﻿PAL-ffiOiNTOLOGY 
  OF 
  ILI.IY 
  

  

  I'inna 
  - 
  \i< 
  i. 
  Bp. 
  nov. 
  

  

  Shell 
  comparatively 
  short, 
  Lanceolate; 
  length 
  about 
  twice 
  as 
  much 
  

   ae 
  the 
  greatest 
  width. 
  Section 
  ovate-elliptical, 
  valves 
  tra\. 
  

   Longitudinally 
  by 
  about 
  twelve 
  to 
  fifteen 
  rather 
  Btrong 
  ribs 
  that 
  are 
  

   most 
  prominent 
  on 
  the 
  middle 
  portion 
  of 
  the 
  shell, 
  and 
  become 
  

   obsolete 
  towards 
  the 
  vental 
  and 
  dorsal 
  margins. 
  Bpaces 
  bet 
  

   the 
  ribs 
  narrow, 
  beak 
  unknown. 
  Angle 
  forim 
  d 
  by 
  the 
  dorsal 
  and 
  

   rental 
  margins 
  abont 
  i" 
  . 
  

  

  This 
  rare 
  Bpeoies 
  is 
  only 
  known 
  from 
  a 
  single 
  Bpeeimen 
  p 
  

   in 
  chert, 
  with 
  both 
  extremities 
  wanting. 
  It 
  may 
  be 
  readily 
  distin- 
  

   tingoished 
  from 
  /'. 
  Missourienris 
  of 
  the 
  Chester 
  group, 
  and 
  from 
  

   any 
  other 
  species 
  known 
  in 
  our 
  Carboniferous 
  rocks, 
  by 
  its 
  shorter 
  

   form 
  and 
  greater 
  proportional 
  width. 
  

  

  Porition 
  and 
  locality: 
  St. 
  Louis 
  limestone. 
  Monroe 
  county. 
  111. 
  

  

  No. 
  "i,: 
  1 
  .!!) 
  Illinois 
  State 
  collection. 
  

  

  CtpbioiBDU? 
  riAxnoi.rin.Nsi-, 
  Bp. 
  nov. 
  

  

  This 
  shell 
  is 
  only 
  known 
  from 
  some 
  casts 
  in 
  limestone, 
  which 
  may 
  

   be 
  briefly 
  described 
  as 
  follows: 
  

  

  Sbell 
  oblong, 
  height 
  from 
  the 
  beak 
  to 
  the 
  ventral 
  margin 
  about 
  

   half 
  the 
  Length, 
  valves 
  moderately 
  oonvei 
  on 
  the 
  anterior 
  portion 
  

   of 
  the 
  shell, 
  and 
  depressed 
  towards 
  the 
  posterior 
  end, 
  where 
  the 
  

   valves 
  were 
  apparently 
  closely 
  joined. 
  Beaks 
  rather 
  large, 
  depressed 
  

  

  and 
  incurved 
  beyond 
  the 
  dorsal 
  margin, 
  and 
  situated 
  about 
  two- 
  

   tifths 
  the 
  distance 
  from 
  the 
  anterior 
  to 
  the 
  posterior 
  extrem 
  

  

  A 
  broad 
  and 
  slightly 
  flattened 
  depression 
  appears 
  on 
  I 
  the 
  

  

  casts, 
  extending 
  from 
  the 
  beak 
  to 
  the 
  ventral 
  margin 
  of 
  the 
  shell. 
  

   :il 
  margin 
  Dearly 
  straight, 
  ventral 
  margin 
  parallel 
  with 
  the 
  

   il 
  for 
  abont 
  two-thirds 
  of 
  its 
  Length, 
  curving 
  abruptly 
  up- 
  

   ward 
  on 
  the 
  anterior, 
  and 
  m 
  tlyon 
  the 
  posterior 
  end. 
  Lonule 
  

   •- 
  ; 
  surface 
  markings 
  unknown. 
  

   I.. 
  Q| 
  th 
  of 
  an 
  a\- 
  1 
  

   thickness, 
  15- 
  L6 
  inch. 
  

  

  •inn 
  tmd 
  locality 
  l 
  V 
  r 
  Limestone) 
  Randolph 
  county. 
  111. 
  

   2,491 
  Illinois 
  Mat. 
  collection. 
  

  

  