THE CLUB-MOSSES 191 



sible to place any reliance on Pleuromeia as a 

 connecting link, until this discrepancy has been 

 cleared up. 



Some Cretaceous and Tertiary fossils appar- 

 ently related to Isoetes are known, but they 

 throw no light on its affinities. 



We must thus leave open the question of the 

 later history of the Lepidodendrese; the great 

 Palaeozoic family may have become wholly ex- 

 tinct early in Mesozoic times, or may possibly 

 have left a dwindling race of degenerate de- 

 scendants, which reached their final stage of re- 

 duction in the dwarfed plantlets of the amphibi- 

 ous Isoetes. We may sum up, in a few words, 

 what we know of the evolution of the Lycopods 

 generally. 



Of the history of the Club-mosses with spores 

 of one kind, we know practically nothing. The 

 characters of the group suggest that it may be 

 an ancient and primitive one, but we have no 

 further evidence. 



The Selaginella group, among the hetero- 

 sporous forms, has nourished ever since Car- 

 boniferous times, and was then not very differ- 

 ent from what it is now. Some of its early mem- 

 bers were on the same level as recent forms, 

 others rather less advanced, others again dis- 

 tinctly more advanced, as shown by the posses- 

 sion of organs analogous to seeds. 



