340 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1918. 



Following is a summary of the types which are probably referable 

 to the Pteridosperm phylum : 



Lyginopteraceae — Lyginopteris (Telangium Lagenostoma Lagenospermum, 

 Pterispermostrobus) Sphenopteris, Calymmotheca, etc., 

 Heterangium (Sphenopteris Sphaerostoma, etc.). 

 Medullosaceae — Medullosa (Myeloxylon, Neuropteris, Alethopteris, Linopteris, 



Trigonocarpus, Codonotheca, Schiitzia, Whittlesaya, Dolerophyl- 



lum, etc.). 



Colpoxylon. 



Rhexoxylon. 



Sutcliffia. 

 Steloxyleae ( ?) — Steloxylon. 

 Megaloxyleae — Megaloxylon. 

 Rhetinangieae — Rhetinangium. 

 Stenomyeleae — Stenomyelon. 

 Cyeadoxyleae — Cycadoxylon. 



Ptychoxylon. 

 Calamopityeae — Calamopitys ( Kalymma ) . 



Eristophyton. 

 Cladoxyleae — Gladoxylon. 



Volkelia. 

 Protopityeae — Protopitys. 



Incertae sedis — Pecopteris pluckeneti, Eremopteris artemisaefolia, Wardia, 

 Adiantites bellidulus, Ottokaria, Strobilites, Gigantopteris, 

 Glossopteris (?), etc. 



PHYLUM CYCADOPHYTA. 



No existing group of plants has excited more interest in recent 

 years than the existing cycads (order Cycadales). Before the pecu- 

 liarly organized Mesozoic forms were understood, the wealth of 

 foliar impressions of cycad-like fronds in the Mesozoic rocks 

 throughout the world and similar less abundant remains in the later 

 Paleozoic, led to the conclusion that the cycad line was simply an- 

 other example of an ancient, persistent, rather uniform stock derived 

 from the ferns, whose existing representatives were the straggling 

 survivors of a type which attained its maximum development in the 

 older Mesozoic. The researches of Carruthers, Solms Laubach, Na- 

 thorst, Lignier, and Wieland have shown that the group was large 

 and diversified, and includes at least two extinct orders very differ- 

 ent from the existing cycads; that its origin is to be looked for 

 among the seed ferns rather than the true ferns; and that existing 

 cycads represent relatively modern and never very abundant deriva- 

 tives of this ancient stock. 



In sketching the morphology of the Cycadophytes the reader has 

 to bear in mind that we are dealing with an extensive group that ap- 

 peared in the record as early as the Carboniferous (WestphaJian) 

 and continued to the present, and that aside from the recent forms and 

 a few exceptional fossil forms like the Rhaetic Wielandiella and the 



