﻿INVEKTEBEATES. 
  303 
  

  

  arranged 
  in 
  alternate 
  series 
  of 
  thick 
  and 
  thinner 
  joints. 
  This 
  beau- 
  

   tiful 
  species, 
  the 
  first 
  discovered 
  in 
  the 
  Keokuk 
  limestone 
  in 
  Illinois, 
  

   I 
  take 
  pleasure 
  in 
  dedicating 
  to 
  its 
  discoverer, 
  Mr. 
  L. 
  A. 
  Cox, 
  of 
  Keo- 
  

   kuk, 
  to 
  whom 
  I 
  am 
  indebted 
  for 
  the 
  use 
  of 
  the 
  typical 
  specimen. 
  

  

  Position 
  and 
  locality: 
  Upper 
  beds 
  of 
  the 
  Keokuk 
  limestone, 
  Ham- 
  

   ilton, 
  Illinois. 
  

  

  No. 
  400 
  of 
  Mr. 
  Cox's 
  collection. 
  

  

  Zeacbinus 
  Keokuk, 
  Worfchen. 
  

  

  PL 
  XXVIII. 
  Fig. 
  3. 
  

  

  Zeacrinus 
  Keokuk, 
  Wobthen, 
  February, 
  1882. 
  

  

  Bulletin 
  No. 
  1, 
  of 
  the 
  Illinois 
  State 
  Museum 
  of 
  Natural 
  History, 
  P- 
  28. 
  

  

  Body 
  of 
  medium 
  size, 
  shallow, 
  basin- 
  shaped, 
  about 
  twice 
  as 
  wide 
  

   as 
  high. 
  Base 
  depressed 
  and 
  basal 
  plates 
  concealed 
  by 
  the 
  first 
  

   columnar 
  joints. 
  

  

  Subradials 
  on 
  the 
  anterior 
  side 
  hexagonal, 
  curving 
  below 
  into 
  the 
  

   basal 
  concavity, 
  their 
  upper 
  angles 
  extending 
  up 
  about 
  half 
  the 
  

   length 
  of 
  the 
  radial 
  plates. 
  

  

  Kadials 
  pentagonal, 
  nearly 
  once 
  and 
  a 
  half 
  as 
  wide 
  as 
  long. 
  

   Brachials 
  single 
  on 
  four 
  of 
  the 
  rays, 
  pentagonal, 
  a 
  little 
  larger 
  

   than 
  the 
  radial 
  below, 
  and 
  supporting 
  the 
  first 
  divisions 
  of 
  the 
  

   rays. 
  The 
  anterior 
  ray 
  has 
  four 
  brachials, 
  the 
  first 
  as 
  long 
  as 
  both 
  

   the 
  succeeding 
  ones, 
  quadrangular 
  and 
  as 
  wide 
  below 
  as 
  the 
  radial 
  

   on 
  which 
  it 
  rests. 
  The 
  two 
  succeeding 
  brachial 
  plates 
  are 
  short 
  and 
  

   quadrangular, 
  a 
  little 
  narrower 
  than 
  the 
  first. 
  The 
  fourth 
  is 
  also 
  

   short, 
  subtriangular, 
  and 
  supports 
  the 
  first 
  divisions 
  of 
  this 
  ray. 
  

   Both 
  branches 
  of 
  the 
  anterior 
  ray 
  divide 
  again 
  on 
  the 
  tenth 
  plate, 
  

   and 
  the 
  outer 
  division 
  the 
  second 
  time 
  on 
  the 
  tenth 
  plate 
  above, 
  

   making 
  six 
  arms 
  to 
  this 
  ray. 
  One 
  of 
  the 
  antero-lateral 
  rays, 
  after 
  

   its 
  first 
  division 
  on 
  the 
  brachial 
  plate, 
  sends 
  off 
  an 
  arm 
  from 
  each 
  

   division 
  on 
  the 
  sixth 
  plate, 
  the 
  outer 
  branches 
  dividing 
  again 
  on 
  the 
  

   eighth 
  to 
  the 
  tenth 
  plate, 
  making 
  eight 
  arms 
  to 
  this 
  ray. 
  The 
  arm 
  

   plates 
  are 
  but 
  slightly 
  rounded 
  exteriorly, 
  and 
  nearly 
  quadrangular 
  

   in 
  form. 
  Anal 
  plates 
  unknown. 
  

  

  Column 
  round, 
  and 
  composed 
  near 
  the 
  body 
  of 
  rather 
  thick, 
  alter- 
  

   nating 
  with 
  very 
  thin 
  plates. 
  

  

  Position 
  and 
  locality.- 
  Upper 
  part 
  of 
  the 
  geodiferous 
  shales 
  of 
  the 
  

   Keokuk 
  group, 
  one 
  mile 
  below 
  Keokuk. 
  

  

  No. 
  217 
  of 
  Mr. 
  L. 
  A. 
  Cox's 
  collection. 
  

  

  