4 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 492 



TAXONOMY 



Megaphyton Artis, 1825 



Synonym : Zippea Corda, 1845 



Emended diagnosis . — Stem of tree fern (compression or impres- 

 ion) ; leaf scars in two vertical rows on opposite sides of the stem; 

 leaf scars oval to rectangularly oval; trace of vascular bundle with 

 Stewart iopteroid or stipitopteroid configuration. 



Discussion . — Specimens of Megaphyton can be distinguished from 

 those of Caulopteris only if at least half of the stents outer surface 

 is preserved. If there is only one row of leaf scars without adjacent 

 tissue, the specimen may belong to either genus. 



Megaphyton protuberans Lesquereux, 1866 

 Text fig. 3, A; pi. 5, fig. 1 



Basionym : Megaphytum protuberans Lesquereux, L., 1866, Report 

 on the fossil plants of Illinois, in: Worthen, A. H. , 1866, Palaeon- 

 tology: Geological Survey of Illinois, v. 2, p. 458, pi. 47, figs. 1-2. 



Ho lo type : ISM 1632. 



Occurrence : Silty, yellowish sandstone, Bay City, Pope County, 

 Illinois. 



Age : Chesterian (probably early) . 



The specimen was figured first by Lesquereux and later by 

 Janssen; in both figures the specimen was upside down, probably because 

 the lower third of the leaf scar protrudes steeply outward and the 

 boundary of the leaf scar is most clearly visible there. Therefore, 

 the lower third was considered the distal end of the leaf scar. However, 

 assuming that the vascular bundle was open towards the adaxial side, the 

 correct position of the specimen would be that shown in the figures of 

 this paper. 



The specimen is 65 cm long, has a diameter of more than 10 cm, 

 and displays nine leaf scars. The scars are badly preserved, but a few 

 show a horseshoe-shaped vascular bundle that occupies only the lower 

 third of the leaf scar. Measurements: 





Height 

 75 mm 



Width 



H:W 



Leaf scar: 



50 mm 



1.36 





65 mm 



55 ram 



1.18 



Vascular bundle: 



21 mm 



26 mm 



0.8 



The leaf scars are 5 mm apart vertically. 



