﻿PLATE 
  XXVIII. 
  

  

  Platyostoma 
  Niagaeense 
  Hall. 
  

   Page 
  175. 
  

  

  Fig. 
  1. 
  A 
  small 
  specimen, 
  showing 
  strong 
  revolving 
  strife 
  and 
  with 
  a 
  slight 
  

  

  depression 
  on 
  the 
  upper 
  surface 
  of 
  the 
  last 
  volution. 
  

   Figs. 
  2-4. 
  Basal, 
  summit 
  and 
  lateral 
  views 
  of 
  a 
  specimen 
  similarly 
  striated, 
  

  

  which 
  is 
  sulcated 
  above 
  and 
  below, 
  with 
  two 
  distinct 
  folds 
  on 
  the 
  

  

  lower 
  surface 
  of 
  the 
  volution. 
  

   Figs. 
  5-7. 
  Three 
  views 
  of 
  a 
  larger, 
  loosely 
  coiled 
  specimen, 
  with 
  a 
  distinct 
  sul- 
  

  

  cation 
  above 
  and 
  below 
  the 
  middle 
  of 
  the 
  volution. 
  

   Figs. 
  8, 
  9. 
  Two 
  views 
  of 
  a 
  more 
  ventricose 
  specimen 
  with 
  regularly 
  convex 
  

  

  volutions. 
  

   Figs. 
  10, 
  11. 
  The 
  summit 
  and 
  ventral 
  view 
  of 
  a 
  large 
  loosely 
  coiled 
  specimen. 
  

  

  the 
  outer 
  volution 
  beino; 
  free. 
  

   Fig. 
  12. 
  The 
  spire 
  of 
  a 
  large 
  ventricose 
  specimen, 
  with 
  closely 
  coiled 
  volutions. 
  

  

  PLATYOSTOilA 
  NlAGARE^SE 
  ? 
  

  

  Fig. 
  13. 
  A 
  specimen 
  with 
  its 
  aperture 
  showing 
  a 
  twisted 
  inner 
  lip 
  of 
  the 
  peris- 
  

   tome. 
  This 
  feature 
  is 
  produced 
  by 
  the 
  folds 
  on 
  the 
  inner 
  part 
  of 
  

   the 
  volution 
  and 
  is 
  not 
  a 
  true 
  columella. 
  

  

  Platyostoma 
  plebium 
  Hall. 
  

  

  Page 
  175. 
  

  

  Figs. 
  14, 
  15. 
  The 
  opposite 
  sides 
  of 
  a 
  specimen, 
  showing 
  the 
  height 
  of 
  the 
  spire 
  

   and 
  form 
  of 
  the 
  volution 
  and 
  aperture. 
  

  

  