﻿INVEETEBEATES. 
  323 
  

  

  DESCRIPTIONS 
  OF 
  SOME 
  NEW 
  SPECIES 
  OF 
  FOSSIL 
  SHELLS 
  

  

  FKOM 
  THE 
  

  

  LOWER 
  CARBONIFEROUS 
  LIMESTONES 
  

  

  COAL 
  MEASURES 
  OF 
  ILLINOIS.- 
  

  

  By 
  A. 
  H. 
  Woethkn. 
  

  

  Orthoceras 
  Illinoiensis, 
  Sp. 
  nov. 
  

  

  Shell 
  of 
  medium 
  size, 
  gradually 
  enlarging 
  from 
  the 
  apex; 
  section 
  

   slightly 
  ovate, 
  siphuncle 
  rather 
  large, 
  and 
  placed 
  near 
  the 
  margin 
  

   of 
  the 
  shell. 
  

  

  Septa 
  moderately 
  convex 
  and 
  oblique 
  to 
  the 
  axis, 
  being 
  arched 
  

   strongly 
  upward 
  about 
  twice 
  their 
  width 
  on 
  the 
  siphuncular 
  side, 
  

   and 
  equaling 
  in 
  width 
  about 
  one-fifth 
  of 
  the 
  shortest 
  diameter 
  of 
  the 
  

   shell. 
  Surface 
  markings 
  unknown. 
  

  

  Length 
  of 
  the 
  largest 
  specimen 
  seen, 
  about 
  6 
  inches 
  ; 
  greatest 
  

   diameter 
  of 
  the 
  outer 
  chamber, 
  2£ 
  inches 
  ; 
  greatest 
  width 
  at 
  the 
  

   apex, 
  f 
  inch. 
  

  

  This 
  rare 
  shell 
  is 
  only 
  known 
  from 
  three 
  imperfect 
  specimens 
  ob- 
  

   tained 
  from 
  the 
  upper 
  limestone 
  at 
  Chester. 
  

  

  No. 
  2,484, 
  of 
  the 
  Illinois 
  State 
  collection. 
  

  

  'Note. 
  These 
  brief 
  descriptions 
  are 
  published 
  with 
  the 
  hope 
  that 
  the 
  species 
  may 
  be 
  

   properly 
  illustrated 
  in 
  a 
  subsequent 
  volume 
  of 
  these 
  reports. 
  The 
  originals, 
  all 
  of 
  which 
  

   belong 
  to 
  the 
  State 
  Museum 
  of 
  Natural 
  History, 
  will 
  be 
  found 
  properly 
  catalogued 
  in 
  the 
  

   cases 
  of 
  the 
  Museum, 
  where 
  they 
  will 
  be 
  accessible 
  to 
  those 
  who 
  may 
  desire 
  to 
  conipap) 
  

   them 
  with 
  similar 
  forms 
  from 
  other 
  localities. 
  

  

  