﻿80 
  

  

  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  

  

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

   (very 
  rare) 
  . 
  

   Hohtype.— 
  Cat. 
  No. 
  69934, 
  U.S.N.M. 
  

  

  CLAUSA 
  ZONIFERA, 
  new 
  species 
  

  

  Plate 
  17, 
  figs. 
  8-11; 
  Plate 
  31, 
  fig. 
  9 
  

  

  Description.— 
  The 
  zoarium 
  is 
  free, 
  cylindrical, 
  borne 
  upon 
  a 
  slightly 
  

   expanded 
  base, 
  branching 
  dichotomously 
  in 
  the 
  same 
  plane; 
  the 
  

   branches 
  are 
  cylindrical, 
  rarely 
  claviform. 
  The 
  peristomes 
  are 
  very 
  

   thin, 
  nonsalient, 
  grouped 
  in 
  irregular 
  zones, 
  and 
  separated 
  by 
  polyg- 
  

   onal 
  dactylethrae 
  few 
  

   in 
  number. 
  The 
  tubes 
  

   are 
  cylindrical, 
  with 
  

   peripheral 
  gemmation 
  

   regularly 
  developed 
  

   around 
  a 
  central 
  axis 
  

   and 
  at 
  all 
  heights. 
  The 
  

   ovicell 
  is 
  unknown. 
  

  

  Measurements. 
  — 
  D 
  i 
  - 
  

   ameter 
  of 
  orifice, 
  0.12 
  

   mm. 
  ; 
  diameter 
  of 
  peri- 
  

   stome, 
  0.15 
  mm. 
  ; 
  diam- 
  

   eter 
  of 
  large 
  branches, 
  

   2.50 
  mm. 
  

  

  Structure. 
  — 
  Exterior- 
  

   ly 
  this 
  species 
  has 
  the 
  

   appearance 
  of 
  a 
  Zono- 
  

   pora. 
  The 
  grouping 
  of 
  

   the 
  peristomes 
  in 
  circu- 
  

   lar 
  zones 
  is 
  a 
  deceptive 
  

   generic 
  character 
  be- 
  

   cause 
  it 
  does 
  not 
  al- 
  

   ways 
  correspond 
  to 
  the 
  

   same 
  internal 
  struc- 
  

   ture. 
  It 
  is 
  the 
  same 
  as 
  

   in 
  the 
  clavulate 
  zoarial 
  

   form; 
  indeed, 
  in 
  this 
  species 
  we 
  have 
  observed 
  this 
  form, 
  although 
  

   rarely, 
  and 
  we 
  figure 
  a 
  superb 
  unbranched 
  specimen. 
  

  

  In 
  longitudinal 
  sections 
  the 
  tubes 
  are 
  cylindrical, 
  recurved 
  at 
  their 
  

   extremity, 
  more 
  or 
  less 
  long 
  according 
  to 
  their 
  distance 
  from 
  the 
  

   central 
  axis, 
  and 
  narrowed 
  at 
  their 
  base. 
  Their 
  walls 
  divide 
  in 
  two, 
  

   engendering 
  thus 
  a 
  new 
  tube. 
  This 
  is 
  the 
  usual 
  method 
  of 
  gemma- 
  

   tion 
  in 
  the 
  heteroporoids 
  (peripheral). 
  The 
  peripheral 
  tubes 
  are 
  thus 
  

  

  Fig. 
  41. 
  — 
  Clausa 
  zonifera, 
  new 
  species. 
  A. 
  Longitudinal 
  section, 
  

   X 
  16. 
  The 
  dactylethrae 
  are 
  produced 
  by 
  dichotomous 
  branching 
  

   of 
  the 
  walls 
  (peripheral 
  gemmation). 
  B. 
  Transverse 
  section, 
  

   X 
  16. 
  The 
  dispersion 
  of 
  the 
  small 
  tubes 
  among 
  the 
  large 
  ones 
  

   show 
  that 
  gemmation 
  occurs 
  at 
  all 
  distances 
  from 
  the 
  central 
  

   axis 
  by 
  regular 
  peripheral 
  dichotomous 
  branching. 
  Lower 
  Cre- 
  

   taceous 
  (Aptian): 
  Faringdon, 
  England 
  

  

  