﻿:;;i 
  i" 
  roLOGY 
  of 
  illink 
  

  

  imbricate 
  upward, 
  and 
  the 
  two 
  rows 
  adjoining 
  the 
  ambulacra] 
  a 
  

   imbricate 
  outward, 
  but 
  whether 
  the 
  imbrication 
  is 
  from 
  the 
  central 
  

   range 
  outward, 
  as 
  is 
  usual 
  in 
  Buch 
  annot 
  be 
  determined, 
  for 
  

  

  tbe 
  central 
  w 
  ms 
  to 
  be 
  depressed, 
  which 
  may 
  have 
  resulted 
  

  

  from 
  the 
  orushing 
  the 
  fossil 
  lias 
  received. 
  

  

  The 
  plates 
  bore 
  two 
  kinds 
  of 
  spines; 
  those 
  bearing 
  the 
  larger 
  kind 
  

  

  Based 
  a 
  Bingle 
  centra] 
  spine, 
  but 
  those 
  bearing 
  the 
  smaller 
  kind 
  

  

  i 
  two 
  <t 
  more 
  submargina] 
  ones. 
  Tbe 
  central 
  supporting 
  

  

  tuberole 
  is 
  a 
  moderately 
  large 
  smooth 
  hemispherical 
  nipple 
  with 
  a 
  

  

  central 
  perforation. 
  Only 
  one 
  plate 
  of 
  this 
  kind 
  is 
  shown 
  upon 
  tbe 
  

  

  typical 
  specimen, 
  and 
  it 
  is 
  in 
  the 
  second 
  range 
  from 
  the 
  ambul 
  

  

  at 
  about 
  the 
  sixth 
  plate 
  from 
  the 
  genitals. 
  Tbe 
  secondary 
  

   spines 
  were 
  borne 
  by 
  both 
  rows 
  of 
  plates 
  on 
  each 
  side 
  of 
  the 
  am- 
  

   bulacrals, 
  as 
  indicated 
  by 
  small, 
  more 
  or 
  less 
  conical 
  (leva* 
  

   some 
  of 
  which 
  show 
  a 
  minute 
  perforation, 
  and 
  indeed 
  may). 
  

   borne 
  by 
  tbe 
  plates 
  in 
  the 
  other 
  ranges. 
  Other 
  characters 
  of 
  the 
  

   species 
  unknown. 
  

  

  The 
  plates, 
  in 
  the 
  interainbulacral 
  areas 
  of 
  this 
  sp< 
  

   in 
  number, 
  order 
  of 
  arrangement, 
  and 
  spinous 
  character 
  so 
  much 
  

   more 
  nearly 
  with 
  Peri$ckodomu» 
  than 
  with 
  Lcpidechinm, 
  the 
  most 
  

   nearly 
  approximating 
  genus 
  in 
  other 
  known 
  respects, 
  that 
  we 
  have 
  

   little 
  doubt 
  of 
  the 
  correctness 
  of 
  tl 
  rio 
  reference, 
  though 
  it 
  

  

  would 
  be 
  unnecessary 
  to 
  point 
  out 
  how 
  it 
  differs 
  from 
  the 
  Eur. 
  

   forms 
  for 
  the 
  purpose 
  of 
  specific 
  distinction. 
  

  

  Collected 
  by 
  A. 
  11. 
  Wort 
  hen 
  from 
  the 
  Chester 
  limestone 
  at 
  

   City, 
  Pope 
  county. 
  Illinois. 
  

  

  No. 
  -1. 
  is:i 
  Illinois 
  State' 
  collection. 
  

  

  