﻿308 
  P. 
  H. 
  CARPENTER 
  ON 
  THE 
  RELATIONS 
  OE 
  

  

  was 
  discovered 
  by 
  Prof. 
  Wetherby*, 
  together 
  with 
  Hijbocrinus, 
  in 
  

   the 
  Trenton 
  beds 
  of 
  the 
  Kentucky 
  river-section 
  already 
  referred 
  to. 
  

  

  He 
  speaks 
  of 
  it 
  as 
  the 
  first 
  fossil 
  found 
  " 
  which 
  so 
  closely 
  unites 
  

   characters 
  both 
  of 
  the 
  Crinoidea 
  and 
  Cystoidea, 
  with 
  the 
  reference 
  

   of 
  the 
  former 
  characters 
  to 
  those 
  of 
  an 
  undoubted 
  Crinoid 
  of 
  very 
  

   near 
  relationship." 
  The 
  Crinoid 
  in 
  question 
  is 
  Hybocrinus; 
  and 
  

   according 
  to 
  Prof. 
  Yv'etherby 
  the 
  resemblance 
  is 
  " 
  so 
  striking, 
  that 
  

   the 
  sexual 
  question 
  is 
  at 
  once 
  suggested 
  as 
  between 
  the 
  two." 
  His 
  

   generic 
  description 
  of 
  this 
  remarkable 
  fossil 
  is 
  as 
  follows. 
  — 
  " 
  General 
  

   outline 
  of 
  the 
  body 
  very 
  similar 
  to 
  that 
  of 
  Hybocrinus 
  tumidus, 
  

   Billings. 
  It 
  consists 
  of 
  series 
  of 
  plates, 
  five 
  each 
  in 
  the 
  first 
  two, 
  

   arranged 
  as 
  in 
  Hybocrinus. 
  As 
  in 
  that 
  genus, 
  the 
  lower 
  azygos 
  

   plate 
  bears 
  a 
  second 
  and 
  a 
  radial 
  upon 
  its 
  upper 
  face. 
  Arms 
  three, 
  

   one 
  upon 
  each 
  side 
  of 
  the 
  upper 
  azygos 
  plate, 
  and 
  one 
  immediately 
  

   opposite 
  it. 
  The 
  plates 
  of 
  the 
  upper 
  series 
  between 
  these 
  arms, 
  on 
  

   either 
  side, 
  are 
  excavated 
  by 
  a 
  groove 
  that 
  is 
  continued 
  downward, 
  

   and 
  half 
  or 
  two 
  thirds 
  across 
  the 
  plate 
  of 
  the 
  lower 
  series 
  beneath 
  

   it. 
  These 
  grooves 
  meet 
  in 
  the 
  vault 
  at 
  a 
  common 
  point 
  with 
  those 
  

   .of 
  the 
  arms, 
  and 
  form 
  a 
  part 
  of 
  the 
  ambulacral 
  system. 
  

  

  " 
  The 
  mouth, 
  or 
  ambulacral 
  orifice, 
  is 
  situated 
  nearly 
  centrally 
  

   upon 
  the 
  upper 
  surface. 
  The 
  valvular 
  anal 
  opening 
  is 
  placed 
  be- 
  

   tween 
  the 
  upper 
  azygos 
  plate 
  and 
  the 
  mouth. 
  The 
  arms 
  are 
  deeply 
  

   furrowed, 
  the 
  grooves 
  being 
  covered 
  by 
  a 
  series 
  of 
  cuneiform 
  inter- 
  

   locking 
  plates. 
  Pinnuke 
  not 
  observed. 
  Proboscis 
  or 
  ventral 
  sac 
  

   indicated 
  by 
  the 
  presence 
  of 
  the 
  upper 
  azygos 
  plate. 
  Column 
  small, 
  

   round, 
  and 
  placed 
  excentrically 
  as 
  in 
  Hybocrinus. 
  Vault 
  covered 
  by 
  

   plates, 
  of 
  which 
  the 
  arrangement 
  cannot 
  be 
  determined. 
  There 
  are 
  

   no 
  evidences 
  of 
  pectinated 
  rhombs 
  or 
  poriferous 
  plates. 
  This 
  genus 
  

   combines 
  in 
  a 
  remarkable 
  degree 
  characters 
  both 
  of 
  the 
  Crinoids 
  

   and 
  Cystids." 
  

  

  " 
  Remarks. 
  — 
  The 
  almost 
  perfect 
  identity 
  of 
  the 
  arrangement 
  of 
  

   the 
  plates 
  with 
  those 
  of 
  Hybocrinus; 
  the 
  three 
  arms; 
  the 
  two 
  

   ambulacra 
  running 
  down 
  the 
  sides 
  of 
  the 
  body, 
  as 
  in 
  the 
  appressed 
  

   arms 
  of 
  many 
  Cystidcans 
  ; 
  the 
  valvular 
  anal 
  opening 
  ; 
  the 
  presence 
  

   of 
  a 
  proboscis 
  or 
  ventral 
  sac, 
  as 
  indicated 
  by 
  the 
  prominent 
  azygos 
  

   plate 
  ; 
  and 
  the 
  uncovered 
  area 
  of 
  the 
  vault 
  adjacent 
  to 
  it> 
  all 
  taken 
  

   together, 
  form 
  a 
  mixture 
  of 
  characters 
  not 
  united 
  in 
  any 
  fossil 
  of 
  

   this 
  difficult 
  class 
  hitherto 
  described. 
  I 
  have 
  referred 
  it 
  to 
  the 
  

   Cystideae 
  with 
  some 
  hesitation, 
  but 
  mainly 
  on 
  account 
  of 
  the 
  

   anomalous 
  arrangement 
  of 
  the 
  ambulacral 
  system, 
  three 
  rays 
  of 
  

   which 
  are 
  upright 
  and 
  two 
  appressed, 
  and 
  on 
  account 
  of 
  the 
  posi- 
  

   tion 
  of 
  the 
  anal 
  opening, 
  which 
  is 
  the 
  same 
  as 
  that 
  in 
  Agelacrinites, 
  

   Hemicystitcs, 
  and 
  Caryocrinus. 
  with 
  the 
  slight 
  modification 
  in 
  posi^ 
  

   tion 
  caused 
  by 
  the 
  presence 
  of 
  a 
  ventral 
  sac." 
  

  

  It 
  will 
  be 
  understood 
  from 
  the 
  above 
  description 
  that 
  Prof* 
  

  

  "Wetherby 
  considers 
  Hybocystites 
  as 
  possessing 
  three 
  arms 
  like 
  those 
  

  

  of 
  the 
  Crinoids, 
  and 
  two 
  appressed 
  ambulacra 
  such 
  as 
  occur 
  in 
  the 
  

  

  Cystids. 
  As 
  regards 
  the 
  latter 
  I 
  am 
  quite 
  in 
  accordance 
  with 
  him 
  ; 
  

  

  * 
  Lor. 
  tit. 
  pp. 
  6-9. 
  

  

  