THE PENNSYLVANIAN PERIOD. 



593 



The Filicales. — Fern-like leaves surpassed all other fossil forms 

 in number, but it is now known that many, perhaps even a majority, 

 of these belonged to the transition group, Cycadoftlices . True ferns 

 were present and apparently abundant, but precisely how abundant 

 is yet undetermined. The ferns were a strangely persistent type, like 

 the brachiopods in the sea. At their first appearance in the record, 

 they had already the distinctive forms of existing ferns (Figs. 275, 276, 

 a-c, and 277). Later they played a notable part in the floras of 



Fig. 276. — A group of fern fronds: a, Neuropteris auriculata, Brgt.; b, N. angustifolia, 

 Brgt. ; c, N, vermicularis , Lx. ; d, Odontopteris cornuta, Lx. ; e, Pecopteris unita, Brgt. ; 

 /, Dictyopteris rubelia, Lx.; g, Archceopteris bochsiana, Goepp. ; h, Sphenopteris 

 splendens,~Lx. 



many periods, and they are yet an appreciable feature in the plant 

 world. Ferns may be found to-day that might, so far as outer 

 form is concerned, be referred to genera prevalent in Carboniferous 

 time; yet under this general similarity and persistency of form, they 

 have undergone notable changes of structure and function. In Car- 



