﻿148 
  Williams 
  — 
  Devonian 
  Interval 
  in 
  nortJiern 
  Arkansas. 
  

  

  and 
  giniis 
  of 
  that 
  species. 
  They 
  are 
  evidently 
  the 
  same 
  species 
  

   figured 
  on 
  Plate 
  Nl 
  A 
  of 
  the 
  New 
  York 
  Yolurae 
  V^II, 
  

   Braoliiopoda 
  I, 
  and 
  called 
  Orthis 
  sp. 
  ? 
  (compare 
  0. 
  penelope)^ 
  

   from 
  the 
  AYaverly 
  group 
  of 
  Granville, 
  Ohio. 
  

  

  As 
  a 
  name, 
  I 
  think 
  it 
  is 
  probable 
  that 
  Hall 
  first 
  distinguished 
  

   the 
  species 
  in 
  question, 
  in 
  the 
  Iowa 
  Report 
  of 
  1858,* 
  under 
  the 
  

   name 
  Orthis 
  michelini^ 
  var. 
  hurlingtonensis^ 
  so 
  that 
  they 
  

   should 
  be 
  called 
  Hhipodomella 
  hurlingtonensis 
  Hall. 
  The 
  

   specimens 
  correspond 
  more 
  nearly 
  to 
  specimens 
  in 
  like 
  condi- 
  

   tion 
  in 
  the 
  Burlington 
  than 
  t(» 
  the 
  typical 
  O. 
  vanuxemi 
  or 
  

   penelope, 
  though 
  in 
  some 
  features 
  recalling 
  the 
  latter. 
  Another 
  

   species, 
  Rhipidornella 
  thiemii 
  (White), 
  is 
  a 
  small 
  species, 
  and 
  

   may 
  prove 
  to 
  be 
  but 
  a 
  young 
  or 
  small 
  form 
  of 
  the 
  hurlington- 
  

   ensis 
  species, 
  but, 
  as 
  it 
  is 
  frequently 
  seen 
  of 
  the 
  diminished 
  

   size, 
  it 
  is 
  safe 
  to 
  refer 
  to 
  it 
  as 
  a 
  distinct 
  species. 
  

  

  Schizojjhoria 
  is 
  represented 
  by 
  a 
  couple 
  of 
  faint 
  impres- 
  

   sions 
  in 
  the 
  black 
  shale 
  of 
  1279 
  Al 
  (Y489). 
  This, 
  for 
  purposes 
  

   of 
  identification, 
  may 
  be 
  referred 
  to 
  S. 
  sivalloioi 
  Hall, 
  with 
  a 
  

   query 
  ; 
  sufticient 
  evidence 
  is 
  present 
  to 
  refer 
  it 
  to 
  this 
  genus, 
  

   but 
  the 
  crushed 
  condition 
  of 
  the 
  specimen 
  makes 
  it 
  impossible 
  

   to 
  tell 
  what 
  its 
  original 
  form 
  was. 
  

  

  Strophoinenidoe. 
  — 
  Among 
  the 
  Strophomenidse, 
  a 
  few 
  dis- 
  

   tinct 
  representatives 
  of 
  the 
  Leptmna 
  rhomhoidalis 
  have 
  been 
  

   seen 
  in 
  the 
  green 
  shale 
  of 
  1291. 
  

  

  Tereh'atidoid 
  shells 
  s^re 
  difiicult 
  to 
  identify, 
  even 
  when 
  per- 
  

   fect, 
  from 
  the 
  exterior 
  alone, 
  but 
  a 
  crushed 
  fragment 
  in 
  the 
  

   green 
  shale 
  of 
  (1279 
  Al) 
  suggests 
  strongly 
  the 
  form 
  Dielasma 
  

   hurlingtonense. 
  — 
  We 
  may 
  refer 
  to 
  this 
  as 
  a 
  possible 
  species 
  

   of 
  the 
  fauna. 
  

  

  In 
  addition 
  to 
  the 
  specimens 
  whose 
  generic 
  afiinities 
  may 
  be 
  

   distinguished, 
  there 
  are 
  Conodont 
  teeth^ 
  fragments 
  of 
  ^/i'Vi 
  hones 
  

   which 
  must 
  have 
  belonged 
  to 
  large 
  mailed 
  fish, 
  and 
  Crinoid 
  

   steins. 
  

  

  When 
  the 
  whole 
  fauna 
  is 
  critically 
  examined, 
  though 
  the 
  

   specimens 
  are 
  nearly 
  all 
  in 
  very 
  imperfect, 
  distorted 
  condition, 
  

   enough 
  may 
  be 
  made 
  out 
  of 
  their 
  zoological 
  afiinities 
  to 
  settle 
  

   the 
  question 
  of 
  general 
  horizon. 
  The 
  black 
  shale, 
  when 
  it 
  

   stands 
  out 
  distinct 
  with 
  a 
  limestone 
  below 
  and 
  above, 
  presents 
  

   a 
  fauna 
  which 
  would 
  link 
  the 
  horizon 
  with 
  that 
  of 
  the 
  Genesee 
  

   black 
  shale 
  of 
  JN'ew 
  York. 
  But 
  when 
  we 
  examine 
  it, 
  where 
  

   followed 
  gradually 
  by 
  a 
  green 
  shale, 
  becoming 
  finally 
  calcare- 
  

   ous, 
  and 
  running 
  up 
  into 
  thin, 
  shaly 
  limestone 
  beds 
  with 
  the 
  

   green 
  shale 
  alternating 
  with 
  it, 
  before 
  the 
  pure 
  limestone 
  enters 
  

   the 
  section, 
  the 
  evidence 
  of 
  precise 
  horizon 
  is 
  less 
  positive. 
  In 
  

   such 
  a 
  case 
  the 
  fact, 
  that 
  the 
  Genesee 
  black 
  shale 
  has 
  a 
  definite 
  

   s-eoloorical 
  horizon 
  in 
  the 
  New 
  York 
  sections, 
  must 
  not 
  be 
  

  

  * 
  Geol. 
  of 
  Iowa, 
  vol. 
  i, 
  part 
  2. 
  

  

  