﻿90 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  67 
  

  

  The 
  characters 
  of 
  these 
  two 
  species 
  must 
  be 
  sought 
  chiefly 
  in 
  the 
  

   work 
  of 
  Wether 
  by, 
  above 
  cited, 
  where 
  the 
  descriptions 
  are 
  accom- 
  

   panied 
  by 
  excellent 
  illustrations 
  made 
  from 
  a 
  series 
  of 
  finely 
  pre- 
  

   served 
  specimens 
  of 
  both, 
  which 
  exhibit 
  the 
  structure 
  of 
  the 
  arms 
  

   and 
  ventral 
  sac. 
  Although 
  himself 
  in 
  doubt 
  as 
  to 
  their 
  identity 
  with 
  

   the 
  species 
  previously 
  described 
  from 
  imperfect 
  material, 
  he 
  rede- 
  

   scribed 
  and 
  figured 
  them 
  under 
  the 
  original 
  names. 
  This 
  course 
  as 
  

   to 
  the 
  second 
  species 
  was 
  not 
  accepted 
  by 
  Wachsmuth 
  and 
  Springer, 
  

   who 
  changed 
  it 
  to 
  H. 
  wetherbyi. 
  A 
  large 
  quantity 
  of 
  excellent 
  

   material 
  derived 
  from 
  Wetherby's 
  locality 
  enables 
  me 
  to 
  confirm 
  his 
  

   observations 
  in 
  several 
  particulars, 
  and 
  to 
  add 
  some 
  newly 
  discovered 
  

   facts. 
  These 
  forms 
  are 
  of 
  interest 
  because 
  they 
  represent 
  the 
  cul- 
  

   mination 
  of 
  the 
  inflated 
  sac 
  in 
  the 
  later 
  American 
  Lower 
  Carboni- 
  

   ferous, 
  and 
  because 
  the 
  two 
  species, 
  although 
  occuring 
  closely 
  asso- 
  

   ciated 
  in 
  the 
  same 
  localities, 
  are 
  so 
  completely 
  distinct 
  : 
  

  

  H. 
  depressus. 
  Basal 
  cavity 
  large, 
  deep, 
  rather 
  pentagonal, 
  in- 
  

   volving 
  most 
  of 
  BB, 
  the 
  IBB 
  being 
  buried 
  at 
  the 
  bottom; 
  stem 
  

   pentagonal. 
  IBr 
  single, 
  axillary 
  and 
  spiniferous 
  except 
  in 
  the 
  ante- 
  

   rior 
  ray, 
  where 
  one 
  or 
  two 
  additional 
  biserial 
  pairs 
  of 
  brachials 
  are 
  

   interposed, 
  and 
  the 
  bifurcation 
  and 
  spine 
  are 
  on 
  the 
  second 
  or 
  third 
  

   brachial. 
  Arms 
  biserial, 
  dividing 
  on 
  the 
  third 
  IIBr, 
  followed 
  by 
  

   three 
  or 
  four 
  divisions 
  at 
  intervals 
  of 
  about 
  4 
  brachials, 
  always 
  from 
  

   the 
  outer 
  arm 
  of 
  the 
  dichotom, 
  the 
  inner 
  branch 
  remaining 
  single 
  

   (the 
  reverse 
  of 
  the 
  British 
  species), 
  giving 
  34-42 
  ultimate 
  branches, 
  

   the 
  number 
  in 
  the 
  anterior 
  ray 
  being 
  diminished. 
  Summit 
  of 
  sac 
  

   composed 
  of 
  a 
  central 
  area 
  of 
  numerous 
  irregular 
  plates 
  surrounded 
  

   by 
  a 
  peripheral 
  band 
  of 
  plates 
  terminated 
  by 
  spines 
  projecting 
  hori- 
  

   zontally 
  or 
  a 
  little 
  downward, 
  20-35 
  plates 
  in 
  all. 
  

  

  H. 
  wethebyi. 
  Basal 
  cavity 
  small, 
  shallow, 
  almost 
  restricted 
  to 
  

   the 
  infrabasals; 
  stem 
  round; 
  BB 
  mostly 
  visible. 
  IBr 
  single 
  all 
  

   around, 
  axillary 
  and 
  spiniferous. 
  Arms 
  dividing 
  on 
  the 
  sixth 
  or 
  

   seventh 
  brachial 
  above 
  IAx, 
  with 
  not 
  over 
  two 
  divisions 
  at 
  intervals 
  

   of 
  7 
  or 
  8 
  brachials; 
  usually 
  only 
  the 
  outer 
  branch 
  bifurcating, 
  giv- 
  

   ing 
  about 
  26 
  final 
  branches; 
  all 
  axillaries 
  nodose 
  or 
  spiniferous; 
  

   brachials 
  cuneate, 
  interlocking 
  to 
  biserial. 
  Summit 
  of 
  sac 
  without 
  

   any 
  inner 
  set 
  of 
  plates, 
  but 
  composed 
  entirely 
  of 
  spiniferous 
  plates 
  

   meeting 
  in 
  the 
  middle, 
  from 
  5 
  to 
  7 
  or 
  8 
  in 
  number. 
  

  

  Thus 
  the 
  two 
  species 
  can 
  be 
  recognized 
  from 
  fragments 
  only 
  by 
  

   either: 
  (1) 
  The 
  base, 
  with 
  or 
  without 
  a 
  section 
  of 
  the 
  stem; 
  (2) 
  

   the 
  calyx, 
  if 
  the 
  anterior 
  ray 
  can 
  be 
  seen 
  to 
  the 
  bifurcation; 
  (3) 
  

   the 
  arms; 
  or 
  (4) 
  the 
  summit 
  of 
  the 
  sac. 
  H. 
  depressus 
  is 
  the 
  more 
  

   abundant 
  species, 
  being 
  represented 
  in 
  the 
  collection 
  by 
  170 
  speci- 
  

   mens, 
  and 
  H. 
  wetherbyi, 
  much 
  rarer, 
  by 
  30. 
  The 
  characters 
  above 
  

   specified 
  are 
  constant 
  throughout 
  them 
  all. 
  

  

  