﻿6 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  which 
  he 
  described 
  under 
  it, 
  may 
  be 
  readily 
  recognized. 
  Therefore 
  

   his 
  name 
  will 
  have 
  to 
  stand, 
  under 
  the 
  rules 
  of 
  nomenclature 
  as 
  now 
  

   interpreted. 
  Inasmuch 
  as 
  in 
  the 
  type 
  species 
  of 
  Herpetocrinus, 
  H. 
  

   fletcheri, 
  as 
  redescribed 
  by 
  Bather, 
  the 
  composition 
  of 
  the 
  calyx 
  has 
  

   been 
  definitely 
  shown 
  to 
  be 
  essentially 
  that 
  of 
  the 
  Heterocrinidae, 
  

   but 
  with 
  only 
  four 
  rays, 
  while 
  in 
  at 
  least 
  one 
  of 
  the 
  American 
  spe- 
  

   cies 
  it 
  is 
  now 
  known 
  to 
  be 
  somewhat 
  different, 
  it 
  might 
  be 
  suggested 
  

   that 
  Salter's 
  name 
  should 
  be 
  retained, 
  at 
  least 
  for 
  that 
  species. 
  But 
  

   from 
  the 
  little 
  we 
  know 
  of 
  the 
  crown 
  it 
  is 
  probable 
  that 
  the 
  Silurian 
  

   species 
  in 
  America 
  are 
  similarly 
  deformed, 
  and 
  so 
  the 
  separation 
  of 
  

   genera 
  on 
  this 
  ground 
  is 
  problematic. 
  Therefore 
  I 
  think 
  it 
  the 
  safe 
  

   course, 
  with 
  our 
  present 
  knowledge, 
  to 
  treat 
  all 
  the 
  species 
  under 
  the 
  

   name 
  first 
  published. 
  

  

  Six 
  American 
  species 
  have 
  been 
  described 
  : 
  M. 
  convolutus 
  Hall 
  

   and 
  HI. 
  brachiatus 
  Hall, 
  from 
  the 
  Rochester 
  shale; 
  M. 
  gorbyi 
  S. 
  A. 
  

   Miller, 
  perhaps 
  from 
  the 
  Waldron 
  ; 
  M. 
  bridgeporteiisis 
  S. 
  A. 
  Miller, 
  

   from 
  the 
  Racine 
  dolomite; 
  M. 
  {Eomyelodactylus) 
  rotundatus 
  

   Foerste, 
  from 
  the 
  Brassfield; 
  M. 
  (Brachiocvinus) 
  nodosarius 
  Hall, 
  

   from 
  the 
  Helderbergian. 
  To 
  these 
  will 
  be 
  added 
  two 
  new 
  species 
  

   from 
  the 
  Niagaran; 
  also 
  one 
  from 
  the 
  Keyser, 
  and 
  one 
  from 
  the 
  

   Linden 
  beds 
  of 
  the 
  Lower 
  Devonian. 
  Furthermore, 
  I 
  have 
  rec- 
  

   ognized 
  from 
  the 
  American 
  rocks 
  of 
  Niagaran 
  age 
  one 
  of 
  Doctor 
  

   Bather's 
  Gotland 
  species 
  of 
  the 
  equivalent 
  Wenlockian, 
  which 
  also 
  

   occurs 
  in 
  England. 
  From 
  data. 
  now 
  available 
  as 
  to 
  the 
  occurrence 
  

   of 
  these 
  several 
  species, 
  it 
  may 
  be 
  said 
  that 
  the 
  Silurian 
  type 
  ranges 
  

   from 
  the 
  early 
  Niagaran 
  through 
  most 
  of 
  its 
  principal 
  formations, 
  

   and 
  continues 
  into 
  the 
  Lower 
  Devonian. 
  It 
  has 
  not 
  thus 
  far 
  been 
  

   recognized 
  from 
  the 
  Middle 
  or 
  Upper 
  Devonian, 
  although 
  a 
  re- 
  

   markable 
  modification 
  of 
  it 
  is 
  now 
  known 
  from 
  the 
  former 
  horizon 
  

   and 
  will 
  be 
  herein 
  described, 
  which 
  is 
  perhaps 
  more 
  nearly 
  related 
  

   to 
  the 
  Lower 
  Carboniferous 
  phase 
  of 
  the 
  coiled 
  stem 
  type. 
  

  

  Genus 
  MYELODACTYLUS 
  Hall 
  

  

  Plates 
  1-5 
  

  

  Myelodactylus 
  Hall, 
  Pal. 
  New 
  York, 
  vol. 
  2, 
  1S52, 
  p. 
  191. 
  

   Herpet?-oorinus 
  Bather, 
  Crinoidea 
  of 
  Gotland, 
  1893, 
  p. 
  36. 
  

   Silurian 
  to 
  Devonian. 
  

  

  Hall's 
  generic 
  diagnosis, 
  based 
  on 
  the 
  idea 
  that 
  the 
  coiled 
  stem 
  

   was 
  an 
  arm, 
  is 
  of 
  no 
  service, 
  but 
  the 
  form 
  can 
  be 
  recognized 
  from 
  

   the 
  two 
  species 
  which 
  he 
  figured 
  and 
  described. 
  With 
  our 
  present 
  

   knowledge 
  its 
  characters 
  may 
  be 
  stated 
  as 
  follows 
  : 
  

  

  An 
  Inadunate 
  crinoid 
  with 
  coiled 
  stem, 
  which 
  more 
  or 
  less 
  com- 
  

   pletely 
  envelops 
  the 
  crown. 
  Stem 
  in 
  proximal 
  region 
  evolute, 
  cir- 
  

   cular 
  in 
  section, 
  composed 
  of 
  very 
  thin 
  uniform 
  ossicles; 
  in 
  middle 
  

  

  