﻿(r. 
  R. 
  Wieland 
  — 
  On 
  Liassic 
  Floras. 
  

  

  275 
  

  

  ally 
  is 
  this 
  so 
  because 
  of 
  the 
  lack 
  of 
  other 
  sections 
  yielding 
  as 
  

   abundant 
  and 
  exactly 
  located 
  forms 
  throughout 
  such 
  great 
  

   thicknesses 
  of 
  strata. 
  In 
  this 
  respect 
  the 
  Rio 
  Consuelo 
  section 
  

   is 
  so 
  nearly 
  unique 
  that 
  it 
  has 
  been 
  found 
  necessary 
  to 
  regard 
  

   the 
  plant 
  beds 
  as 
  a 
  unit 
  when 
  attempting 
  comparison 
  with 
  

   other 
  sections. 
  

  

  Consequently 
  in 
  any 
  first 
  effort 
  to 
  determine 
  the 
  relative 
  age 
  

   of 
  these 
  beds 
  it 
  is 
  safest 
  to 
  fix 
  the 
  attention 
  on 
  a 
  thoroughly 
  

   simplified 
  list 
  of 
  the 
  plants 
  of 
  the 
  entire 
  section. 
  And 
  such 
  a 
  

   list 
  of 
  positive 
  value 
  is 
  best 
  obtained 
  by 
  excluding 
  from 
  Table 
  

   I 
  the 
  varieties, 
  the 
  sole 
  Equisetum, 
  the 
  Tseniopterids, 
  the 
  

   doubtful 
  Glossopterids, 
  and 
  most 
  of 
  the 
  cycad 
  fruits 
  which 
  so 
  

   far 
  have 
  been 
  of 
  much 
  too 
  seldom 
  occurrence 
  for 
  grouping 
  

   according 
  to 
  age. 
  By 
  thus 
  dealing 
  with 
  the 
  larger 
  features 
  — 
  

   the 
  irreducible 
  minimum 
  of 
  genera 
  and 
  species 
  to 
  which 
  no 
  

   one 
  can 
  take 
  exception, 
  rather 
  than 
  resting 
  the 
  case 
  on 
  more 
  or 
  

   less 
  moot 
  species, 
  the 
  chances 
  for 
  error 
  most 
  be 
  very 
  markedly 
  

   lessened. 
  The 
  list 
  when 
  condensed 
  is 
  as 
  follows 
  : 
  

  

  Table 
  VI. 
  — 
  Condensed 
  list 
  of 
  Mixteca 
  Alta 
  Plants. 
  

  

  Cycads 
  = 
  

  

  Anomozamites 
  Lindleyanus 
  

  

  Cycadolepis 
  

  

  Cycas 
  (?) 
  

  

  Podozamites 
  sp. 
  

  

  Ptilophyllum 
  

  

  Otozamites 
  obtusus 
  

   Peglei 
  

   Molinianus 
  

   Mandelsohi 
  

   hespera 
  

   paratypus 
  

   JDiazii 
  

   Juarezii 
  

  

  Pterophyllum 
  cf. 
  contiguum. 
  

   " 
  milnsteri 
  

  

  Pterozamites 
  angustifolium 
  

  

  Williamsonia 
  (stems 
  and 
  

   fruits 
  in 
  profusion) 
  

  

  Williamsonia 
  mexicana 
  

  

  Zamites 
  Rolkeri 
  

  

  Gymnosperms 
  of 
  non- 
  

  

  cycadaceous 
  ancient 
  

  

  type 
  =15% 
  ± 
  

  

  Araucarioxylon 
  

   Noeggerathiposis 
  

   lihabdocarpus 
  

   Trigonocarpus 
  

  

  Ferns 
  of 
  old 
  and 
  new 
  

   types 
  equally 
  divided 
  

  

  Alethopteris 
  

   Cladophlebis 
  

   Coniopteris 
  

   Sagenopteris 
  r 
  hoi 
  folia 
  

   Sphenopteris 
  

   Tceniopteris 
  Zeilleri 
  

  

  