780 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 



Classification and Diagnosis. 



Psilophytales : A Class of Pteridophyta characterised by the sporangia 

 being borne at the ends of certain branches of the stem without any 

 relation to leaves or leaf-like organs. 



Rhynia Givynne-Vaughani, Kidston and Lang, n.g. and n. sp. 



Psilophyton princeps, Dawson (pars). 



"Fossil Plants of the Devonian and Upper Silurian Formation of Canada," Geol. Survey Canada, 1871, 

 p. 37, pi. ix, figs. 97-110; pi. x, figs. 112-114, 118-120; pi. xi, figs. 127, 128, 133, 134. 



Rhynia, Kidston and Lang, n.g. 



Diagnosis. — Aerial stems without leaves or spines but bearing small protuber- 

 ances ; sporangium large, cylindrical, terminal on ultimate branches. 



Rhynia Gwynne-Vaughani, Kidston and Lang, n. sp. 



Diagnosis. — Plant gregarious, rootless and leafless. Underground rhizomes with 

 rhizoids, generally situated on large, downwardly directed protuberances of the 

 cortex. Aerial stems cylindrical, tapering upwards, about 8 inches in height, 

 bearing small hemispherical protuberances. Stems sparingly dichotomous and also 

 bearing lateral adventitious branches. 



Sporangium large, cylindrical, and terminating an aerial stem. Sporangial wall 

 thick, of many layers of cells. Homosporous, spores developed in tetrads about 65 fi 

 in diameter. 



Stele throughout the plant small, cylindrical, consisting of a solid strand of 

 annular tracheides, surrounded by a zone of thin-walled phloem. Cortex consisting 

 of an inner and outer zone. Epidermis of aerial stems with cuticularised outer wall 

 and stomata. 



Locality. — Muir of Rhynie, Aberdeenshire. 



Horizon. — Old Red Sandstone (not younger than the Middle Division of the 

 Old Red Sandstone of Scotland). 



In conclusion, we wish to express our thanks to Dr W. Mackie, Elgin, for 

 placing his slides in our hands for description as well as supplying us with material ; 

 to Dr J. S. Flett, F.R.S., Director of the Geological Survey of Scotland, for kind 

 assistance ; and to Mr D. Tait for much help given when examining the chert band 

 at Rhynie. 



We also gratefully acknowledge our indebtedness to the Executive Committee 

 of the Carnegie Trust for a grant towards defraying the expense of the plates 

 illustrating this memoir. 





