﻿Report 
  of 
  the 
  State 
  Geologist. 
  1111 
  

  

  The 
  great 
  gulf 
  which 
  has 
  seemed 
  to 
  exist 
  between 
  the 
  Inarticu- 
  

   late 
  or 
  Lyopomatous, 
  and 
  the 
  Articulate 
  or 
  Arthropomatous 
  divi- 
  

   sions 
  of 
  the 
  Class 
  Brachiopoda 
  ; 
  those 
  without 
  teeth, 
  and 
  those 
  

   with 
  teeth 
  ; 
  those 
  with 
  a 
  largely 
  corneous 
  shell, 
  and 
  those 
  whose 
  

   shell 
  is 
  essentially 
  calcareous, 
  is 
  not 
  yet 
  fully 
  spanned 
  at 
  many 
  

   points. 
  

  

  These 
  divisions 
  were 
  based 
  upon 
  the 
  study 
  of 
  living 
  brachiopods 
  

   in 
  which 
  all 
  the 
  characteristic 
  differences 
  are 
  pronounced 
  and 
  

   fixed. 
  It 
  is 
  natural, 
  however, 
  to 
  find 
  among 
  the 
  early 
  brachiopods, 
  

   in 
  which 
  the 
  adjustment 
  of 
  the 
  organism 
  to 
  its 
  conditions 
  was 
  

   highly 
  sensitive, 
  that 
  the 
  oscillation 
  and 
  specialization 
  of 
  charac- 
  

   ters 
  has 
  been 
  very 
  rapid. 
  The 
  development 
  of 
  articulating 
  

   processes 
  has 
  already 
  been 
  noticed 
  among 
  the 
  linguloids 
  in 
  

   Barroisella, 
  Tomasina 
  and 
  Trimerella, 
  among 
  the 
  oboloids 
  in 
  

   Spondyloboltjs, 
  and 
  among 
  the 
  siphon 
  otretoids 
  in 
  Trematoboltts. 
  

   It 
  is 
  known 
  that 
  the 
  shell 
  of 
  many 
  inarticulates 
  is 
  almost 
  wholly 
  

   calcareous, 
  as 
  in 
  the 
  Trimerellidje, 
  and 
  all 
  of 
  the 
  Gasteropegmata. 
  

   The 
  alteration 
  in 
  the 
  nature 
  of 
  the 
  shell-substance 
  from 
  the 
  pro- 
  

   toconch 
  or 
  its 
  exemplar, 
  Paterina, 
  which 
  appears 
  to 
  be 
  wholly 
  

   or 
  essentially 
  corneous, 
  to 
  the 
  typical 
  articulate 
  brachiopod, 
  in 
  

   which 
  the 
  corneous 
  substance 
  is 
  reduced 
  to 
  a 
  thin 
  epidermal 
  film, 
  

   is 
  a 
  gradual 
  process 
  whose 
  various 
  stages 
  are 
  well 
  understood. 
  In 
  

   Obolella, 
  Elkania, 
  and 
  the 
  early 
  forms 
  of 
  Lingttla, 
  the 
  deposition 
  

   of 
  calcareous 
  salts 
  in 
  the 
  shell 
  was 
  already 
  advanced, 
  these 
  layers 
  

   alternating 
  with 
  thinner 
  layers 
  of 
  corneous 
  substance. 
  The 
  

   gradual 
  and 
  eventual 
  predominance 
  of 
  the 
  calcareous 
  shell-matter 
  

   along 
  both 
  of 
  these 
  lines 
  of 
  development 
  is 
  seen 
  in 
  the 
  ponderous 
  

   Trimerellids 
  of 
  the 
  later 
  Silurian. 
  The 
  graduation 
  of 
  the 
  corne- 
  

   ous 
  Paterina 
  {Kutorgina 
  Zabradorica, 
  var. 
  Swantonensis) 
  through 
  

   Kutorgina 
  Zabradorica, 
  and 
  into 
  the 
  true 
  calcareous 
  Kutorginas 
  

   (K 
  cingulata, 
  K 
  Whitfieldi), 
  is 
  similar 
  evidence. 
  In 
  Kutorgina 
  

   Zatourensis, 
  Matthew 
  described 
  a 
  minute 
  tooth 
  on 
  either 
  side 
  of 
  

   the 
  pedicle-opening, 
  and 
  it 
  has 
  been 
  stated 
  that 
  K 
  cingulata 
  

   shows 
  faint 
  traces 
  of 
  articulating 
  processes 
  at 
  or 
  near 
  the 
  extremi- 
  

   ties 
  of 
  the 
  cardinal 
  line. 
  Such 
  cases 
  indicate 
  a 
  direct 
  transgres- 
  

   sion 
  in 
  the 
  texture 
  and 
  composition 
  of 
  the 
  shell 
  from 
  the 
  most 
  

   primitive 
  inarticulate 
  type 
  to 
  the 
  articulate. 
  In 
  this 
  feature 
  only, 
  

   the 
  connection 
  between 
  the 
  two 
  divisions 
  of 
  the 
  class 
  is 
  no 
  closer 
  or 
  

   more 
  clearly 
  manifested 
  than 
  in 
  the 
  instances 
  mentioned, 
  but 
  it 
  

  

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