PENNSYLVANIAN FLORA 01 NORTHERN ILLINOIS 17 



As mentioned in an earlier chapter, the group name Filicales is still used 

 in this report for the fern-like impressions. 



For two very characteristic fern stem types the generic names of 

 Megaphyton and Ptychopteris are used. They are marked by very large 



leaf scars which were produced after the leaf stems or petioles had fallen 

 Off. 



The fern-like leaves are divided into genera according to the following 

 characters: 



a. The form of attachment of the smallest leaf units (pinnules) to 



the stem that bears them. 



b. The general shape of the pinnules and their arrangement and de- 

 velopment in the fronds. 



c. The venation of the pinnules. 



On the basis of these distinctions we have arranged our material into 

 the following genera: 



1. Sphenopteris. The pinnule is contracted at its base and is lobed 

 or dissected. Some Sphenopteris species were Cycadofilicales. 



2. Palmatopteris. This genus resembles Sphenopteris but has very 

 deeply dissected pinnules. It is a Cycadofilicales. 



3. Megalopteris. This is a large-leafed fern type with a simple pin- 

 nate frond and was probably herbaceous. It is rarely found and occurs 

 only in the Pottsville formation. It is present in the Rock Island district. 

 It is a Cycadofilicales. 



4. Mariopteris. This genus has a large frond that is divided many 

 times. Its pinnules have a broad base and arch-shaped secondary veins 

 projecting from the base of the pinnule. Frequently no midrib is visible. 

 It is a Cycadofilicales. 



5. Neuropteris. Pinnules have a narrow base from which arch-shaped 

 veins emerge. There is usually a midrib. The veins fork dichotomously 

 from one to several times but are not connected. At the base of the com- 

 posite frond are rounded leaves with a radiating venation. These leaves 

 were originally called Cyclopteris and were considered as belonging to a 

 distinct genus. For the sake of convenience, this name has been retained 

 to characterize such types of leaves. 



6. Linopteris. The shape of the pinnule is exactly like that of Neurop- 

 teris, but the veins are anastomosed and form a net. It is a Cycadofilicales. 



7. Pecopteris. A large number of species belong to this genus which 

 is especially w r ell represented in the higher strata of the Pennsylvanian. 

 The pinnules are generally small and possess a distinct midrib usually with 

 few secondary veins and a broad base. The name Asterotheca and Ptycho- 

 carpus are used for certain Pecopteris forms which show spore capsules. 



8. Odontopteris. This genus has a pinnule like Pecopteris except that 

 there is no midrib and the veins enter parallel from the base. It is a Cycado- 

 filicales. 



9. Alethopteris. The pinnules also have a broad attachment, but their 

 bases are decurrent. The midrib is always very distinct and the secondary 

 veins numerous. It is a Cycadofilicales. 



