﻿BTBOCREJUS, 
  BAEROCRINUS, 
  AND 
  HYBOCYSTITES. 
  301 
  

  

  In 
  the 
  following 
  year 
  (1867) 
  this 
  question 
  was 
  rendered 
  still 
  

   more 
  complicated 
  by 
  Grewingk*, 
  who 
  was 
  fortunate 
  enough 
  to 
  

   succeed 
  in 
  removing 
  much 
  of 
  the 
  matrix 
  that 
  obscured 
  the 
  solitary 
  

   specimen 
  of 
  Baerocrinus 
  from 
  Erras. 
  According 
  to 
  his 
  observations 
  

   Baerocrinus 
  is 
  a 
  very 
  peculiar 
  type, 
  and 
  totally 
  different 
  from 
  

   Hybocrinus-, 
  for 
  on 
  the 
  basals 
  rest 
  five 
  radials 
  in 
  a 
  continuous 
  

   series, 
  only 
  three 
  of 
  them, 
  however, 
  bearing 
  arms, 
  for 
  which 
  pur- 
  

   pose 
  they 
  are 
  provided 
  with 
  distinct 
  articular 
  facets, 
  while 
  the 
  

   other 
  two 
  radials 
  have 
  straight 
  or 
  slightly 
  infolded 
  upper 
  margins 
  

   but 
  no 
  trace 
  of 
  facets. 
  This 
  is 
  very 
  well 
  shown 
  in 
  his 
  side 
  view 
  

   (PI. 
  XI. 
  fig. 
  1) 
  and 
  diagram 
  of 
  the 
  edge 
  of 
  the 
  cup 
  (fig. 
  II. 
  b), 
  to 
  

   • 
  

   Pig. 
  II. 
  — 
  Diagrams 
  of 
  Hybocrinus 
  and 
  Baerocrinus. 
  

  

  A. 
  Calyx 
  of 
  a 
  typical 
  Hybocrinus 
  dvpentas, 
  as 
  seen 
  in 
  outline 
  from 
  above, 
  

  

  B. 
  A 
  similar 
  view 
  of 
  Baerocrinus 
  TJngemi. 
  The 
  two 
  edges 
  of 
  every 
  arm-bearing 
  

  

  radial 
  are 
  joined 
  by 
  dotted 
  lines. 
  After 
  Grewingk. 
  

  

  which, 
  however, 
  he 
  hardly 
  refers, 
  not 
  seeming 
  to 
  attach 
  much 
  

   importance 
  to 
  this 
  point. 
  Yolborth's 
  organ 
  was 
  regarded 
  by 
  him 
  as 
  

   a 
  monstrosity, 
  and 
  as 
  in 
  no 
  way 
  comparable 
  to 
  the 
  ventral 
  side 
  of 
  

   Pleurocy 
  stiles. 
  He 
  gave 
  an 
  excellent 
  description 
  and 
  figure 
  of 
  

   II. 
  dipentas, 
  the 
  latter 
  (PI. 
  XI. 
  fig. 
  2) 
  being 
  taken 
  from 
  a 
  specimen 
  

   that 
  had 
  been 
  found 
  some 
  time 
  previously 
  at 
  Eeval. 
  Like 
  Yol- 
  

   borth, 
  he 
  disputed 
  Eichwald's 
  reference 
  of 
  this 
  type 
  to 
  Homocrinus, 
  

   though 
  he 
  did 
  not 
  follow 
  him 
  in 
  calling 
  it 
  Hybocrinus. 
  Por 
  he 
  

   pointed 
  out 
  that 
  while 
  there 
  are 
  two 
  anal 
  plates 
  in 
  the 
  American 
  

   species, 
  the 
  Eussian 
  forms 
  have 
  but 
  one 
  ; 
  and 
  he 
  proposed 
  to 
  

   establish 
  a 
  genus 
  Hoplocrinus 
  for 
  the 
  reception 
  of 
  these 
  last, 
  basing 
  

   the 
  name 
  on 
  the 
  hoofshaped 
  articular 
  facets 
  on 
  the 
  radials 
  and 
  arm- 
  

   jointst. 
  There 
  are 
  five 
  of 
  these 
  facets; 
  and 
  the 
  outline 
  of 
  the 
  calyx 
  

   is 
  pentagonal 
  (fig. 
  II. 
  a), 
  and 
  not 
  triangular 
  as 
  it 
  is 
  in 
  Baerocrinus 
  

   (fig. 
  II. 
  b). 
  Arm- 
  facets 
  of 
  this 
  shape, 
  however, 
  are 
  common 
  enough 
  

   in 
  other 
  Pala30crinoids, 
  including 
  the 
  Canadian 
  Hybocrinus 
  tumidus, 
  

   and 
  in 
  the 
  various 
  species 
  referred 
  by 
  Hall 
  to 
  Homocrinus; 
  and 
  

   though 
  the 
  absence 
  of 
  the 
  second 
  anal 
  plate 
  may 
  be 
  a 
  good 
  character, 
  

   distinguishing 
  the 
  Eussian 
  from 
  the 
  Canadian 
  species, 
  it 
  hardly 
  seems 
  

   to 
  me 
  of 
  sufficient 
  importance 
  to 
  constitute 
  a 
  generic 
  differentia. 
  

   Grewingk's 
  paper 
  naturally 
  elicited 
  a 
  forcible 
  criticism 
  from 
  

  

  * 
  Loc. 
  cit. 
  t 
  b-\i). 
  

  

  