﻿art 
  9 
  UNUSUAL 
  FORMS 
  OF 
  FOSSIL 
  CRINOIDS 
  SPRINGER 
  27 
  

  

  The 
  peculiar 
  modification 
  in 
  stem 
  structure 
  which 
  is 
  manifested 
  

   in 
  the 
  genus 
  Camptocrinus 
  is 
  itself 
  subject 
  to 
  some 
  singular 
  varia- 
  

   tions, 
  of 
  which 
  one 
  of 
  the 
  most 
  striking 
  seems 
  to 
  be 
  connected 
  with 
  

   an 
  effort 
  toward 
  resumption 
  of 
  the 
  usual 
  arrangement 
  of 
  cirri 
  in 
  

   whorls 
  upon 
  a 
  rounded 
  stem. 
  This 
  tendency 
  is 
  evidenced 
  by 
  the 
  

   presence 
  of 
  incipient, 
  immature, 
  or 
  rudimentary 
  cirri, 
  supplemental 
  

   to 
  those 
  in 
  the 
  marginal 
  rows, 
  usually 
  much 
  dwarfed 
  in 
  size; 
  they 
  

   consist 
  of 
  a 
  few 
  small 
  cirrals, 
  often 
  of 
  only 
  a 
  single 
  ossicle 
  breaking 
  

   through 
  at 
  the 
  suture 
  between 
  the 
  paired 
  nodal 
  segments, 
  rounded 
  

   off 
  distally 
  and 
  without 
  any 
  axial 
  canal 
  through 
  which 
  further 
  

   growth 
  could 
  be 
  innervated. 
  Rarely 
  also 
  it 
  results 
  in 
  fully 
  devel- 
  

   oped, 
  fairly 
  equal 
  cirri 
  in 
  whorls 
  of 
  five, 
  upon 
  a 
  stem 
  which 
  retains 
  

   in 
  part 
  the 
  elliptic 
  section. 
  

  

  In 
  this 
  genus 
  the 
  form 
  of 
  the 
  coiled 
  stem 
  differs 
  considerably 
  in 
  

   transverse 
  section 
  from 
  that 
  of 
  Myelodactylus 
  ; 
  instead 
  of 
  being 
  

   <?rescentic, 
  with 
  a 
  decided 
  concavity 
  at 
  the 
  inner 
  side 
  as 
  in 
  the 
  latter 
  

   (pi. 
  1, 
  fig. 
  6), 
  it 
  is 
  here 
  simply 
  elliptic, 
  with 
  the 
  curvature 
  at 
  the 
  

   inner 
  and 
  outer 
  sides 
  almost 
  alike, 
  sometimes 
  but 
  little 
  flattened 
  and 
  

   tending 
  to 
  become 
  circular 
  (pi. 
  8, 
  various 
  outline 
  figures). 
  

  

  In 
  this 
  genus 
  also 
  the 
  rounded 
  proximal 
  part 
  of 
  the 
  stem, 
  or 
  neck, 
  

   is 
  usually 
  materially 
  shorter 
  than 
  in 
  Myelodactylus. 
  

  

  Distribution. 
  — 
  Mississippian, 
  Burlington 
  to 
  latest 
  Chester; 
  lim- 
  

   ited, 
  so 
  far 
  as 
  hitherto 
  known, 
  to 
  North 
  America, 
  but 
  now 
  found 
  to 
  

   occur 
  in 
  the 
  East 
  Indies, 
  in 
  a 
  formation 
  claimed 
  to 
  be 
  Permian. 
  

  

  CAMPTOCRINUS 
  PRAENUNTIUS, 
  new 
  species 
  

  

  Plate 
  7, 
  fig. 
  1 
  

  

  Of 
  large 
  size; 
  stem 
  with 
  broad 
  open 
  coil; 
  round, 
  slender, 
  with 
  

   reversed 
  curvature 
  in 
  the 
  proximal 
  region, 
  much 
  enlarged 
  in 
  the 
  

   middle 
  region, 
  and 
  tapering 
  to 
  the 
  distal 
  end, 
  where 
  it 
  begins 
  to 
  

   assume 
  a 
  bilateral 
  form, 
  with 
  a 
  few 
  short 
  cirri. 
  Crown 
  not 
  closely 
  

   enveloped 
  by 
  the 
  stem; 
  it 
  is 
  of 
  the 
  type 
  of 
  Dichocrinus 
  angustus, 
  

   with 
  ten 
  uniserial 
  arms 
  ; 
  apparently 
  only 
  a 
  single 
  primibrach, 
  as 
  long 
  

   as 
  the 
  usual 
  two. 
  

  

  This 
  species 
  from 
  the 
  Burlington 
  limestone 
  may 
  be 
  considered 
  

   as 
  the 
  beginning 
  of 
  the 
  modification 
  leading 
  to 
  the 
  fully 
  developed 
  

   Camptocrinus. 
  It 
  is 
  the 
  largest 
  of 
  the 
  known 
  species, 
  the 
  stem 
  hav- 
  

   ing 
  a 
  total 
  length 
  of 
  19 
  cm. 
  In 
  the 
  great 
  diminution 
  of 
  the 
  other- 
  

   wise 
  thick 
  stem 
  in 
  the 
  proximal 
  region, 
  its 
  reversed 
  curvature, 
  and 
  

   the 
  position 
  of 
  the 
  crown 
  in 
  relation 
  to 
  it, 
  the 
  habitus 
  of 
  the 
  species 
  

   is 
  thoroughly 
  characteristic 
  of 
  the 
  type; 
  but 
  it 
  lacks 
  the 
  close 
  en- 
  

   velopment 
  of 
  the 
  crown 
  by 
  the 
  stem 
  and 
  cirri, 
  the 
  stem 
  being 
  round 
  

   for 
  the 
  greater 
  part 
  of 
  its 
  length. 
  The 
  cirri 
  occur 
  at 
  the 
  inner 
  side 
  

  

  