 
  wedge-shaped, 
  anterior 
  edge 
  making 
  an 
  acutely 
  rounded 
  

   angle, 
  expanding 
  below 
  into 
  the 
  inferior 
  shoulder, 
  which 
  is 
  aharply 
  

   constricted 
  at 
  the 
  dorsal 
  line 
  to 
  the 
  plain 
  hase. 
  Lateral 
  surfaces 
  

   slightly 
  convex, 
  the 
  hony 
  surface 
  showing 
  an 
  impressed 
  line 
  parallel 
  

   with 
  the 
  posterior 
  ( 
  .Ige 
  as 
  usually 
  observed 
  under 
  similar 
  conditions 
  

   of 
  BUrfaoe 
  exfoliation. 
  

  

  The 
  description 
  refers 
  to 
  a 
  unique 
  example 
  belonging 
  to 
  the 
  ooJ- 
  

  

  hction 
  of 
  Washington 
  University. 
  It 
  represents 
  nearly 
  the 
  entire 
  

  

  outline, 
  hut 
  as 
  so 
  frequently 
  occurs 
  with 
  the 
  small 
  specimens 
  of 
  the 
  

   g( 
  mis, 
  the 
  posterior 
  faoe 
  is 
  worn 
  away, 
  the 
  pulp 
  cavity 
  making 
  a 
  

  

  groove 
  throughout 
  its 
  exposed 
  extent. 
  Tli< 
  exposed 
  portion 
  of 
  the 
  

   Bpine, 
  also, 
  is 
  denuded 
  Of 
  the 
  original 
  longitudinal 
  costa 
  and 
  tulxr- 
  

   culation. 
  of 
  which 
  not 
  a 
  \c-tigc 
  remains 
  from 
  which 
  to 
  infer 
  the 
  

  

  oharacter 
  of 
  the 
  Buperfioia] 
  ornamentation. 
  The 
  strong 
  ourvata 
  

   the 
  spine 
  recalls 
  the 
  forms 
  to 
  which 
  the 
  nanus 
  Phgt 
  parvuhu, 
  

  

  and 
  Ph. 
  Cestriensi$, 
  derived 
  respectively 
  from 
  the 
  Keokuk 
  and 
  t 
  

  

  ter 
  formations. 
  ha\. 
  bl 
  • 
  D 
  IVCn. 
  It 
  18, 
  houev. 
  r. 
  a 
  much 
  more 
  shndt 
  r 
  

  

  form, 
  not 
  attaining 
  near 
  the 
  breadth 
  of 
  the 
  above 
  named 
  spines. 
  It 
  

   i-. 
  indeed, 
  possible 
  that 
  it 
  prove 
  to 
  be 
  :i 
  young 
  individual 
  of 
  the 
  

  

  I'h. 
  Alton* 
  it. 
  J. 
  and 
  YY.. 
  of 
  the 
  -aim 
  formation, 
  though 
  

  

  the 
  latter 
  identity 
  seems 
  highly 
  improbable. 
  

  

  logical 
  position 
  'in<l 
  locality, 
  St. 
  Louis 
  lit 
  mis, 
  

  

  M 
  ouri. 
  

  

  

  