﻿210 
  Twenty-eighth 
  Repokt 
  on 
  the 
  State 
  Museum. 
  

  

  Walls 
  composed 
  of 
  very 
  small 
  polygonal 
  plates 
  varying 
  in 
  

   diameter 
  from 
  .5 
  to 
  one 
  mm. 
  ; 
  surface 
  smooth, 
  without 
  special 
  

   ornamentation. 
  

  

  The 
  specimen 
  described 
  shows, 
  on 
  the 
  exterior, 
  eleven 
  lobes, 
  

   which 
  present 
  great 
  variations 
  in 
  comparative 
  volume. 
  Its 
  

   greatest 
  vertical 
  diameter 
  is 
  40 
  mm., 
  and 
  its 
  transverse 
  diame- 
  

   ters 
  are 
  46 
  and 
  55 
  mm., 
  respectively. 
  The 
  basal 
  area 
  is 
  sub- 
  

   circular, 
  and 
  measures 
  about 
  23 
  mm. 
  

  

  This 
  form 
  is 
  distinguished 
  from 
  C. 
  Saffordi 
  with 
  which 
  it 
  

   is 
  associated, 
  in 
  its 
  more 
  irregular 
  form, 
  larger 
  base, 
  and 
  more 
  

   numerous 
  ambulacra. 
  In 
  the 
  comparative 
  size 
  of 
  the 
  basal 
  

   area 
  it 
  more 
  nearly 
  corresponds 
  to 
  C. 
  stellatus, 
  but 
  its 
  form 
  

   and 
  the 
  structure 
  of 
  the 
  walls 
  are 
  very 
  different. 
  The 
  speci- 
  

   men 
  forming 
  the 
  basis 
  of 
  the 
  description 
  possesses 
  features 
  

   which 
  are 
  apparently 
  of 
  specific 
  importance 
  as 
  above 
  indi- 
  

   cated, 
  while 
  showing 
  the 
  variation 
  and 
  want 
  of 
  a 
  constant 
  

   definition, 
  which 
  characterize 
  these 
  bodies. 
  

  

  The 
  great 
  inequality 
  exhibited 
  in 
  the 
  lobes 
  may, 
  in 
  other 
  

   specimens, 
  produce 
  a 
  general 
  form 
  very 
  unlike 
  those 
  de- 
  

   scribed. 
  The 
  form 
  of 
  the 
  body, 
  and 
  the 
  size 
  and 
  disposition 
  

   of 
  the 
  lobes 
  seems 
  to 
  be 
  the 
  most 
  inconstant 
  feature 
  of 
  the 
  

   three 
  species 
  here 
  described. 
  

  

  Formation 
  and 
  locality. 
  In 
  the 
  Lower 
  Helderberg, 
  lime- 
  

   stone, 
  Hardin 
  county, 
  Tennessee. 
  

  

  