﻿HYBOCEIXTJS, 
  BAEEOCEINUS, 
  AND 
  HYBOCYSTITES. 
  305 
  

  

  ' 
  Re 
  vision,' 
  from 
  which, 
  curiously 
  enough, 
  the 
  Russian 
  HyhocHnus 
  

   dipentas 
  is 
  omitted. 
  

  

  Although 
  Hyhocrinus 
  was 
  discovered 
  in 
  Canada 
  as 
  long 
  ago 
  as 
  

   1856, 
  it 
  has 
  not 
  been 
  met 
  with 
  in 
  the 
  United 
  States 
  until 
  quite 
  

   recently. 
  Prof. 
  A. 
  G. 
  "Wetherby* 
  has 
  obtained 
  it, 
  however, 
  to- 
  

   gether 
  with 
  some 
  other 
  most 
  remarkable 
  Echinoclerms, 
  from 
  a 
  sili- 
  

   cified 
  limestone 
  near 
  the 
  top 
  of 
  the 
  Trenton 
  group 
  in 
  Mercer 
  

   County, 
  Kentucky. 
  One 
  specimen 
  of 
  H. 
  conicus 
  was 
  found, 
  and 
  

   sixteen 
  of 
  H. 
  tumidus, 
  of 
  "which 
  last 
  Prof. 
  "Wetherby 
  gives 
  four 
  

   excellent 
  figures. 
  He 
  describes 
  the 
  upper 
  azygos 
  plate 
  as 
  rounded 
  

   and 
  crenulated 
  at 
  its 
  distal 
  extremity, 
  as 
  well 
  as 
  much 
  thickened, 
  

   and 
  goes 
  on 
  to 
  say 
  that 
  " 
  the 
  form 
  of 
  the 
  plate 
  is 
  sufficient 
  evidence 
  

   that 
  it 
  supported 
  a 
  strong 
  ventral 
  sac, 
  and 
  the 
  crenulated 
  condition 
  

   of 
  the 
  articulating 
  upper 
  surface 
  of 
  this 
  plate 
  indicates 
  the 
  place 
  of 
  

   the 
  lower 
  exterior 
  openings 
  into 
  this 
  sac." 
  I 
  think 
  it 
  probable 
  

   enough 
  that 
  the 
  anal 
  plate 
  of 
  Hyhocrinus 
  did 
  support 
  a 
  strong 
  

   ventral 
  sac, 
  as 
  suggested 
  by 
  Prof. 
  Wetherby 
  ; 
  but 
  its 
  upper 
  surface 
  

   can 
  hardly 
  be 
  described 
  as 
  " 
  articulating.*' 
  It 
  has 
  no 
  articular 
  

   facet 
  with 
  fossse 
  for 
  the 
  attachment 
  of 
  muscles, 
  such 
  as 
  occur 
  on 
  the 
  

   terminal 
  surfaces 
  of 
  the 
  ray- 
  and 
  arm-plates 
  ; 
  and 
  it 
  is 
  only 
  when 
  

   there 
  is 
  a 
  movable 
  joint 
  of 
  this 
  kind 
  between 
  any 
  plate 
  and 
  the 
  

   one 
  above 
  it 
  that 
  its 
  upper 
  surface 
  can 
  be 
  properly 
  described 
  as 
  

   " 
  articulating." 
  Such 
  an 
  articular 
  surface 
  occurs 
  on 
  the 
  radials 
  of 
  

   Hyhocrinus 
  ; 
  but 
  there 
  is 
  nothing 
  of 
  the 
  kind 
  on 
  the 
  anal 
  plate. 
  

   In 
  a 
  specimen 
  kindly 
  sent 
  to 
  me 
  by 
  Mr. 
  Wachsmuth, 
  I 
  find 
  the 
  

   upper 
  third 
  of 
  this 
  plate 
  to 
  be 
  somewhat 
  thickened 
  ; 
  and 
  the 
  outer 
  

   face 
  meets 
  the 
  nearly 
  vertical 
  inner 
  face 
  along 
  a 
  curved 
  but 
  toler- 
  

   ably 
  sharp 
  edge, 
  on 
  which 
  I 
  can 
  make 
  out 
  little 
  or 
  no 
  trace 
  of 
  

   crenulation. 
  Somewhat 
  below 
  the 
  middle 
  of 
  this 
  edge 
  there 
  rises 
  

   from 
  the 
  inner 
  surface 
  of 
  the 
  plate 
  a 
  little 
  nipple-shaped 
  projection, 
  

   which 
  may, 
  perhaps, 
  indicate 
  the 
  position 
  of 
  the 
  anal 
  tube. 
  

  

  Hyhocrinus 
  is 
  a 
  Crinoid 
  of 
  a 
  very 
  embryonic 
  type. 
  The 
  relatively 
  

   large 
  size 
  of 
  the 
  basals 
  and 
  the 
  retention 
  of 
  the 
  anal 
  plate, 
  together 
  

   with 
  the 
  simplicity 
  of 
  its 
  arms 
  and 
  the 
  absence 
  of 
  pinnules, 
  all 
  

   indicate 
  its 
  low 
  stage 
  of 
  organization. 
  The 
  typical 
  forms 
  of 
  the 
  

   Russian 
  species 
  (fig. 
  I. 
  b 
  ; 
  PI. 
  XI. 
  fig. 
  2) 
  differ 
  from 
  the 
  American 
  

   ones 
  (fig. 
  I. 
  a 
  ; 
  PI. 
  XL 
  figs. 
  3-5) 
  in 
  having 
  only 
  a 
  single 
  anal 
  

   or 
  azygos 
  plate. 
  This 
  supports 
  the 
  small 
  right 
  posterior 
  radial 
  on 
  

   the 
  one 
  side 
  ; 
  but 
  the 
  other 
  (left) 
  side 
  bears 
  no 
  second 
  anal 
  plate, 
  

   though 
  the 
  whole 
  plate 
  may 
  be 
  readily 
  regarded 
  as 
  equivalent 
  to 
  

   the 
  combined 
  large 
  and 
  small 
  anal 
  plates 
  of 
  H. 
  tumidus. 
  

  

  The 
  position 
  of 
  the 
  large 
  azygos 
  plate 
  in 
  line 
  with 
  the 
  four 
  larger 
  

   radials 
  is 
  a 
  very 
  striking 
  feature 
  in 
  this 
  genus. 
  Wachsmuth 
  t 
  has 
  

   pointed 
  out 
  that 
  the 
  small 
  radial 
  which 
  it 
  bears 
  " 
  evidently 
  cor- 
  

   responds 
  to 
  the 
  upper 
  half 
  of 
  the 
  compound 
  plate 
  in 
  JDendrocrinus 
  

   (fig. 
  III. 
  a), 
  while 
  the 
  lower 
  half, 
  which 
  is 
  here 
  apparently 
  absent, 
  

   is 
  perhaps 
  represented 
  in 
  a 
  portion 
  of 
  the 
  large 
  undivided 
  anal 
  

  

  * 
  " 
  Bemarks 
  on 
  the 
  Trenton 
  Limestone 
  of 
  Kentucky," 
  Journal 
  Cincinn. 
  Soc. 
  

   Nat, 
  Hist. 
  vol. 
  iii. 
  July 
  1880. 
  

   I 
  Revision, 
  part 
  i. 
  p. 
  74. 
  

  

  