﻿HYBOCBINTJS, 
  BAEKOCBINT7S, 
  AND 
  HYBOCYSTITES. 
  299 
  

  

  PI, 
  XI. 
  fig. 
  2). 
  It 
  had 
  been 
  found 
  at 
  Pulkowa, 
  in 
  the 
  neighbour- 
  

   hood 
  of 
  St. 
  Petersburg, 
  in 
  the 
  Orthoceratite-limestone 
  or 
  " 
  Yagi- 
  

   naten-Kalk" 
  of 
  the 
  Lower-Silurian 
  period 
  ; 
  but 
  its 
  discovery 
  seems 
  

   to 
  have 
  been 
  unknown 
  to 
  Billings. 
  Had 
  he 
  been 
  acquainted 
  with 
  

   it, 
  he 
  would 
  assuredly 
  have 
  recognized 
  its 
  resemblance 
  to 
  his 
  Cana- 
  

   dian 
  species, 
  and 
  its 
  difference 
  from 
  the 
  Mesozoic 
  Apiocrinus. 
  This 
  

   last 
  point 
  was 
  noticed 
  by 
  Schmidt*, 
  who 
  had 
  met 
  with 
  a 
  specimen 
  

   from 
  the 
  same 
  horizon 
  at 
  Beval 
  in 
  Estland 
  ; 
  but 
  he 
  did 
  not 
  attempt 
  

   to 
  define 
  its 
  systematic 
  position. 
  

  

  The 
  first 
  efforts 
  in 
  this 
  direction 
  were 
  those 
  of 
  Eichwald 
  f, 
  who 
  

   referred 
  Leuchtenberg's 
  specimen, 
  together 
  with 
  a 
  somewhat 
  dif- 
  

   ferent 
  one 
  from 
  a 
  slightly 
  higher 
  horizon, 
  the 
  " 
  Brandschiefer" 
  of 
  

   Erras 
  (fig. 
  I. 
  e 
  ; 
  PI. 
  XI. 
  fig. 
  1), 
  to 
  the 
  genus 
  Homocrinus, 
  Hall. 
  

   The 
  calyx 
  of 
  this 
  genus, 
  however, 
  had 
  been 
  described 
  as 
  composed 
  

   of 
  three 
  series 
  of 
  five 
  plates 
  each 
  ; 
  and 
  the 
  difference 
  between 
  this 
  

   character 
  and 
  that 
  of 
  the 
  dicyclic 
  Apiocrinus 
  dipentas 
  led 
  Yolborth 
  :£ 
  

   to 
  dispute 
  the 
  correctness 
  of 
  Eichwald's 
  determination. 
  

  

  At 
  the 
  same 
  time 
  he 
  established 
  a 
  new 
  genus, 
  Baerocrinus^ 
  for 
  

   the 
  Erras 
  specimen, 
  on 
  account 
  of 
  its 
  greater 
  size, 
  and 
  of 
  the 
  dif- 
  

   ferences 
  between 
  its 
  calyx 
  and 
  arms 
  and 
  those 
  of 
  Leuchtenberg's 
  

   type 
  — 
  though 
  he 
  was 
  unable 
  to 
  work 
  these 
  out 
  in 
  much 
  detail, 
  

   owing 
  to 
  the 
  specimen 
  being 
  partially 
  obscured 
  by 
  matrix. 
  On 
  one 
  

   point, 
  however, 
  he 
  laid 
  considerable 
  stress. 
  The 
  suture 
  between 
  

   two 
  of 
  the 
  radials 
  and 
  the 
  subjacent 
  basal 
  is 
  concealed 
  by 
  a 
  slight 
  

   triangular 
  swelling, 
  occupied 
  by 
  what 
  appears 
  to 
  be 
  about 
  twenty 
  

   minute 
  plates. 
  Volborth 
  suggested 
  that 
  this 
  might 
  possibly 
  be 
  a 
  

   madreporite 
  or 
  a 
  genital 
  organ, 
  and 
  hinted 
  at 
  a 
  comparison 
  of 
  it 
  

   with 
  the 
  ventral 
  side 
  of 
  Pleurocystites. 
  In 
  fact, 
  it 
  seems 
  to 
  have 
  

   been 
  the 
  presence 
  of 
  this 
  " 
  Yolborth's 
  Organ," 
  as 
  it 
  has 
  since 
  been 
  

   called, 
  that 
  was 
  his 
  chief 
  reason 
  for 
  placing 
  the 
  Erras 
  specimen 
  

   in 
  another 
  genus 
  than 
  Hybocrinus, 
  Billings, 
  to 
  which 
  he 
  very 
  rightly 
  

   referred 
  Leuchtenberg's 
  original 
  specimen 
  from 
  Pulkowa 
  and 
  other 
  

   similar 
  ones. 
  

  

  A 
  vigorous 
  controversy 
  now 
  ensued 
  between 
  Yolborth 
  and 
  Eich- 
  

   wald 
  §. 
  The 
  latter 
  insisted 
  strongly 
  upon 
  the 
  identity 
  of 
  the 
  Erras 
  

   and 
  Pulkowa 
  specimens, 
  and 
  defended 
  as 
  strongly 
  his 
  reference 
  of 
  both 
  

   of 
  them 
  to 
  Homocrinus. 
  Yolborth 
  || 
  replied 
  by 
  emphasizing 
  the 
  charac- 
  

   ters 
  of 
  Baerocrinus 
  ; 
  and 
  he 
  (Yolborth) 
  pointed 
  out 
  that 
  Leuchtenberg 
  

   had 
  only 
  described 
  a 
  dicyclic 
  calyx 
  in 
  Apiocrinus 
  dipentas, 
  which 
  he 
  

   regarded 
  as 
  a 
  Hybocrinus. 
  Eichwald 
  % 
  answered 
  with 
  a 
  diagram 
  

   and 
  analysis 
  of 
  the 
  Homocrinus-calyx 
  ; 
  and 
  stated 
  that 
  the 
  Pulkowa 
  

   and 
  Erras 
  specimens 
  agree 
  with 
  it 
  most 
  perfectly 
  in 
  the 
  number 
  of 
  

   plates, 
  " 
  only 
  with 
  the 
  difference 
  that 
  the 
  two 
  lower 
  series** 
  some- 
  

  

  * 
  Untersuckungen 
  iiber 
  die 
  silurische 
  Formation 
  von 
  Ehstland, 
  Nord-Livland 
  

   und 
  Oesel 
  (Dorpat, 
  1858), 
  p. 
  219. 
  

  

  t 
  Lethsea 
  Eossica, 
  Band 
  i. 
  1, 
  pp. 
  582, 
  584. 
  

  

  I 
  " 
  Ueber 
  Baerocrinus, 
  eine 
  neue 
  Crinoideen-Gattung 
  aus 
  Ehstland," 
  Bulletin 
  

   St. 
  Petersb. 
  Acad. 
  torn. 
  viii. 
  1865, 
  p. 
  178. 
  

  

  § 
  Bulletin 
  de 
  la 
  Soc. 
  Imp. 
  cles 
  Nat. 
  de 
  Moscou, 
  1865, 
  ii. 
  p. 
  150. 
  

  

  || 
  Ibid. 
  p. 
  442. 
  f 
  Moscow 
  Bulletin, 
  1866, 
  part 
  i. 
  pp. 
  146-161, 
  tab. 
  viii. 
  

  

  I.e. 
  under-basals 
  and 
  basals. 
  

  

  