﻿320 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  In 
  addition 
  to 
  these 
  furrows 
  each 
  valve 
  is 
  marked 
  hy 
  ahout 
  

   thirty-two 
  longitudinal 
  ridges 
  that 
  are 
  a 
  little 
  wider 
  than 
  tfa 
  

   between 
  them. 
  Th( 
  Be 
  commence 
  at 
  the 
  dorsal 
  margin 
  near 
  the 
  

  

  . 
  and 
  when 
  they 
  cross 
  the 
  posterior 
  furrow 
  already 
  di 
  

   they 
  are 
  deflected 
  abruptly 
  forward 
  to 
  a 
  right 
  angle 
  with 
  their 
  

   former 
  oourse, 
  about 
  two 
  out 
  of 
  every 
  three 
  ending 
  at 
  the 
  anti 
  

   furrow, 
  while 
  the 
  others 
  are 
  continuous 
  that 
  to 
  the 
  anterior 
  

  

  border 
  of 
  the 
  shell. 
  

  

  A 
  small 
  fragment 
  of 
  the 
  shell, 
  attached 
  to 
  the 
  cast, 
  shows 
  that 
  

   the 
  surface 
  was 
  finely 
  striated 
  obliquely 
  from 
  the 
  l»*ak 
  to 
  the 
  front, 
  

   and 
  with 
  a 
  good 
  lens 
  the 
  stria- 
  are 
  seen 
  to 
  consi.-t 
  of 
  rows 
  of 
  minute 
  

   granules. 
  

  

  Dedicated 
  to 
  Mrs. 
  Orestes 
  St. 
  John, 
  by 
  whom 
  this 
  fine 
  specimen 
  

   was 
  discovered, 
  and 
  to 
  whom 
  I 
  am 
  indebted 
  for 
  the 
  ose 
  of 
  it. 
  

  

  Position 
  ami 
  locality 
  : 
  Upper 
  Coal 
  M- 
  a-nn 
  s. 
  Slmwi.u 
  county. 
  Kan. 
  

  

  