﻿888 
  Forty- 
  seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  Commencing 
  with 
  a 
  species 
  having 
  two 
  ranges 
  of 
  apertures 
  

   without 
  a 
  median 
  keel 
  we 
  see 
  a 
  gradual 
  change 
  through 
  forms 
  

   with 
  strong 
  carinas 
  to 
  the 
  typical 
  forms 
  of 
  Hemitrypa. 
  

  

  20 
  

  

  24 
  

  

  <§> 
  

  

  4 
  

  

  21 
  

  

  

  22 
  

  

  25 
  

  

  # 
  

  

  26 
  

  

  1 
  

  

  23 
  

  

  6 
  

  

  s 
  

  

  TIT 
  

  

  In 
  fig. 
  20 
  the 
  branches 
  are 
  rounded 
  with 
  no 
  median 
  keel; 
  fig. 
  

   21 
  has 
  a 
  very 
  slight 
  keel 
  ; 
  in 
  fig. 
  22 
  the 
  keel 
  is 
  slightly 
  more 
  

   elevated 
  ; 
  in 
  fig. 
  23 
  the 
  keel 
  is 
  still 
  more 
  elevated, 
  and 
  in 
  fig. 
  

   24 
  the 
  keel 
  is 
  much 
  more 
  prominent 
  and 
  attenuated 
  above; 
  in 
  

   fig. 
  25 
  the 
  keel 
  is 
  slightly 
  thickened 
  at 
  the 
  summit 
  ; 
  in 
  fig. 
  

   26 
  the 
  keel 
  is 
  more 
  elevated 
  and 
  is 
  laterally 
  expanded 
  above 
  ; 
  in 
  

   fig. 
  27a 
  the 
  keel 
  is 
  elevated 
  and 
  much 
  expanded 
  above, 
  having 
  

   on 
  each 
  margin 
  of 
  the 
  expanded 
  portion 
  a 
  row 
  of 
  minute 
  nodes 
  

   or 
  spinule-like 
  projections 
  ; 
  the 
  upper 
  figure, 
  b, 
  is 
  a 
  view 
  looking 
  

   upon 
  the 
  celluliferous 
  face 
  of 
  a 
  similar 
  form 
  ; 
  in 
  Hg. 
  28 
  the 
  keel 
  

   is 
  elevated 
  and 
  expanded 
  above, 
  the 
  nodes 
  on 
  the 
  margins 
  are 
  in 
  

   some 
  instances 
  prolonged 
  until 
  those 
  of 
  adjacent 
  carina 
  from 
  

   contiguous 
  branches 
  meet, 
  coalesce, 
  and 
  form 
  bars 
  connecting 
  the 
  

   summits 
  of 
  adjacent 
  carinas. 
  

  

  The 
  species 
  from 
  which 
  this 
  drawing 
  was 
  made 
  is 
  Fenestella 
  

   precursor 
  of 
  the 
  Lower 
  Helderberg 
  group, 
  the 
  same 
  feature 
  is 
  

   shown 
  in 
  F. 
  perplexa 
  of 
  the 
  Upper 
  Helderberg 
  group 
  and 
  is 
  

   still 
  more 
  pronounced 
  in 
  an 
  undescribed 
  species 
  from 
  the 
  Hamil- 
  

   ton 
  group, 
  where 
  a 
  portion 
  of 
  the 
  frond 
  has 
  marginal 
  nodes 
  as 
  in 
  

   fig. 
  28, 
  and 
  other 
  portions 
  are 
  of 
  precisely 
  the 
  same 
  character 
  as 
  

   represented 
  in 
  fig. 
  29. 
  

  

  In 
  fig. 
  29 
  the 
  keel 
  is 
  elevated 
  and 
  expanded 
  above, 
  and 
  the 
  

   summits 
  of 
  the 
  carinas 
  are 
  connected 
  by 
  lateral 
  processes 
  ; 
  looking 
  

   on 
  these 
  from 
  above 
  they 
  have 
  the 
  appearance 
  of 
  dissepiments, 
  

   and 
  they 
  are 
  the 
  characteristic 
  feature 
  upon 
  which 
  is 
  founded 
  

   the 
  genus 
  Unitrypa. 
  

  

  