18 PENNSYLVANIAN FLORA OF NORTHERN ILLINOIS 



10. Callipteridium. This differs primarily by its broad, bluntly ending 

 pinnules from Alethopteris. In Europe Callipteridium is an index fossil 

 of Permian and Sub-Permian strata. It is a Cycadofilicales. 



Some basal leaves of fern-like fronds are called Aphlebiae. Sometimes 

 young leaves which are still coiled are found. Although the generic name, 

 Spiropteris, is well suited to these forms, it seems rather useless to dis- 

 tinguish species, for every individual fossil of this kind would have to re- 

 ceive a species name. 



The only true ferns (Filicales) among the leaf impressions found at 

 Mazon Creek and Braidwood belong to the genera Sphenopteris and 

 Pecopteris. 



Cycadofilicales 



Numerous seeds of gymnospermic character but associated with fern- 

 like leaves, such as Codonospermum, Tripterospermum, Pachytesta, 

 Stephanospermum, Trigonocarpum are known. Codonotheca, which was 

 first found by E. H. Sellards in Illinois and described by him, is probably 

 a microspore-bearing organ of Neuropteris. Staphylopteris may have 

 had the same function but was associated with Sphenopteris. 



CORDAITALES 



These were gymnospermic trees with tall shafts whose branches bore 

 tufts of very large ribbon-shaped leaves. The male reproductive organs 

 of this order received the generic name of Cordaianthus, the female, that 

 of Cardiocarpus, and the leaves that of Cordaites. 



