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  RELATIONS 
  OF 
  ni'BOCEINUS, 
  EAEEOCTJNTTS, 
  AND 
  HYBOCYSTITES. 
  

  

  wliicli 
  has 
  many 
  Blastoid 
  affinities. 
  In 
  the 
  variety 
  minor 
  of 
  C. 
  ab- 
  

   hreviatus 
  there 
  arc 
  only 
  two 
  ami-joints. 
  If 
  the 
  second 
  one 
  be 
  

   imagined 
  as 
  bent 
  back 
  upon 
  the 
  first 
  so 
  that 
  the 
  flattened 
  dorsal 
  

   surfaces 
  of 
  the 
  two 
  joints 
  met 
  and 
  united, 
  the 
  result 
  would 
  be 
  a 
  

   morphological 
  condition 
  somewhat 
  similar 
  to 
  that 
  of 
  Hybocystites. 
  

   It 
  would 
  have 
  most 
  resemblance 
  to 
  the 
  condition 
  of 
  the 
  right 
  

   posterior 
  ambulacrum 
  in 
  Wachsmuth's 
  larger 
  specimen 
  (fig. 
  18). 
  

   As 
  pointed 
  out 
  above, 
  this 
  ambulacrum 
  does 
  not 
  come 
  down 
  onto 
  

   the 
  large 
  azygos 
  plate, 
  which 
  I 
  regard 
  as 
  a 
  modified 
  radial, 
  any 
  

   more 
  than 
  the 
  recurved 
  ambulacrum 
  of 
  the 
  Cit/pressocrinus 
  " 
  arm 
  ' 
  ' 
  

   would 
  pass 
  onto 
  the 
  radial 
  below 
  it. 
  If 
  I 
  understand 
  Wachsmuth's 
  

   writings 
  aright, 
  this 
  is 
  somewhat 
  the 
  view 
  which 
  he 
  takes 
  of 
  the 
  

   ambulacra 
  of 
  the 
  Mastoids 
  generally, 
  one, 
  however, 
  which 
  I 
  do 
  not 
  

   altogether 
  share, 
  for 
  reasons 
  which 
  will 
  be 
  explained 
  elsewhere. 
  

  

  Thus, 
  then, 
  I 
  regard 
  Hybocystites 
  as 
  combining 
  Blastoid 
  rather 
  

   than 
  Cysticlean 
  characters 
  with 
  those 
  of 
  the 
  Crinoids 
  : 
  though 
  I 
  

   should 
  hesitate 
  for 
  the 
  present 
  to 
  refer 
  it 
  to 
  the 
  Blastoidea, 
  which 
  

   form 
  on 
  the 
  whole 
  a 
  fairly 
  compact 
  group 
  possessing 
  certain 
  well- 
  

   defined 
  characteristics. 
  

  

  Hybocystites 
  is 
  only 
  one 
  among 
  many 
  palaeozoic 
  Echinoderms 
  to 
  

   which 
  no 
  definite 
  position 
  can 
  as 
  yet 
  be 
  assigned. 
  It 
  is 
  much 
  to 
  be 
  

   hoped 
  that 
  other 
  and 
  better 
  specimens 
  of 
  this 
  remarkable 
  type 
  may 
  

   soon 
  be 
  discovered, 
  so 
  that 
  some 
  light 
  may 
  be 
  thrown 
  upon 
  the 
  

   many 
  structural 
  characters 
  respecting 
  which 
  we 
  are 
  as 
  yet 
  alto- 
  

   gether 
  in 
  the 
  dark. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XL 
  

  

  Fig. 
  1. 
  Baeroetinns 
  Ungemii, 
  slightly 
  restored. 
  After 
  G-rewingk. 
  

   2. 
  Hybocrinus 
  dipentas, 
  anal 
  side. 
  After 
  G-rewingk. 
  

   3 
  to 
  5. 
  ffybocrinHx 
  tumidus, 
  X 
  l.j. 
  Trenton 
  Limestone, 
  Kentucky. 
  3, 
  

  

  left 
  side 
  ; 
  4, 
  right 
  side 
  : 
  5, 
  anal 
  side. 
  

   6-24. 
  Hybocystites 
  problematicus. 
  Trenton 
  Limestone, 
  Kentucky. 
  

   (5, 
  7. 
  Copied 
  from 
  Wctherb}' 
  ; 
  fig. 
  6, 
  right 
  side, 
  X 
  2 
  ; 
  fig. 
  7, 
  anal 
  side, 
  

  

  natural 
  size. 
  

   8-13. 
  Prof. 
  Wetherby's 
  specimen, 
  X 
  2. 
  8, 
  front 
  view 
  ; 
  9, 
  left 
  side 
  ; 
  10, 
  

  

  summit 
  ; 
  11, 
  dorsal 
  aspect 
  ; 
  12, 
  right 
  side 
  ; 
  13, 
  anal 
  side. 
  

   14-19. 
  Mr. 
  Wachsmuth's 
  larger 
  specimen, 
  X 
  2. 
  14, 
  front 
  view; 
  15, 
  

  

  left 
  side 
  ; 
  10, 
  summit 
  ; 
  17, 
  dorsal 
  aspect 
  ; 
  18, 
  right 
  side 
  ; 
  19, 
  anal 
  

  

  side. 
  

   20-24. 
  Mr. 
  Wachsmuth's 
  smaller 
  specimen, 
  X 
  3. 
  20, 
  front 
  view 
  ; 
  21, 
  

  

  left 
  side 
  ; 
  22, 
  dorsal 
  aspect 
  ; 
  23, 
  right 
  side 
  ; 
  24, 
  anal 
  side. 
  

  

  Discussion, 
  

  

  Dr. 
  Caeeenter 
  said 
  that 
  the 
  paper 
  contained 
  very 
  carefully 
  

   worked 
  out 
  descriptions 
  of 
  a 
  curious 
  osculant 
  form 
  between 
  the 
  

   Blastoids 
  and 
  the 
  ordinary 
  Crinoids, 
  which 
  were 
  in 
  process 
  of 
  discovery 
  

   in 
  the 
  older 
  rocks, 
  especially 
  in 
  IS". 
  America. 
  He 
  was 
  glad 
  that 
  his 
  

   son 
  had 
  devoted 
  himself, 
  with 
  such 
  good 
  results, 
  to 
  the 
  study 
  of 
  

   these 
  difficult 
  forms, 
  at 
  which 
  he 
  had 
  once 
  worked 
  himself; 
  and 
  he 
  

   thanked 
  the 
  Society 
  for 
  the 
  cordial 
  welcome 
  which 
  they 
  had 
  always 
  

   accorded 
  him. 
  

  

  