﻿Report 
  of 
  the 
  State 
  Geologist. 
  1115 
  

  

  retained 
  in 
  Chonetes, 
  Prodttotella, 
  Strophalosia 
  and 
  Aulosteg-es, 
  

   become 
  wholly 
  obliterated 
  in 
  the 
  direct 
  line 
  of 
  productoid 
  

   development. 
  In 
  all 
  these 
  forms 
  the 
  "reniform 
  impressions" 
  

   retained 
  on 
  the 
  inner 
  surface 
  of 
  the 
  brachial 
  valve 
  are 
  evidence 
  

   of 
  fleshy 
  brachia 
  possessing 
  a 
  similar 
  curvature 
  to 
  those 
  of 
  the 
  

   Str 
  ophomenibje. 
  

  

  This 
  group 
  of 
  genera 
  has 
  long 
  been 
  designated 
  by 
  the 
  family 
  

   name 
  Probuctib^e, 
  introduced 
  by 
  Gray 
  in 
  1840, 
  though, 
  in 
  cor- 
  

   relating 
  the 
  various 
  divisions 
  of 
  Waagen's 
  group, 
  Aphaneropeg- 
  

   mata, 
  there 
  would 
  be 
  excellent 
  reason 
  for 
  considering 
  the 
  chone- 
  

   tids 
  and 
  productids 
  components 
  of 
  a 
  subfamily 
  inferior 
  in 
  value 
  

   to 
  the 
  Str 
  ophomenibje 
  and 
  quantivalent 
  to 
  the 
  divisions 
  Ortho- 
  

   thetince,W8L8LgQn, 
  1884, 
  and 
  JBajlnesquinince, 
  Schuchert 
  (emendatus), 
  

   1893. 
  

  

  Returning 
  to 
  the 
  point 
  of 
  departure, 
  we 
  shall 
  find 
  that 
  in 
  the 
  

   genus, 
  Orthis, 
  which 
  in 
  its 
  broadest 
  significance 
  is 
  tantamount 
  to 
  

   the 
  family 
  Orthibje, 
  Woodward, 
  1852, 
  since 
  the 
  elimination 
  of 
  

   several 
  heterogenous 
  branches, 
  the 
  deltidium 
  was 
  resorbed 
  at 
  an 
  

   early 
  stage 
  of 
  growth, 
  leaving 
  the 
  delthyrium 
  a 
  wide, 
  uncovered 
  

   aperture 
  during 
  all 
  the 
  later 
  stages 
  of 
  existence. 
  The 
  pedicle 
  in 
  

   this 
  group 
  of 
  shells 
  was 
  undoubtedly 
  large 
  and 
  vigorously 
  func- 
  

   tional 
  throughout 
  all 
  mature 
  conditions, 
  as 
  it 
  is 
  very 
  rarely 
  that 
  

   any 
  secretions 
  of 
  calcareous 
  matter 
  are 
  found 
  in 
  the 
  apex 
  of 
  the 
  

   delthyrium, 
  such 
  as 
  are 
  frequently 
  observed 
  in 
  mature 
  and 
  senile 
  

   conditions 
  of 
  Spirifer. 
  The 
  sharp 
  delimitation 
  of 
  the 
  pedicle- 
  

   cavity 
  containing 
  all 
  the 
  muscular 
  scars 
  of 
  the 
  pedicle-valve, 
  

   which 
  occurs 
  in 
  the 
  earlier 
  forms 
  (those 
  of 
  Orthis 
  in 
  its 
  restricted 
  

   meaning, 
  such 
  as 
  0. 
  callaetis, 
  0. 
  costalis, 
  etc.) 
  is 
  maintained 
  in 
  all 
  

   the 
  numerous 
  subdivisions 
  of 
  the 
  genus, 
  with 
  the 
  exception 
  of 
  

   Rhipidomella 
  in 
  which 
  there 
  is 
  a 
  great 
  expansion 
  of 
  the 
  muscu- 
  

   lar 
  scars, 
  similar 
  to 
  that 
  in 
  the 
  StrophomenidjE 
  and 
  to 
  which 
  

   reference 
  has 
  just 
  been 
  made. 
  Otherwise 
  the 
  sessile 
  condition 
  of 
  

   the 
  spondylium 
  is 
  not 
  modified 
  throughout 
  the 
  entire 
  history 
  of 
  

   this 
  group. 
  

  

  The 
  elevation 
  of 
  the 
  spondylioid 
  plate, 
  or 
  the 
  base 
  of 
  the 
  

   pedicle-cavity, 
  into 
  a 
  true 
  spondylium 
  is 
  a 
  phenomenon 
  of 
  equally 
  

   early 
  age 
  to 
  the 
  two 
  conditions 
  already 
  discussed. 
  It 
  appears 
  in 
  

   a 
  highly-developed 
  state 
  in 
  conjunction 
  with 
  the 
  unmodified 
  

   deltidium, 
  first 
  in 
  Protorthis, 
  of 
  the 
  Cambrian, 
  then 
  in 
  Polytce- 
  

  

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