﻿INVERTEBRATES. 
  329 
  

  

  Cholaster 
  peculiaris, 
  Sp. 
  nov. 
  

  

  PI. 
  XXXI. 
  Fig. 
  4. 
  a. 
  Dorsal 
  view, 
  natural 
  size; 
  6. 
  Section 
  of 
  a 
  ray 
  enlarged, 
  showing 
  

   the 
  arrangement 
  of 
  the 
  plates. 
  

  

  The 
  general 
  form 
  of 
  the 
  body 
  is 
  that 
  of 
  a 
  truncated 
  pentagonal 
  

   star, 
  with 
  a 
  large 
  circular 
  disc. 
  A 
  centro-dorsal 
  plate 
  is 
  surrounded 
  

   by 
  five 
  others, 
  all 
  of 
  which 
  are 
  much 
  larger 
  than 
  other 
  plates 
  of 
  

   the 
  body, 
  and 
  occupy 
  a 
  centro-dorsal 
  depression. 
  The 
  position 
  of 
  

   these 
  five 
  plates 
  is 
  that 
  of 
  radials, 
  resting 
  upon 
  a 
  basal, 
  and 
  there- 
  

   fore, 
  all 
  other 
  plates 
  of 
  the 
  body 
  might 
  be 
  regarded 
  as 
  radials 
  and 
  

   interradials, 
  the 
  latter 
  being 
  very 
  numerous, 
  because 
  of 
  the 
  wide 
  

   separation 
  of 
  the 
  rays 
  at 
  their 
  junction 
  with 
  the 
  body. 
  The 
  inter- 
  

   radials 
  are 
  polygonal, 
  convex, 
  or 
  subspinous 
  plates, 
  without 
  much 
  

   variation 
  in 
  size 
  whether 
  filling 
  the 
  larger 
  or 
  smaller 
  interradial 
  

   spaces. 
  The 
  plates 
  following 
  the 
  larger 
  radial 
  plates, 
  as 
  above 
  de- 
  

   fined, 
  in 
  the 
  direction 
  of 
  the 
  rays, 
  are 
  not, 
  however, 
  by 
  their 
  form 
  

   or 
  arrangement 
  to 
  be 
  distinguished 
  from 
  the 
  interradials, 
  though 
  

   differing 
  from 
  those 
  forming 
  the 
  rays. 
  The 
  plates 
  covering 
  the 
  

   dorsal 
  side 
  are 
  thus 
  divided 
  into 
  three 
  kinds, 
  viz. 
  : 
  First, 
  the 
  larger 
  

   plates 
  filling 
  the 
  centro-dorsal 
  depression 
  ; 
  second, 
  the 
  disc 
  plates 
  

   which 
  cover 
  all 
  other 
  parts 
  of 
  the 
  body 
  except 
  the 
  rays, 
  and, 
  third, 
  

   the 
  plates 
  which 
  cover 
  the 
  rays 
  proper, 
  which 
  in 
  this 
  species 
  are 
  

   easily 
  distinguished 
  from 
  the 
  central 
  disc 
  plates. 
  

  

  The 
  rays 
  are 
  short, 
  abruptly 
  truncated, 
  and 
  slightly 
  expanded 
  at 
  

   the 
  apices 
  by 
  reason 
  of 
  an 
  enlargement 
  of 
  the 
  terminal 
  plates. 
  

   They 
  are 
  widely 
  separated 
  from 
  each 
  other, 
  though 
  not 
  at 
  uniform 
  

   distances, 
  and 
  present 
  the 
  appearance 
  of 
  having 
  been 
  stuck 
  on 
  

   the 
  central 
  disc, 
  instead 
  of 
  having 
  grown 
  from 
  :t, 
  an 
  appearance 
  

   more 
  marked, 
  by 
  reason 
  of 
  the 
  change 
  in 
  the 
  form 
  of 
  the 
  plates, 
  

   from 
  the 
  disc 
  to 
  the 
  rays. 
  

  

  One 
  of 
  the 
  interradial 
  spaces 
  is 
  much 
  greater 
  than 
  the 
  others, 
  so 
  

   that 
  a 
  line 
  may 
  be 
  drawn 
  across 
  the 
  disc, 
  leaving 
  three 
  entire 
  rays 
  

   upon 
  the 
  smaller 
  half. 
  The 
  back 
  of 
  each 
  ray 
  is 
  covered 
  by 
  a 
  series 
  

   of 
  transversely 
  elongated 
  plates 
  separated 
  from 
  the 
  side 
  series 
  by 
  a 
  

   longitudinally 
  impressed 
  line. 
  A 
  single 
  series 
  of 
  plates 
  covers 
  either 
  

   side 
  of 
  a 
  ray, 
  ' 
  interlocking 
  with 
  the 
  transverse 
  dorsal 
  series 
  and 
  di- 
  

   rected 
  backward 
  toward 
  the 
  disc. 
  

  

  The 
  oral 
  plates 
  are 
  unknown, 
  and 
  no 
  madreporiform 
  tubercle 
  has 
  

   been 
  detected. 
  

  

  Position 
  and 
  locality: 
  Same 
  as 
  the 
  last. 
  

  

  No. 
  2,480 
  Illinois 
  State 
  collection 
  of 
  1880. 
  

  

  