﻿art. 
  5 
  THE 
  GENUS 
  PENTACRINUS 
  SPRINGER 
  7 
  

  

  pinnules 
  much 
  better 
  preserved 
  than 
  any 
  specimens 
  we 
  have 
  here. 
  The 
  ventral 
  

   edges 
  of 
  some 
  of 
  the 
  pinnulars 
  show 
  about 
  four 
  notches 
  or 
  crenulation?. 
  I 
  am 
  

   unable 
  to 
  detect 
  those 
  in 
  any 
  of 
  our 
  specimens, 
  but 
  the 
  material 
  is 
  insufficient. 
  

   I 
  should 
  certainly 
  refer 
  these 
  specimens 
  to 
  P. 
  subangularis 
  in 
  the 
  broad 
  sense. 
  

   Quenstedt, 
  you 
  will 
  remember, 
  confessed 
  that 
  his 
  attempts 
  to 
  divide 
  up 
  that 
  

   species 
  were 
  not 
  very 
  satisfactory 
  to 
  him. 
  

  

  Perhaps 
  the 
  most 
  interesting 
  feature 
  of 
  the 
  Alaskan 
  discovery 
  is 
  

   its 
  bearing 
  upon 
  the 
  • 
  geographical 
  distribution 
  of 
  this 
  vigorous 
  

   Jurassic 
  crinoidal 
  type, 
  which 
  now 
  appears 
  to 
  have 
  spread 
  into 
  al- 
  

   most 
  all 
  waters, 
  and 
  to 
  have 
  flourished 
  in 
  great 
  profusion 
  in 
  regions 
  

   remote 
  from 
  each 
  other. 
  Isolated 
  stem-ossicles 
  from 
  Dakota 
  and 
  

   from 
  Utah 
  described 
  as 
  Pentacrinus 
  asteriscus 
  by 
  Meek 
  and 
  Hay- 
  

   den, 
  12 
  and 
  as 
  P. 
  whitei 
  by 
  W. 
  B. 
  Clark, 
  show 
  a 
  still 
  wider 
  spread 
  

   upon 
  the 
  American 
  continent. 
  And 
  when 
  we 
  consider 
  the 
  further 
  

   evidence 
  now 
  in 
  hand 
  of 
  the 
  existence 
  of 
  a 
  closely 
  related 
  form 
  in 
  

   the 
  East 
  Indian 
  archipelago, 
  as 
  given 
  in 
  my 
  paper 
  before 
  cited, 
  we 
  

   are 
  impressed 
  with 
  the 
  cosmopolitan 
  range 
  of 
  the 
  genus, 
  far 
  exceed- 
  

   ing 
  that 
  of 
  any 
  crinoid 
  of 
  the 
  present 
  ocean. 
  It 
  is 
  a 
  good 
  illustration 
  

   of 
  the 
  result 
  of 
  conditions 
  prevailing 
  in 
  the 
  Jurassic 
  and 
  Cretaceous 
  

   periods 
  of 
  deep 
  and 
  clear 
  seas, 
  which 
  were 
  favorable 
  to 
  the 
  develop- 
  

   ment 
  and 
  spread 
  of 
  marine 
  faunas 
  over 
  large 
  areas 
  with 
  a 
  minimum 
  

   of 
  checks 
  and 
  interference, 
  in 
  contrast 
  to 
  those 
  of 
  subsequent 
  periods 
  

   down 
  to 
  the 
  present, 
  in 
  which 
  owing 
  to 
  the 
  great 
  changes 
  in 
  land 
  

   form 
  affecting 
  the 
  conditions 
  of 
  marine 
  life, 
  and 
  to 
  increasing 
  com- 
  

   petition 
  arising 
  from 
  the 
  multiplication 
  of 
  forms, 
  the 
  tendency 
  has 
  

   been 
  toward 
  progressively 
  greater 
  restriction 
  of 
  faunal 
  areas. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  

  

  Pentacrinus 
  subangularis 
  var. 
  alaska, 
  new 
  variety 
  

  

  Fig. 
  1. 
  Part 
  of 
  a 
  set 
  of 
  arms, 
  with 
  ra 
  mules 
  and 
  pinnules 
  finely 
  preserved. 
  

   Natural 
  size. 
  U. 
  S. 
  National 
  Museum. 
  Black 
  Island, 
  Canning 
  River. 
  

  

  2. 
  A 
  small 
  slab 
  filled 
  with 
  stem-fragments, 
  many 
  showing 
  the 
  joint-faces 
  

  

  in 
  detail, 
  and 
  some 
  in 
  side 
  view 
  showing 
  the 
  very 
  unequal 
  columnals 
  

   with 
  interpolated 
  lacunae. 
  Natural 
  size. 
  U. 
  S. 
  National 
  Museum. 
  

   Overthrust 
  Creek, 
  near 
  international 
  boundary- 
  

   Lower 
  Jurassic, 
  Kingak 
  shale; 
  northern 
  Alaska. 
  

  

  Pentacrinus 
  subangularis 
  Miller 
  

  

  3. 
  A 
  typical 
  joint-face, 
  enlarged, 
  for 
  comparison 
  of 
  structures. 
  X2. 
  

  

  Author's 
  collection. 
  

  

  Lower 
  Jurassic. 
  Upper 
  Lias 
  ; 
  Boll, 
  Wurtemburg. 
  

  

  Pentacrinus 
  rotiensis 
  Springer 
  

  

  4. 
  A 
  stem-fragment 
  containing 
  a 
  complete 
  internode 
  of 
  ?>even 
  pairs" 
  of 
  

  

  internodals, 
  to 
  show 
  the 
  mode 
  of 
  growth 
  of 
  younger 
  ossicles 
  by 
  inter- 
  

   polation 
  in 
  the 
  form 
  of 
  small 
  lacunae 
  not 
  yet 
  meeting 
  at 
  the 
  exterior 
  

   to 
  form 
  a 
  complete 
  columnal. 
  Collection 
  Dr. 
  G. 
  A. 
  F. 
  Molengraaff, 
  

   Delft, 
  Holland. 
  

  

  Jurassic. 
  Island 
  of 
  Roti, 
  Dutch 
  East 
  Indies. 
  

   12 
  Pal. 
  Upper 
  Missouri, 
  1865, 
  p. 
  G7, 
  pi. 
  3, 
  figs. 
  2, 
  a-b. 
  

  

  o 
  

  

  