﻿art. 
  2i 
  CYCLOSTOMATOUS 
  BEYOZOA 
  CANU 
  AND 
  BASSLER 
  53 
  

  

  Genotype. 
  — 
  Plethopora 
  verrucosa 
  Hagenow, 
  1851. 
  Cretaceous 
  

   (Aptian, 
  Maastrichtian). 
  

  

  The 
  place 
  of 
  the 
  nematopores 
  is 
  variable 
  in 
  the 
  Cytisidae, 
  according 
  

   to 
  the 
  nature 
  of 
  the 
  genera. 
  In 
  Plethopora 
  they 
  are 
  arranged 
  entirely 
  

   around 
  the 
  zoarium, 
  while 
  in 
  other 
  genera 
  they 
  are 
  found 
  only 
  on 
  the 
  

   dorsal. 
  

  

  PLETHOPORA 
  APTENSIS, 
  new 
  species 
  

  

  Plate 
  7, 
  figs. 
  3, 
  4 
  

  

  Description. 
  — 
  The 
  zoarium 
  is 
  free, 
  cylindrical, 
  bifurcated. 
  The 
  

   zooecia 
  are 
  grouped 
  in 
  fascicles, 
  which 
  are 
  salient 
  and 
  orbicular. 
  

   The 
  nematopores 
  are 
  small, 
  polygonal, 
  arranged 
  entirely 
  around 
  the 
  

   zoarium. 
  

  

  Measurements. 
  — 
  Diameter 
  of 
  fascicles, 
  0.56 
  mm.; 
  diameter 
  of 
  

   branches, 
  2 
  mm. 
  

  

  Structure. 
  — 
  In 
  longitudinal 
  section 
  the 
  tubes 
  are 
  cylindrical, 
  long, 
  

   with 
  peripheral 
  gemmation; 
  they 
  occupy 
  the 
  essential 
  and 
  principal 
  

   part 
  of 
  the 
  zoarium. 
  The 
  nematopores 
  appear 
  solely 
  on 
  the 
  zoarial 
  

   margin 
  in 
  small 
  spaces 
  between 
  the 
  fascicles, 
  thus 
  confirming 
  the 
  

   thin 
  section 
  of 
  Hennig. 
  

  

  In 
  transverse 
  sections 
  the 
  larger 
  tubes 
  are 
  in 
  the 
  middle. 
  These, 
  in 
  

   branching, 
  engender 
  the 
  axial 
  tubes 
  of 
  the 
  fascicles. 
  On 
  the 
  borders 
  

   the 
  small 
  pores 
  are 
  those 
  of 
  the 
  peripheral 
  nematopores. 
  

  

  Affinities. 
  — 
  The 
  distinction 
  between 
  the 
  species 
  of 
  this 
  genus 
  is 
  

   rather 
  difficult 
  to 
  make 
  from 
  the 
  published 
  figures. 
  Comparisons 
  of 
  

   specimens, 
  on 
  the 
  contrary, 
  permit 
  a 
  differentiation, 
  according 
  to 
  the 
  

   relative 
  size 
  of 
  the 
  orifices, 
  of 
  the 
  nematopores, 
  and 
  the 
  form 
  of 
  the 
  

   fascicles. 
  The 
  circular 
  form 
  of 
  the 
  latter 
  and 
  the 
  large 
  size 
  of 
  the 
  

   zoarium 
  well 
  characterize 
  this 
  species. 
  

  

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

   (rare) 
  . 
  

  

  Cotypes.— 
  Cat. 
  No. 
  G9903, 
  U.S.N.M. 
  

  

  Genus 
  PLETHOPORELLA 
  Canu 
  and 
  Bassler, 
  1922 
  

  

  The 
  ovicell 
  is 
  elliptical, 
  elongated, 
  large, 
  little 
  convex, 
  smooth. 
  

   The 
  tubes 
  are 
  cylindrical, 
  without 
  peristome, 
  with 
  orbicular 
  orifice; 
  

   their 
  walls 
  are 
  moniliform; 
  they 
  are 
  recurved 
  at 
  their 
  extremity. 
  

   The 
  gemmation 
  is 
  peripheral 
  around 
  a 
  bundle 
  of 
  axial 
  tubes. 
  No 
  

   adventitous 
  tubes. 
  

  

  Genotype. 
  — 
  Plethoporella 
  (Plethopora) 
  ramulosa 
  D'Orbigny, 
  1847. 
  

  

  Range. 
  — 
  Cretaceous 
  (Campanian, 
  Maastrichtian). 
  

  

  History. 
  — 
  D'Orbigny 
  was 
  in 
  error 
  in 
  comparing 
  the 
  genotype 
  with 
  

   Plethopora 
  verrucosa 
  Hagenow, 
  1851. 
  The 
  internal 
  structure 
  is 
  very 
  

   different, 
  for 
  not 
  only 
  are 
  there 
  no 
  nematopores 
  but 
  the 
  tuberosities 
  

   which 
  ornament 
  the 
  zoarial 
  surface 
  are 
  not 
  formed 
  of 
  bundles 
  of 
  

   tubes. 
  

  

  