﻿78 
  

  

  PROCEEDINGS 
  OF 
  THE 
  NATIONAL, 
  MUSEUM 
  

  

  little 
  numerous. 
  There 
  are 
  zonal 
  lines, 
  rather 
  regular, 
  very 
  convex, 
  

   scattered 
  in 
  the 
  inferior 
  part 
  of 
  the 
  branches 
  and 
  approaching 
  more 
  

   closely 
  at 
  the 
  summit. 
  The 
  zoarial 
  margins 
  are 
  occupied 
  by 
  epithe- 
  

   cal 
  lines, 
  very 
  numerous, 
  close 
  together, 
  represented 
  in 
  a 
  drawing 
  

   with 
  difficulty. 
  The 
  diaphragms 
  are 
  widely 
  spaced 
  and 
  their 
  simul- 
  

   taneous 
  occurrence 
  forms 
  the 
  zonal 
  lines. 
  The 
  extremity 
  of 
  the 
  

   tubes 
  is 
  thickened 
  and 
  moniliform; 
  the 
  tubes 
  are 
  not 
  then 
  rigorously 
  

   cylindrical 
  but 
  show 
  constrictions 
  more 
  and 
  more 
  close 
  to 
  each 
  other. 
  

   In 
  transverse 
  sections 
  the 
  tubes 
  are 
  polygonal, 
  with 
  thin 
  and 
  

   adjacent 
  walls. 
  On 
  the 
  edge 
  the 
  epithecal 
  lines 
  are 
  so 
  close 
  together 
  

  

  Fig. 
  40.— 
  Leiosoecia 
  constanti 
  D'Orbigny, 
  185D. 
  A. 
  Longitudinal 
  section, 
  X 
  16, 
  showing 
  the 
  zonal 
  lines 
  

   and 
  the 
  undulated 
  tubes 
  with 
  their 
  diaphragms. 
  B. 
  Portion 
  of 
  a 
  transverse 
  section, 
  X 
  16, 
  illustrating 
  

   the 
  polygonal 
  form 
  of 
  the 
  tubes. 
  Lower 
  Crntaceous 
  (Valangian): 
  Sainte-Croix, 
  Switzerland 
  

  

  that 
  they 
  form 
  an 
  exterior 
  epithecal 
  zone 
  so 
  opaque 
  that 
  photog- 
  

   raphy 
  can 
  show 
  its 
  complexity 
  only 
  imperfectly. 
  

  

  In 
  tangential 
  section 
  the 
  tubes 
  are 
  little 
  polygonal 
  and 
  the 
  meso- 
  

   pores 
  are 
  very 
  small. 
  The 
  calcareous 
  tissue 
  which 
  surrounds 
  them 
  

   is 
  alveolar. 
  

  

  This 
  species 
  has 
  the 
  same 
  internal 
  structure 
  as 
  Leiosoecia 
  multi- 
  

   porosa 
  and 
  Leiosoecia 
  grandipora, 
  but 
  the 
  zonal 
  lines 
  and 
  the 
  epithe- 
  

   cal 
  lines 
  are 
  more 
  numerous. 
  

  

  Occurrence. 
  — 
  Lower 
  Cretaceous: 
  Sainte-Croix. 
  Switzerland 
  (Valan- 
  

   gian); 
  Grandpre 
  (Ardennes), 
  France 
  (Aptian). 
  

  

  Plesiotypes.— 
  Cat. 
  No. 
  69933, 
  U.S.N.M 
  

  

  