﻿146 
  Williams 
  — 
  Devonian 
  Interval 
  in 
  northern 
  Arkansas. 
  

  

  York-Ohio 
  region, 
  on 
  the 
  supposition 
  that 
  the 
  modification 
  

   from 
  the 
  minute 
  forms 
  to 
  tlie 
  broader, 
  oval, 
  flat, 
  enlarged 
  

   forms 
  of 
  the 
  Carboniferous 
  horizons 
  is 
  one 
  due 
  to 
  gradual 
  

   evolution. 
  But 
  I 
  do 
  not 
  feel 
  perfectly 
  confident 
  that 
  this 
  is 
  

   the 
  case. 
  I 
  think 
  it 
  more 
  likely 
  that 
  the 
  conditions 
  of 
  environ- 
  

   ment 
  at 
  the 
  same 
  time 
  would 
  find 
  expression 
  in 
  something 
  of 
  

   this 
  modification. 
  That 
  the 
  species 
  is 
  peculiar 
  to 
  the 
  kind 
  of 
  

   sediments 
  which, 
  in 
  their 
  purity, 
  constitute 
  the 
  black 
  shale, 
  is 
  

   quite 
  evident 
  from 
  a 
  wide 
  study 
  of 
  their 
  occurrences. 
  

  

  Cyrtina. 
  — 
  In 
  the 
  brownish-black 
  shale 
  of 
  station 
  1279 
  Al 
  

   several 
  specimens, 
  which 
  I 
  refer 
  to 
  Cyrtina 
  acutirostris 
  

   Shumard, 
  are 
  found. 
  Several 
  of 
  the 
  specimens 
  are 
  much 
  

   crushed, 
  but 
  the 
  high 
  beak, 
  the 
  attenuated 
  upper 
  part, 
  and 
  

   broad 
  and 
  rather 
  extended 
  mesial 
  sinus 
  and 
  few 
  lateral 
  plica- 
  

   tions, 
  which 
  are 
  not 
  so 
  broadly 
  rounded 
  as 
  in 
  the 
  figure, 
  are 
  

   the 
  characters 
  suggesting 
  the 
  species. 
  The 
  characteristic 
  punc- 
  

   tations 
  are 
  not 
  evident. 
  

  

  Spirifer. 
  — 
  Several 
  species 
  of 
  this 
  genus 
  are 
  recognized. 
  

   The 
  specimens 
  from 
  1291 
  C 
  (Y 
  200) 
  are 
  clearly 
  S. 
  marionensis. 
  

   Those 
  from 
  1279 
  Al 
  (Y 
  423) 
  are 
  crushed 
  and 
  only 
  fragments, 
  

   but 
  what 
  is 
  evident 
  agrees 
  with 
  the 
  similar 
  parts 
  of 
  perfect 
  

   specimens 
  of 
  S. 
  marionensis. 
  This 
  species 
  is 
  frequently 
  seen 
  

   in 
  the 
  higher 
  beds 
  and 
  across 
  the 
  line 
  in 
  Missouri 
  ; 
  it 
  is 
  charac- 
  

   teristic 
  of 
  the 
  corresponding 
  shales 
  at 
  the 
  base 
  of 
  the 
  Carbonif- 
  

   erous. 
  S. 
  hiplicatus 
  Hall 
  is 
  suggested 
  by 
  some 
  crushed 
  speci- 
  

   mens 
  (Y 
  171), 
  but 
  the 
  material 
  is 
  too 
  imperfect 
  for 
  certain 
  

   identification. 
  S. 
  winchelli 
  Herrick, 
  cf. 
  S. 
  mesacostalis^ 
  a 
  very 
  

   perfect 
  specimen 
  (Y 
  199), 
  resembles 
  very 
  closely 
  some 
  speci- 
  

   mens 
  of 
  the 
  smaller 
  variety 
  of 
  S. 
  77iesacostalis 
  from 
  the 
  Ithaca 
  

   group 
  (Devonian) 
  of 
  New 
  York. 
  It 
  is 
  the 
  type 
  described 
  by 
  

   Herrick, 
  from 
  the 
  Waverly 
  of 
  Ohio, 
  under 
  the 
  name 
  S. 
  10171- 
  

   chelli. 
  Mr. 
  Herrick 
  suggests 
  the 
  close 
  resemblance 
  to 
  S. 
  inesa- 
  

   costalis, 
  but 
  in 
  a 
  note 
  to 
  the 
  writer 
  he 
  says 
  that 
  Professor 
  

   Winchell 
  considered 
  it 
  to 
  be 
  undoubtedly 
  a 
  distinct 
  species. 
  

  

  S. 
  ? 
  compactiis 
  Meek. 
  — 
  Some 
  crushed 
  specimens 
  (Y 
  172) 
  

   from 
  the 
  green 
  shales 
  at 
  Eureka 
  springs 
  (1410 
  M2) 
  may 
  belong 
  

   to 
  this 
  species. 
  It 
  has 
  the 
  form 
  of 
  pmguis 
  or 
  suhorhicularis 
  

   Hall, 
  and 
  yet 
  is 
  too 
  crushed 
  to 
  well 
  make 
  out 
  the 
  true 
  propor- 
  

   tions. 
  

  

  Spiriferhia 
  ? 
  octoplicata. 
  — 
  Specimens 
  (Y 
  173), 
  fairly 
  repre- 
  

   senting 
  the 
  character 
  of 
  this 
  species, 
  occur 
  in 
  the 
  green 
  shale 
  

   at 
  Eureka 
  Springs 
  (1410 
  M2). 
  

  

  Athyris 
  is 
  represented 
  in 
  the 
  green 
  shales 
  (1291) 
  by 
  speci- 
  

   mens, 
  which 
  are 
  referred 
  to 
  ^. 
  hannihalensis 
  Swallow 
  (Y201). 
  

   Another 
  specimen 
  is 
  referred 
  w^ith 
  doubt 
  to 
  A. 
  fultonensis 
  

   Swallow, 
  from 
  the 
  green 
  shales 
  of 
  Eureka 
  Springs 
  ( 
  141 
  M2). 
  

  

  