﻿Lower 
  Heldeeberg 
  Crinoidea. 
  209 
  

  

  It 
  is 
  not 
  at 
  once 
  evident 
  as 
  to 
  what 
  constitutes 
  the 
  important 
  

   specific 
  differences 
  of 
  these 
  fossils. 
  The 
  specimens 
  referred 
  to 
  

   O. 
  stellatus 
  show 
  a 
  somewhat 
  more 
  depressed 
  and 
  symmetri- 
  

   cal 
  form, 
  the 
  basal 
  area 
  is 
  comparatively 
  larger, 
  with 
  more 
  

   numerous 
  ambulacra, 
  and 
  the 
  ornamentation 
  of 
  the 
  exterior 
  

   walls 
  of 
  the 
  dome 
  is 
  conspicuously 
  different 
  from 
  C. 
  Saffordi. 
  

   In 
  contrast 
  with 
  C. 
  ClarMi, 
  the 
  species 
  here 
  described 
  has 
  a 
  

   more 
  regular 
  form, 
  with 
  fewer 
  internal 
  chambers 
  and 
  corre- 
  

   sponding 
  ambulacra, 
  and 
  the 
  basal 
  area 
  is 
  considerably 
  

   smaller. 
  

  

  The 
  projecting 
  margin 
  around 
  the 
  basal 
  area 
  is 
  broken 
  and 
  

   imperfect 
  in 
  all 
  the 
  specimens 
  examined, 
  and 
  its 
  original 
  extent 
  

   is 
  not 
  known 
  ; 
  but 
  whatever 
  variation 
  there 
  .may 
  be 
  in 
  the 
  

   form 
  of 
  the 
  body, 
  this 
  area 
  is 
  well 
  defined 
  and 
  distinctly 
  

   limited, 
  having 
  a 
  subcircular 
  or 
  unequally 
  pentagonal 
  out- 
  

   line. 
  The 
  substance 
  of 
  the 
  dome 
  is 
  usually 
  silicified, 
  and 
  this 
  

   change 
  has 
  obscured 
  the 
  minute 
  structure 
  of 
  the 
  walls, 
  

   which 
  is 
  preserved 
  in 
  but 
  few 
  of 
  the 
  specimens. 
  

  

  Fig. 
  1, 
  pi. 
  36, 
  represents 
  the 
  bases 
  of 
  two 
  small 
  columns 
  be- 
  

   sides 
  the 
  large 
  central 
  one, 
  suggesting 
  the 
  idea 
  that 
  this 
  hy- 
  

   drocyst 
  furnished 
  a 
  float 
  or 
  support 
  to 
  a 
  colony 
  of 
  individu- 
  

   als. 
  In 
  fig. 
  5, 
  there 
  is 
  a 
  cicatrice 
  such 
  as 
  would 
  be 
  produced 
  

   by 
  the 
  separation 
  of 
  a 
  similar 
  accessory 
  column. 
  The 
  external 
  

   resemblance 
  of 
  the 
  specimens 
  of 
  this 
  species 
  to 
  a 
  Favosite 
  is 
  

   even 
  more 
  marked 
  than 
  in 
  C. 
  stellatus 
  ,and 
  is 
  well 
  represented 
  

   in 
  fig. 
  4. 
  

  

  Formation 
  and 
  locality. 
  In 
  limestone 
  referred 
  to 
  the 
  Lower 
  

   Helderberg 
  group, 
  Hardin 
  county, 
  Tennessee. 
  

  

  Camakocrinus 
  Claekii 
  n. 
  sp. 
  

  

  Plate, 
  36, 
  figs. 
  7, 
  8; 
  Plate 
  37, 
  fig. 
  3. 
  

  

  Body 
  of 
  an 
  irregular 
  ovoid 
  form, 
  marked 
  by 
  numerous 
  

   unequal 
  lobes 
  corresponding 
  to 
  the 
  internal 
  chambers 
  ; 
  base 
  

   flattened. 
  

  

  Basal 
  area 
  large 
  and 
  well 
  defined, 
  having 
  a 
  diameter 
  of 
  

   somewhat 
  less 
  than 
  one-half 
  the 
  transverse 
  diameter 
  of 
  the 
  

   dome. 
  Rays 
  numerous, 
  connected 
  by 
  small 
  polygonal 
  

   plates 
  ; 
  bifurcating 
  near 
  the 
  periphery 
  of 
  the 
  basal 
  area 
  and 
  

   surrounding 
  small 
  ambulacra 
  leading 
  into 
  the 
  internal 
  

   cavities. 
  

  

  The 
  interior 
  of 
  the 
  hydrocyst 
  is 
  divided 
  by 
  vertical, 
  hori- 
  

   zontal, 
  and 
  oblique 
  partitions, 
  into 
  numerous 
  unequal 
  cham- 
  

   bers, 
  which 
  are 
  shown 
  on 
  the 
  exterior 
  as 
  rounded 
  lobes. 
  

   Each 
  of 
  these 
  chambers 
  has 
  an 
  ambulacral 
  opening 
  in 
  the 
  

   basal 
  area. 
  

  

  