﻿52 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  tially 
  alike 
  in 
  size 
  and 
  form. 
  Exceptions 
  to 
  this 
  rule 
  must 
  be 
  noted 
  

   in 
  the 
  cases 
  of 
  compound 
  radials, 
  of 
  a 
  primitive 
  radianal, 
  and 
  of 
  

   many 
  genera 
  in 
  which 
  there 
  is 
  a 
  regular 
  difference 
  among 
  the 
  rays 
  

   in 
  the 
  number 
  of 
  arm 
  openings 
  or 
  of 
  arm 
  branches 
  ; 
  30 
  also 
  some 
  

   slight 
  irregularities 
  in 
  the 
  size 
  of 
  radials 
  and 
  other 
  plates, 
  as 
  in 
  

   Dolatocrinus. 
  31 
  A 
  conspicuous 
  example 
  of 
  complete 
  departure 
  from 
  

   equality 
  among 
  the 
  radials 
  is 
  furnished 
  by 
  the 
  family 
  Catillo- 
  

   crinidae, 
  in 
  which 
  certain 
  radials 
  regularly 
  exceed 
  the 
  others 
  greatly 
  

   in 
  size, 
  and 
  bear 
  a 
  greater 
  number 
  of 
  arms, 
  which 
  I 
  have 
  alread) 
  r 
  

   discussed 
  in 
  a 
  separate 
  paper 
  ; 
  S2 
  and 
  another 
  equally 
  striking 
  by 
  the 
  

   family 
  Cremacrinidae, 
  in 
  which, 
  in 
  conjunction 
  with 
  the 
  bending 
  

   of 
  the 
  crown, 
  one 
  or 
  mostly 
  two 
  arms 
  have 
  disappeared, 
  and 
  of 
  those 
  

   that 
  remain 
  two 
  are 
  peculiarly 
  modified; 
  the 
  group 
  has 
  been 
  

   elaborately 
  treated 
  by 
  Bather 
  33 
  under 
  the 
  name 
  Calceocrinidae- 
  

   Other 
  isolated 
  instances 
  of 
  defective 
  radiation 
  arising 
  from 
  the 
  loss 
  

   or 
  atrophy 
  of 
  certain 
  rays 
  may 
  be 
  cited, 
  such 
  as 
  Atelestocrinus, 
  

   Tribrachiacrinus, 
  Trigonocrinus, 
  7'etracrinus, 
  Lageniocrinus, 
  Mono- 
  

   b?'achiacrinus, 
  Embryocrinus, 
  and 
  other 
  new 
  genera 
  described 
  by 
  

   Wanner 
  from 
  Timor. 
  

  

  Another 
  remarkable 
  case 
  of 
  this 
  kind 
  is 
  to 
  be 
  seen 
  in 
  the 
  Silurian 
  

   genus 
  Cholocrinus 
  of 
  the 
  Flexibilia, 
  which 
  I 
  have 
  described 
  when 
  

   treating 
  of 
  that 
  group. 
  34 
  In 
  that 
  genus, 
  while 
  the 
  radials 
  themselves 
  

   are 
  not 
  so 
  very 
  different 
  in 
  size, 
  the 
  arms 
  in 
  the 
  two 
  antero-lateral 
  

   raj^s 
  are 
  dwarfed 
  almost 
  to 
  the 
  extent 
  of 
  atrophy. 
  In 
  the 
  discussion 
  

   I 
  alluded 
  to 
  a 
  species 
  described 
  by 
  Whitfield 
  from 
  the 
  Chester 
  

   in 
  which 
  an 
  opposite 
  irregularity 
  appears, 
  the 
  antero-lateral 
  rays 
  

   being 
  disproportionately 
  enlarged. 
  The 
  inequality 
  of 
  the 
  rays 
  in 
  

   Whitfield's 
  species 
  goes 
  one 
  step 
  farther 
  than 
  that 
  seen 
  in 
  other 
  

   species, 
  in 
  that 
  while 
  in 
  them 
  it 
  occurs 
  among 
  the 
  different 
  rays 
  

   of 
  the 
  same 
  specimen, 
  in 
  this 
  it 
  lies 
  also 
  between 
  the 
  two 
  branches 
  

   of 
  the 
  same 
  ray, 
  taking 
  the 
  form 
  of 
  a 
  distinct 
  and 
  constant 
  hyper- 
  

   trophy 
  of 
  certain 
  arms. 
  I 
  wish 
  here 
  to 
  consider 
  it 
  in 
  somewhat 
  

   greater 
  detail 
  partly 
  for 
  that 
  reason, 
  and 
  partly 
  because 
  it 
  proves 
  

   to 
  be 
  related 
  to 
  a 
  genus 
  which 
  is 
  closely 
  associated 
  geologically 
  with 
  

   some 
  of 
  those 
  just 
  discussed, 
  and 
  which, 
  although 
  one 
  of 
  the 
  most 
  

   numerous 
  and 
  widely 
  distributed 
  forms 
  of 
  the 
  Chester 
  group, 
  and 
  

   the 
  subject 
  of 
  frequent 
  mention 
  in 
  crinoid 
  literature 
  upon 
  morpho- 
  

   logical 
  grounds, 
  has 
  hitherto 
  not 
  been 
  understood, 
  namely: 
  

  

  30 
  Springer, 
  Crinoidea 
  Flexibilia, 
  1920, 
  p. 
  171-2. 
  

  

  Sl 
  Springer, 
  Bull. 
  115, 
  U. 
  S. 
  Nat. 
  Mus., 
  1921, 
  p. 
  18. 
  

  

  82 
  On 
  the 
  Fossil 
  crinoid 
  family 
  Catillocrinidae, 
  Smithsonian 
  Misc. 
  Coll., 
  vol. 
  76, 
  1923, 
  

   No 
  3. 
  

  

  83 
  Crinoidea 
  of 
  Gotland, 
  1893, 
  p. 
  54. 
  Also 
  Jackel, 
  Philogenie 
  und 
  System, 
  1918, 
  pp.. 
  

   86, 
  88. 
  

  

  31 
  Crinoidea 
  Flexibilia, 
  1920, 
  p. 
  170. 
  

  

  