145 



specifically between the different regions of the Northern 

 Hemisphere, but they everywhere show their common 

 relation to a new and distinctly Carboniferous stock, so 

 that in spite of varying generic names their consanguinity 

 is unmistakable. Thus the Aneimites ("Cyclopteris" and 

 "Adiantites"), acadicus, so characteristic of the Horton, 

 is congeneric with and specifically close to the A. bellidula 

 and other forms of the genus in the more northern regions, 

 as well as probably with the genus Triphyllopteris of the 

 Virginian region of the Appalachian trough. Some of 

 the widely variant forms of the Horton plants are difficult 

 to distinguish from the Triphyllopteris virginiana in the 

 Pocono of the last-named region, though the species in 

 their ensemble are distinct. Descendants of this stock 

 are found in Eremopteris and possibly in Rhacopteris. 



The stems described by Dawson as Lepidodendron 

 corrugatum, the other monopolist of the Horton flora, 

 present an almost bewildering cortical variation, which 

 is well illustrated in the report of the "Plants of the Lower 

 Carboniferous and Millstone Grit Formations of Canada." 

 This singular and well marked Lepidodendroid type 

 belongs to the older, composite, stock of the Devonian 

 known as Archceosigillaria, in which the alignment of the 

 leaf bases in vertical and transverse rows sometimes, 

 when the growth was slow, produced vertical ribs resem- 

 bling the Rhytidolepis group of Sigillariae, while in other 

 cases, especially when the growth was more rapid and the 

 leaf scars were longitudinally more remote, it caused a 

 verticillate aspect of the scars. The Archceosigillaria type 

 of scar, first noted in Archceosigillaria ("Lepidodendron") 

 gaspiana and A. primceva, the latter from the Portage 

 group in New York, survive in Eskdalia and in Bothroden- 

 dron. Archceosigillaria corrugata is perhaps indistinguish- 

 able in any of its phases from the equally omnipresent and 

 likewise monopolistic Lycopod described by Meek from 

 the Pocono formation of the eastern United States as 

 Lepidodendron scobiniforme. The latter is similarly varied 

 in its cortical features. The Horton tree has its close 

 correspondents in several contemporaneous Arctic species, 

 such as Lepidodendron glincanum. 



The dominant Cycadofilic and Lepidodendroid types of 



the basal Carboniferous flora of North America were 



evidently in a state of great plasticity and variation, under 



the new environmental conditions (coal formation) in 



35063—10 



