﻿PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  

  

  frontal 
  dorsal 
  are 
  aborted 
  and 
  engender 
  the 
  vacuoles 
  of 
  the 
  non- 
  

   cellular 
  face. 
  

  

  Our 
  longitudinal 
  sections 
  do 
  not 
  correspond 
  exactly 
  with 
  those 
  of 
  

   Gregory, 
  1899 
  (p. 
  364), 
  which 
  seem 
  to 
  show 
  parietal 
  mesopores 
  

   ( 
  = 
  maculae). 
  The 
  sections 
  of 
  Lonsdale 
  are 
  incomplete. 
  

  

  The 
  meridian 
  section 
  confirms 
  the 
  longitudinal 
  section, 
  but 
  the 
  

   tubes 
  are 
  symmetrically 
  arranged 
  on 
  each 
  side 
  of 
  the 
  central 
  axis. 
  

   Moreover, 
  diaphragms 
  appear 
  sometimes. 
  

  

  In 
  transverse 
  sections 
  the 
  zoarial 
  epitheca 
  is 
  thick, 
  lamellar, 
  per- 
  

   forated 
  by 
  irregularly 
  scattered 
  vacuoles; 
  the 
  tubes 
  here 
  are 
  almost 
  

   equal 
  and 
  polygonal. 
  

  

  Fig. 
  44.— 
  Genus 
  Siphodictyum 
  Lonsdale, 
  1849. 
  A-E. 
  Siphodictyum 
  irregulare, 
  new 
  species. 
  A. 
  Trans- 
  

   verse 
  section, 
  X 
  16, 
  showing 
  the 
  polygonal 
  tubes. 
  B. 
  Another 
  transverse 
  section, 
  X 
  lfi, 
  exhibiting 
  the 
  

   central 
  axis. 
  C. 
  Tangential 
  section, 
  X 
  16, 
  illustrating 
  the 
  arrangement 
  of 
  the 
  vacuoles 
  around 
  the 
  

   orifices 
  D. 
  Longitudinal 
  section, 
  X 
  16. 
  The 
  vacuoles 
  perforate 
  the 
  epitheca 
  all 
  around 
  the 
  zoarium. 
  

   E. 
  Longitudinal 
  section, 
  X 
  16, 
  showing 
  the 
  cylindrical 
  tubes 
  and 
  the 
  vacuoles 
  perforating 
  the 
  epitheca. 
  

   Lower 
  Cretaceous 
  (Aptian) 
  : 
  Faringdon, 
  England. 
  F-H. 
  Siphodictyum 
  gracile 
  Lonsdale, 
  1879. 
  F. 
  Trans- 
  

   verse 
  section, 
  X 
  16. 
  Q. 
  Meridian 
  section, 
  X 
  16. 
  H. 
  Longitudinal 
  section, 
  X 
  16, 
  with 
  the 
  vacuoles 
  

   perforating 
  the 
  thick 
  epitheca. 
  Lower 
  Cretaceous 
  (Aptian): 
  Faringdon, 
  England 
  

  

  In 
  these 
  various 
  sections 
  the 
  zoarial 
  pores 
  appear, 
  therefore, 
  as 
  the 
  

   extremities 
  of 
  small 
  tubes 
  perforating 
  the 
  zoarial 
  epitheca; 
  these 
  are 
  

   vacuoles, 
  as 
  in 
  the 
  genus 
  Hornera. 
  Moreover, 
  the 
  general 
  aspect 
  of 
  

   the 
  species 
  is 
  also 
  that 
  of 
  Hornera, 
  although 
  the 
  ovicell 
  is 
  decidedly 
  

   different, 
  being 
  that 
  of 
  the 
  Ascosoeciidae. 
  

  

  Affinities. 
  — 
  This 
  species 
  differs 
  from 
  Siphodictyum 
  irregulare 
  in 
  the 
  

   salient 
  peristomes 
  arranged 
  in 
  transverse 
  rows 
  and 
  more 
  numerous 
  

   on 
  the 
  cellular 
  face; 
  finally, 
  branches 
  formed 
  entirely 
  of 
  vacuoles 
  

   have 
  never 
  been 
  observed. 
  

  

  Occurrence. 
  — 
  Lower 
  Cretaceous 
  (Aptian) 
  : 
  Faringdon, 
  Folkestone, 
  

   etc., 
  England. 
  

  

  Plesiotypes.— 
  Cat. 
  No. 
  69943, 
  U.S.N.M. 
  

  

  