52 



CHAPTER V 



RECENT ADVANCES IN OUR KNOWLEDGE 



OF THE MORPHOLOGY OF THE 



ARCHAEOPTERIS FLORA 



BEFORE discussing the phylogenetic deductions which, as it 

 appears to us, may be drawn from a consideration of the Psilo- 

 phyton flora, it may be well to review our present knowledge of 

 the later or Archaeopteris flora of the younger Devonian rocks 

 (see table, p. 9). 



This flora is clearly Cormophytic and Pteridophytic but it 

 sprang from the Psilophyton flora which as we have seen was 

 Thallophytic. 



In this case again we shall only notice the less obscure types, 

 and in the case of genera which are well known and described 

 in every text-book, we have not added any diagnoses. 



SPHENOPSIDA. 



Sphenophyllum, Brongn., 

 1828 (Fig. 24). Only a single 

 species of this well-known 

 genus is recorded from the 

 Upper Devonian of Bear Is- 

 land 1 . Like all the earlier 

 representatives of the genus 

 it has small, very narrow, 

 highly divided leaves. The 

 species with entire or nearly 

 entire wedge-shaped leaves 

 are not known earlier than 

 the Upper Carboniferous. The 

 Devonian type is very similar 

 to, perhaps even identical with, 

 a species occurring in the 

 Lower 'Carboniferous. 

 1 Nathorst (1902). 



Fig. 24. Sphenophyllum subtenerri- 

 mum, Nath., from the Upper De- 

 vonian of Bear Island. Considerably 

 reduced. After Nathorst (1902). 



