﻿90 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  vol.67 
  

  

  Affinities. 
  — 
  This 
  species 
  differs 
  from 
  Siplwdictyum 
  gracile 
  Lonsdale, 
  

   1849, 
  in 
  its 
  more 
  slender 
  branches 
  showing 
  only 
  3 
  or 
  4 
  longitudinal 
  

   series 
  of 
  tubes 
  and 
  in 
  the 
  presence 
  of 
  noncellular 
  zoarial 
  portions. 
  

  

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

  

  Coty 
  pes. 
  —Cat. 
  No. 
  69944, 
  U.S.N.M. 
  

  

  Genus 
  ZONOPORA 
  D'Orbigny, 
  1854 
  

  

  ZONOPORA 
  COMPRESSA. 
  new 
  species 
  

  

  Plate 
  15, 
  figs. 
  15-17; 
  Plate 
  31, 
  fig. 
  1 
  

  

  Description. 
  — 
  The 
  zoarium 
  is 
  free, 
  dichotomous; 
  the 
  fronds 
  are 
  

   much 
  compressed. 
  The 
  peristomes 
  are 
  small, 
  thin,nonsalient, 
  arranged 
  

   in 
  irregular 
  quincunx, 
  grouped 
  in 
  zones 
  separated 
  by 
  wide 
  areas 
  of 
  

   mesopores 
  and 
  surrounded 
  by 
  some 
  mesopores. 
  

  

  Measurements. 
  — 
  Diameter 
  of 
  orifice, 
  0.10 
  mm.; 
  diameter 
  of 
  meso- 
  

   pores, 
  0.04-0.06 
  mm.; 
  distance 
  of 
  peristomes, 
  0.24-0.26 
  mm.; 
  sepa- 
  

   ration 
  of 
  peristomes, 
  0.36-0.40 
  mm. 
  

  

  Structure. 
  — 
  The 
  sectioned 
  specimens 
  were 
  accidentally 
  hollow, 
  giv- 
  

   ing 
  the 
  sections 
  a 
  strange 
  aspect 
  which 
  might 
  make 
  them 
  appear 
  

   to 
  belong 
  to 
  another 
  genus. 
  However, 
  we 
  have 
  found 
  the 
  usual 
  

   structure 
  seen 
  in 
  sections 
  of 
  Zonopora. 
  

  

  The 
  longitudinal 
  section 
  in 
  Zonopora 
  is 
  very 
  difficult 
  to 
  interpret 
  

   because 
  of 
  the 
  great 
  multiplicity 
  of 
  tubes 
  and 
  of 
  their 
  vesicular 
  walls. 
  

   Those 
  which 
  we 
  have 
  made 
  are 
  not 
  clear 
  enough 
  to 
  be 
  reproduced, 
  

   but 
  we 
  have 
  been 
  able 
  to 
  observe 
  the 
  essential 
  characters. 
  

  

  Affinities. 
  — 
  This 
  is 
  the 
  only 
  species 
  of 
  Zonopora 
  in 
  which 
  the 
  fronds 
  

   are 
  compressed. 
  

  

  Occurrence. 
  — 
  Lower 
  Cretaceous 
  (Valangian) 
  : 
  Sainte-Croix, 
  Swit- 
  

   zerland. 
  

  

  Cotype.— 
  Cat. 
  No. 
  69945, 
  U.S.N.M. 
  

  

  ZONOPORA 
  ARBOREA 
  Koch 
  and 
  Dunker, 
  1837 
  

  

  Plate 
  15, 
  figs. 
  7-10; 
  Plate 
  31, 
  figs. 
  2-4 
  

  

  1909. 
  Multizonopora 
  arborea 
  Gregory, 
  Catalogue 
  Cretaceous 
  Bryozoa 
  in 
  the 
  

   British 
  Museum, 
  vol. 
  2, 
  p. 
  220, 
  figs. 
  57-61. 
  (Bibliography 
  and 
  geologic 
  

   distribution.) 
  

  

  Measurements. 
  — 
  Diameter 
  of 
  the 
  orifices, 
  0.08 
  mm.; 
  diameter 
  of 
  

   the 
  mesopores, 
  0.04 
  mm. 
  

  

  Structure. 
  — 
  The 
  specimens 
  from 
  Sainte-Croix 
  are 
  large 
  and 
  rough, 
  

   but 
  they 
  are 
  not 
  multilamellar. 
  The 
  cellular 
  zones 
  are 
  very 
  irregular 
  

   and 
  quite 
  variable 
  in 
  their 
  extent. 
  The 
  determination 
  by 
  the 
  exterior 
  

   features 
  alone 
  is 
  always 
  difficult 
  if 
  the 
  observer 
  is 
  not 
  acquainted 
  

   with 
  all 
  the 
  known 
  variations 
  in 
  such 
  fossils. 
  

  

  The 
  illustrated 
  sections 
  of 
  this 
  species 
  are 
  those 
  of 
  Pergens, 
  1889, 
  

   and 
  of 
  Gregory, 
  1909. 
  Our 
  specimens 
  from 
  Sainte-Croix 
  were 
  silici- 
  

  

  