﻿HyEOCEINTJS, 
  BAEEOCKINITS, 
  AND 
  HYBOCYSTITES. 
  303 
  

  

  it 
  be 
  established 
  by 
  Eichwald's 
  dictum 
  that 
  if 
  Baerocrinus 
  were 
  

   only 
  3-armedit 
  would 
  only 
  have 
  three 
  parabasals, 
  while 
  as 
  a 
  matter 
  

   of 
  fact 
  five 
  are 
  present. 
  But 
  five 
  can 
  only 
  be 
  counted 
  on 
  the 
  

   supposition 
  that 
  the 
  three 
  arm-bearing 
  plates 
  are 
  primitively 
  

   double, 
  for 
  which 
  Eichwald 
  had 
  no 
  warrant 
  whatever, 
  except 
  that 
  

   it 
  was 
  necessary 
  to 
  support 
  his 
  theory 
  ; 
  and 
  although 
  the 
  number 
  

   five 
  " 
  does 
  so 
  predominate 
  in 
  the 
  structure 
  of 
  all 
  Crinoids 
  that 
  it 
  is 
  

   to 
  be 
  regarded 
  as 
  a 
  fundamental 
  law 
  determining 
  their 
  general 
  

   form," 
  yet 
  there 
  are 
  many 
  well-known 
  exceptions 
  to 
  the 
  rule. 
  

  

  Schmidt* 
  appears 
  to 
  accept 
  as 
  correct 
  Grewingk's 
  description 
  of 
  

   Baerocrinus 
  as 
  only 
  3-armed 
  ; 
  but 
  he 
  regards 
  it 
  only 
  as 
  an 
  ab- 
  

   normal 
  and 
  imperfect 
  specimen 
  of 
  Hybocrinus 
  dipentas. 
  He 
  has 
  

   examined 
  a 
  specimen 
  from 
  the 
  " 
  Jewesche 
  Schicht" 
  of 
  Altenhof, 
  which 
  

   has 
  five 
  arms 
  with 
  all 
  the 
  characters 
  of 
  those 
  of 
  Baerocrinus, 
  while 
  

   its 
  calyx 
  is 
  that 
  of 
  Hybocrinus 
  dipentas, 
  and 
  is 
  without 
  any 
  trace 
  

   of 
  a 
  Volborth's 
  organ. 
  He 
  has 
  also 
  met 
  with 
  three 
  examples 
  of 
  the 
  

   latter 
  species 
  in 
  which 
  there 
  are 
  only 
  four 
  arms 
  (fig. 
  I. 
  d), 
  the 
  right 
  

   anterior 
  one 
  remaining 
  undeveloped 
  ; 
  and 
  he 
  seems 
  to 
  regard 
  these 
  

   as 
  affording 
  a 
  connecting 
  link 
  with 
  Baerocrinus, 
  which 
  genus 
  he, 
  

   like 
  EichAvald, 
  absorbs 
  into 
  Hybocrinus 
  dipentas. 
  

  

  It 
  is 
  perhaps 
  rash 
  for 
  one 
  who 
  has 
  not 
  seen 
  any 
  of 
  the 
  speci- 
  

   mens 
  to 
  attempt 
  to 
  form 
  an 
  opinion 
  on 
  this 
  much 
  disputed 
  question. 
  

   But, 
  after 
  a 
  careful 
  consideration 
  of 
  all 
  the 
  evidence, 
  I 
  venture 
  to 
  

   offer 
  the 
  following 
  conclusions 
  for 
  what 
  they 
  may 
  be 
  worth. 
  

  

  There 
  can, 
  I 
  think, 
  be 
  little 
  doubt 
  that 
  Yolborth 
  and 
  Schmidt 
  

   were 
  right 
  in 
  referring 
  Apiocrinus 
  dipentas 
  to 
  Hybocrinus 
  ; 
  but 
  

   this 
  necessitates 
  a 
  modification 
  of 
  Billings's 
  definition 
  of 
  the 
  latter 
  

   genus. 
  The 
  American 
  examples 
  have 
  two 
  " 
  anal" 
  plates, 
  while 
  in 
  

   H. 
  dipentas 
  there 
  is 
  only 
  one, 
  which, 
  however, 
  is 
  probably 
  equiva- 
  

   lent 
  to 
  the 
  two 
  present 
  in 
  Billings's 
  species. 
  This 
  point 
  seems 
  to 
  

   have 
  escaped 
  the 
  notice 
  both 
  of 
  Zittelt 
  and 
  of 
  Wachsmuth 
  and 
  

   Springer 
  %, 
  who 
  quote 
  Apiocrinus, 
  Leuchtenberg, 
  and 
  Hoplocrinus, 
  

   Grewingk, 
  as 
  synonymous 
  with 
  Hybocrinus, 
  without, 
  however, 
  

   making 
  any 
  alteration 
  in 
  Billings's 
  diagnosis 
  of 
  Hybocrinus 
  in 
  this 
  

   respect. 
  

  

  In 
  the 
  American 
  species 
  of 
  Hybocrinus 
  the 
  small 
  right 
  posterior 
  

   radial 
  is 
  rather 
  above 
  the 
  level 
  of 
  the 
  other 
  four 
  (fig. 
  I. 
  a; 
  PI. 
  XI. 
  

   figs. 
  4, 
  5) 
  ; 
  but 
  in 
  the 
  type 
  of 
  H. 
  dipentas 
  it 
  is 
  more 
  nearly 
  in 
  a 
  

   line 
  with 
  them, 
  though 
  resting 
  principally 
  upon 
  the 
  large 
  azygos 
  

   plate 
  (fig. 
  I. 
  b; 
  PI. 
  XI. 
  fig. 
  2). 
  In 
  one 
  specimen 
  from 
  Pawlowsk, 
  

   however, 
  the 
  small 
  radial 
  rests 
  equally 
  on 
  the 
  azygos 
  plate 
  and 
  on 
  

   the 
  right 
  anterior 
  radial, 
  and 
  is 
  consequently 
  somewhat 
  raised 
  

   above 
  the 
  general 
  line 
  of 
  the 
  radials 
  (fig. 
  I. 
  c). 
  As 
  already 
  pointed 
  

   out 
  by 
  Schmidt, 
  this 
  affords 
  a 
  transition 
  to 
  the 
  4- 
  armed 
  individual 
  

   already 
  mentioned, 
  which 
  differs 
  from 
  it 
  only 
  in 
  the 
  absence 
  of 
  a 
  

   right 
  anterior 
  arm 
  (fig. 
  I. 
  d). 
  The 
  plate 
  which 
  would 
  naturally 
  

   bear 
  this 
  arm 
  has 
  no 
  facet 
  upon 
  it. 
  so 
  that 
  the 
  small 
  right 
  posterior 
  

  

  * 
  Loc. 
  cit. 
  pp. 
  5-8. 
  

  

  t 
  Handbucb 
  der 
  Palaontologie, 
  vol. 
  i. 
  p. 
  350, 
  

  

  % 
  Revision, 
  vol. 
  i. 
  p. 
  74. 
  

  

  