﻿2 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  vol. 
  67 
  

  

  carried 
  by 
  means 
  of 
  currents 
  produced 
  by 
  minute 
  cilia 
  to 
  the 
  oral 
  

   center, 
  or 
  mouth. 
  The 
  arms 
  when 
  gathering 
  food 
  are 
  stretched 
  up- 
  

   ward 
  or 
  outward, 
  but 
  may 
  be 
  folded 
  together 
  when 
  not 
  so 
  employed 
  

   in 
  such 
  a 
  manner 
  that 
  the 
  vital 
  organs 
  and 
  soft 
  parts 
  are 
  protected 
  

   by 
  an 
  outer 
  envelope 
  of 
  hard 
  calcareous 
  material. 
  The 
  excrement 
  

   is 
  discharged 
  through 
  an 
  orifice, 
  either 
  directly 
  piercing 
  the 
  tegmen, 
  

   or 
  roof, 
  or 
  at 
  the 
  end 
  or 
  side 
  of 
  a 
  projecting 
  tube, 
  or 
  exceptionally 
  

   through 
  the 
  side 
  wall 
  of 
  the 
  cup. 
  

  

  The 
  plates 
  of 
  which 
  the 
  calyx 
  is 
  composed 
  are 
  arranged 
  usually 
  

   according 
  to 
  a 
  quinqueradiate 
  plan, 
  most 
  plainly 
  developed 
  on 
  the 
  

   lower 
  side 
  to 
  which 
  the 
  stem 
  is 
  attached, 
  from 
  which 
  the 
  radiation 
  

   extends 
  upward 
  and 
  continues 
  into 
  the 
  arms. 
  This 
  is 
  called 
  the 
  

   dorsal 
  side, 
  in 
  contradistinction 
  to 
  that 
  next 
  to 
  which 
  the 
  arms 
  are 
  

   located, 
  which 
  is 
  the 
  ventral 
  side 
  or 
  tegmen; 
  and 
  the 
  part 
  of 
  the 
  

   calyx 
  below 
  the 
  origin 
  of 
  the 
  arms 
  is 
  called 
  the 
  dorsal 
  cup, 
  or 
  simply 
  

   the 
  cup, 
  which 
  incloses 
  or 
  supports 
  the 
  visceral 
  organs. 
  

  

  This 
  cup 
  in 
  the 
  usual 
  crinoid 
  is 
  made 
  up 
  of 
  a 
  base, 
  consisting 
  either 
  

   of 
  a 
  single 
  ring 
  of 
  five, 
  four, 
  three, 
  or 
  two 
  plates 
  (or 
  some 
  of 
  these 
  

   coalesced 
  into 
  a 
  single 
  undivided 
  disk), 
  called 
  basals; 
  or 
  of 
  this 
  

   and 
  another 
  alternating 
  ring 
  below 
  it 
  of 
  five 
  or 
  three 
  plates 
  (also 
  

   sometimes 
  fused 
  into 
  one), 
  called 
  infrabasals; 
  and 
  following 
  the 
  

   basal 
  ring 
  another 
  set 
  of 
  five 
  alternating 
  plates, 
  called 
  radials, 
  with 
  

   sometimes 
  a 
  ring 
  of 
  interradials 
  in 
  line 
  with 
  them. 
  

  

  The 
  two 
  rings 
  of 
  cup 
  plates 
  — 
  basals 
  and 
  radials 
  — 
  are 
  the 
  funda- 
  

   mental 
  elements 
  of 
  the 
  adult 
  crinoid 
  structure. 
  They 
  are 
  found 
  

   throughout 
  all 
  the 
  major 
  divisions 
  of 
  the 
  class, 
  and 
  of 
  the 
  blastoids 
  

   also. 
  In 
  the 
  typical 
  crinoid 
  these 
  two 
  elements 
  are 
  symmetrically 
  

   arranged 
  in 
  alternating 
  contact 
  with 
  each 
  other, 
  and 
  the 
  radials 
  are 
  

   symmetric 
  among 
  themselves. 
  This 
  is 
  the 
  plan 
  in 
  the 
  great 
  majority 
  

   of 
  fossil, 
  and 
  practically 
  all 
  the 
  existing, 
  crinoids. 
  But 
  to 
  this 
  gen- 
  

   eralized 
  type 
  there 
  are 
  numerous 
  exceptions. 
  

  

  The 
  general 
  tendency 
  of 
  the 
  crinoids 
  as 
  a 
  class, 
  starting 
  in 
  the 
  

   earliest 
  Paleozoic 
  with 
  the 
  asymmetric 
  form 
  which 
  they 
  inherited 
  

   from 
  cystidean 
  ancestors, 
  was 
  toward 
  that 
  of 
  complete 
  pentamerous 
  

   symmetry. 
  This 
  was 
  attained 
  in 
  the 
  Mesozoic 
  and 
  Recent 
  crinoids 
  

   generally, 
  and 
  in 
  a 
  few 
  genera 
  of 
  the 
  Paleozoic. 
  In 
  most 
  of 
  the 
  

   Paleozoic 
  crinoids 
  an 
  incomplete 
  pentamerous 
  symmetry 
  was 
  

   reached, 
  modified 
  by 
  the 
  bilaterial 
  symmetry 
  due 
  to 
  the 
  presence 
  of 
  

   anal 
  structures. 
  The 
  course 
  of 
  this 
  development 
  was 
  by 
  no 
  means 
  

   one 
  of 
  continual 
  progress. 
  It 
  was 
  marked 
  by 
  numerous 
  recessions 
  

   and 
  sudden 
  changes. 
  

  

  Two 
  of 
  the 
  major 
  divisions 
  of 
  the 
  crinoids, 
  Camerata 
  and 
  Flexi- 
  

   bilia, 
  and 
  for 
  the 
  most 
  part 
  the 
  third, 
  Inadunata, 
  culminated 
  and 
  

   were 
  extinguished 
  before 
  the 
  end 
  of 
  the 
  Paleozoic. 
  During 
  this 
  vast 
  

   stretch 
  of 
  time 
  manv 
  peculiar 
  modifications 
  of 
  the 
  type 
  as 
  we 
  chiefly 
  

  

  