﻿PLATE 
  XI— 
  (Continued). 
  

  

  Fenestella 
  ambigtja 
  n. 
  sp. 
  

   Page 
  123. 
  

  

  Fig. 
  17. 
  The 
  inner 
  surface 
  of 
  a 
  frond, 
  natural 
  size. 
  

  

  Pigs. 
  18, 
  19. 
  Enlarged 
  views 
  of 
  the 
  opposite 
  faces 
  of 
  the 
  above 
  specimen, 
  show- 
  

   ing 
  a 
  slight 
  difference 
  in 
  the 
  character 
  of 
  the 
  striation 
  of 
  the 
  two 
  

   sides 
  of 
  the 
  frond. 
  

  

  Fig. 
  20. 
  The 
  exterior 
  surface 
  of 
  a 
  flattened 
  frond, 
  showing 
  a 
  portion 
  of 
  the 
  

   interior 
  surface 
  at 
  the 
  right 
  hand 
  side. 
  

  

  Fig. 
  21. 
  An 
  enlargement 
  from 
  the 
  edge 
  of 
  the 
  specimen 
  fig. 
  20, 
  showing 
  a 
  sec- 
  

   tion. 
  The 
  rays 
  of 
  the 
  inner 
  and 
  outer 
  layers 
  of 
  the 
  frond 
  are 
  con- 
  

   nected 
  by 
  the 
  vertical 
  extensions, 
  and 
  the 
  rays 
  of 
  the 
  same 
  layer 
  

   connected 
  by 
  the 
  transverse 
  or 
  horizontal 
  dissepiments. 
  

  

  Thamniscus 
  Niagabensis 
  Hall. 
  

  

  Page 
  126. 
  

   ■ 
  

   Fig. 
  22. 
  The 
  non-poriferous 
  face 
  of 
  a 
  frond, 
  natural 
  size, 
  showing 
  the 
  mode 
  of 
  

  

  growth 
  and 
  absence 
  of 
  transverse 
  dissepiments. 
  

   Fig. 
  23. 
  An 
  enlargement 
  of 
  the 
  poriferous 
  face 
  of 
  a 
  frond, 
  to 
  two 
  diameters. 
  

   Fig. 
  24. 
  A 
  still 
  farther 
  enlargement 
  of 
  the 
  right 
  hand 
  third 
  of 
  the 
  frond 
  fig. 
  23, 
  

  

  to 
  show 
  the 
  angular 
  crest 
  of 
  the 
  branches 
  and 
  the 
  disposition 
  of 
  

  

  the 
  pores 
  upon 
  its 
  surface. 
  

   Fig. 
  25. 
  An 
  enlargement, 
  to 
  three 
  diameters, 
  of 
  another 
  fragment, 
  showing 
  the 
  

  

  base 
  of 
  attachment, 
  the 
  angular 
  crest 
  of 
  the 
  branches 
  and 
  the 
  

  

  extensions 
  of 
  the 
  pores 
  over 
  the 
  root-like 
  base. 
  

  

  

  